Evaluation of SARS-CoV-2 antibody titers and potency for convalescent plasma donation: a brief commentary

Quality assessment and harmonization of laboratories across Europe for multiple SARS-CoV-2 serology assays

BACKGROUND AND OBJECTIVES

There is a need for conversion of SARS-CoV-2 serology data from different laboratories to a harmonized international unit. We aimed to compare the performance of multiple SARS-CoV-2 antibody serology assays among 25 laboratories across 12 European countries.

MATERIALS AND METHODS

To investigate this we have distributed to all participating laboratories a panel of 15 SARS-CoV-2 plasma samples and a single batch of pooled plasma calibrated to the WHO IS 20/136 standard.

RESULTS

All assays showed excellent discrimination between SARS-CoV-2 seronegative plasma samples and pre-vaccinated seropositive plasma samples but differed substantially in raw antibody titres. Titres could be harmonized to binding antibody units per millilitre by calibration in relation to a reference reagent.

CONCLUSION

The standardization of antibody quantification is of paramount importance to allow interpretation and comparison of serology data reported in clinical trials in order to identify donor cohorts from whom the most effective convalescent plasma can be collected.

Intranasal administration of convalescent plasma protects against SARS-CoV-2 infection in hamsters

BACKGROUND

Convalescent plasma (CP) transfusion is an early option for treating infections with pandemic potential, often preceding vaccine or antiviral drug rollout. Heterogenous findings from randomized clinical trials on transfusion of COVID-19 CP (CCP) have been reported. However, meta-analysis suggests that transfusion of high titer CCP is associated with a mortality benefit for COVID-19 outpatients or inpatients treated within 5 days after symptom onset, indicating the importance of early administration.

METHODS

We tested if CCP is an effective prophylactic against SARS-CoV-2 infection by the intranasal administration of 25 μL CCP/nostril (i.e. 0.01-0.06 mg anti-RBD antibodies/kg) in hamsters exposed to infected littermates.

FINDINGS

In this model, 40% of CCP treated hamsters were fully protected and 40% had significantly reduced viral loads, the remaining 20% was not protected. The effect seems dose-dependent because high-titer CCP from a vaccinated donor was more effective than low-titer CCP from a donation prior to vaccine rollout. Intranasal administration of human CCP resulted in a reactive (immune) response in hamster lungs, however this was not observed upon administration of hamster CCP.

INTERPRETATION

We conclude that CCP is an effective prophylactic when used directly at the site of primary infection. This option should be considered in future prepandemic preparedness plans.

FUNDING

Flanders Innovation & Entrepreneurship (VLAIO) and the Foundation for Scientific Research of the Belgian Red Cross Flanders.

Immune Plasma for the Treatment of COVID-19: Lessons Learned so far

COVID-19 convalescent plasma (CCP) has been explored as one of the treatment options for COVID-19. Results of many cohort studies and clinical trials have been recently published. At first glance, the results of the CCP studies appear to be inconsistent. However, it became clear that CCP is not beneficial if CCP with low anti-SARS-CoV-2 antibody concentrations is used, if it is administered late in advanced disease stages, and to patients who already mounted an antibody response against SARS-CoV-2 at the time of CCP transfusion. On the other hand, CCP may prevent progression to severe COVID-19 when very high-titer CCP is given early in vulnerable patients. Immune escape of new variants is a challenge for passive immunotherapy. While new variants of concern developed resistance to most clinically used monoclonal antibodies very rapidly, immune plasma from individuals immunized by both a natural SARS-CoV-2 infection and SARS-CoV-2 vaccination retained neutralizing activity against variants. This review briefly summarizes the evidence on CCP treatment to date and identifies further research needs. Ongoing research on passive immunotherapy is not only relevant for improving care for vulnerable patients in the ongoing SARS-CoV-2 pandemic, but even more as a model for passive immunotherapy in case of future pandemics with a newly evolving pathogen. Compared to other drugs, which must be newly developed in a pandemic (e.g., monoclonal antibodies, antiviral drugs), convalescent plasma is rapidly available, inexpensive to produce, and can be adaptive to viral evolution by selection of contemporary convalescent donors.

