CD8A and COVID-19: Three key findings are shown from our systemic analysis: (1) TCR repertoire diversity decreased quickly after recovering from COVID-19, without changing the global frequency of VDJ gene usage; (2) The dynamics of TCR repertoire was linked to a profound change of gene signatures from anti-viral response to metabolism adaptation; (3) The top expanded T cell clones (~10% of total T cells) determined the principal features of CD8+ T cells, indicating the vital role of antigen-specific T cells in fighting against SARS-CoV-2 infection.