Regulatory T-cells are central hubs for age-, sex- and severity-associated cellular networks during COVID-19

Using single-cell proteomics by mass cytometry, we investigate changes to a broad selection of over 10,000,000 immune cells in a cohort of moderate, severe, and critical Japanese COVID-19 patients and healthy controls with a particular focus on regulatory T-cells (Tregs). We find significant disruption within all compartments of the immune system and the emergence of atypical CTLA-4^high CD4 T-cells and proliferating HLA-DR^lowCD38^high Tregs associated with critical patients. We also observed disrupted regulation of humoral immunity in COVID-19, with a loss of circulating T follicular regulatory T cells (Tfr) and altered T follicular helper (Tfh)/Tfr and plasma cell/Tfr ratios, all of which are significantly lower in male patients. Shifting ratios of CXCR4 and CXCR5 expression in B-cells provides further evidence of an autoimmune phenotype and dysregulated humoral immunity. These results suggest that Tregs are central to the changing cellular networks of a wide range of cells in COVID-19 and that sex specific differences to the balance of Tfr, Tfh and plasma cells may have important implications for the specificity of the humoral immune response to SARS-CoV-2.