COVID-19 convalescent plasma: Current status, lessons from the past and future perspectives

When the COVID-19 pandemic hit, blood transfusion services worldwide started collection of convalescent plasma as early as possible, as exemplified by the response in Norway. There were challenges related to donor selection, donor safety, testing for relevant antibodies and indications for and dosing of the convalescent plasma. As more knowledge became available, the product quality was more standardised. Multiple case reports, observational studies and some randomized studies were published during the pandemic, as well as laboratory studies reporting different approaches to antibody testing. The results were conflicting and the importance of convalescent plasma was disputed.

Even though there has been strong international collaboration with involvement of many key organisations, we may better prepare for the next pandemic. An even stronger, more formalised collaboration between these organisations could provide more clear evidence of the importance of convalescent plasma, based on the principles of passive immunisation.

Persistence of SARS-CoV-2 total immunoglobulins in a series of convalescent plasma and blood donors

Background

The vast majority of COVID-19 cases both symptomatic and asymptomatic develop immunity after COVID-19 contagion. Whether lasting differences exist between infection and vaccination boosted immunity is yet to be known. The aim of this study was to determine how long total anti-SARS-CoV2 antibodies due to past infection persist in peripheral blood and whether sex, age or haematological features can influence their lasting.

Material and methods

A series of 2421 donations either of SARS-CoV-2 convalescent plasma or whole blood from 1107 repeat donors from January 2020 to March 2021 was analysed. An automated chemiluminescence immunoassay for total antibodies recognizing the nucleocapsid protein of SARS-CoV-2 in human serum and plasma was performed. Sex, age, blood group, blood cell counts and percentages and immunoglobulin concentrations were extracted from electronic recordings. Blood donation is allowed after a minimum of one-month post symptom’s relapse. Donors were 69.7% males and their average age was 46. The 250 donors who had later donations after a positive one underwent further analysis. Both qualitative (positivity) and quantitative (rise or decline of optical density regarding consecutive donations) outcomes were evaluated.

Results and discussion

In 97.6% of donors with follow-up, anti-SARS-CoV-2 protein N total antibodies remained positive at the end of a follow-up period of 12.4 weeks median time (1–46, SD = 9.65) after the first positive determination. The blood group was not related to antibody waning. Lower lymphocyte counts and higher neutrophils would help predict future waning or decay of antibodies. Most recovered donors maintain their total anti-SARS-CoV-2 N protein antibodies for at least 16 weeks (at least one month must have been awaited from infection resolution to blood donation). The 10 individuals that could be followed up longer than 40 weeks (approximately 44 weeks after symptom’s relapse) were all still positive.

Results of the CAPSID randomized trial for high-dose convalescent plasma in patients with severe COVID-19

BACKGROUNDCOVID-19 convalescent plasma (CCP) has been considered a treatment option for COVID-19. This trial assessed the efficacy of a neutralizing antibody containing high-dose CCP in hospitalized adults with COVID-19 requiring respiratory support or intensive care treatment.METHODSPatients (n = 105) were randomized 1:1 to either receive standard treatment and 3 units of CCP or standard treatment alone. Control group patients with progress on day 14 could cross over to the CCP group. The primary outcome was a dichotomous composite outcome of survival and no longer fulfilling criteria for severe COVID-19 on day 21.ResultsThe primary outcome occurred in 43.4% of patients in the CCP group and 32.7% in the control group (P = 0.32). The median time to clinical improvement was 26 days in the CCP group and 66 days in the control group (P = 0.27). The median time to discharge from the hospital was 31 days in the CCP group and 51 days in the control group (P = 0.24). In the subgroup that received a higher cumulative amount of neutralizing antibodies, the primary outcome occurred in 56.0% of the patients (vs. 32.1%), with significantly shorter intervals to clinical improvement (20 vs. 66 days, P < 0.05) and to hospital discharge (21 vs. 51 days, P = 0.03) and better survival (day-60 probability of survival 91.6% vs. 68.1%, P = 0.02) in comparison with the control group.ConclusionCCP added to standard treatment was not associated with a significant improvement in the primary and secondary outcomes. A predefined subgroup analysis showed a significant benefit of CCP among patients who received a larger amount of neutralizing antibodies.Trial registrationClinicalTrials.gov NCT04433910.FundingBundesministerium für Gesundheit (German Federal Ministry of Health): ZMVI1-2520COR802.

