High‐throughput detection of antibodies targeting the SARS‐CoV‐2 Spike in longitudinal convalescent plasma samples

Anand, Sai Priya; Prévost, Jérémie; Richard, Jonathan; Perreault, Josée; Tremblay, Tony; Drouin, Mathieu; Fournier, Marie‐Josée; Lewin, Antoine; Bazin, Renée; Finzi, Andrés

BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) virus is the cause of the ongoing coronavirus disease 2019 (COVID‐19) pandemic, infecting millions of people and causing more than two million deaths. The SARS‐CoV‐2 Spike glycoproteins mediate viral entry and represent the main target for antibody responses. Humoral responses were shown to be important for preventing and controlling infection by coronaviruses. A promising approach to reduce the severity of COVID‐19 is the transfusion of convalescent plasma. However, longitudinal studies revealed that the level of antibodies targeting the receptor‐binding domain (RBD) of the SARS‐CoV‐2 Spike declines rapidly after the resolution of the infection. STUDY DESIGN AND METHODS: To extend this observation beyond the RBD domain, we performed a longitudinal analysis of the persistence of antibodies targeting the full‐length SARS‐CoV‐2 Spike in the plasma from 15 convalescent donors. We generated a 293T cell line constitutively expressing the SARS‐CoV‐2 Spike and used it to develop a high‐throughput flow cytometry‐based assay to detect SARS‐CoV‐2 Spike‐specific antibodies in the plasma of convalescent donors. RESULTS AND CONCLUSION: We found that the level of antibodies targeting the full‐length SARS‐CoV‐2 Spike declines gradually after the resolution of the infection. This decline was not related to the number of donations but strongly correlated with the decline of RBD‐specific antibodies and the number of days post‐symptom onset. These findings help to better understand the decline of humoral responses against the SARS‐CoV‐2 Spike and provide important information on when to collect plasma after recovery from active infection for convalescent plasma transfusion.