key: cord-0836542-vtyqzzmq
authors: Rijnders, Bart JA.; Huygens, Sammy; Mitjà, Oriol
title: Evidence based dosing of convalescent plasma for COVID-19 in future trials
date: 2022-02-10
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2022.01.026
sha: be5aa4e83cdd9151e529cdde73c850d024bdb2c4
doc_id: 836542
cord_uid: vtyqzzmq

BACKGROUND: Two years into the pandemic, convincing evidence in favor of convalescent plasma(ConvP) as a treatment for COVID-19 is still lacking. This contrasts sharply with the efficacy of potent virus-neutralizing monoclonal antibodies. However, resistance of the Omicron variant against almost all licensed monoclonals turns back the clock and we can expect that ConvP will regain interest. Indeed, the effectivity of virus-neutralizing monoclonal antibodies supports the premise that ConvP will work when used at the right time, at the right dose, containing antibodies with the right affinity. OBJECTIVES: Review available evidence on dosing of ConvP for COVID-19 and provide guidance for future trials or patient care. SOURCES: As no dose finding human trials were ever performed, we reviewed COVID-19 animal model studies and human trials that provide (in)direct data on the pharmacokinetics and pharmacodynamics of ConvP. We also discuss the identification of appropriate ConvP donors in the context of emerging SARS-COV2 variants. CONTENT: Compared with dosing in animal studies, almost all human trials used substantially lower doses. Identifying donors with sufficiently high virus neutralizing antibody titers is challenging, in particular when new variants escape immunity induced by ancestral variants. Ways to avoid underdosing are 1. The use of ConvP from two different donors 2. Only use ConvP known to neutralize the variant the patient is infected with. 3. Use 2 convalescent plasma units with a NAb titer ≥1/1250. When only one plasma unit is available, a NAb titer of ≥1/2500 is recommended. 4. Use an antibody test that correlates well with virus neutralization. The use of international units for virus neutralization is strongly encouraged. 5. The use of donors shortly after a third mRNA vaccination may simplify the donor selection process. IMPLICATIONS: In future trials on ConvP for COVID-19, more stringent donor selection criteria and/or higher volume transfusions should be used.

Two years into the COVID-19 pandemic, convincing evidence in favor of convalescent plasma (ConvP) as a treatment for COVID-19 is still lacking. Any future role of ConvP for COVID-19 was therefore considered limited and the most recent WHO guideline formally recommends against the use of ConvP for hospitalized patients, unless in the context of a clinical trial. Also, several highly potent virus-neutralizing monoclonal antibodies have become a valuable part of our COVID-19 armamentarium. This seemed to limit any role of ConvP even further.

Until recently, newly emerging SARS-CoV-2 variants of concern (VOC) had a limited impact on the therapeutic value of monoclonal antibodies. Unfortunately, high-level resistance of the Omicron VOC against casirivimab/imdevimab has recently been described by several independent laboratories (1, 2) .

Almost all other licensed monoclonals seem to be impacted by Omicron as well, with sotrovimab as a possible exception (2) . Even when this exception is confirmed, we can expect that the demand for this drug will vastly exceed the supply and future variants may result in loss of this monoclonal antibody as well.

So, what nobody had foreseen is that ConvP may become relevant again as a treatment for COVID-19. The effectivity of virus-neutralizing monoclonal antibodies supports the premise that passive immunotherapy alters the viral pathogenesis, and therefore it is very likely that ConvP will work as long as it is used at the right dose, with the right affinity, in the right patient and at the right time. Specifically, ConvP has hypothesized advantages including that a polyvalent Ab approach may provide broader antiviral activity. But before we start studying ConvP again, it is vital that we learn from our recent mistakes. We learned that the risk of underdosing of ConvP is high and that discrepancy between the VOC that infected the donor and recipient can affect efficacy. We also learned that antibody-based therapy works best in patients who are not yet producing virus-neutralizing antibodies. This implies that the window of opportunity is small. In this paper, we focus on the former and try to provide guidance towards appropriate dosing of ConvP in future trials or when ConvP is considered for the treatment of immunocompromised patients unable to clear SARS-CoV-2.

