Thymosin α1 modulated the immune landscape of COVID-19 patients revealed by single-cell RNA and TCR sequencing

Background: The Coronavirus disease-19 (COVID-19) pandemic has posed a serious threat to global health. Thymosin alpha 1 (T alpha 1) was considered to be applied in COVID-19 therapy. However, the data remains limited.Methods: Participants with or without T alpha 1 treatment were recruited. Single cell RNA-sequencing (scRNA-seq) and T cell receptor-sequencing (TCR-seq) of the peripheral blood mononuclear cell (PBMC) samples were done to analyze immune features. The differential expression analysis and functional enrichment analysis were performed to explore the mechanism of T alpha 1 therapy.Results: 33 symptomatic SARS-CoV-2-infected individuals (COV) and 11 healthy controls (HC) were enrolled in this study. The proportion of CD3+ KLRD1+ NKT, TBX21+ CD8+ NKT was observed to increase in COVID-19 patients with T alpha 1 treatment (COVT) than those without T alpha 1 (COV) (p = 0.024; p = 0.010). These two clusters were also significantly higher in Health controls with T alpha 1 treatment (HCT) than those without T alpha 1 (HC) (p = 0.016; p = 0.031). Besides, a series of genes and pathways related to immune responses were significantly higher enriched in T alpha 1 groups TBX21+ CD8+ NKT, such as KLRB1, PRF1, natural killer cell-mediated cytotoxicity pathway, chemokine signaling pathway, JAK-STAT signaling pathway. The increased TRBV9-TRBJ1-1 pair existed in both HCs and COVID-19 patients after T alpha 1 treatment. 1389 common complementarity determining region 3 nucleotides (CDR 3 nt) were found in COV and HC, while 0 CDR 3 nt was common in COVT and HCT.Conclusions: T alpha 1 increased CD3+ KLRD1+ NKT, TBX21+ CD8+ NKT cell proportion and stimulated the diversity of TCR clones in COVT and HCT. And T alpha 1 could regulate the expression of genes associated with NKT activation or cytotoxicity to promote NKT cells. These data support the use of T alpha 1 in COVID-19 patients.