key: cord-0040577-xxicioma
authors: Sprangers, Ben; Pirenne, Jacques; Mathieu, Chantal; Waer, Mark
title: Other Forms of Immunosuppression
date: 2014-03-18
journal: Kidney Transplantation-Principles and Practice
DOI: 10.1016/b978-1-4557-4096-3.00022-2
sha: 290dac8bf97322db9abdc6eca2f353d71809da4c
doc_id: 40577
cord_uid: xxicioma

nan

Leflunomide, initially developed as an agriculture herbicide, was explored as an immunosuppressant because of its ability to inhibit the enzyme dihydroorotate dehydrogenase. 14 The potential of leflunomide as an immunosuppressant in the field of transplantation was extensively demonstrated in various experimental studies, but its long half-life (several days) poses the problem of potential overimmunosuppression in transplant patients. Analogues of the active metabolite of leflunomide have been developed and are called malononitrilamides (MNAs). FK778 (also known as MNA715 or HMR1715) is the best studied synthetic MNA, and as it has a much shorter half-life than leflunomide (6-45 hours versus 15-18 days) it was believed to represent an attractive alternative to leflunomide for application in organ transplantation. 112 

Leflunomide (N-(4)) trifluoro-methylphenyl-5-methylisoxawol-4-carboximide) is a prodrug and is rapidly converted to its biologically active metabolite teriflunomide

Chemical (A771703) . Serum levels of teriflunomide are referred to as leflunomide levels. The half-life of teriflunomide is long in humans (approximately 15 days). The drug enters the enterohepatic recirculation and is excreted by the intestinal and urinary systems in equal proportions. Leflunomide is insoluble in water and is suspended in 1% carboxymethylcellulose for oral administration.

The MNAs are designed to be structurally similar to A771726. Oral bioavailability of FK778 is not substantially affected by food, and no gender effect on pharmacokinetics was observed in phase I studies.

Leflunomide and its analogues have strong antiproliferative effects on both T lymphocytes and B lymphocytes, thus limiting the formation of antibodies. 41, 228 Inhibition of pyrimidine synthesis is the most important mechanism of action as leflunomide directly inhibits the enzyme dihydroorotate dehydrogenase. 289 Lymphocytes rely entirely on the de novo pathway of pyrimidine biosynthesis and cannot use another, the so-called "pyrimidine salvage pathway." Dihydroorotate dehydrogenase inhibition leads to depletion of the nucleotide precursors uridine triphosphate and cytidine triphosphate which are necessary for the synthesis of RNA and DNA, and hence strongly suppress DNA and RNA synthesis.

The in vivo mechanism of action of leflunomide may depend on factors such as drug levels, disposable uridine pools, and the immune activation pathway involved. Studies have indicated that, in addition to inhibition of dihydroorotate dehydrogenase, leflunomide and the MNAs may act through inhibition of tyrosine kinases. Phosphorylation of the epidermal growth factor receptor of human fibroblasts has been shown to be inhibited by leflunomide. 160 It was shown that leflunomide directly inhibited the interleukin (IL)-2-stimulated protein tyrosine kinase activity of p56lck and p59fyn, 160 which is associated with activation through the T-cell receptor/CD3 complex. At higher concentrations, A771726 also inhibited IL-2-induced tyrosine phosphorylation of Janus kinase (JAK)1 and JAK3 protein tyrosine kinases. 60 Leflunomide analogues have also been shown to possess strong inhibitory activity on the antiapoptotic tyrosine kinase Bruton's tyrosine kinase, a key factor for T-cell-independent antibody formation. 150 The hypothesis that leflunomide may exhibit more than one mechanism of action in vivo was further illustrated in mice where uridine restored proliferation and IgM production by lipopolysaccharidestimulated B cells, whereas suppression of IgG production was not reversed. This phenomenon correlated in a dose-dependent manner with tyrosine phosphorylation of JAK3 and STAT6 proteins, known to be involved in IL-4-induced signal transduction pathways. 228 This double in vivo mechanism of action was confirmed in rats, in which xenoreactivity was counteracted by the administration of uridine, whereas alloreactivity was not. 42 Also inhibition of various macrophage functions by leflunomide and MNAs has been described; in particular, inhibition of the production of oxygen radicals, 15, 116, 156 the inhibition of IgE-mediated hypersensitivity responses, 110 the expression of IL-8 receptor type A, as well as tumor necrosis factor (TNF)-mediated nuclear factor kappa B (NF-κB) activation. 155 Tacrolimus also inhibits maturation of dendritic cells by preventing upregulation of activation markers and IL-12 production, and this phenomenon was not reversible by exogenous uridine. FK778 has equivalent or stronger immunosuppressive activity than leflunomide, both in vitro and in vivo. 112 The immunosuppressive effect is synergistic with that of calcineurin inhibitors (CNI) and mycophenolate mofetil (MMF). 21, 53 Interestingly, FK778 and leflunomide have been shown to possess antiviral effects, although the precise mechanism is unclear: inhibition of viral replication of members of the herpesvirus family by preventing tegument acquisition by viral nucleocapsids during the late stage of virion assembly has been implicated. 65,121 Leflunomide is effective against multidrug-resistant cytomegalovirus (CMV) in vitro, 284 although this in vitro activity is modest and the selectivity index is low. 67 This anti-CMV effect of leflunomide and FK778 was confirmed in a rat model of heterotopic heart transplantation. 43, 298 Another interesting feature is that both leflunomide and FK778 have vasculoprotective effects, independent of the inhibition of dihydroorotate dehydrogenase. 54, 216 

In various rodent transplantation studies, leflunomide was shown to be at least equally potent as cyclosporine, 14 and able to synergize with cyclosporine to induce tolerance. 143 Specific characteristics of leflunomide-mediated immunosuppression in rats were its ability to interrupt ongoing acute rejections, 288 and its efficacy in preventing and treating chronic vascular rejection. 291 One of the most attractive characteristics of leflunomide and the MNAs is their strong capacity to delay xenograft rejection and to induce partial xenograft tolerance. 142 This may be related to the strong suppressive effects of leflunomide on T-cell-independent xenoantibody formation, and on its capacity to induce natural killer cell nonresponsiveness and to modulate xenoantigen expression. 38 Monotherapy with FK778 in rats, 183 and its combination with microemulsified cyclosporine in dogs 129 or tacrolimus in non-human primates, 197 reduced chronic allograft nephropathy 183 and significantly prolonged renal allograft survival. 129, 183, 197 

The main role of leflunomide in renal transplantation nowadays is the treatment of BK virus nephropathy (BKVN). 115, 287 Based on the in vitro effective anti-BK concentration, an in vivo target level of 50-100 mg/mL has been proposed. In a prospective study, 26 renal transplant recipients with biopsy-proven BKVN were treated with leflunomide in combination with discontinuation of MMF and reduction of tacrolimus to a 4-6 ng/ mL range. 287 Although the leflunomide levels were in the lower range (on average 50 mg/mL), a significant reduction in serum and urine BKV titers was obtained, allograft function stabilized, and the overall graft loss rates because of BKV were only 15%. 115 Less encouraging results were obtained in another prospective openlabel study in which viral clearance was only obtained in 40% of patients with significant toxicity, resulting in discontinuation of the drug in 17% of patients. 66 The contribution of reduction of immunosuppressive agents and leflunomide to the efficacy of BKVN treatment is unclear at this moment. 59, 114, 265 Based on recent in vitro data, it has been suggested that the combination of sirolimus with leflunomide might be an effective treatment approach. 140 FK778 has also been studied in the context of BKVN, but although it was able to decrease BK viral load, FK778 treatment was associated with more acute rejections, decreased renal function, and more adverse events compared with reduction of immunosuppression. 94 In animal studies, leflunomide was able to reverse acute and chronic rejection. Two clinical studies reported that leflunomide was capable of stabilizing allograft function in patients with worsening allograft function due to chronic allograft dysfunction. 135 A phase II multicenter study was performed with FK778 involving 149 renal transplant patients, 276 where FK778 was combined with tacrolimus and corticosteroids. The patients receiving FK778 experienced a reduced number of acute rejections, but there was no effect on graft survival at week 16. 276 The reduction of acute rejection episodes was most pronounced in the subgroup in which target levels were obtained in the second week. Of note, mean total and low-density lipoprotein cholesterol levels were 20% lower in the FK778 group versus the placebo group. 276 The validity of these results was hampered by the design of the study, and, at this time, the development of FK778 in the field of organ transplantation has ceased.

Although rats tolerate leflunomide well, dogs readily develop anemia and gastrointestinal ulcerations. Reportedly, the most frequent side effects in arthritis patients receiving long-term leflunomide treatment were diarrhea (17%), nausea (10%), alopecia (8%), and rash (10%), leading to a dropout rate of ±5%. 230 Recently, thrombotic microangiopathy attributed to leflunomide was reported in patients treated for BKVN. 135 In the above-mentioned phase II study involving FK778, there was a dose-dependent increase in side effects, including anemia, hypokalemia, symptomatic myocardial ischemia, and esophagitis. 276 Other reported side effects are pneumonitis and peripheral neuropathy. 39,118 Leflunomide has teratogenic effects in both animals and humans, and a washout period with cholestyramine is advised for both women and men before considering conception. 177 Combining leflunomide with methotrexate might increase the risk for bone marrow suppression and liver toxicity. 47, 241 Furthermore, rifampin accelerates the conversion of leflunomide to teriflunomide, and might increase the levels. Combination with warfarin potentially increases the international normalized ratio.

The role of leflunomide in renal transplantation is limited to the treatment of patients with BKVN and some promising results have been reported in this respect.

The MNAs -because of their shorter half-life -were considered a promising class of immunosuppressants but results in randomized clinical trials have been disappointing, and the development of these agents in organ transplantation has been halted.

Chemical Structure and Pharmacology FTY720 or 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3propanediol hydrochloride is a synthetic structural analogue of myriocin, a metabolite of the ascomycete Isaria sinclairii, a type of vegetative wasp. 79,80,215 Maximal concentration and area under the curve are proportional to the dose, indicating that the pharmacokinetic profile of FTY720 is linear. The volume of distribution is largely superior to the blood volume, indicating a widespread tissue penetration. FTY720 undergoes hepatic metabolism and has a long half-life (around 100 hours).

