key: cord-0721727-6df12ddp authors: Baker, James R.; Farazuddin, Mohammad; Wong, Pamela T.; O’Konek, Jessica J. title: The unfulfilled potential of mucosal immunization date: 2022-05-13 journal: J Allergy Clin Immunol DOI: 10.1016/j.jaci.2022.05.002 sha: 156dfb29742951d7df9cbb1aa12d356e7b719162 doc_id: 721727 cord_uid: 6df12ddp Recent events involving the global coronavirus pandemic have focused attention on vaccination strategies. While tremendous advances have been made in subcutaneous and intramuscular vaccines during this time, one area that has lagged in implementation is mucosal immunization. Mucosal immunization provides several potential advantages over subcutaneous and intramuscular routes, including protection from localized infection at the site of entry, clearance of organisms on mucosal surfaces, induction of long-term immunity through establishment of central and tissue resident memory cells and the ability to shape regulatory responses. Despite these advantages, significant barriers remain to achieving effective mucosal immunization. The epithelium itself provides many obstacles to immunization and the activation of immune recognition and effector pathways that lead to mucosal immunity has been difficult to achieve. This review will highlight the potential advantages of mucosal immunity, define the barriers to mucosal immunization, examine the immune mechanisms that need to be activated on mucosal surfaces and finally address recent developments in methods for mucosal vaccination that have shown promise in generating immunity on mucosal surfaces human trials. gut-associated lymphoid tissue (GALT) nasopharyngeal-associated lymphoid tissue (NALT) antigen-presenting cells (APCs) dendritic cells (DCs) membrane-bound Toll-like receptors (TLRs) C-type lectin receptors (CLRs) NOD-like receptors (NLRs) RIG-I-like receptors (RLRs mucosal conventional type 1 dendritic cells (cDC1) mucosal conventional type 1 dendritic cells (cDC2) retinoic acid (RA) chemokine CC receptor 5 (CCR5) alpha 4 beta 7 integrin (α4β7) 1 Abstract 2 Recent events involving the global coronavirus pandemic have focused attention on vaccination 3 strategies. While tremendous advances have been made in subcutaneous and intramuscular 4 vaccines during this time, one area that has lagged in implementation is mucosal immunization. 5 Mucosal immunization provides several potential advantages over subcutaneous and 6 intramuscular routes, including protection from localized infection at the site of entry, clearance 7 of organisms on mucosal surfaces, induction of long-term immunity through establishment of 8 central and tissue resident memory cells and the ability to shape regulatory responses. Despite 9 these advantages, significant barriers remain to achieving effective mucosal immunization. The 10 epithelium itself provides many obstacles to immunization and the activation of immune 11 recognition and effector pathways that lead to mucosal immunity has been difficult to achieve. 12 This review will highlight the potential advantages of mucosal immunity, define the barriers to 13 mucosal immunization, examine the immune mechanisms that need to be activated on mucosal 14 surfaces and finally address recent developments in methods for mucosal vaccination that have 15 shown promise in generating immunity on mucosal surfaces human trials. (1). This has piqued interest in mucosal immunization, as it provides numerous 19 potential advantages over subcutaneous and intramuscular vaccination routes (2). These major 20 advantages include immune responses composed of secretory antibodies and tissue-resident 21 effector-and long-lived memory-T cells at mucosal surfaces (3, 4) . As the mucosa is the port of 22 entry for most major pathogens ranging from respiratory viruses to pathogens causing sexually 23 transmitted and enteric diseases, mucosal immunity is a major asset in blocking establishment of 24 initial infection and preventing transmission should infection be established (5). The importance 25 of the latter has been underscored by the continued transmission of SARS-CoV-2 by infected 26 vaccinated individuals (6). 