Determination of SARS-COV-2 CD4 and CD8 T Cell responses prior to COVID-19 Pandemic among Ugandan adults

Abstract

The Coronavirus disease-19, caused by SARS-CoV-2, became a public health concern in 2020. The distribution of COVID-19 deaths and infections has been skewed. Compared to sub-Saharan Africa (SSA), the Western world accounts for most cases and deaths. It has been hypothesized that prior exposure of the human population in SSA to other coronaviruses resulted in some degree of cross-protection against SARS-CoV-2 infections. This study assessed the cross-reactivity of SARS-CoV-2 T cell responses in Peripheral Blood Mononuclear Cell (PBMC) samples collected before the COVID-19 pandemic. Forty-three paired samples were collected at baseline and after twelve months from fishing communities around Lake Victoria. These samples were part of the Simulated Vaccine Efficacy Trials (SIVET). The PBMCs were stimulated with SARS-CoV-2 virus-specific CD4 and CD8 peptides for 24 hours, and the Activation Induced Marker flow cytometric assay was used to detect virus-specific CD4 and CD8 T cell responses. Data were analysed using FlowJo, and percentage responses were exported to Microsoft Excel for statistical analysis and graphing in Stata and GraphPad Prism. Cross-reactivity of SARS-CoV-2 T cell responses was detected in the PBMC samples collected before the COVID-19 pandemic. The CD4+ T cell responses predominated than CD8+ T cell responses. Pre-existing immunity to SARS-CoV-2 may imply that prior exposure to circulating human coronaviruses is the likely source of SARSCoV-2 T cell cross-reactivity. In addition, there was no significant difference in T cell responses in samples collected at baseline and after12 months. T cell responses detected at baseline persisted for twelve months in the samples analysed. The findings show that there were high levels SARS-CoV-2 specific T cell responses present before the COVID-19 pandemic in Ugandan population. However, the exact role the T cell response plays in mild disease is unknown. It is recommended that a larger sample size be used, with more assays targeting the functionality and magnitude of T cell responses in the Ugandan setting