FTY720 has a unique mechanism of action as it mainly affects lymphocyte trafficking. 38,97,154,159 FTY720 acts as a high-affinity agonist of the sphingosine 1-phosphate receptor-1 (S1PR1 or Edg1). Binding of its receptor results in internalization of S1PR1, rendering lymphocytes unable to respond to the naturally occurring gradient of S1P (low concentrations in thymus and secondary lymphoid organs, high concentrations in lymph and plasma) retaining lymphocytes in the low-S1P environment of lymphoid organs. 159, 186 Following FTY720 administration in mice, B and T cells immediately leave the peripheral blood and migrate to the peripheral lymph nodes, mesenteric lymph nodes. and Peyer's patches. The cells return to the peripheral blood after withdrawal of the drug without undergoing apoptotic death. 297 This altered cell trafficking is accompanied by a reduction of lymphocyte infiltration into grafted organs. 96, 297, 299 Interestingly, lymphocytes treated ex vivo with FTY720 and reintroduced in vivo similarly migrate to the peripheral lymphoid tissues, indicating that FTY720 acts directly on lymphocytes. This process of accelerated homing was completely blocked in vivo by co-administration of anti-CD62L, anti-CD49d, and anti-CD11a monoclonal antibody. 38 In vitro, FTY720 in the presence of TNF-α increases the expression of certain intercellular adhesion molecules on human endothelial cells. 139 Thus, alteration of cell trafficking by FTY720 may result not only from its direct action on lymphocytes, but also from an effect on endothelial cells.

Interestingly, it has been suggested that CD4 + CD25 + regulatory T cells are differently affected by FTY720 compared to T-effector cells. 217 CD4 + CD25 + regulatory T cells express lower levels of S1P 1 and S1P 4 receptors and, hence, show reduced response to FTY720. Furthermore, in vitro FTY720-treated CD4 + CD25 + T-regulatory cells possess an increased suppressive activity in an antigen-specific proliferation assay. 217, 300 Unlike CNI, FTY720 is a poor inhibitor of T-cell function in vitro. 267 In particular, FTY720 does not influence antigen-induced IL-2 production. In vitro exposure to high FTY720 concentrations (4 × 10 -6 ) induces chromatin condensation, typical DNA fragmentation, and formation of apoptotic bodies. Whether administration of FTY720 in vivo is also associated with significant apoptosis is a matter of debate. 38, 158 S1PR are also present on murine dendritic cells. Upon administration of FTY720, dendritic cells in lymph nodes and spleen are reduced, the expression of CD11b, CD31/PECAM-1, CD54/ICAM-1, and CCR-7 is downregulated, and transendothelial migration to CCL19 is diminished. 132 In a recent study it was demonstrated that FTY720 inhibited lymphangiogenesis and thus prolonged allogeneic islet survival in mice. 295 Experimental Experience FTY720 given daily by oral gavage has marked antirejection properties in mice, rats, dogs, and monkeys. 158, 249, 267, 294 FTY720 (0.1-10 mg/kg) prolongs survival of skin allografts in highly allogeneic rodent models. 37 In a DA to LEW rat combination, a short course of peritransplant oral FTY720 (5 mg/kg; days -1 and 0) prolongs cardiac allograft survival and is as efficient as a 10-day posttransplant treatment with tacrolimus at 1 mg/kg. 292 Cardiac and liver allograft survival is prolonged in the ACI to Lew rat model by either induction or maintenance treatment with FTY720. 247 Even delayed administration of FTY720 interrupts an ongoing allograft rejection, suggesting a role for FTY720 as a rescue agent. 248,293 FTY720 blocks not only rejection but also graft-versus-host disease after rat intestinal transplantation. 163 FTY720 may also protect form ischemia-reperfusion injury, partially through its cytoprotective actions. 52, 82, 153, 242 Both small-and large-animal models provide evidence that FTY720 acts in synergy with CNI, and that this benefit does not result from pharmacokinetic interactions. 248 An induction course with FTY720 acts in synergy with posttransplant tacrolimus in prolongating cardiac allograft survival in rats. 293 A similar phenomenon has been observed when FTY720 is used posttransplant in combination with cyclosporine in rat skin and heart allografts. 102,248 FTY720 shows synergistic effect with CNI in heart and liver transplant in the ACI to Lew rat model. 294 FTY720 shows synergy with cyclosporine in dog kidney (0.1-5 mg/kg/day) and monkey kidney (0.1-1 mg/kg/day) transplantation. 267 Finally, FTY720 (0.1 mg/kg) synergizes with CNI in dog liver transplantation. 250 Synergy between FTY720 and rapamycin was also observed in rat cardiac transplantation. 286 KRP-203 or 2-amino-2-(2-[4-3(-benzyloxyphenylthio)-2-cholorophenyl]ethyl)-1,3-propanediol hydrochloride has a similar molecular structure as FTY720. KRP-203 alone or in combination with low-dose cyclosporine or MMF prolonged skin, heart, and renal allograft survival. 78,224,246

Stable renal transplant patients maintained on cyclosporine tolerate well one oral dose of FTY720 (0.25-3.5 mg). Similarly to its effect in animals, single doses of FTY720 cause a lymphopenia that is dose-dependent in intensity and duration, and that equally affects CD4 cells, CD8 cells, memory T cells, naïve T cells, and B cells. 29 In phase II and III studies in de novo renal transplantation, it was shown that 2.5 mg FTY720 in combination with full-dose cyclosporine and steroids is as effective as MMF in combination with full-dose cyclosporine and steroids, although the FTY720-treated patients had lower creatinine clearance at 12 months. 260,261 FTY720 5 mg did not allow a 50% reduction in cyclosporine exposure. 214,260 FTY720 2.5 mg in combination with reduced-dose cyclosporine resulted in underimmunosuppression. 165 Also in combination with tacrolimus, FTY720 2.5 mg was not superior to MMF in a recent study in de novo renal transplant recipients. 100 Recently, it was reported that FTY720 in combination with everolimus was not beneficial with regard to prevention of acute rejection and preservation of allograft function in renal transplant recipients at high risk for delayed graft function. 259

The side effects of FTY720 are in general similar to those of other immunosuppressants, with hypertension, anemia, constipation, and nausea most commonly reported. Side effects specific for FTY720 are bradycardia, macular/retinal edema, dyspnea, and a transient rise in liver function tests. 165, 214 Although it is considered a main impediment of further clinical development, reduction of heart rate after the first dose of FTY720 is transient and does not persist in the maintenance phase. 61, 176 Importantly, typical side effects of CNI -nephrotoxicity, neurotoxicity, and diabetogenicity -have not been observed with FTY720.

FTY720 has a unique mechanism of action. The available clinical studies show that FTY720 is not superior to standard care and therefore its future in organ transplantation is uncertain.

Chemical Structure and Pharmacology 1,25-Dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) and some of its new synthetic structural analogues are promising immunomodulators with effects in autoimmunity and transplantation immunology. Besides its well-known role in mineral and bone homeostasis, non-classical effects of vitamin D have been increasingly recognized, such as modulation of growth, differentiation, and function of various cell types, regulation of immune responses, cardiovascular processes, and cancer prevention. 20,277 Local vitamin D metabolism allows immune cells to modulate immune response autonomously. Optimal immune functioning of this autocrine and/or paracrine circuit crucially depends on the availability of circulating 1,25(OH) 2 D 3 . The exact levels of circulating 1,25(OH) 2 D 3 needed to meet the requirements of "vitamin D sufficiency" are still a matter of debate, especially in the light of the non-classical effects of vitamin D.

A role for 1,25(OH) 2 D 3 in immune regulation is suggested by the presence of its receptor (vitamin D receptor or VDR) in almost all immune cells, including activated CD4 and CD8 cells, B cells, neutrophils, and antigen-presenting cells, hence modulating both innate and adaptive immune responses. 196, 251 Moreover, the VDR expression in some immune cells is controlled by immune signals. 10 Furthermore, most immune cells express vitamin D metabolizing enzymes such as CYP27B1 in T and B lymphocytes, and CYP2R1 in dendritic cells. 178, 236 This allows for the local conversion of 25(OH)D 3 into 1,25(OH) 2 D 3 , and represents an important mechanism by which immune cells can reach supraphysiological levels of 1,25(OH) 2 D 3 needed to influence immune responses without affecting systemic levels of 1,25(OH) 2 D 3 . Furthermore, the expression of CYP27B1 in immune cells is controlled by immune signals. For example, CYP27B1 expression by monocytes/macrophages is upregulated by interferon-γ (IFN-γ), lipopolysaccharide, Mycobacterium tuberculosis-derived 19 kDa lipoprotein and viral infections. Moreover, CYP27B1 expression in macrophages and dendritic cells is not suppressed by 1,25(OH) 2 D 3 itself, allowing for massive local production of 1,25(OH) 2 D 3 by macrophages in patients with granulomatous diseases. As an alternative negative-feedback loop 1,25(OH) 2 D 3 upregulates CYP24 in immune cells. 56 Upon exposure to 1,25(OH) 2 D 3 monocytes acquire phenotypical features of macrophages, and macrophages obtain increased chemotactic and phagocytic activities. 91 Moreover, Toll-like receptor activation of monocytes/ macrophages results in upregulation of VDR and VDR target genes leading to the induction of cathelicidin antimicrobial peptide and killing of Mycobacterium tuberculosis. 144 1,25(OH) 2 D 3 inhibits dendritic cell maturation (decreased levels of major histocompatibility complex class II and costimulatory molecules), enhances endocytic capacity, inhibits the production of IL-12 and IL-23, and enhances the release of IL-10 and macrophage inflammatory protein-3α. Dendritic cells are thereby deviated towards a more immature or tolerogenic phenotype, having in vitro as well as in vivo the capacity to induce the development of regulatory T cells. 89, 188, 275 Upon T-cell activation, VDR expression is dramatically increased. Furthermore, 1,25(OH) 2 D 3 also directly alters the cytokine profile of T cells by inhibiting the production of inflammatory Th1-cytokines such as IL-2 and IFN-γ, as well as the Th17-derived cytokines IL-17 and IL-21. 111, 257 CD4 + CD25 high CD127 low regulatory T cells were induced after vitamin D exposure and IL-10 was selectively induced within CD4 T cells. The molecular pathways by which 1,25(OH) 2 D 3 modulates the expression of these and other genes in the immune system varies widely (reviewed in reference 11). Next to the classical interaction with VDR-specific binding sites in the promoter region of target genes (vitamin D-responsive elements), as in the inhibition of IFN-γ, 45 1,25(OH) 2 D 3 also interferes with other pathways of transcription regulation. For example, 1,25(OH) 2 D 3 -mediated inhibition of IL-2 is due to impairment of nuclear factor of activated T cells/activating protein-1 (AP-1) complex formation and subsequent association with its binding site within the IL-2 promoter. 5, 253 Exposing B cells to 1,25(OH) 2 D 3 inhibits the proliferation, plasma cell differentiation, immunoglobulin secretion (IgG and IgM), and memory B-cell generation, and induces B-cell apoptosis. 36 Finally, 1,25(OH) 2 D 3 was put forward as an important regulator of lymphocyte trafficking. Active 1,25(OH) 2 D 3 imprints activated T cells and terminally differentiating B cells with skin-homing properties via induction of the skin-homing receptor CCR10. 225, 229 