Results of the CAPSID randomized trial for high-dose convalescent plasma in patients with severe COVID-19

BACKGROUNDCOVID-19 convalescent plasma (CCP) has been considered a treatment option for COVID-19. This trial assessed the efficacy of a neutralizing antibody containing high-dose CCP in hospitalized adults with COVID-19 requiring respiratory support or intensive care treatment.METHODSPatients (n = 105) were randomized 1:1 to either receive standard treatment and 3 units of CCP or standard treatment alone. Control group patients with progress on day 14 could cross over to the CCP group. The primary outcome was a dichotomous composite outcome of survival and no longer fulfilling criteria for severe COVID-19 on day 21.ResultsThe primary outcome occurred in 43.4% of patients in the CCP group and 32.7% in the control group (P = 0.32). The median time to clinical improvement was 26 days in the CCP group and 66 days in the control group (P = 0.27). The median time to discharge from the hospital was 31 days in the CCP group and 51 days in the control group (P = 0.24). In the subgroup that received a higher cumulative amount of neutralizing antibodies, the primary outcome occurred in 56.0% of the patients (vs. 32.1%), with significantly shorter intervals to clinical improvement (20 vs. 66 days, P < 0.05) and to hospital discharge (21 vs. 51 days, P = 0.03) and better survival (day-60 probability of survival 91.6% vs. 68.1%, P = 0.02) in comparison with the control group.ConclusionCCP added to standard treatment was not associated with a significant improvement in the primary and secondary outcomes. A predefined subgroup analysis showed a significant benefit of CCP among patients who received a larger amount of neutralizing antibodies.Trial registrationClinicalTrials.gov NCT04433910.FundingBundesministerium für Gesundheit (German Federal Ministry of Health): ZMVI1-2520COR802.

A novel competition ELISA for the rapid quantification of SARS-CoV-2 neutralizing antibodies in convalescent plasma

Background

COVID‐19 convalescent plasma (CCP) ideally contains high titers of (neutralizing) anti‐SARS‐CoV‐2 antibodies. Several scalable immunoassays for CCP selection have been developed. We designed an enzyme‐linked immunosorbent assay (ELISA) that measures neutralizing antibodies (of all isotypes) in plasma by determining the level of competition between CCP and a mouse neutralizing antibody for binding to the receptor binding domain (RBD) of SARS‐CoV‐2.

Methods

Plasma was collected from 72 convalescent individuals and inhibition of viral infection was determined by plaque reduction neutralization (PRNT50). The level of neutralizing antibodies was measured in the novel competition ELISA and in a commercially available ELISA that measures inhibition of recombinant ACE2 binding to immobilized RBD. These results were compared with a high throughput chemiluminescent microparticle immunoassay (CMIA).

Results

The results from both ELISAs were correlating, in particular for high titer CCP (PRNT50 ≥ 1:160) (Spearman r = .73, p < .001). Moderate correlation was found between the competition ELISA and CMIA (r = .57 for high titer and r = .62 for low titer CCP, p < .001). Receiver operator characteristic analysis showed that the competition ELISA selected CCP with a sensitivity and specificity of 61% and 100%, respectively. However, discrimination between low and high titer CCP had a lower resolution (sensitivity: 34% and specificity: 89%).

Conclusion

The competition ELISA screens for neutralizing antibodies in CCP by competition for just a single epitope. It exerts a sensitivity of 61% with no false identifications. These ELISA designs can be used for epitope mapping or for selection of CCP.

Qualifying coronavirus disease 2019 convalescent plasma donors in Israel

Background and Objectives

Passive immunization using investigational COVID‐19 convalescent plasma (CCP) is a promising therapeutic strategy and could improve outcome if transfused early and contain high levels of anti‐SARS‐CoV‐2 antibodies. We report the management of a national CCP collection and distribution program in Israel.

