PRF1 and COVID-19: The appearance of HLA-DR+CD38+CD8+ T cells has also been described for other viruses like HIV and Influenza A and was associated with worse outcomes and impaired T-cell function.18,19 For COVID-19 others have shown that conversely to their activated phenotype HLA-DR+CD38+CD8+ T cells also expressed exhaustion markers like PD-1 but were still functional by producing e.g., IFN-γ, granzyme B, and perforin, suggesting that these cells are not generally functionally impaired by their PD-1 expression.20,21