The fact that 1,25(OH) 2 D 3 and its analogues influence the immune system by immunomodulation through the induction of immune shifts and regulator cells makes these products very appealing for clinical use, especially in the treatment and prevention of autoimmune diseases. In the NOD mouse, upregulation of regulator cells and a shift away from Th1 towards Th2 could be observed in 1,25(OH) 2 D 3 -treated mice, both locally in the pancreas as well as in the peripheral immune system. 90, 179 Moreover, a restoration of the defective sensitivity to apoptosis characteristic for NOD T lymphocytes was observed, resulting in a better elimination of autoreactive effector cells. 33, 51 This increased sensitivity to apoptosis has been described for different apoptosis-inducing signals. This mechanism may explain why an early and short-term 1,25(OH) 2 D 3 treatment before the clinical onset of autoimmunity can lead to long-term protection and restoration of self-tolerance.

A clear additive and even synergistic effect was observed between 1,25(OH) 2 D 3 or its analogues and other more classical immunosuppressants such as cyclosporine, sirolimus, or MMF, both in vitro and in several in vivo autoimmune disease models, such as autoimmune diabetes 34,95 and experimental autoimmune encephalomyelitis. 26, 27, 272 Moreover, 1,25(OH) 2 D 3 and its analogues were investigated in various transplantation models such as pancreatic islet allo-and xenotransplantation in mice, 89, 95 allogeneic heart 113 and skin transplantation in mice, 18,278 allogeneic aorta, 199 bone marrow, 180 heart, 106,136 kidney, 201 and liver transplantation in rats. 202 The overall conclusion that can be drawn from these studies is that, as monotherapy, 1,25(OH) 2 D 3 and its analogues provoke only a modest prolongation of graft function. This is not surprising in view of the rather weak intrinsic effects of 1,25(OH) 2 D 3 and its analogues on T cells. However, in conjunction with other immunosuppressants, strong synergistic effects often can be observed. In addition, in view of its effect on antigen presentation and on directing the immune system in the Th2 direction, 1,25(OH) 2 D 3 may help to induce tolerance. 89

Multiple groups have reported a correlation between vitamin D deficiency and susceptibility to respiratory infections, especially in the context of infections by Mycobacterium tuberculosis and Gram-negative bacteria. 105 Autier and Gandini performed a meta-analysis including 18 independent randomized controlled trials, demonstrating that administration of vitamin D supplementation is associated with a decrease in overall mortality rates (relative risk 0.93, 95% confidence interval 0.87-0.99). 9 There is still a lack of non-biased large cohort studies that can sustain the proposed benefits of vitamin D supplementation for optimal immune function.

Mutations in the CYP2R1 gene, as well as in the CYP17B1 gene, impairing their enzymatic activity, have been described and polymorphisms in these genes have been proposed to be associated with type 1 diabetes mellitus susceptibility. 146, 200 Analogues of vitamin D could successfully block progression of insulitis in prediabetic NOD mice, along with preventing recurrence of autoimmune diabetes in NOD mice after syngeneic islet transplantation, when combined with other immunomodulating agents. 34,89

A major concern remains the side effects of 1,25(OH) 2 D 3 on calcium and bone metabolism. The use of 1,25(OH) 2 D 3 analogues which have maintained or amplified immunomodulatory effects in combination with reduced effects on calcium and bone partially conquer this problem. 273 The additional use of calcium-lowering conditions, such as limited nutrient calcium intake, and bone resorption inhibitors, such as bisphosphonates, aid in further bypassing the negative side effects of hypercalcemia and excessive bone resorption, 271 thereby facilitating the step towards the clinical applicability of 1,25(OH) 2 D 3 and its analogues for their potent immunomodulatory properties.

With the discovery of VDRs and vitamin D-metabolizing enzymes in immune cells, it is now evident that 1,25(OH) 2 D 3 exerts a plethora of effects targeting both the innate and adaptive immune compartment. The emerging data linking inadequate vitamin D levels to immune anomalies, such as increased infection rates and autoimmunity, are of interest in this context. VDR agonists, and especially hypocalcemic vitamin D analogues, are plausible candidates for the prevention and/or treatment of infections such as tuberculosis and several autoimmune disorders.

Bredinin, 4-carbamoyl-1-b-d-ribofurano-syhmidazolium-5-olate, is a nucleoside analogue that is structurally similar to ribavirin. It was first isolated from the culture media of the ascomycetes Eupenicillium brefeldianum harvested from the soil of Hachijo Island (Japan, 1971). It has weak antibiotic activity against Candida albicans. 164

Bredinin exerts its immunosuppressive function through selective inhibition of the enzymes inosine monophosphate dehydrogenase and guanosine monophosphate synthetase, both of which are required for the generation of guanosine monophosphate from inosine monophosphate in the de novo pathway. In contrast to azathioprine, bredinin is not incorporated into nucleic acids in the cells, resulting in fewer side effects, such as myelosuppression and hepatoxicity. Bredinin was found to inhibit both humoral and cellular immunity by selectively inhibiting lymphocyte proliferation. 108

In a canine model of renal transplantation, bredinin prolonged graft survival. In humans, as compared to azathioprine, bredinin showed equally potent immunosuppressive activity and fewer adverse effects. 8, 122, 254, 256 As expected based on its similarity in structure to ribavirine, bredinin exhibits in vitro antiviral activity against CMV, respiratory syncytial virus, measles, hepatitis C, corona virus, parainfluenza, and influenza virus. 103, 169, 210, 223 In a recent study, bredinin was substituted for MMF in patients with BKV in their urine. BKV DNA in the urine became negative in five out of seven patients. 83 In the remaining two patients, there was a significant decrease in urinary BKV DNA. No acute rejection or deterioration of graft function occurred during the study period. 83

The principal adverse reactions associated with the use of bredinin were leukopenia, abnormal hepatic function, rash, increased levels of uric acid, and vomiting.

Bredinin has mainly been used in Japan and is infrequently used elsewhere. As a consequence, experience with bredinin is limited, but results show that it is a safe and effective immunosuppressant in human kidney transplantation. Because of its antiviral activity, bredinin might be yet another drug to be evaluated in the setting of BKVN. 

Of the multiple potential candidate compounds, one has entered clinical trials -the ATP congener CP-690,550 (CP; tasocitinib or tofacitinib, Pfizer, NJ), which binds to the ATP catalytic site on JAK molecules. It has been proposed that analysis of P-STAT5 at the cellular level could be an adequate means to monitor the immunomodulatory effect of CP-690,550. 198

JAK3 is a tyrosine kinase essential for the signal transduction from the common gamma-chain of the cytokine receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 to the nucleus. As the expression of the receptors is restricted to immune cells, this makes them an attractive target for new immunosuppressants. Signal transduction mediated by JAK3 is obligatory for lymphocyte activation, differentiation, and homeostasis, as evidenced by the finding that deficiency in JAK3 results in severe combined deficiency syndrome. 148, 204, 206, 207 A possible detrimental effect of interference with IL-2 signaling relates to the fact that tolerance induction is essentially dependent on the IL-2 pathway. 128, 151, 152 Thus, the challenge for immunosuppressive drug design has been to achieve selective inhibition of JAK3 versus JAK2 activities. Although Pfizer claimed a 20-fold selectivity for JAK3 using an in vitro assay, clinical data suggest that this ratio is far less than 20-fold. This narrow selectivity was confirmed by the work of Karaman et al. 117

CP-690,550 is the most potent (inhibitory potency of 1nM) and selective JAK3 inhibitor developed to date. In both rodents and non-human primates, CP-690,550 exerted strong suppression of immune reactions and prolonged the survival of cardiac and renal allografts. In monotherapy it significantly delayed the onset of rejection in kidney allografts. 24,25,35 In non-human primates, CP-690,550 significantly reduced IL-2-enhanced IFN-γ production and CD25 and CD71 expression by T cells. Furthermore, CP-690,550 inhibited cellular alloimmune responses in vitro. 35, 184 Administration in vivo resulted in a reduction of NK cell and T-cell numbers, whereas CD8 effector memory T-cell levels were unaltered. 46, 184 Recently, it was shown that CP-690,550 selectively inhibits T-cell effector function while preserving the suppressive activity of CD4 + CD25 high regulatory T cells. 222

CP-690,550 was evaluated as induction and maintenance therapy in a phase IIA, multicenter, open-label, randomized controlled trial in kidney transplant recipients. 31 All patients received induction therapy, MMF, and steroids. Patients in group 1 received tacrolimus, while patients in groups 2 and 3 were administered CP-690,550 15 mg and 30 mg twice a day, respectively. 31 Because of the high incidence of BKVN in the CP-690,550 groups, the protocol was adjusted to stop MMF and decrease the steroid exposure. Compared to tacrolimus, both CP-690,550 groups showed similar rates of acute rejection episodes and allograft function, but experienced greater incidences of hyperlipidemia and infections (suggestive of additional JAK2 inhibition). 31 A phase IIB trial compared cyclosporine at standard dosage versus CP-690,550 15 mg twice a day for 6 months then 10 mg twice a day, or CP-690,550 15 mg twice a day for 3 months then 10 mg twice a day. All patients received in addition induction therapy, MMF, and steroids. Unexpectedly, the lower CP-690,550 dosage arm showed a trend toward the lowest rejection rate and a superior allograft function. However, in this study there were important adverse events, including increased CMV infection rates, and BKVN in both CP-690,550 arms (data presented at 2011 American Transplant Congress).

