Both the percentage (39.7%, range 20.7–60.7 vs. 32.5%, range 3.25–49.44, P = 0.025 ) and absolute levels (87.5×106/L, range 19–218 vs. 55.3×106/L, range 4–182, P = 0.009) of CD161+CD4+ T cells in peripheral blood were found to be significantly reduced in patients with acute GVHD (Figure 3A). Here, KLRB1 is linked to acute graft versus host disease.