key: cord-1023388-z15os6bn authors: Bainbridge, Emma D; Hsue, Priscilla Y; Esensten, Jonathan H; Lynch, Kara L; Hendrickson, Carolyn M; Doernberg, Sarah B; Fung, Monica; Chin-Hong, Peter; Di Germanio, Clara; Norris, Philip J; Simmons, Graham; Glidden, David V; Luetkemeyer, Anne F title: Characteristics of high titer convalescent plasma and antibody dynamics following administration in patients with severe COVID-19 date: 2021-07-16 journal: Open Forum Infect Dis DOI: 10.1093/ofid/ofab385 sha: b888d6afb7e5f7fae62214ea4b32872e299a8224 doc_id: 1023388 cord_uid: z15os6bn We characterized the antibody composition of COVID-19 convalescent plasma (CCP) and the immunologic responses of hospitalized COVID-19 patients after receiving CCP or non-immune fresh frozen plasma (FFP). Despite selection of CCP with significantly higher total IgG than recipients, neutralizing antibody levels did not differ between donor plasma and CCP recipients. A c c e p t e d M a n u s c r i p t 4 Background Convalescent plasma has been used to treat coronavirus disease 2019 (COVID-19) and may hasten recovery through passive transfer of antibodies that neutralize SARS-CoV-2 virus, enhancement of antibody dependent cytotoxicity and other immunomodulation factors. The US Food and Drug Administration (FDA) requires a high IgG titer for COVID-19 convalescent plasma (CCP) [1] . CCP efficacy may be influenced not only by antibody quantity, but also neutralizing activity, binding avidity, diversity of response, and antibody isotypes, which are not well characterized in CCP [2] . Notably, antibody avidity has been associated with survival in a small cohort [3] and has been proposed as an additional criterion for plasma donor selection [4] . While antibody dynamics have been characterized in patients with COVID-19 infection, little is known about the spectrum of antibody response after CCP receipt [3, 5] , including the potential for impaired humoral response, as has been reported after respiratory syncytial virus (RSV) passive immunization [6] . This analysis aims to characterize the antibody composition of CCP and antibody responses of COVID-19 infected individuals after CCP receipt. We characterized antibodies from CCP units and CCP recipients enrolled in a randomized, doubleblinded, placebo-controlled trial evaluating the efficacy and safety of CCP in hospitalized, hypoxic, non-ventilated adults with confirmed COVID-19 (NCT04421404). FFP served as a control because of plasma's potential impact on the coagulation cascade in COVID-19. Participants enrolled June through October 2020 at two hospitals in San Francisco, California were randomized 1:1 to receive one unit of convalescent plasma or non-immune fresh frozen plasma (200-250 ml). We selected CCP with the highest anti-SARS-CoV-2 IgG antibody levels available. All units met FDA high titer criteria by VITROS® Anti-SARS-CoV-2 IgG assay (Ortho Clinical Diagnostics) [1] . Control FFP was collected before [7] . An internal IgG avidity assay targeted RBD [8] . Nasopharyngeal swabs obtained study days 1, 2, 5, and 8 were tested for SARS-CoV-2 viral load using quantitative PCR (Integrated DNA Technologies) and reported as cycle thresholds (CT). Antibody results are reported as medians and interquartile ranges (IQR). Antibody levels and PCR CT were compared between groups using Mann-Whitney non-parametric t-tests and between time points using paired Wilcoxon rank-sum tests. P<0.05 was considered statistically significant. Results from the primary endpoint will be reported through the COMPILE consortium [9] . Participants provided written consent for study inclusion. This study was approved by the Advarra Institutional Review Board and FDA under IND 21774. This study enrolled 34 study participants, 16 received CCP and 18 received non-immune FFP. The investigators and study monitoring committee closed the study before completing target enrollment due to declining COVID-19 cases in San Francisco in October 2020. Baseline characteristics were similar between the two groups ( In CCP recipients, median IgG and avidity levels significantly increased from day 1 to day 29, but neutralizing antibody, IgA, and IgM levels did not ( Figure 1B see Figure 1C . There were no significant differences between groups in the proportion with undetectable virus or the median CT values at days 2, 5, and 8 ( Figure 1D ). There was a nonsignificant trend towards lower viral load at days 2 and 5 in the FFP recipients. A c c e p t e d M a n u s c r i p t 7 Studies suggest that CCP is most beneficial when administered to high-risk patients early in infection [10] . We present additional evidence that CCP specifically selected for higher IgG levels did not inhibit the humoral immune response to SARS-CoV-2, supporting the reassuring safety profile of CCP [11] . Compared to antibodies present in plasma recipients, the spectrum of antibodies in high titer CCP differed in type and activity. The robust IgG and avidity levels exceeded existing antibody levels in recipients, suggesting that high titer IgG was an appropriate surrogate for high avidity. There were no differences between IgA, IgM and neutralizing antibody levels in CCP units and recipients at baseline. Though units of CCP were specifically selected to ensure higher IgG levels, they did not provide neutralizing antibody levels consistently higher than those of recipients. Neutralizing activity may decline in the months following infection; thus plasma collected later in recovery may have lower neutralizing antibody levels despite persistently elevated IgG [12, 13] . In participants who received CCP, there was a significant increase in IgG and avidity levels from day 1 to day 29 that did not differ from the antibody increases in the FFP group. Importantly, we found no evidence that CCP impaired participants' native humoral response, as has been postulated based on RSV convalescent plasma experience [6] . CCP did not produce a more robust humoral response to COVID-19, nor did it reduce viral load in the nasopharynx more than FFP. Indeed, there was a trend towards a steeper decline in SARS-CoV-2 viral load in the FFP arm. The lack of correlation between A c c e p t e d M a n u s c r i p t 8 symptom duration and viral load may reflect heterogenous viral shedding and also highlights the subjectivity of patient-reported symptom onset. Strengths of our study include an extensive analysis of antibody isotypes and functional activity to characterize both the composition of high titer CCP and the recipient immune response before and after CCP or control FFP infusion. This study was limited by the small sample of hospitalized, hypoxic patients. Most participants were beyond 72 hours of symptom onset, the period when studies suggest CCP is most likely to be beneficial [10] . Antibody testing was not available for all participants at each timepoint. Antibody dynamics between study days 1 and 29 may have been missed. Finally, data on the timing of CCP donation compared to initial COVID-19 infection was unavailable. In summary, CCP specifically selected for higher IgG levels did not promote or inhibit the humoral immune response to SARS-CoV-2 by day 29. These findings may be relevant to the settings where CCP may have a role for COVID-19 treatment, such as within 72 hours in high-risk elderly patients [10] and in those with impaired humoral immunity, or for COVID-19 use as passive immunization. Future studies of CCP could consider selection of plasma with high neutralizing antibodies in addition to overall high IgG, which correlated with higher avidity, to maximize activity. The contribution of neutralizing activity to the clinical efficacy of convalescent plasma merits further evaluation. 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