J o u r n a l P r e -p r o o f

In a study in rhesus macaques, purified immunoglobulins (Ig) that had been obtained from ConvP with a SARS-CoV-2 50% plaque reduction neutralizing antibody titer (NAb) of 1/1581 was used to treat COVID-19. Immediately after the administration of the Ig at a dose of 250mg/kg or 25mg/kg the NAb titers in the treated animals were 1/511-571 and 1/42-49, respectively. Both the 250mg and 25mg/kg dose was effective at preventing disease but for treatment, it became apparent that only the higher dose was effective. The peak viral load in bronchoalveolar lavage fluid and in the nasopharynx was reduced by 1.84 and 1.26 log with the 250 mg/Kg dose but the viral load reduction in BAL after the 25mg/kg dose was much more limited (0.64 log) and completely absent in the nasopharynx (3).

The study in macaques may provide a framework for an initial extrapolation of the successful 250mg/Kg dose in the animal to human dose. With an average total Ig in plasma of +-13 gram/L, a macaque weighing 3kg would need +-60ml (= 750mg/(13000mg/1000ml)) of ConvP to get the 250mg/kg dose of Ig. Compared with the total plasma volume of +-160ml, this means a transfusion of 37,5% of the plasma volume of the animal. To achieve a human-macaque equivalent systemic exposure we could adjust for bodyweight dosing and total plasma volume. Hence, an adult weighing 70 Kg and receiving ConvP with the 1/1280 titer would require 17.5 g of immunoglobulins, which equals approx. 1350mL of ConvP to reach a 250mg/kg dose. Even when using plasma from donors with NAb titers of 1/2560, 600-800 mL of ConvP would still be required.

In our experience with 115 human ConvP donors, we found a median Nab titer of 1/160, with only 17% (20/115) of them having Nab titers of 1/1280 or greater. A stringent donor selection process is thus crucial to identify the donors with the highest SARS-CoV-2 antibody.

A different approach was taken in a pre-exposure prophylaxis study in a COVID-19 syrian hamster model in which inoculation with SARS-CoV-2 results in viral pneumonitis and temporary weight loss.

Preceding the viral challenge, the animals received 0.5 ml of human ConvP, which is 10% of the plasma volume of hamsters and therefore comparable to a 300ml ConvP transfusion in humans. While ConvP with a NAb titer of 1/320 did not prevent disease, ConvP with a NAb titer of 1/2560 fully prevented J o u r n a l P r e -p r o o f weight loss and limited viral pneumonitis (4). This study, therefore, confirmed that ConvP with extremely high NAb titers of 1/2560 would be required if only 300ml of ConvP is used. Takamatsu et al. took this experiment one step further and also showed protection from disease when the ConvP was administered 24h after virus inoculation. However, they used 2.0 ml rather than 0.5 ml and showed efficacy with NAb titers of 1400, 1100, and 400 but not with 200 or lower titers. Extrapolating this dose to humans would mean that at least 300ml with NAb titer of 1/1600, or 600ml with a titer of 1/800 would be required (5) .

The animal data described above suggest that the administration of ConvP that results in NAb titers of +-1/500 in the recipient peripheral's blood, will result in a positive treatment effect. We measured NAb titers in 11 consecutive immunocompromised seronegative patients treated with ConvP for COVID-19

and observed that after a median of 600ml of ConvP with a NAb titer of 1/640-1/1280, the post-transfusion NAb titer increased from <1/20 to 1/40 or 1/80 (6) . In an ongoing phase 1/2 study (7), we evaluated the pharmacokinetics of NAb in 5 immunocompromised but otherwise healthy patients who had remained SARS-CoV-2 antibody negative despite vaccination. 24 hours after the infusion of 600ml (n=6) of ConvP with a NAb titer of 1/900, the NAb titers in the patient's serum increased from <1/20 to 1/125 (IQR 86-165) respectively (figure 1). This illustrates that doses as high as 600ml ConvP with a NAb titer of 1/2560 (and preferable 1/5120) would be required to achieve a NAb titer that approaches the 1/500 titer that was most effective in the rhesus macaque model.