In a dose escalation study, the most frequent adverse events were infection and gastrointestinal side effects. CP-690,550 15 mg and 30 mg twice a day were associated with a mean decrease in hemoglobin from baseline of 11%. 274 There was in addition a decrease in natural killer cells and B cells. There were no changes in the number of neutrophils, total lymphocytes, platelets, or CD4 or CD8 T cells. 274 

In summary, combination of CP-690,550 with MMF resulted in acceptable rates of acute rejection with evidence of overimmunosuppression when CP-690,550 30 mg twice a day was combined with MMF. CP-690,550 15 mg twice a day co-administered with MMF resulted in similar outcomes while associated with modest lipid elevations and a higher rate of viral infections. In our opinion, considering the known side-effect profile of CNI, further evaluation of CP-690,550 is warranted. Given the side effects reported with the use of CP-690,550, the challenge remains to develop immunosuppressive drugs with truly selective inhibition of JAK3 versus JAK2 activities. The lack of success in developing a selective antagonist of JAK3 probably relates to the focus on chemical analogues of ATP while more success is to be expected from developing molecules displaying allosteric inhibition via binding of non-catalytic sites.

Sotrastaurin (AEB071) is a low-molecular-weight, synthetic compound that potently and reversibly inhibits all 10 isoforms of protein kinase C (PKC) -most importantly, PKC-θ, PKC-α, and PKC-β, with lesser activity on PKC-δ. 123 Sotrastaurin is primarily metabolized through hepatic CYP3A4 into inactive metabolites and N-desmethyl-sotrastaurin, which has similar potency as sotrastaurin and is present at low blood concentrations (less than 5% of the parent exposure). Renal excretion of sotrastaurin is negligible and only a small amount is excreted in the bile (1% of the dose). The elimination half-life of sotrastaurin averages 6 hours. In clinical trials, it is recommended that patients administer sotrastaurin consistently either with or without food to avoid foodrelated fluctuations in drug exposure over time. 123 Clinical drug interaction studies to date have demonstrated that sotrastaurin increases the area under the concentration-time curve of everolimus (1.2-fold) and of tacrolimus (2-fold). 124 Sotrastaurin increased tacrolimus concentration inasmuch as the tacrolimus dose needed to achieve a given C 0 was up to 47% lower when combined with sotrastaurin versus MMF. 124 Conversely, sotrastaurin area under the concentration-time curve is increased up to 1.8-fold by cyclosporine and 4.6-fold by ketoconazole. 125

PKC is a family of serine/threonine-specific protein kinases involved in diverse signal transduction pathways that modulate a whole range of cellular processes, including activation, proliferation, differentiation, apoptosis, and autophagy. 231 PKC-θ has been shown to be essential in the T-cell receptor/CD3 signal transduction pathway. PKC-α modulates Th1 responses, including IFN-γ production. PKC-β controls B-cell receptorinduced NF-κB transactivation and T-independent B-cell responses. Finally, PKC-ε influences macrophage function. 161, 255 

Of note, sotrastaurin was demonstrated to be non-toxic when added to human islet cultures. 162 These results suggest AEB071 to be an appropriate immunosuppressive candidate for clinical trials in islet transplantation. Recently, it was shown in non-human primates that sotrastaurin in combination with cyclosporine at subtherapeutic doses resulted in markedly prolonged renal allograft survival, indicating synergistic immunosuppressive effects. 19

In a phase II randomized controlled trial, sotrastaurin with standard or reduced tacrolimus was compared with standard tacrolimus alone, in addition to induction therapy and steroids. 30 Three months posttransplant, stable patients on sotrastaurin were switched from tacrolimus to MMF. The three arms showed equal efficacy up to 3 months; at the end of the study there was no difference in allograft function, although the incidence of acute rejection was significantly higher in the standard tacrolimus with sotrastaurin arm. 30 Because of lack of efficacy, this study was prematurely discontinued. In another recent trial in de novo renal transplant recipients with immediate graft function, study subjects were randomized to sotrastaurin or tacrolimus. 73 All patients received basiliximab, MMF, and steroids. This study demonstrated a lower degree of efficacy but better renal function with the CNI-free regimen of sotrastaurin with MMF versus the tacrolimus-based control. 73 A study combining sotrastaurin with everolimus is currently ongoing.

In the above-mentioned clinical trial, there was a 12% incidence of tachycardia and 18% of serious infections. 30,73 A dose-dependent chronotropic effect has been observed in preclinical and phase I sotrastaurin studies; therefore the higher heart rate and tachycardia observed with the sotrastaurin in combination with MMF were not unexpected. All tachycardia adverse events were mild and the majority occurred soon after transplantation.

Sotrastaurin blocks PKC-mediated early T-cell activation, 20 providing a new approach for immunosuppression distinct from CNI. However, the efficacy results of this phase II study do not support the combination of sotrastaurin 300 mg twice a day with MMF as a CNI-free regimen. Based on the results recently reported by Bigaud et al. in non-human primates, 19 sotrastaurin as a CNI-sparing agents warrants further evaluation in future clinical trials.

Bortezomib is a proteasomal inhibitor approved by the Food and Drug Administration for the treatment of multiple myeloma. Bortezomib is increasingly used in the setting of solid-organ transplantation. Bortezomib was administered in four doses of 1.3 mg/m 2 intravenously in 3-5-minute infusions over an 11-day period in kidney transplant recipients. Prior to bortezomib administration, patients need to be premedicated with methylprednisolone. Peak serum concentration is reached at 30 minutes and the drug is cleared within 1 hour. 62

Bortezomib is a selective inhibitor of the 26S proteasome, preventing the activation of NF-κB. 244 It induces apoptosis of rapidly dividing, metabolically active cells with extensive protein synthesis. The ability of bortezomib to target plasma cells spurred interest as a new therapeutic approach in the treatment or prevention of alloantibody formation in organ transplantation.

In vitro, bortezomib was associated with a reduction in the number of bone marrow-derived plasma cells and attenuated alloantibody production. 193 Bortezomib primarily acts through plasma cell depletion, resulting in reduced antibody production to T-dependent antigens. As marginal zone B cells are resistant to bortezomibmediated effects, T-independent type 2 responses are less affected. 133 In a mouse model of lupus, bortezomib depleted both short-and long-lived plasma cells, resulting in a reduction of anti-double-stranded DNA antibody production. 170 Vogelbacher et al. recently established that bortezomib alone or in combination with sirolimus can also prevent alloantibody formation in a rat model of kidney transplantation. 279

Bortezomib therapy for antibody-mediated rejection has resulted in mixed results. 55 ,63, 218 Everly et al. administered bortezomib to 6 patients with antibody-mediated rejection with concomitant acute cellular rejection refractory to currently available therapies. 63 Bortezomib administration resulted in resolution of antibody-mediated rejection in all 6 patients, a decrease of donor-specific antibody levels, and improvement of allograft function. 63 In another study, Walsh et al. reported the results of bortezomib treatment in 28 patients with antibodymediated rejection. 285 Bortezomib treatment was associated with variable results, with better responses in early (occurring in the first 6 months after transplantation) versus late (occurring 6 months or more after transplantation) antibody-mediated rejection. 285 In contrast, in the study of Sberro-Soussan et al., bortezomib treatment did not result in a decrease of donor-specific antibody mean fluorescence intensity when used as sole desensitization therapy in four renal transplant recipients with subacute antibody-mediated rejection with persistent donorspecific antibodies. 218 However, in this study bortezomib therapy was not initiated until weeks or months following the diagnosis of antibody-mediated rejection, and repeat biopsies were not performed following bortezomib treatment. 218

The most common side effects associated with bortezomib treatment are gastrointestinal toxicity, thrombocytopenia, and neuropathy. 63 These can be potentially severe and disabling. To date, no increase in rate of opportunistic infections has been reported. Importantly, although bortezomib is associated with substantial reductions in donor-specific antibody levels, it does not result in a decrease in protective antibody levels. 64

Proteasome inhibitor therapy has potential in the treatment of antibody-mediated rejection in kidney transplant recipients both as primary and rescue therapy. Optimal responses with bortezomib are obtained when antibodymediated rejection occurs early posttransplant and bortezomib treatment is initiated promptly. Bortezomib has recently also been shown to provide effective therapy for antibody-mediated rejection in heart and lung transplant recipients. 57, 171 Others Cladiribine is an adenosine deaminase-resistant analogue of deoxyadenosine and is used in the treatment of leukemia and lymphoma. A number of studies have explored the immunosuppressive capacity of cladiribine. In vitro, cladribine inhibits both B-and T-cell proliferation. 86 In vivo, cladiribine monotherapy was shown to prolong skin allograft survival in mice, 87 in combination with cyclosporine it prolonged liver and heart allograft survival in rats, 221 and was more effective than cyclosporine monotherapy in small-bowel allografts. 174 However, no clinical trials are published to date.

The farnesyltransferase inhibitor A 228839 was developed as an anticancer compound that inhibits Ras GTPases. A 228839 inhibited lectin-induced proliferation and antigen-presenting cell-induced T-cell proliferation. The compound also inhibited lymphocyte Th1 cytokine production and promoted apoptosis in lectinactivated lymphocytes. 227 Another farnesyltransferase inhibitor, ABT-100 was shown in vitro to block the secretion of IFN-γ and IL-4 by naïve T cells and suppressed alloreactivity. In a rat heterotopic cardiac transplant model, ABT-100 alone or in combination with subtherapeutic dose of cyclosporine delayed the development of acute rejection. 226 Given its combined antirejection and antioncogenic effects, farnesyltransferase inhibitors could represent an attractive new class of immunosuppressants in malignancy-prone organ transplant recipients if future clinical trials confirm their efficacy.

