Evaluation of T cell immune memory response after BBIBP-CorV, gam-COVID-Vac, and heterologous gam-COVID-Vac /mRNA-1273 COVID-19 vaccination schemes against different SARS-CoV-2 variants

Abstract

Introduction: The adaptive immune response plays a crucial role in resolution of viral infections; however, there is limited data on the T cell response to SARS-CoV-2 vaccines such as BBIBP-CorV, Gam-COVID-Vac, and especially for the heterologous combination Gam-COVID-Vac/mRNA-1273 scheme. Furthermore, emerging variants may compromise the adaptive immune response established in the population.Objective: To evaluate the T cell immune response induced by the BBIBP-CorV, Gam-COVID-Vac and Gam-COVID-Vac/mRNA-1273, against the ancestral wild type (WT) virus and the Gamma and Omicron variants.Methods: Serum levels of IgG antibodies were assessed by CMIA (Abbott Diagnostics, Abbott Park, Illinois). T cell responses against WT virus, Gamma and Omicron were evaluated through an activation-induced marker assay. Sixty individuals, evenly distributed across the BBIBP-CorV, Gam-COVID-Vac, and Gam-COVID-Vac/mRNA-1273 groups, were included.Results: The median age of participants was 48 years (IQR: 34-56), with 58.3 % (n = 35) being female. Seventeen (28.3 %) individuals had a prior confirmed COVID-19 infection. Gam-COVID-Vac/mRNA-1273 scheme elicited significantly higher humoral responses (p < 0.001). However, the three vaccination platforms showed consistent T cell responses across the three stimuli tested. Particularly, all three schemes induced stronger CD8+ responses against the WT virus. In addition, more responders to WT were observed in the BBIBP-CorV and Gam-COVID-Vac groups, while the Gam-COVID-Vac/mRNA-1273 group showed a greater proportion of responders to Omicron.Conclusion: This study provides new data on effective humoral and cellular immune responses against the ancestral WT virus as well as the Gamma and Omicron variants. Moreover, memory CD4+ and CD8+ T cell responses remain protective, and the heterologous scheme may elicit stronger T cell responses against emerging variants.