Abstract
Since the outbreak of the coronavirus disease 2019 (COVID-19) epidemic in 2019, the public health system has faced enormous challenges. Tracking the individuals who test positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a key step for interrupting chains of transmission of SARS-CoV-2 and reducing COVID-19-associated mortality. With the increasing of asymptomatic infections, it is difficult to track asymptomatic infections through epidemiological surveys and virus whole-genome sequencing. However, due to the cross-reactivity of neutralizing antibodies produced by multiple virus subtypes, neutralizing antibody detection cannot be used to determine whether an individual has a history of infection with a specific subtype of SARS-CoV-2. We recruited 4 human leukocyte antigen A2 (HLA-A2) infections, 15 individuals who received three doses of inactivated vaccines, and 30 breakthrough infections after vaccination and discussed a case-tracking approach to detect epitope-specific CD8+ T cells in the peripheral blood of close contacts, including accurate HLA typing based on ribonucleic acid (RNA)-sequencing and flow cytometry data and the comparison and characterization of SARS-CoV-2 HLA-A2 and HLA-A24 epitope-specific CD8+ T cells. From individuals who received three doses of inactivated vaccine, we observed that the CD8+ T cell specificity for ancestral epitopes was significantly higher than for mutated epitopes, and the fold change of CD8+ T cells corresponding to mutated epitopes relative to ancestral epitopes was less than 1. The enzyme-linked immunospot (ELISpot) results further validate this result. This study forms a "method for understanding the infection history of SARS-CoV-2 subtypes based on the proportion of epitope-specific CD8+ T cells in the peripheral blood of subjects", covering up to 46 % of the population, including HLA-A2+ and HLA-A24+ donors, providing a novel method for SARS-CoV-2 infected case tracing.