When a T-cell receptor recognizes its specific antigen the lymphoid cell-specific kinase lck is phosphorylated and, together with the receptor-associated CD3 complex, phosphorylates zinc-associated phosphorylase 70. These events trigger the downstream cascade that increases intracellular calcium, activating calcineurin. Inhibitors of lck have become available recently. A-770041 and structurally similar molecules have been shown to prolong the survival of heterotopic murine heart and renal subcapsular islet grafts as well as to blunt the production of immunoglobulin IgG2a. Emodin (C 15 H 10 O 5 ), the cyclic derivative from rhubarb root and rhizomes, has been shown to prolong murine skin graft survival and to dampen IL-2 production. 145 However, neither of these archetypal compounds shows sufficient specificity for lck versus other kinases to warrant clinical development. 227 FR 252921, an immunosuppressive agent isolated from the culture of Pseudomonas fluorescens, inhibits AP-1 transcription activity, and acts predominantly against antigen-presenting cells. FR 252921 demonstrated synergy with tacrolimus in vitro and in vivo. In murine models of skin transplantation, compared with the optimal dose of tacrolimus alone, the combination of FR 252921 and tacrolimus prolonged graft survival. [75] [76] [77] Brequinar sodium exerts its immunosuppressive effects through the inhibition of the enzyme dihydroorotate dehydrogenase, resulting in inhibition of both T and B lymphocytes. Although the characteristics of brequinar suggest that it would be an attractive immunosuppressant, the suboptimal pharmacologic profile jeopardizes its use in transplant patients. The future use of this drug in the field of transplantation will require the development of analogues exhibiting a shorter half-life and reduced toxicity.

Spergualin was originally isolated from the culture filtrate of Bacillus laterosporus, and explored as a new anticancer or antibiotic substance. Its analogue 15-deoxyspergualin subsequently became widely known as a promising new immunosuppressant. The precise mode of action of 15-deoxyspergualin is largely unknown and, because of its poor oral bioavailability, 15-deoxyspergualin must be delivered parenterally, which hampers its widespread clinical use. 263 Its efficacy has been demonstrated in the treatment of kidney allograft rejection, ABO-incompatible kidney transplantation, and transplantation in sensitized patients. 6, 93, 252 Until analogues are developed that allow oral administration, 134 the major clinical indication of 15-deoxyspergualin is limited to the treatment of rejection crises where 15-deoxyspergualin may be an interesting alternative to steroids or antilymphocyte agents. The fact that it remains effective after recurrent administration is promising.

Upon cellular uptake, cyclophosphamide is extensively metabolized into its active compounds phosphoramide mustard and acrolein. 22, 49 The reaction of the phosphoramide mustard with DNA results in cell death. 50 Because of its limited efficacy and multiple side effects, the only standard indication for cyclophosphamide in transplantation today is the desensitization of highly sensitized recipients prior to kidney transplantation. 1 Most of these protocols involve repeated plasmapheresis, in combination with cyclophosphamide, either with or without continuation of steroids, until a kidney transplant becomes available.

For several decades, total lymphoid irradiation (TLI) has been used for the treatment of Hodgkin's disease. The possibility of applying TLI as an immunosuppressive regimen rather than an anticancer treatment was discovered by investigators at Stanford University. 81 Procedure TLI is delivered through two ports. A first so-called mantle port includes the lymph nodes of the neck, axilla, and mediastinum. The other port is called the "inverted Y" and encompasses aortic, iliac and pelvic lymph nodes, and spleen. Usually, a total dose of 40-50 Gy (1 Gy = 100 rad) is administered in daily fractions of 1.5-2.5 Gy.

Much of the currently available experimental evidence on the immunological mechanisms underlying TLI-induced tolerance points to the importance of suppressor cells. The group of Strober identified post-TLI suppressors cells as host-type natural killer T cells, as the protective effect of TLI against graft-versus-host disease was abrogated in mice with a CD1d inactivated gene. 130 These host-type natural killer T cells produced IL-4 and stimulated donor-type cells to produce IL-4 also. 130, 131 Definitive evidence of the functional importance and activity of these suppressor cells was delivered by the demonstration that they could prevent graft-versus-host disease in vivo. 99 Post-TLI attenuation of effector T-lymphocyte reactivity was equally proposed to be responsible for the observed immunosuppressed state after TLI. 16, 68, 69 This intrinsic T-cell defect was dependent on the irradiation of both thymus and extrathymic tissues. 181 After TLI, anergized T cells were shown to be incapable of proliferating even in the presence of exogenous IL-2. 71 In other studies, TLI was shown to lead to thymic clonal deletion of donor-or host-reactive lymphocytes. 211 TLI-treated mice also exhibited decreased antidonor cytotoxic T-cell precursor frequencies. 72 Finally, Strober's group showed that Th2 lymphocytes recover soon after TLI, whereas Th1 lymphocytes remain deficient for several months, 15 and showed that this defect can also be prevented by thymic shielding during irradiation. 16 This Th2 dominance after TLI has been confirmed by other groups in rodents 70 and in large animals. 233 Recently, Nador et al. demonstrated that tolerance induction after conditioning with TLI and antithymocyte globulin (ATG) depends upon the ability of naturally occurring regulatory natural killer T cells and regulatory T cells to suppress the residual alloreactive T cells that are capable of rejecting the allograft. 167

TLI-treated BALB/c mice receiving fully allogeneic C57BL6 bone marrow and skin graft on the first day after TLI became stable hematopoietic chimeras without signs of graft-versus-host disease, and developed permanent donor-specific tolerance with preserved anti-third-party reactivity. 239 Tolerance induction was critically dependent on the width of the irradiation field, the time of transplantation after TLI, the total dose of TLI, and the absence of presensitization. 239, 280, 281 Although bone marrow chimerism could be easily induced, tolerance to either heart 88 or kidney allografts 104 was not obtained, suggesting that TLI-induced bone marrow chimerism does not necessarily create tolerance toward organ-specific antigens.

The combination of TLI and low-dose cyclosporine was found to be effective and clinically safe in rats, 208 and TLI with postoperative ATG induced permanent and specific transplantation tolerance toward heart allografts in about 40% of transplanted dogs. 238 These encouraging results led to a similar trial in clinical kidney transplantation. Myburgh et al. applied a modified TLI regimen in baboons, with low dosage and wide-field exposure, and showed that tolerance can be achieved in larger animals without concomitant bone marrow transplantation. 166 Also, in heart or heart-lung transplantation experiments between xenogeneic non-human primate species, preoperative TLI, when administered in combination with cyclosporine and ATG, 209 cyclosporine and splenectomy 23 or cyclosporine and medrol, 185 was more efficient than any other treatment regimen. Pretransplant TLI, combined with cyclosporine and methotrexate in a pig heart-into-baboon model, resulted in a graft survival time of more than 2 weeks. This regimen was able to inhibit xenoreactive natural antibody production but not the xenoreactivity of macrophages. In a pig islet-into-rat xenograft model, TLI in combination with deoxyspergualin was extremely effective, 262 and even in a discordant lamb-into-pig model, TLI synergized with cyclosporine and azathioprine to provoke a 30-fold increase of the mean xenograft survival time. 264 The principal disadvantage for the clinical application of TLI is that the complete regimen of fractionated daily irradiations needs to be administered and completed before, and sufficiently close to, the moment of transplantation, and finding a suitable donor organ within such a restricted timeframe is problematic. Investigators have therefore explored the possibility of using TLI after transplantation. In mouse and rat heart allograft models, posttransplant TLI significantly prolonged graft survival when combined with monoclonal anti-CD4 antibodies 266 or with infusion of donor-type dendritic cell precursors. 98

The first clinical kidney transplants utilizing TLI were performed at the University of Minnesota in 20 patients who had previously rejected a renal allograft. 168 Because similar results (an increase of about 30% 1-year graft survival compared with historical control data) were achieved in this patient population using cyclosporine, and because of the ease of administration, the investigators concluded to prefer cyclosporine over TLI.

In the 1980s, a controlled trial was performed at the University of Leuven, in which end-stage diabetic nephropathy patients received cadaveric kidney allografts, investigating the effect of pretransplant TLI (20 daily fractions of 1 Gy, followed by 1 weekly TLI dose until a suitable donor was found) followed by low-dose posttransplant prednisone maintenance treatment. 283 Longterm (8-year) follow-up revealed that rejection episodes were more frequent, and patient and graft survival significantly inferior in the TLI-treated group. 282 The excess mortality in the TLI-treated patients was due to sepsis, resulting from high-dose steroid therapy needed to treat rejection crises. This clinical experience confirmed the animal data that also showed that TLI by itself is insufficient to provoke long-term graft survival or tolerance and that extra manipulations are needed.

In a study at Stanford University, 24 patients received a first, and one patient a second, cadaveric renal allograft using TLI and ATG. 138 The actuarial graft survival was 76% and 68% at 1 and 2 years, respectively. Ten of the 25 patients never had a rejection crisis despite an overall poor HLA-matching between donor and recipient. In follow-up studies, a specific antidonor mixed lymphocyte culture hypo-or non-responsiveness was demonstrated 44 and, in some patients, all immunosuppressive drugs could be withdrawn. 237 An evaluation in a larger group of 52 patients treated with the same protocol at the same center showed a 3-year graft survival of about 50%, which is less than in cyclosporine-treated patients (around 75%). 138 Posttransplant TLI in combination with anti-CD3 monoclonal antibodies, or with ATG and donor-specific blood transfusions, seemed very effective in a rat heart allograft model. On the basis of these results, the efficacy of TLI was evaluated in heart transplant patients with therapy-resistant or early vascular rejection. 107, 137, 213 This resulted in a significant reduction of rejection recurrences, an effect which was maintained for at least 2 years. In the meantime, these favorable results have been confirmed by several other groups. Also, TLI-treated patients develop less coronary atherosclerosis than matched controls despite multiple rejection episodes. 7, 40, 149, 187, 270 Scandling et al. have reported the use of TLI to induce tolerance in the setting of combined kidney/hematopoietic stem cell transplantation between HLA-matched donor/recipient pairs. 219, 220 Patients received a conditioning regimen of 10 doses of TLI (80-120 cGy), five doses of rabbit ATG, MMF for 1 month, and cyclosporine for at least 6 months. Donor hematopoietic stem cells were injected intravenously on day 11 in the outpatient infusion center. 220 The majority of patients (8/12) were able to discontinue antirejection medications, and all patients had excellent graft function at the last observation point. The reason for continued immunosuppressive therapy was recurrence of focal segmental glomerulosclerosis in one of four patients and rejection episodes during the tapering of cyclosporine in the three other patients. 220 Conclusion TLI has been shown to be a safe immunosuppressive regimen. It has been abandoned in clinical practice for organizational reasons, except for the treatment of therapy-resistant rejection of heart or heart-lung transplant. However, its ability to induce tolerance -in combination with ATG and hematopoietic stem cell transplantationmight renew interest in this treatment modality. To date, no evidence of radiation-related late effects has been documented with TLI. 141

Extracorporeal photopheresis is a technique in which leukocytes, removed from patients by leukopheresis, are exposed to 8-methoxypsoralen and ultraviolet A light. It was developed as an immunoregulatory treatment for erythrodermic cutaneous T-cell lymphoma. 58 Subsequently, the procedure was shown to be safe as an alternative treatment for various human immune and autoimmune diseases. 192 Furthermore, in rats 191 and monkeys, 189 the regimen was shown to result in extended skin allograft and cardiac allograft and xenograft survival.

