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

<b><i>Background:</i></b> 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. <b><i>Methods:</i></b> Patients who had recovered from CO­VID-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. <b><i>Results:</i></b> 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 &lt;1:20 to &gt;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. <b><i>Conclusion:</i></b> 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.

<b><i>背景：</i></b> 恢复期血浆（convalescent plasma）是目前多项临床试验正在研究的COVID-19治疗方案之一。深入了解供体与制品特性，对于优化恢复期血浆的制备至关重要。<b><i>方法：</i></b> 本研究针对重症COVID-19患者开展新型冠状病毒肺炎恢复期血浆（COVID-19 convalescent plasma, CCP）治疗的随机临床试验（CAPSID试验），招募已康复的COVID-19患者作为CCP供体。采用空斑减少中和试验（plaque-reduction neutralization test, PRNT）检测中和抗体效价。分析了抗体效价与宿主因素的相关性，以及重复供体体内中和抗体效价随时间的演变情况。<b><i>结果：</i></b> 本研究共纳入144名供体（女性占比41%，男性占比59%；中位年龄40岁），累计完成319次血浆单采术，单次采集的中位体积为850mL，每台次采集平均获得2.7个治疗单位。多数供体在感染COVID-19后表现为轻症或中症病程。CCP供体的中和抗体效价差异显著，范围介于<1:20至>1:640之间。供体相关因素（性别、年龄、ABO血型、体重）与中和抗体效价无显著相关性。本研究观察到，中和效价与报告的COVID-19症状数量、从确诊SARS-CoV-2感染至血浆单采的时间间隔呈显著正相关。58%的重复CCP供体体内中和抗体水平随时间保持稳定或有所升高。重复供体首次采集与末次采集的中和抗体平均效价无显著差异（首次为1:86，末次为1:87）。采用PRNT检测的中和抗体水平，与采用酶联免疫吸附试验（enzyme-linked immunosorbent assay, ELISA）检测的抗SARS-CoV-2 IgG及IgA抗体水平呈显著相关。抗SARS-CoV-2 IgG抗体含量高于第25百分位数的CCP捐献制品，其中和抗体水平普遍更高。<b><i>结论：</i></b> 本研究证实，在统一标准化方案下批量采集CCP制品用于随机临床试验具备可行性。在部分重复供体中，中和抗体水平随时间保持稳定或有所升高。既往感染COVID-19后症状更多、免疫检测中抗SARS-CoV-2 IgG及IgA抗体水平更高的供体，其捐献的血浆具备更高的中和活性，可作为优先筛选标准。