Background/Case Studies: In a previous study, the humoral response to COVID-19 vaccination was examined in individuals with various plasma donation histories. The results showed that, despite a reduction in circulating IgG levels in frequent plasma donors (p< 0.0001), the humoral response to SARS-CoV-2 antigen challenge was similar in magnitude, irrespective of lifetime donation history (Bazin et al, Transfusion 2023:118A). Although there is a correlation between the number of plasma donations and circulating IgG levels, recent analyses have shown that some individuals have particularly low IgG levels (< 6 mg/ml) on their first plasma donation, while some frequent donors ( > 100 donations) maintain high circulating IgG levels exceeding 12 mg/ml (unpublished). Therefore, the study changed focus to compare the humoral response to COVID-19 vaccination among plasma donors based on their circulating IgG levels, rather than lifetime donations.
Study
Design/Methods: Plasma samples were sourced from plasma donors enrolled in the PlasCoV biobank (Germain et al, BMJ Open 2023). Participants were selected based on their low or high total circulating IgG levels, as determined during routine qualification, and the availability of paired pre- and post-COVID-19 vaccine plasma samples within the biobank. Total IgG levels were measured using a standard double-sandwich ELISA. The titers of SARS-CoV-2 Spike receptor binding domain (RBD) antibodies were assessed using a previously described ELISA (Perreault et al, Blood 2020) with serial plasma dilutions (1/100-1/3200). Only participants negative for anti-RBD in the pre-vaccination sample (i.e. uninfected) were considered for the subsequent analyses.
Results/Findings: Participants were classified into high (8.9 ± 0.6 mg/ml; n=8) and low (3.9 ± 0.6 mg/ml; n=9) total IgG groups. The lifetime donation number was not significantly different between the 2 groups. All participants in the high IgG group were seropositive for anti-RBD at the 1/1600 dilution; all but one were still positive at the 1/3200 dilution. Conversely, individuals in the low IgG group exhibited lower seropositivity rates, particularly at higher dilutions (56% at 1/1600 and 11% at 1/3200). Comparison of the anti-RBD absorbances, indicative of antibody levels, corroborates the significantly lower response in the low IgG group at each dilution (Mann-Whitney). Conclusions: This preliminary study suggests that the production of specific antibodies in response to antigen challenge may align more closely with the intrinsic circulating IgG level than with the lifetime donation history of plasma donors. However, confirmation of this association requires further analysis involving a larger cohort of plasma samples from individuals with varying circulating IgG levels. This work is currently underway.