Different mechanisms have been shown to contribute to the immunomodulatory effect of photopheresis: selective inhibition of effector cells, 190, 191 induction of a high rate of apoptosis, 296 increased capacity to phagocytose apoptotic T cells, resulting in the induction of anticlonotypic immune responses, 205 shift towards Th2 immune activation, 12 and induction of regulatory CD4 and CD8 cells. 84, 92 In clinical transplantation, photopheresis has been applied as both a therapeutic and prophylactic option. It has been applied in the treatment of recurrent or resistant acute rejection in renal transplant patients, 12, 48, 85, 101, 127, 243, 290 but the number of patients included in these studies is limited, and prospective randomized trials are needed. The safety and efficacy of photopheresis in the prevention of acute rejection of cardiac allografts have been evaluated in primary cardiac allograft recipients, randomly assigned to standard triple-drug immunosuppressive therapy (cyclosporine, azathioprine, and prednisone) alone or in conjunction with 24 photopheresis sessions performed during the first 6 months after transplantation. After 6 months of follow-up, photopheresis-treated patients developed significantly fewer multiple rejections, and there were no significant differences in the rates or types of infection. Although there was no significant effect on graft survival rates at 6 or 12 months, this study indicated that photopheresis may be an effective new immunosuppressive regimen in transplant recipients. 13 In patients with refractory bronchiolitis obliterans after lung transplantation, photopheresis resulted in a stabilization of graft function and/or in some of these patients in histological reversal of rejection. 173, 212 SPLENECTOMY Pretransplant splenectomy in the recipient before transplantation was first proposed by Starzl et al. in 1963 as a means of improving graft survival. 234 Although splenectomy is a standard procedure for patients who develop hypersplenism or azathioprine-associated leukopenia, evidence on the role of splenectomy in enhancing graft survival is controversial. 175, 195, 234, 240 A large prospective randomized trial in Minneapolis showed splenectomy improved graft survival significantly, 74 but longer-term follow-up showed loss of beneficial effects because of an increased infection-related mortality. 245 Several other single-center studies have shown an alarming risk of sepsis and death, nullifying any early benefits of splenectomy on graft survival, 2, 194 and a multicenter analysis from the South Eastern Organ Procurement Foundation confirmed a modest improvement in graft survival after splenectomy, but a relentless increase in patient mortality. 147 Splenectomy has a place in the preparation of a recipient who is to receive an ABO-incompatible graft, a practice that is likely to become more widely employed in living related donor transplantation, where an ABOincompatible but otherwise suitable donor is the only available donor. Alexandre et al. reported a series of 38 such ABO-incompatible living donor transplants in which the recipient was prepared by plasmapheresis, donor-specific platelet transfusion, and splenectomy. 3, 203, 232 Although the authors believe that the need for plasmapheresis and donor-specific platelet transfusion should be re-evaluated, splenectomy was thought to be important, since 3 of 38 recipients who did not have a splenectomy lost their grafts from acute vascular rejection, in contrast to only 5 of 33 who did undergo splenectomy. A smallscale but successful experience with postsplenectomy ABO-incompatible living donor kidney transplantation has also been reported by Ishikawa et al. in Japan. 109 In the setting of ABO-incompatible kidney transplantation, antigen-specific immunoadsorption, rituximab, and bortezomib treatment have been developed as alternatives to plasmapheresis and splenectomy. This will further reduce the indications for splenectomy in organ transplantation. 268, 269 PLASMAPHERESIS Plasmapheresis has been applied in three settings related to organ transplantation. The first is in the treatment of steroid-resistant acute rejection that is morphologically predominantly vascular, and considered to be antibodymediated rather than cell-mediated. Although some initial reports suggested a beneficial effect, 32 controlled trials were unconvincing. 4,120 Nojima et al. reported the successful treatment of antibody-mediated acute renal allograft rejection by combining plasmapheresis with 15-deoxyspergualin. 172 The second setting is in the preparation of recipients of ABO-incompatible living donor kidneys, referred to earlier, 3, 203, 232 although Brynger et al. have reported some successful ABO-incompatible grafts without prior plasmapheresis of the recipient. 28 In a third setting, plasmapheresis is used in an attempt to reduce the titer and the broad reactivity of HLA antibodies in highly sensitized candidate transplant dialysis patients, where it is combined with cyclophosphamide/rituximab therapy to prevent reappearance of the antibodies. 157 Encouraging early results of this approach have been reported, although they were associated with considerable morbidity. 258 Immunoabsorption has been applied as an alternative to plasmapheresis, and was found to be an equally efficient method. 182, 268 Studies of this approach in highly sensitized candidate transplant recipients are continuing. 

Plasmapheresis in HLA-immunosensitized patients prior to kidney transplantation

The late adverse effect of splenectomy on patient survival following cadaveric renal transplantation

Present experiences in a series of 26 ABO-incompatible living donor renal allografts

Plasma exchange in acute renal allograft rejection. A controlled trial

Transcriptional repression of the interleukin-2 gene by vitamin D3: direct inhibition of NFATp/ AP-1 complex formation by a nuclear hormone receptor

Outline and longterm prognosis in 15-deoxyspergualin-treated cases. Japan Collaborative Transplant Study Group of NKT-01

Total lymphoid irradiation for refractory rejection in pediatric heart transplantation

Immunosuppression with lowdose cyclosporine combined with bredinin and prednisolone

Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials

Human T lymphocytes are direct targets of 1,25-dihydroxyvitamin D3 in the immune system

Vitamin D: modulator of the immune system

Immunomodulatory effect of extracorporeal photopheresis after successful treatment of resistant renal allograft rejection

Photopheresis for the prevention of rejection in cardiac transplantation. Photopheresis Transplantation Study Group

HWA 486), a novel immunomodulating compound for the treatment of autoimmune disorders and reactions leading to transplantation rejection

Evidence for mouse Th1-and Th2-like helper T cells in vivo. Selective reduction of Th1-like cells after total lymphoid irradiation

Deficits in T helper cells after total lymphoid irradiation (TLI): reduced IL-2 secretion and normal IL-2 receptor expression in the mixed leukocyte reaction (MLR)

Concomitant inhibition of Janus kinase 3 and calcineurin-dependent signaling pathways synergistically prolongs the survival of rat heart allografts

Long-term follow-up after total lymphoid irradiation in pediatric heart transplant recipients

Leflunomide, a novel immunomodulatory agent: in vitro analyses of the mechanism of immunosuppression

In vivo activity of leflunomide: pharmacokinetic analyses and mechanism of immunosuppression

Concurrent antiviral and immunosuppressive activities of leflunomide in vivo

Renal transplant patients treated with total lymphoid irradiation show specific unresponsiveness to donor antigens the mixed leukocyte reaction (MLR)

Vitamin D3: a transcriptional modulator of the interferon-gamma gene

The JAK3 inhibitor CP-690550 selectively reduces NK and CD8+ cell numbers in cynomolgus monkey blood following chronic oral dosing

Elevated liver enzyme tests among patients with rheumatoid arthritis or psoriatic arthritis treated with methotrexate and/or leflunomide

Successful treatment of recurrent rejection in renal transplant patients with photopheresis

Clinical pharmacokinetics of cyclophosphamide

Population pharmacokinetics of cyclophosphamide and its metabolites 4-hydroxycyclophosphamide, 2-dechloroethylcyclophosphamide, and phosphoramide mustard in a high-dose combination with Thiotepa and Carboplatin

Defect in activationinduced cell death in non-obese diabetic (NOD) T lymphocytes

Reduction of ischemia-reperfusion injury in the rat kidney by FTY720, a synthetic derivative of sphingosine

Immunosuppression with FK778 and mycophenolate mofetil in a rat cardiac transplantation model

FK778 attenuates lymphocyte-endothelium interaction after cardiac transplantation: in vivo and in vitro studies

The impact of proteasome inhibition on alloantibody-producing plasma cells in vivo

gamma-Interferoninduced resistance to 1,25-(OH)2 D3 in human monocytes and macrophages: a mechanism for the hypercalcemia of various granulomatoses

Bortezomib for refractory antibody-mediated cardiac allograft rejection

Treatment of cutaneous T-cell lymphoma by extracorporeal photochemotherapy. Preliminary results

Inhibition of polyomavirus BK-specific T-cell responses by immunosuppressive drugs

The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms

Pharmacokinetics, pharmacodynamics, safety, and tolerability of single-dose fingolimod (FTY720) in adolescents with stable renal transplants

Proteasome inhibition for antibody-mediated rejection

CDA): an inhibitor of human B and T cell activation in vitro

2-Chloro-2-deoxyadenosine -a novel immunosuppressive agent

Engraftment of allogeneic bone marrow without graft-versus-host disease in mongrel dogs using total lymphoid irradiation

Regulatory T cells induced by 1 alpha,25-dihydroxyvitamin D3 and mycophenolate mofetil treatment mediate transplantation tolerance

A 1alpha,25-dihydroxyvitamin D(3) analog enhances regulatory T-cells and arrests autoimmune diabetes in NOD mice

Vitamin D and its analogs as regulators of immune activation and antigen presentation

Apoptotic cells induce tolerance by generating helpless CD8+ T cells that produce TRAIL

Deoxyspergualin in allogeneic kidney and xenogeneic islet transplantation: early clinical trials

Assessment of efficacy and safety of FK778 in comparison with standard care in renal transplant recipients with untreated BK nephropathy

A combination of KH1060, a vitamin D(3) analogue, and cyclosporin prevents early graft failure and prolongs graft survival of xenogeneic islets in nonobese diabetic mice

