Knowledge on the vaccine-induced cellular and humoral immunity and on immunogenicity of vector-based and mRNA vaccines in solid organ transplant recipients is limited. Therefore, SARS-CoV-2 specific T-cells and antibodies were analyzed in 40 transplant recipients and 70 age-matched controls after the first dose of vector-based or mRNA vaccines. Plasmablasts and SARS-CoV-2 specific CD4 and CD8 T-cells were quantified using flow-cytometry. Specific antibodies were analyzed by ELISA and neutralization assay. SARS-CoV-2 specific antibodies and T-cells were induced in both groups with significantly lower levels in patients. While antibodies were detected in 80% of controls and 5.3% of patients, specific CD4 and/or CD8 T-cells were more frequently found in both controls (84.3%) and patients (23.7%). The two vaccine types showed notable differences, as IgG and neutralizing activity were more pronounced after mRNA vaccination (p<0.0001 each), whereas CD4 and CD8 T-cell levels were higher after vector vaccination (p=0.009; p<0.0001). Plasmablast numbers were significantly higher in controls and correlated with SARS-CoV-2 specific IgG- and CD4 T-cell levels. In conclusion, assessment of antibodies is not sufficient to identify COVID-19-vaccine responders. Together with differences in immunogenicity among vaccines, this necessitates combined analysis of humoral and cellular immunity to reliably assess responders among immunocompetent and immunocompromised individuals.
Cellular immunity predominates over humoral immunity after the first dose of COVID-19 vaccines in solid organ transplant recipients