Successful treatment of COVID-19 with convalescent plasma in B-cell depleted patients may promote cellular immunity

ABSTRACT

Introduction: Treatment with convalescent plasma has been shown to be safe in COVID-19 infection, however, there remain conflicting results regarding its efficacy in immunocompetent patients. Nevertheless, neutralizing antibodies are a key requisite in the fight against viral infections. Patients depleted of antibody producing B-cells such as those treated with rituximab e.g. for hematological malignancies lack a fundamental part of their adaptive immunity. Therefore, treatment with convalescent plasma might still be of benefit in this particularly vulnerable cohort. Methods: Peripheral blood samples were taken from three COVID-19 patients, who were B cell-depleted after previous rituximab treatment, during the course of treatment with convalescent plasma. Flow cytometric analysis of activation markers with or without prior in vitro stimulation with SARS-CoV-2 spike and nucleocapsid antigen revealed antigen-specific T cell responses. Serum levels of SARS-CoV-2-specific IgG and IgM antibodies were measured by automated CLIA. RT-PCR was used to monitor viral load in nasopharyngeal swabs. Results: All three patients made a full recovery from infection following convalescent treatment, even though serum antibody levels decline rapidly after each plasma administration. The recovery coincided with an increase in SARS-CoV-2-specific CD4+ and CD8+ T cells in peripheral blood. Conclusions: We demonstrate efficacy of treatment with convalescent plasma in three patients unable to mount an antibody response by themselves and for the first time show that although application of convalescent plasma only leads to short-lived detectable systemic antibody levels, it appears to boost long-lasting specific T-cell responses.