Novel insights into the mechanism of action of FTY720 in a transgenic model of allograft rejection: implications for therapy of chronic rejection

The S1P-analog FTY720 differentially modulates T-cell homing via HEV: T-cell-expressed S1P1 amplifies integrin activation in peripheral lymph nodes but not in Peyer patches

Monocyte-derived dendritic cell precursors facilitate tolerance to heart allografts after total lymphoid irradiation

Prevention of graft-versus-host disease by natural suppressor cells

FTY720 combined with tacrolimus in de novo renal transplantation: 1-year, multicenter, open-label randomized study

Photopheresis for renal allograft rejection

FTY720, a novel immunosuppressant possessing unique mechanisms. II. Longterm graft survival induction in rat heterotopic cardiac allografts and synergistic effect in combination with cyclosporine A

Comparative inhibitory effects of various nucleoside and nonnucleoside analogues on replication of influenza virus types A and B in vitro and in ovo

Kidney allograft survival in dogs treated with total lymphoid irradiation

Vitamin D and respiratory health

Prolongation of allograft survival by 1,25-dihydroxyvitamin D3

Total lymphoid irradiation for treatment of intractable cardiac allograft rejection

The immunosuppressive mode of action of mizoribine

Experience of ABOincompatible living kidney transplantation after double filtration plasmapheresis

Inhibition of murine IgE and immediate cutaneous hypersensitivity responses to ovalbumin by the immunomodulatory agent leflunomide

1,25-Dihydroxyvitamin D3 and IL-2 combine to inhibit T cell production of inflammatory cytokines and promote development of regulatory T cells expressing CTLA-4 and FoxP3

A novel leflunomide derivative, FK778, for immunosuppression after kidney transplantation in dogs

MC 1288-a vitamin D analogue with immunosuppressive effects on heart and small bowel grafts

Treatment of polyomavirus infection in kidney transplant recipients: a systematic review

Treatment of renal allograft polyoma BK virus infection with leflunomide

Protective effects of leflunomide against ischemia-reperfusion injury of the rat liver

A quantitative analysis of kinase inhibitor selectivity

Leflunomide-induced peripheral neuropathy

Tyrphostin AG-490 inhibits cytokine-mediated JAK3/STAT5a/b signal transduction and cellular proliferation of antigen-activated human T cells

A controlled trial of plasmapheresis in the treatment of renal allograft rejection

Inhibition of herpes simplex virus type 1 by the experimental immunosuppressive agent leflunomide

A new triple-drug induction therapy with low dose cyclosporine, mizoribine and prednisolone in renal transplantation

Overview of sotrastaurin clinical pharmacokinetics

Pharmacokinetics of sotrastaurin combined with tacrolimus or mycophenolic acid in de novo kidney transplant recipients

Sotrastaurin and cyclosporine drug interaction study in healthy subjects

The novel JAK-3 inhibitor CP-690550 is a potent immunosuppressive agent in various murine models

Photopheresis for the treatment of refractory renal graft rejection

Immune responses in interleukin-2-deficient mice

Immunosuppression with a combination of the leflunomide analog, FK778, and microemulsified cyclosporine for renal transplantation in mongrel dogs

Host conditioning with total lymphoid irradiation and antithymocyte globulin prevents graftversus-host disease: the role of CD1-reactive natural killer T cells

Predominance of NK1.1 + TCR alpha beta + or DX5 + TCR alpha beta + T cells in mice conditioned with fractionated lymphoid irradiation protects against graft-versushost disease: "natural suppressor" cells

The sphingosine-1-phosphate receptor agonist FTY720 modulates dendritic cell trafficking in vivo

The early marginal zone B cell-initiated T-independent type 2 response resists the proteasome inhibitor bortezomib

Structure-immunosuppressive activity relationships of new analogues of 15-deoxyspergualin. 1. Structural modifications of the hydroxyglycine moiety

Leflunomide use in renal transplantation

Prolongation of the survival of murine cardiac allografts by the vitamin D3 analogue 1,25-dihydroxy-delta 16-cholecalciferol

Total lymphoid irradiation (TLI) in the cyclosporine era -use of TLI in resistant cardiac allograft rejection

Treatment of cadaveric renal transplant recipients with total lymphoid irradiation, antithymocyte globulin, and low-dose prednisone

FTY720, a novel immunosuppressive agent, enhances upregulation of the cell adhesion molecular ICAM-1 in TNF-alpha treated human umbilical vein endothelial cells

Anti-BK virus mechanisms of sirolimus and leflunomide alone and in combination: toward a new therapy for BK virus infection

Short-course total lymphoid irradiation for refractory cardiac transplantation rejection

Induction of specific transplantation tolerance across xenogeneic barriers in the T-independent immune compartment

short-term combination therapy with cyclosporine and rapamycin or leflunomide induces longterm heart allograft survival in a strongly immunogenic strain combination in rats

Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response

Immunosuppressive effects of emodin: an in vivo and in vitro study

CYP27B1 polymorphisms variants are associated with type 1 diabetes mellitus in Germans

Effects of pretransplant splenectomy: univariate and multivariate analyses

Mutations of Jak-3 gene in patients with autosomal severe combined immune deficiency (SCID)

Intermediate term results of total lymphoid irradiation for the treatment of non-specific graft dysfunction after heart transplantation

Rational design and synthesis of a novel anti-leukemic agent targeting Bruton's tyrosine kinase (BTK), LFM-A13 [alpha-cyano-beta-hydroxy-beta

Tolerance, not immunity, crucially depends on IL-2

CD4 regulatory T cells prevent lethal autoimmunity in IL-2Rbeta-deficient mice. Implications for the nonredundant function of IL-2

FTY720 attenuates hepatic ischemia-reperfusion injury in normal and cirrhotic livers

Alteration of lymphocyte trafficking by sphingosine-1-phosphate receptor agonists

Immunosuppressive leflunomide metabolite (A77 1726) blocks TNF-dependent nuclear factorkappa B activation and gene expression

Leflunomide suppresses TNF-induced cellular responses: effects on NF-kappa B, activator protein-1, c-Jun N-terminal protein kinase, and apoptosis

Desensitization protocols and their outcome

FTY720, a novel immunosuppressant, possessing unique mechanisms. IV. Prevention of graft versus host reactions in rats

Lymphocyte egress from thymus and peripheral lymphoid organs is dependent on S1P receptor 1

Inhibition of the epidermal growth factor receptor tyrosine kinase activity by leflunomide

Protein kinase Cdelta controls self-antigen-induced B-cell tolerance

AEB071 (sotrastaurin) does not exhibit toxic effects on human islets in vitro, nor after transplantation into immunodeficient mice

Prevention of graft rejection and graft-versus-host reaction by a novel immunosuppressant, FTY720, in rat small bowel transplantation

Studies on bredinin. I. Isolation, characterization and biological properties

FTY720/ cyclosporine regimens in de novo renal transplantation: a 1-year dose-finding study

Total lymphoid irradiation in kidney and liver transplantation in the baboon: prolonged graft survival and alterations in T cell subsets with low cumulative dose regimens

The changed balance of regulatory and naive T cells promotes tolerance after TLI and anti-T-cell antibody conditioning

Fractionated total lymphoid irradiation as preparative immunosuppression in high risk renal transplantation: clinical and immunological studies

Mizoribine inhibits hepatitis C virus RNA replication: effect of combination with interferonalpha

The proteasome inhibitor bortezomib depletes plasma cells and protects mice with lupus-like disease from nephritis

Bortezomib in lung transplantation: a promising start

Combined therapy of deoxyspergualin and plasmapheresis: a useful treatment for antibody-mediated acute rejection after kidney transplantation

Photopheresis in the treatment of refractory bronchiolitis obliterans complicating lung transplantation

Evidence that 2-chlorodeoxyadenosine in combination with cyclosporine prevents rejection after allogeneic small bowel transplantation

Effect of splenectomy on human renal transplants

Impact of longterm therapy with FTY720 or mycophenolate mofetil on cardiac conduction and rhythm in stable adult renal transplant patients

Disease specific problems related to drug therapy in pregnancy

Identification and immune regulation of 25-hydroxyvitamin D-1-alphahydroxylase in murine macrophages

25-dihydroxyvitamin D3 induces an autoantigen-specific T-helper

helper 2 immune shift in NOD mice immunized with GAD65 (p524-543)

MC1288, a vitamin D analog, prevents acute graft-versus-host disease in rat bone marrow transplantation

Effects of thymus irradiation on the immune competence of T cells after totallymphoid irradiation

Removal of anti-HLA antibodies by extracorporeal immunoadsorption to enable renal transplantation

FK778, a powerful new immunosuppressant, effectively reduces functional and histologic changes of chronic rejection in rat renal allografts

Effects of JAK3 inhibition with CP-690,550 on immune cell populations and their functions in nonhuman primate recipients of kidney allografts

One-year survival of heterotopic heart primate xenografts treated with total lymphoid irradiation and cyclosporine

Promotion of lymphocyte egress into blood and lymph by distinct sources of sphingosine-1-phosphate

Coronary atherosclerosis in cardiac transplant patients treated with total lymphoid irradiation

25-dihydroxyvitamin D3 inhibits differentiation, maturation, activation, and survival of dendritic cells leading to impaired alloreactive T cell activation

Primate cardiac allo-and xenotransplantation: modulation of the immune response with photochemotherapy

Inhibition of antiskin allograft immunity by infusions with syngeneic photoinactivated effector lymphocytes

Inhibition of antiskin allograft immunity induced by infusions with photoinactivated effector T lymphocytes (PET cells)

Feasibility and safety of a new technique of extracorporeal photochemotherapy: experience of 240 procedures

Proteasome inhibition causes apoptosis of normal human plasma cells preventing alloantibody production

Splenectomy and death in renal transplant patients

The effect of splenectomy on the survival of first and second renal homotransplants in man

1,25-dihydroxyvitamin D3 receptors in human leukocytes

Significant prolongation of renal allograft survival by delayed combination therapy of FK778 with tacrolimus in nonhuman primates

Monitoring of the immunomodulatory effect of CP-690,550 by analysis of the JAK/ STAT pathway in kidney transplant patients

A vitamin D analog, MC1288, inhibits adventitial inflammation and suppresses intimal lesions in rat aortic allografts

