Longitudinal analysis of the anti-RBD antibody response in 15 repeat CCP donors. Males and females with no history of pregnancy who recovered from a diagnosed COVID-19 infection were invited to donate plasma after informed consent. A volume of 500 to 750 mL plasma was collected by plasmapheresis (TRIMA Accel; Terumo BCT). Donors were allowed to donate plasma units every 6 days, for a maximum of 12 weeks. The level of anti-RBD antibodies was determined in our semiquantitative in-house ELISA (see supplemental Methods), using a 1:100 dilution of plasma. (A) Each curve represents the mean OD_450nm ± SD obtained with the plasma of 1 donor at every donation (4-9 donations per donor) as a function of the days after symptom onset. The dotted line represents the cutoff value of the ELISA; some donors became seronegative at their last donation. (B) Same results but presented as the relative anti-RBD antibody level calculated at each time point using the first time point as reference: 1 − [OD_450nm at each donation/OD_450nm at first donation] × 100. (C) Correlation between the number of donations by each donor and the overall decline in anti-RBD level calculated using the following formula: 1 − [OD_450nm at the last donation/maximal OD_450nm obtained] × 100. (D) Correlation between the number of days between symptom onset and the last donation with the overall decline in anti-RBD level for each donor.