27 28 Other less well-defined benefits of mucosal vaccination include the induction of mucosal 29 immunity at one site producing immune crosstalk that provides protection at distal mucosal 30 surfaces (7). Additionally, the constant exposure of mucosal surfaces-particularly the respiratory 31 and gastrointestinal tracts-to microbes and antigens from the environment makes these surfaces 32 valuable for shaping tolerogenic responses in autoimmune and allergic disease (8) The paucity of mucosal vaccines is the result of several significant hurdles facing effective 45 mucosal immunization. The mucosa contains a unique immune cell milieu that functions to 46 selectively identify pathogens within an environment which promotes tolerance towards 47 commensal organisms. To overcome this requires different modes of immune activation that are 48 not directly translatable from parenteral vaccines (12). This review will highlight the potential 49 advantages of attaining mucosal immunity, define the barriers to mucosal immunization, and 50 examine the unique immune processes that need to be engaged on mucosal surfaces for effective 51 immunity. We will then address approaches that could improve the likelihood of achieving 52 effective protective immunity on mucosal surfaces. In this last regard, given there are excellent 53 recent articles that cover preclinical evaluations of these technologies (3, 4, 11) , this review will 54 focus on vaccine approaches that have reached human clinical trials. Mucosal surfaces are the entry point location of most pathogens infectious to humans (4, 5). 59 Addressing infections at their source has several advantages that cannot be achieved through 60 traditional immunization (Summarized in Table 1 ). -Mucosal immunization may modulate adverse immune responses. 114 There has long been interest in using this approach as a means of suppressing autoimmunity, 115 often applying autoantigens to mucosal surfaces to induce tissue resident regulatory T cells. This 116 would provide an antigen specific suppression of autoimmunity. Trials using myelin basic protein 117 to suppress immunity in patients with multiple sclerosis have yielded interesting findings but 118 have yet to show therapeutic value (28). Some of the results have indicated that immune 119 responses can be specifically modulated in patients. There have also been trials examining oral 120 and nasal immunization with several antigens in type 1 diabetics, although again, no positive 121 clinical outcome has been observed (29). 122 123 -Mucosal immunization as an approach to modulate allergic disease 124 A new area of interest in mucosal immunization of interest to allergists is suppressing allergic 125 disease. This involves antigen application to the mucosa to suppress Type II immune responses 126 or re-direct these immune responses to produce protective immunity (30). While the first 127 application of mucosal immunization involved sublingual immunotherapy for treating respiratory 128 allergic disease, including rhinoconjunctivitis, much of the current focus is on food allergy. Both 129 oral and sublingual applications of food antigens have been shown to induce specific immune 130 unresponsiveness to the food. However, this is short lived and ends rapidly after chronic 131 ingestion is discontinued (30). The goal for mucosal immunization, potentially combined with 132 immunomodulation therapeutics, would be to achieve long term tolerance to the food. 135 A major hurdle limiting effective mucosal immunization is the barrier that mucosal surfaces 136 provide to prevent antigen delivery and immune stimulation ( Figure 1 ). These barriers have 137 evolved to protect the mucosa from infectious pathogens, toxins and other noxious agents (26). 138 Therefore, it is no surprise that most effective mucosal vaccines have been adapted from 139 infectious pathogens that have evolved to overcome these barriers (11, 18) . To better pursue 140 rational mucosal vaccine design, one must first define epithelial barriers and understand 141 potential ways that they can be overcome. Activating lymphoid tissues is a central challenge for mucosal vaccines. 