Anti–SARS-CoV-2 Antibody Responses in Convalescent Plasma Donors Are Increased in Hospitalized Patients; Subanalyses of a Phase 2 Clinical Study

Terpos, Evangelos; Politou, Marianna; Sergentanis, Theodoros N.; Mentis, Andreas; Rosati, Margherita; Stellas, Dimitris; Bear, Jenifer; Hu, Xintao; Felber, Barbara K.; Pappa, Vassiliki; Pagoni, Maria; Grouzi, Elisavet; Labropoulou, Stavroula; Charitaki, Ioanna; Ntanasis-Stathopoulos, Ioannis; Moschandreou, Dimitra; Bouhla, Anthi; Saridakis, Stylianos; Korompoki, Eleni; Giatra, Chara; Bagratuni, Tina; Pefanis, Angelos; Papageorgiou, Sotirios; Spyridonidis, Alexandros; Antoniadou, Anastasia; Kotanidou, Anastasia; Syrigos, Konstantinos; Stamoulis, Konstantinos; Panayiotakopoulos, George; Tsiodras, Sotirios; Alexopoulos, Leonidas; Dimopoulos, Meletios A.; Pavlakis, George N.

We evaluated the antibody responses in 259 potential convalescent plasma donors for Covid-19 patients. Different assays were used: a commercial ELISA detecting antibodies against the recombinant spike protein (S1); a multiplex assay detecting total and specific antibody isotypes against three SARS-CoV-2 antigens (S1, basic nucleocapsid (N) protein and receptor-binding domain (RBD)); and an in-house ELISA detecting antibodies to complete spike, RBD and N in 60 of these donors. Neutralizing antibodies (NAb) were also evaluated in these 60 donors. Analyzed samples were collected at a median time of 62 (14–104) days from the day of first symptoms or positive PCR (for asymptomatic patients). Anti-SARS-CoV-2 antibodies were detected in 88% and 87.8% of donors using the ELISA and the multiplex assay, respectively. The multivariate analysis showed that age ≥50 years (p < 0.001) and need for hospitalization (p < 0.001) correlated with higher antibody titers, while asymptomatic status (p < 0.001) and testing >60 days after symptom onset (p = 0.001) correlated with lower titers. Interestingly, pseudotype virus-neutralizing antibodies (PsNAbs) significantly correlated with spike and with RBD antibodies by ELISA. Sera with high PsNAb also showed a strong ability to neutralize active SARS-CoV-2 virus, with hospitalized patients showing higher titers. Therefore, convalescent plasma donors can be selected based on the presence of high RBD antibody titers.