Materials and Methods

From 1 April 2020 to 15 January 2021, 4020 volunteer donors donated 5221 CCP units and 837 (20.8%) donors donated more than once. Anti‐nucleocapsid IgG antibodies were determined using chemiluminescent immunoassay method (Abbott). A statistical model based on repeated IgG tests in sequential donations was created to predict the time of antibody decline below sample/cut‐off (S/CO) level of 4.0.

Results

Ninety‐six percent of CCP donors suffered a mild disease or were asymptomatic. Older donors had higher antibody levels. Higher antibody levels (S/CO ≥4) were detected in 35.2% of the donors. Low positive (S/CO ≥1.4–3.99) were found in 37%, and 27.8% had undetectable antibodies (S/CO ≤1.4). The model predicted decrease antibody thresholds of 0.55%/day since the first CCP donation, providing guidance for the effective timing of future collections from donors with high antibody levels.

Conclusions

An efficient CCP collection and distribution program was achieved, based on performing initial and repeated plasma collections, preferably from donors with higher antibody levels, and only antibody‐rich units were supplied for therapeutic use. The inventory met the quantity and quality standards of the authorities, enabled to respond to the growing demand of the medical system and provide a product that may contribute to improve prognosis in patients with COVID‐19.

Donors for SARS-CoV-2 Convalescent Plasma for a Controlled Clinical Trial: Donor Characteristics, Content and Time Course of SARS-CoV-2 Neutralizing Antibodies

BACKGROUND

Convalescent plasma is one of the treatment options for COVID-19 which is currently being investigated in many clinical trials. Understanding of donor and product characteristics is important for optimization of convalescent plasma.

METHODS

Patients who had recovered from CO-VID-19 were recruited as donors for COVID-19 convalescent plasma (CCP) for a randomized clinical trial of CCP for treatment of severe COVID-19 (CAPSID Trial). Titers of neutralizing antibodies were measured by a plaque-reduction neutralization test (PRNT). Correlation of antibody titers with host factors and evolution of neutralizing antibody titers over time in repeat donors were analysed.

RESULTS

A series of 144 donors (41% females, 59% males; median age 40 years) underwent 319 plasmapheresis procedures providing a median collection volume of 850 mL and a mean number of 2.7 therapeutic units per plasmapheresis. The majority of donors had a mild or moderate course of COVID-19. The titers of neutralizing antibodies varied greatly between CCP donors (from <1:20 to >1:640). Donor factors (gender, age, ABO type, body weight) did not correlate significantly with the titer of neutralizing antibodies. We observed a significant positive correlation of neutralization titers with the number of reported COVID-19 symptoms and with the time from SARS-CoV-2 diagnosis to plasmapheresis. Neutralizing antibody levels were stable or increased over time in 58% of repeat CCP donors. Mean titers of neutralizing antibodies of first donation and last donation of repeat CCP donors did not differ significantly (1:86 at first compared to 1:87 at the last donation). There was a significant correlation of neutralizing antibodies measured by PRNT and anti-SARS-CoV-2 IgG and IgA antibodies which were measured by ELISA. CCP donations with an anti-SARS-CoV-2 IgG antibody content above the 25th percentile were substantially enriched for CCP donations with higher neutralizing antibody levels.

CONCLUSION

We demonstrate the feasibility of collection of a large number of CCP products under a harmonized protocol for a randomized clinical trial. Titers of neutralizing antibodies were stable or increased over time in a subgroup of repeat donors. A history of higher number of COVID-19 symptoms and higher levels of anti-SARS-CoV-2 IgG and IgA antibodies in immunoassays can preselect donations with higher neutralizing capacity.

The Three Pillars of COVID-19 Convalescent Plasma Therapy

The new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has spread rapidly around the world in the last year causing the coronavirus disease 2019 (COVID-19), which still is a severe threat for public health. The therapeutic management of COVID-19 is challenging as, up until now, no specific and efficient pharmacological therapy has been validated. Translating the experience from previous viral epidemics, passive immunotherapy by means of plasma from individuals recovered from COVID-19 has been intensively investigated since the beginning of the pandemic. In this narrative review, we critically analyze the three factors, named “pillars”, that play a key role in determining the clinical effectiveness of this biologic therapy: the convalescent plasma, the disease (COVID-19), and the patients.