174 The mucosal immune system is constantly exposed to inhaled and ingested antigens, so it is 175 biased towards tolerogenic immunity to maintain homeostasis and prevent hyperactive immune 176 responses. Mucosal administered antigens are therefore inherently less immunogenic and 177 mucosal vaccines must include danger signals such as pathogen associated molecular patterns 178 (PAMPs) and/or cytokines to overcome tolerogenic programming (26, 37). The success of 179 mucosal vaccines thus relies on adjuvants as part of novel delivery systems to provide these 180 signals and several vaccine approaches now employ specific innate immune activation strategies 181 to overcome these challenges. While there is convincing evidence these cells exist and are important in humans, no specific 302 methods have been identified that can induce TRMs. This capability would be highly desirable as 303 it could aid sterile immunity due to the ability of TRMs to respond quickly (4). Given the 304 antigen/pathogen specificity, specific immune induction will be necessary, and the site of 305 memory response and generation of specific memory response should be considered while 306 developing a vaccine candidate. It does appear that presentation on specific mucosal sites is 307 important to generating local TRMs, and it is unclear that parenteral vaccination can induce these 308 cells (57). There is no shortage of proposed approaches to overcome the barriers confronting mucosal 323 immunization and provide effective immunity (summarized in Table 2 ). New mucosal vaccines 324 fall into two general areas; live attenuated and genetically modified organisms or synthetic 325 systems to deliver either antigens, DNA or genetic material. While many approaches are in 326 preclinical development, the utility of these for human vaccination is not clear. This is, in part, 327 because animal models of mucosal immunization (other than primates) have not been predictive 328 of success in humans, potentially related to differences in microbiota (59). Reactogenicity and safety have been the major concerns for attenuated live virus vaccines as they 348 are essentially causing low-grade infections. Fever and malaise are common with these vaccines, 349 and caution has been particularly high with viruses that cause severe disability and death. In Focus should also be directed at responses in specific populations (newborns and the aged, those 476 with abnormal immunity, etc.) which are key to addressing those individuals who respond poorly 477 to current vaccines. Limits in our understanding of immune mechanisms of sterilizing immunity 478 towards pathogens that enter at mucosal surfaces also remains a major gap in knowledge. New mucosal vaccine development requires a complex approach that evaluates both 481 immunogenicity and reactogenicity. Despite this complexity, these vaccines have the potential 482 to improve current applications, provide new vaccines against pathogens currently without 483 adequate protection and extend the utility of vaccines to diseases such as cancer and allergies. 484 The effort will require, but also merits the type of investment that resulted in the parenteral 485 COVID-19 vaccines. SARS-CoV-2 Variants, Vaccines, 489 and Host Immunity Intranasal COVID-19 vaccines: From bench to bed Mucosal vaccines: Strategies and challenges Intranasal vaccine: Factors to consider in research and development An Intranasal OMV-Based Vaccine 497 Induces High Mucosal and Systemic Protecting Immunity Against a SARS-CoV-2 Infection SARS-CoV-2 breakthrough infections 500 in vaccinated individuals: measurement, causes and impact Recent Insights into Cellular Crosstalk in Respiratory and Gastrointestinal 502 Mucosal Immune Systems Oral Tolerance as antigen-specific immunotherapy Challenges in mucosal vaccines for the control of infectious diseases Mucosal delivery of vaccines in domestic animals Mucosal vaccines and technology Current prospects and future challenges for nasal vaccine delivery. Hum Vaccine 513 Immunother Distinct systemic and 515 mucosal immune responses during acute SARS-CoV-2 infection Persistent severe acute respiratory syndrome 517 coronavirus 2 detection after resolution of coronavirus disease 2019-associated symptoms/signs. Korean 518 Evidence-Based Therapeutic 520 Benefits of Cupping