Perforin/granzyme B is upregulated in human CD8 T cells after conditioning treatment and GVHD. Blood samples from healthy donors (n = 16), patients receiving chemotherapy or irradiation (n = 20) in preparation for allo-HCT, GVHD patients (n = 8) or patients before conditioning (n = 7). Cells were stained against CD8 and perforin or granzyme B, and analyzed by flow cytometry. (A) Quantification of the flow cytometry data. Values are the percentage of total cells identified as both CD8⁺ and perforin⁺ or granzyme B⁺ (***P < .001). (B) Representative flow cytometry data for CD8⁺ perforin⁺ or CD8⁺ granzyme B⁺ T cells are shown.