CD28H expression identifies resident memory CD8 + T cells with less cytotoxicity in human peripheral tissues and cancers.

The CD28H/B7-H5 pathway is a newly identified pathway of the B7 family. In human peripheral blood, the receptor CD28H is preferentially expressed on naïve T cells and repetitive stimulation of T cells leads to the loss of CD28H expression. Here we examined the expression of the CD28H/B7-H5 pathway in human peripheral tissues, as well as in human cancers. We found that CD28H is preferentially expressed on T cells with tissue-resident phenotypes (T). Supporting that, stimulation via IL-15 and TGF-β, presumably major cytokines essential for T cell homeostasis, sustains CD28H expression on T cells. The ligand B7-H5 is constitutively expressed on normal epithelium of human oral-gastrointestinal tracts. In human cancers, CD28H is preferentially present on tumor infiltrating lymphocytes (TILs) with T features and identifies a T subset with less cytotoxicity. Taken together, our studies suggest that the CD28H/B7-H5 pathway involves the interactions between T cells and epithelium, and could be important for human T homeostasis and function.