In a recent randomized trial that we completed in the Netherlands and Spain, ConvP was compared with regular non-ConvP in 792 outpatients aged 50 or older with <8 days of symptoms from COVID-19. This illustrates that appropriate donor selection is a crucial first step and cannot be based on a qualitative antibody test only. However, direct NAb titer measurement may not be feasible on a large scale in real-time and easier to use quantitative anti-Spike antibody test that correlate reasonably well with NAb titers are often used (10) . It is also important to acknowledge, the substantial inter-laboratory variation of NAb titers. The recently introduced international unit to standardize NAb titer results across laboratories should therefore be used whenever possible (11) . Unfortunately, as soon as a new variant circulates and partially or fully escapes humoral immunity against the ancestral virus, laboratories will have to perform additional standardization steps to be able to express NAb titers in international units in relation to the variant that is circulating. The EU-funded E-support initiative is helping laboratories with this and providing calibrants (12). Even when international standards are used, we suggest using ConvP from 2 different donors whenever possible to reduce the chance that a patient will unintentionally receive ConvP with insufficient NAb.

On December 28, 2021 the FDA revised its emergency use authorization of ConvP and now allows the use of ConvP for immunocompromised patients with COVID19 (13) . The letter concludes that, based on the totality of the scientific evidence available, it is reasonable to believe that the known and potential benefits of COVID-19 ConvP with high titers of anti-SARS-CoV-2 antibodies outweigh its known and potential risks for the treatment of COVID-19 in immunocompromised patients. Unfortunately, the list of antibody tests and the cut-offs provided in table 1 of this document will in no way guarantee that plasma with high titers of NAbs is selected. The provided cut-offs are merely a way to assure that the plasma contains any detectable level of NAbs. For instance, according to the label of the Diasorin TrimericS antibody test, plasma with a titer of +-100 BAU/ml has a median NAb titer of 1/40 (14). In an ongoing phase 1/2 study, we tested plasma from 8 plasma donors with a NAb titer of 1/900 international units with this TrimericS test. The median titer was 3070 (IQR 2263-3607). Therefore, the cut-off of 87 J o u r n a l P r e -p r o o f BAU/ml as well as the other cut-offs in the FDA letter cannot be used to assure that plasma contains high-enough NAb titers. Furthermore, now that Omicron is dominant these cut-offs will not even guarantee any level of neutralizing activity against Omicron.

For the above-mentioned reasons, the accurate identification and collection of ConvP from convalescent patients with very high NAb is challenging. On the upside, now that vaccines are available that predictably induce NAb in almost all immunocompetent persons, the selection of donors should become somewhat easier. Furthermore, several studies have shown that NAb titers increase further after a third vaccination with an mRNA vaccine and in particular mRNA1273 (15) . This seems to be the case against Omicron as well because antibodies induced by a third BNT162b2 vaccination or a BNT162b2 vaccination following infection with the original Wuhan01 virus, neutralized Omicron efficiently with titers comparable or even higher than against Wuhan01 (16) . Therefore, probably the best ConvP donors with the highest NAb titers are young healthy persons 2 to 4 weeks after they received a third vaccination (or after vaccination following a COVID-19 infection). On the downside, NAb assays will have to be updated and validated for the Omicron variant. And it will take some time to learn how well ConvP from patients that recovered from an infection with Omicron will be neutralizing Omicron.

