Abstract

During the SARS-CoV-2 pandemic, the use of convalescent plasma (CP) in high-risk patients was proposed and widely implemented in several countries as a potential COVID-19 therapy. Nonetheless, CP therapy's impact on immune response is nowadays poorly understood, including the correlation between IgG levels, neutralization capacity, and cellular immune response against SARS-CoV-2. Here we evaluated, in a cohort of patients with COVID-19 requiring hospitalization and having received or not CP, as well as in CP donors (recovered from mild disease), the humoral and cellular immune response assessed by titers of SARS-CoV-2 IgG, neutralizing antibodies, and IFN-?+/IL-2+ ELISpot during the first month (early) and up to nine months (long-term) after symptom onset. Results showed higher seropositivity and seroconversion rates between 7–12 days after plasma infusion in CP-recipients. However, similar IgG and neutralizing immune response kinetics between CP-recipients and non-recipients was observed during the first and until the ninth month of analysis. A positive correlation between IgG and neutralizing levels was detected. Compared to outpatient donors, hospitalized individuals showed a higher response at 3 and 6 months after symptoms onset. A sustained SARS-CoV-2-specific CD4+ and CD8+ T cell response was observed in outpatients and hospitalized patients, regardless of the CP treatment. We concluded that the CP infusion did not affect the long-term SARS-CoV-2 specific humoral and cellular immune responses. Nonetheless, CP may provide a therapeutic window by promoting a higher humoral response during the acute phase of COVID-19. © 2025