Gestational diabetes mellitus and vitamin D deficiency: genetic contribution of CYP27B1 and CYP2R1 polymorphisms

25-dihydroxyvitamin D3 shows strong and additive immunomodulatory effects with cyclosporine A in rat renal allotransplants

25-Dihydroxycholecalciferol reduces rejection and improves survival in rat liver allografts

Living-related and unrelated donor kidney transplantation: comparison between ABO-compatible and incompatible grafts

Janus kinase 3 (JAK3) deficiency: clinical, immunologic, and molecular analyses of 10 patients and outcomes of stem cell transplantation

Photopheresis: clinical applications and mechanism of action

Interaction of IL-2R beta and gamma c chains with Jak1 and Jak3: implications for XSCID and XCID

Mutation of Jak3 in a patient with SCID: essential role of Jak3 in lymphoid development

Total lymphoid irradiation: critical timing and combination with cyclosporin A for immunosuppression in a rat heart allograft model

Heart-lung xenotransplantation in primates

Inhibitory effect of mizoribine and ribavirin on the replication of severe acute respiratory syndrome (SARS)-associated coronavirus

Clonal deletion and clonal anergy in allogeneic bone marrow chimeras prepared with TBI or TLI

Adjuvant treatment of refractory lung transplant rejection with extracorporeal photopheresis

Total lymphoid irradiation in the treatment of early or recurrent heart transplant rejection

FTY720 versus MMF with cyclosporine in de novo renal transplantation: a 1-year, randomized controlled trial in Europe and Australasia

Fungal metabolites. Part 14. Novel potent immunosuppressants, mycestericins, produced by Mycelia sterilia

Leflunomide analogue FK778 is vasculoprotective independent of its immunosuppressive effect: potential applications for restenosis and chronic rejection

The sphingosine 1-phosphate receptor agonist FTY720 differentially affects the sequestration of CD4+/CD25+ T-regulatory cells and enhances their functional activity

Bortezomib as the sole post-renal transplantation desensitization agent does not decrease donor-specific anti-HLA antibodies

Tolerance and chimerism after renal and hematopoietic-cell transplantation

Induced immune tolerance for kidney transplantation

2-Chlorodeoxyadenosine (cladribine) in combination with low-dose cyclosporin prevents rejection after allogeneic heart and liver transplantation in the rat

The Jak inhibitor CP-690,550 preserves the function of CD4CD25FoxP3 regulatory T cells and inhibits effector T cells

Recent progress in antiviral chemotherapy for respiratory syncytial virus infections

KRP-203, a novel synthetic immunosuppressant, prolongs graft survival and attenuates chronic rejection in rat skin and heart allografts

1,25-Dihydroxyvitamin D3 induces CCR10 expression in terminally differentiating human B cells

Potent farnesyltransferase inhibitor ABT-100 abrogates acute allograft rejection

Farnesyltransferase inhibition: a novel method of immunomodulation

Inhibition of JAK3 and STAT6 tyrosine phosphorylation by the immunosuppressive drug leflunomide leads to a block in IgG1 production

DCs metabolize sunlight-induced vitamin D3 to 'program' T cell attraction to the epidermal chemokine CCL27

Efficacy and safety of leflunomide compared with placebo and sulphasalazine in active rheumatoid arthritis: a double-blind, randomised, multicentre trial. European Leflunomide Study Group

Protein kinase C and beyond

Lessons learned from ABO-incompatible living donor kidney transplantation: 20 years later

Nonspecific mixed lymphocyte culture inhibitory antibodies in sera of tolerant transplanted baboons conditioned with total lymphoid irradiation

Human renal homotransplantation in the presence of blood group incompatibilities

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

Immune regulation of 1alpha-hydroxylase in murine peritoneal macrophages: unravelling the IFNgamma pathway

Acquired immune tolerance to cadaveric renal allografts. A study of three patients treated with total lymphoid irradiation

Induction of specific unresponsiveness to heart allografts in mongrel dogs treated with total lymphoid irradiation and antithymocyte globulin

Allograft tolerance after total lymphoid irradiation (TLI)

Effect of splenectomy on first cadaver kidney transplants

Newer disease-modifying antirheumatic drugs and the risk of serious hepatic adverse events in patients with rheumatoid arthritis

FTY720 prevents renal T-cell infiltration after ischemia/reperfusion injury

Renal allograft rejection controlled by photopheresis

Novel proteasome inhibitor PS-341 inhibits activation of nuclear factor-kappa B, cell survival, tumor growth, and angiogenesis in squamous cell carcinoma

Results of the Minnesota randomized prospective trial of cyclosporine versus azathioprine-antilymphocyte globulin for immunosuppression in renal allograft recipients

Efficacy of mycophenolic acid combined with KRP-203, a novel immunomodulator, in a rat heart transplantation model

Long-term graft acceptance in allografted rats and dogs by treatment with a novel immunosuppressant, FTY720

A novel immunosuppressant, FTY720, with a unique mechanism of action, induces long-term graft acceptance in rat and dog allotransplantation

An immunosuppressive regimen using FTY720 combined with cyclosporin in canine kidney transplantation

A new immunosuppressant, FTY720, in canine kidney transplantation: effect of single-drug, induction and combination treatments

Human neutrophils express messenger RNA of vitamin D receptor and respond to 1alpha,25-dihydroxyvitamin D3

Prophylactic use of a new immunosuppressive agent, deoxyspergualin, in patients with kidney transplantation from ABO-incompatible or preformed antibody-positive donors

Nuclear factor of activated T cells (NFAT) as a molecular target for 1alpha,25-dihydroxyvitamin D3-mediated effects

Immunosuppression with low-dose cyclosporine, mizoribine, and steroids in livingrelated kidney transplantation

Emerging and diverse roles of protein kinase C in immune cell signalling

Long-term results in mizoribine-treated renal transplant recipients: a prospective, randomized trial of mizoribine and azathioprine under cyclosporine-based immunosuppression

Calcitriol suppresses antiretinal autoimmunity through inhibitory effects on the Th17 effector response

Renal transplantation after removal and prevention of resynthesis of HLA antibodies

FTY720 and everolimus in de novo renal transplant patients at risk for delayed graft function: results of an exploratory one-yr multicenter study

Randomized controlled trial of FTY720 versus MMF in de novo renal transplantation

FTY720 versus mycophenolate mofetil in de novo renal transplantation: six-month results of a double-blind study

Deoxyspergualin is a unique immunosuppressive agent with selective utility in inducing tolerance to pancreas islet xenografts

15-Deoxyspergualin: a novel immunosuppressive drug with clinical potential

Discordant heart xenografts. Experimental study in pigs conditioned by total lymphoid irradiation and cyclosporine A

Activities of different classes of acyclic nucleoside phosphonates against BK virus in primary human renal cells

Cardiac allograft prolongation in mice treated with combined posttransplantation total-lymphoid irradiation and anti-L3T4 antibody therapy

Prophylaxis of acute renal allograft rejection using FTY720 in combination with subtherapeutic doses of cyclosporine

ABO incompatible kidney transplantations without splenectomy, using antigen-specific immunoadsorption and rituximab

ABO-incompatible kidney transplantation and rituximab

Total lymphoid irradiation for refractory acute rejection in heart-lung and lung allografts

Combination of a 1,25-dihydroxyvitamin D3 analog and a bisphosphonate prevents experimental autoimmune encephalomyelitis and preserves bone

Analogs of 1,25-dihydroxyvitamin D3 as dose-reducing agents for classical immunosuppressants

Analogs of 1alpha,25-dihydroxyvitamin D3 as pluripotent immunomodulators

Phase 1 dose-escalation study of CP-690 550 in stable renal allograft recipients: preliminary findings of safety, tolerability, effects on lymphocyte subsets and pharmacokinetics

Redirection of human autoreactive T-cells upon interaction with dendritic cells modulated by TX527, an analog of 1,25 dihydroxyvitamin D(3)

The effects of FK778 in combination with tacrolimus and steroids: a phase II multicenter study in renal transplant patients

Vitamin D: a pleiotropic hormone

New 20-epi-vitamin D3 analogs: immunosuppressive effects on skin allograft survival

Bortezomib and sirolimus inhibit the chronic active antibody-mediated rejection in experimental renal transplantation in the rat

Allogeneic bone marrow transplantation in mice after total lymphoid irradiation: influence of breeding conditions and strain of recipient mice

Influence of radiation field and fractionation schedule of total lymphoid irradiation (TLI) on the induction of suppressor cells and stable chimerism after bone marrow transplantation in mice

Factors determining the success rate of total lymphoid irradiation in clinical kidney transplantation

Total lymphoid irradiation in renal cadaveric transplantation in diabetics

Novel mechanism of inhibition of cytomegalovirus by the experimental immunosuppressive agent leflunomide

Proteasome inhibitor-based primary therapy for antibody-mediated renal allograft rejection

Immunosuppressive effects of FTY720 alone or in combination with cyclosporine and/or sirolimus

Leflunomide for polyomavirus type BK nephropathy

Control of rejection and alloantibody production, reversal of acute rejection, and interaction with cyclosporine

Dihydroorotate dehydrogenase is a high affinity binding protein for A77 1726 and mediator of a range of biological effects of the immunomodulatory compound

Reversal of acute renal allograft rejection by extracorporeal photopheresis: a case presentation and review of the literature

Control and reversal of chronic xenograft rejection in hamster-to-rat cardiac transplantation

Effect of peritransplant FTY720 alone or in combination with post-transplant tacrolimus in a rat model of cardiac allotransplantation

FTY720 compares with FK 506 as rescue therapy in rat heterotopic cardiac transplantation

Effect of a novel immunosuppressant, FTY720, on heart and liver transplantations in rats

Targeting lymphangiogenesis after islet transplantation prolongs islet allograft survival

Apoptosis induction of ultraviolet light A and photochemotherapy in cutaneous T-cell lymphoma: relevance to mechanism of therapeutic action

FTY720 blocks allograft rejection by homing of lymphocytes in vivo

Mechanistic study of malononitrileamide FK778 in cardiac transplantation and CMV infection in rats

Lymphoid sequestration of alloreactive memory CD4 T cells promotes cardiac allograft survival

Immunomodulatory drug FTY720 induces regulatory CD4(+)CD25(+) T cells in vitro