Finally, some methods for pathogen inactivation may alter the immunoglobulins' function. Although neither the U.S. Food and Drug Administration (FDA) nor the European Center for Disease Control (ECDC) is recommending pathogen reduction technologies for ConvP, several national authorities consider that, under emergency settings, donor screening and conventional viral nucleic acid testing would not be enough to ensure safety. The two major approaches to pathogen inactivation involve methods that inactivate lipids (e.g., solvent/detergent treatment) and methods that damage nucleic acids (e.g., amotosalen plus ultraviolet-A light, riboflavin + ultraviolet light, methylene blue plus visible light). Data on the effect of these methods on antibody activity has shown mixed results. For instance, photoinactivation methods do not seem to reduce neutralizing antibody content, nor reduce the cell receptor binding capacity of the Fc-region. Nonetheless, current evidence does not allow ruling out an effect on Fc-dependent functions, including phagocytosis, complement activation, and antibody-dependent cellular toxicity.

In table 1 we summarize our recommendations. Although some antiviral activity was documented with lower doses, extrapolation from animal studies should be done cautiously because in these studies the timing of treatment is optimal (24 hours after inoculation).

With the reality check we face as Omicron is spreading across the globe, the use of ConvP for the treatment of COVID-19 will probably regain interest. Indeed, Omicron demonstrates in vitro resistance against all of the currently licensed monoclonals antibodies with the exception of Sotrovimab. We reviewed in vitro, human, and animal data and propose a ConvP dose that should be considered in future trials or treatments. Our recommendations certainly have their limitations. First, a multitude of methods is being used to measure NAb titers. This makes the comparison of titers between studies difficult and inter-laboratory comparison and the use of the recently introduced international unit for NAb tests is strongly encouraged and will help to evaluate ConvP across clinical trials (16, 17) . Another limitation of our recommendations is the lack of phase 2 dose-finding trials. The only trial so far that suggests a potential benefit of ConvP was limited by its small sample size and in this study, a beneficial effect was only observed in the patients receiving ConvP with much higher titers than the cut-off of 1000 anti-S IgG used to select donors (18). We acknowledge that on the one hand, doses below what we recommend in table 1 may still be effective. But after so many negative trials, we should do everything to avoid underdosing in future trials and we chose to keep the lower limit of our recommendations relatively high. On the other hand, we cannot exclude that higher doses than those recommended may still be more effective. Finally, at least outside the context of a clinical trial ConvP is typically used to treat immunocompromised patients with COVID-19 in whom the autologous antibody response can be limited, delayed or even completely absent. As far as we know, none of the animal models have evaluated ConvP in immuncompromised animals. Also, several case reports have shown viral evolution and development of resistance during treatment of severely immunocompromised patient with ConvP (19). Therefore, it is certainly possible that higher doses will be required in immunocompromised patients, which is another reason to stay on the safe side of dosing.

The dose indications provided above always relate to ConvP from donors that had been infected with the same virus that was used for the NAb measurement. This has become a crucial aspect of trials on J o u r n a l P r e -p r o o f

Reduced Neutralization of SARS-CoV-2 Omicron Variant by Vaccine Sera and monoclonal antibodies

B.1.1.529 escapes the majority of SARS-CoV-2 neutralizing antibodies of diverse epitopes

Correlates of protection against SARS-CoV-2 in rhesus macaques

Neutralizing Human Antibodies Protect Against Lower Respiratory Tract Disease in a Hamster Model

Highly Neutralizing COVID-19 Convalescent Plasmas Potently Block SARS-CoV-2

Replication and Pneumonia in Syrian Hamsters

Effects of treatment of COVID-19 with convalescent plasma in 25 B-cell depleted patients

Convalescent plasma for outpatients with early COVID-19

Effects of potent neutralizing antibodies from convalescent plasma in patients hospitalized for severe SARS-CoV-2 infection

Anti-Spike Protein Assays to Determine SARS-CoV-2 Antibody Levels: a Head-to-Head Comparison of Five Quantitative Assays

SARS-CoV-2 neutralising antibody testing in Europe: towards harmonisation of neutralising antibody titres for better use of convalescent plasma and comparability of trial data

Support-E. Work Packages: Support-E; 2020

Liaison SARS-CoV-2 TrimericS IgG assay: A quantitative assay for immune status monitoring with an accurate correlation of neutralizing IgG antibodies

Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial

mRNA booster immunization elicits potent neutralizing serum activity against the SARS-CoV-2 Omicron variant