Therapy (Hijama): A Comprehensive Review Mechanisms of infectious diarrhea Enteropathogenic Escherichia coli: unravelling pathogenesis. FEMS Microbiol 524 Rev Rotaviruses: from pathogenesis to vaccination Anatomical basis of tolerance and immunity to intestinal antigens Co-530 expression of Interleukin-17A molecular adjuvant and prophylactic Helicobacter pylori genetic vaccine 531 could cause sterile immunity in Treg suppressed mice Infections, Including COVID-19 Vaccine Breakthrough Infections, Associated with Large Public Gatherings Mucosal Immunization Against Pertussis: Lessons From the Past and 536 Perspectives Acellular pertussis vaccines protect against disease but fail 538 to prevent infection and transmission in a nonhuman primate model Clostridium difficile Infection Outbreaks associated with recreational water in the United 542 States Mucosal vaccines -fortifying the frontiers Mucosal Vaccine Approaches for Prevention of HIV and SIV 545 Transmission Beyond the Magic Bullet: Current Progress of Therapeutic Vaccination in 547 Multiple Sclerosis Immunotherapy for type 549 1 diabetes Mechanisms of oral immunotherapy Airway mucus: its components and function Efficient mucosal immunization by mucoadhesive 555 and pH-Sensitive polymeric vaccine delivery system Applications of nanotechnology for immunology Epithelial M cells: differentiation and function Comparative efficacy of 561 inactivated and live attenuated influenza vaccines Adenovirus Vectors: Excellent Tools for Vaccine Development M) cells: important 565 immunosurveillance posts in the intestinal epithelium NALT-versus Peyer's-patch-mediated mucosal immunity The dendritic cell lineage: ontogeny and function of 569 dendritic cells and their subsets in the steady state and the inflamed setting Pathogen recognition and Toll-like receptor targeted therapeutics in innate 572 immune cells Viral proteins recognized by different TLRs Cross-presenting 576 CD103+ dendritic cells are protected from influenza virus infection Environmental cues, dendritic cells and the programming of tissue-578 selective lymphocyte trafficking Selective 580 imprinting of gut-homing T cells by Peyer's patch dendritic cells Th2 allergic immune response to 582 inhaled fungal antigens is modulated by TLR-4-independent bacterial products Dendritic Cell-Mediated Th2 Immunity and Immune 585 Disorders Small intestinal 587 CD103+ dendritic cells display unique functional properties that are conserved between mice and humans. 588 A functionally 590 specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-beta and 591 retinoic acid-dependent mechanism CX3CR1 regulates 595 intestinal macrophage homeostasis, bacterial translocation, and colitogenic Th17 responses in mice Ebola virus 598 glycoprotein stimulates IL-18-dependent natural killer cell responses Protective Immune Responses 600 Elicited by Deglycosylated Live-Attenuated Simian Immunodeficiency Virus Vaccine Are Associated with 601 IL-15 Effector Functions Regulation of the human NK cell compartment by pathogens and vaccines Immunogenicity of 605 standard, high-dose, MF59-adjuvanted, and recombinant-HA seasonal influenza vaccination in older 606 adults Innate Lymphoid Cells: 10 608 Years On Human mucosal tissue-resident memory T cells in health 610 and disease Niches for the Long-Term Maintenance of Tissue-Resident Memory T Cells. Front 612 Immunol Immunoregulatory Sensory Circuits in Group 3 Innate Lymphoid 614 Cell (ILC3) Function and Tissue Homeostasis Mouse models for human intestinal microbiota research: a critical 616 evaluation Properties and behavior of orally administered attenuated poliovirus vaccine Safety and Efficacy of Spray 620 Intranasal Live Attenuated Influenza Vaccine: Systematic Review and Meta-Analysis. Vaccines (Basel) Vaccines against human respiratory syncytial virus in clinical trials, where are 623 we now? Evaluating the Safety and Immunogenicity of a Human Parainfluenza Type 3 (HPIV3) Virus Vaccine 627 in Infants and Children Evaluation of a Live Attenuated 629 Human Metapneumovirus Vaccine in Adults and Children Sabin monovalent oral polio vaccines: review of past experiences and 631 their potential use after polio eradication 635 68. Safety and