CD226 and graft versus host disease: The CD226 allele rs3911730*A protective of relapse in the HSCT discovery cohort was associated with high NK cell in vitro cytotoxicity in the blood donors, and the CD244 alleles rs116433596*G and rs576627*C protective of GVHD were associated with low in vitro cytotoxicity – effects apparently beneficial to the relapse and GVHD risks.