To address this issue, we monitored, in a prospective study, the frequencies of inhibitory CD94/NKG2A and activating CD94/NKG2C receptor expression on NK cells in the post-alloSCT course of one year and related the results to the occurrence of severe acute or chronic GvHD in a cohort of 26 patients undergoing alloSCT. The gene discussed is KLRD1; the disease is graft versus host disease.