Building upon previous research that identified CD70 messenger RNA upregulation in T cells after allogeneic activation6 and considering murine studies suggesting the potential of CD70 as a determinant of GVHD,17,18 we investigated the functional relevance, transcriptional profile, and epigenetic regulation of CD70-expressing T cells in patients undergoing allo-HSCT. Here, CD70 is linked to graft versus host disease.