Kinetics of antibodies against SARS-COV-2 in convalescent plasma donors after eight months from covid-19: Persistence of spike antibodies but loss of neutralizing antibodies in 24% of donors
Authors: E. Terpos, D. Stellas, M. Rosati, T. N. Sergentanis, X. Hu, M. Politou, V. Pappa, I. Ntanasis-Stathopoulos, S. Karaliota, J. Bear, M. Pagoni, E. Grouzi, E. Korompoki, A. Antoniadou, A. Kotanidou, G. Panayiotakopoulos, G. N. Pavlakis, B. K. Felber, M. A. Dimopoulos
Journal: HemaSphere (2021)

Background: Elucidating the characteristics of human immune response against SARS-CoV-2 is of high priority for determining vaccine strategies. The duration of the persistence of anti-SARS-CoV-2 antibodies in individuals who suffered from COVID-19 is not clearly defined yet. Aims: The aim of this study was to assess the kinetics of anti-SARS-CoV-2 antibodies and neutralizing antibodies among convalescent plasma donors during an 8-month period from their first symptoms of COVID-19. Methods: Participants were enrolled in a phase 2 study of plasma donors (NCT04408209) for the use of convalescent plasma for the treatment of COVID-19 in Greece. For the detection of anti-SARS-CoV-2 antibodies, we used four in-house ELISA assays measuring antibodies to (i) trimeric Spike (S), (ii) Spike Receptor Binding Domain (Spike-RBD), (iii) Nucleocapsid, and (ii) Nucleocapsid RNA Binding Domain (N-RBD). For the Neutralizing Antibody (NAb) assay using SARS-CoV-2 pseudotyped virus, serial dilutions of heat-inactivated sera were incubated with an equal volume of the pseudotyped virions (pHIVNLEnv-Nanoluc) and the virion-Ab mixture was used to transduce HEK293T/ACE2wt cells. Two days later, the luciferase levels were measured in the cell extracts and the ID50 (50% Inhibitory Dose) was calculated using GraphPad Prism version 8.0 for MacOS X (GraphPad Software, Inc, La Jolla, CA) with nonlinear regression curve fit using inhibitor vs responses variable slope (four parameters). Results: In total, 148 convalescent plasma donors (median age: 50 years, range: 18-65) with a median follow-up of 8.3 (range 6.8-10.5) months post their first disease symptoms were included in this analysis. Ninetyone patients did not need hospitalization and 57 were hospitalized due to COVID-19. At the initial screen, all patients showed positive antibody responses recognizing trimeric Spike, Spike-RBD, Nucleocapsid and N-RBD. At the 6-month follow-up, we continue to detect positive responses to Spike, Spike-RBD, Nucleocapsid and N-RBD in all plasma donors but at lower levels compared to screening (p<0.001). At the 8-month follow-up, no significant reduction was observed compared to 6-month values. A piecewise, random-effects, generalized least squares multivariate regression analysis showed a two-phase pattern of antibody responses, with more pronounced decrease during the first 6 months and a plateau phase after the 6th month post-symptoms onset. Spike antibodies showed better persistence than Nucleocapsid antibodies, whereas antibodies recognizing only the Spike-RBD or N-RBD persisted less than the mixture of antibodies recognizing the respective complete proteins. Neutralization ability contracted faster, since neutralizing antibodies persisted in 76% of patients at the last time point. In the multivariate analysis, older age and hospitalization were independently associated with higher antibody Spike, Spike-RBD, Nucleocapsid, N-RBD and NAb levels. Summary/Conclusion: We found persistence of anti-SARS-CoV-2 antibodies, especially against Spike and Spike-RBD, up to 8 months post-symptoms onset. However, a loss of neutralizing antibodies became evident in 24% of convalescent donors at 8 months from initial symptoms of COVID-19. A prolonged follow-up of the donors is necessary to further characterize the kinetics of anti-SARS-CoV-2 B-cell mediated immunity over time and to establish a link between the presence of antibodies and the level of protection against re-infection. Such data should help to optimize vaccination strategies and public health decisions.