Although the overall clonotype expansions were similar for STAT3–/– donor T cells that did not cause GVHD and STAT3–/–PD-1–/– T cells that did cause GVHD, approximately 15% to 30% of TCRB and TCRA clonotypes that were not expanded among CD4+ or CD8+ T cells from STAT3–/– donors were expanded among CD4+ or CD8+ T cells from STAT3–/–PD-1–/– donors (Figure 5, C and D, and Supplemental Figure 4, C and D). This evidence concerns the gene PDCD1 and graft versus host disease.