Immunogenicity of COVI-VAC, a Live Attenuated Vaccine Against A Clinical Trial of a Recombinant Adenovirus 5 Vectored COVID-19 Vaccine (Ad5-nCoV) With Two 638 Doses in Healthy Adults Phase 1 Study of Intranasal PIV5-vectored COVID-19 Vaccine Expressing SARS-CoV-2 Spike Protein 642 in Healthy Adults Safety and Immunogenicity of an Intranasal RSV Vaccine Expressing SARS-CoV-2 Spike Protein 648 (COVID-19 Vaccine) in Adults The Science is There: Key 650 Considerations for Stabilizing Viral Vector-Based Covid-19 Vaccines Coronavirus disease 2019 (COVID-19) vaccines: 652 A concise review. Oral Dis. 2021 Antigen targeting to M cells for enhancing the efficacy of mucosal vaccines. Exp 654 Bioengineering virus-like 656 particles as vaccines TMC) and 2-661 hydroxypropyltrimethyl ammonium chloride chitosan (HTCC): The potential immune adjuvants and nano 662 carriers Production and Clinical Evaluation 666 of Norwalk GI.1 Virus Lot 001-09NV in Norovirus Vaccine Development A comprehensive review on recent preparation techniques of liposomes Safety and 674 immunogenicity of a novel nanoemulsion mucosal adjuvant W805EC combined with approved seasonal 675 influenza antigens Review of cancer 679 treatment with immune checkpoint inhibitors : Current concepts, expectations, limitations and pitfalls The immune checkpoint inhibitors: where are we now? Promising predictors of checkpoint inhibitor response in NSCLC. Expert Rev 684 Anticancer Ther Commensal Microbiome During Immune-Targeted Interventions: Focus on Cancer Immune Checkpoint 687 Inhibitor Therapy and Vaccination ADP-ribosylating enterotoxins as vaccine adjuvants Kinetics of immune responses 691 to influenza virus-like particles and dose-dependence of protection with a single vaccination Safety and 694 immunogenicity of the oral, inactivated, enterotoxigenic Escherichia coli vaccine ETVAX in Bangladeshi 695 children and infants: a double-blind, randomised, placebo-controlled phase 1/2 trial Use of the inactivated intranasal 698 influenza vaccine and the risk of Bell's palsy in Switzerland A vaccine 700 combination of lipid nanoparticles and a cholera toxin adjuvant derivative greatly improves lung 701 protection against influenza virus infection Oral delivery of siRNA lipid nanoparticles: Fate in the GI tract Intranasal Nanoparticle 705 Vaccination Elicits a Persistent, Polyfunctional CD4 T Cell Response in the Murine Lung Specific for a Highly 706 Conserved Influenza Virus Antigen That Is Sufficient To Mediate Protection from Influenza Virus Challenge Intranasally administered protein coated 709 chitosan nanoparticles encapsulating influenza H9N2 HA2 and M2e mRNA molecules elicit protective 710 immunity against avian influenza viruses in chickens The safety, 712 immunogenicity, and acceptability of inactivated influenza vaccine delivered by microneedle patch (TIV-713 MNP 2015): a randomised, partly blinded, placebo-controlled, phase 1 trial Towards an evidence based approach for 716 the development of adjuvanted vaccines Prime-Pull Immunization with 718 a Bivalent M-Protein and Spy-CEP Peptide Vaccine Adjuvanted with CAF®01 Liposomes Induces Both 719 Mucosal and Peripheral Protection from. mBio There are several layers of barriers that uniquely 723 challenge mucosal immunization. These barriers can be conceptualized as associated with 724 different components of the epithelial anatomy. The barriers at each level of the mucosa are 725 enumerated on the left side of the figure Figure 2: The optimal approach to activating mucosal-specific immune responses by vaccines When a vaccine is place on the mucosal surface immune activation occurs through DC sampling 731 and activation. This can occur either through direct antigen sampling by DC across the 732 epithelium, DC sampling of infected or dying epithelial cells, or through sampling of antigens 733 passed across the epithelium by M cells. After that first step, activating of PAMPs, along with 734 retinoic acid pathways can activate dendritic cells to induce specific, effector immunity (plus 735 signs) involving cellular cytotoxicity and antibodies J o u r n a l P r e -p r o o f Phase I data shows some immune response.No evidence of toxicity in two phase I studies.