CD4 and viral infectious disease: To garner a more complete understanding of the function of this population as cytotoxic effectors, and potentially their role in transplant rejection, we performed gene set enrichment analysis of the CD4+ T cells analyzed by single-cell RNA sequencing and compared them to canonical activated CD8+ T cell gene signatures—antigen-specific human CD8+ T cell effectors at the peak of response to yellow fever and mouse CD8+ T cells responding to LCMV—and to a gene set generated based on genes correlated with T cell-mediated rejection in patients treated with belatacept or tacrolimus (41).