Influence of donor KIR3DS1 on HSCT outcomes. (A) Incidence of grade II-IV acute GVHD (aGVHD) based on donor KIR3DS1 copy number and presence/absence of recipient HLA-Bw4 KIR epitope. Grade II-IV aGVHD was lower among HLA-Bw4⁺ recipients with a KIR3DS1⁺ donor. Donor KIR3DS1 homozygosity is associated with the lowest rate of grade II-IV aGVHD (39%). (B) Probability of TRM stratified by donor KIR3DS1 copy number. TRM is similarly affected by donor KIR3DS1 copy number; the lowest TRM is associated with donor KIR3DS1 homozygosity (31%, P = .02). (C) Kaplan-Meier survival analysis demonstrating an association of overall survival with donor KIR3DS1 copy number (P = .03). (D) There is no association of donor KIR3DS1 with risk of relapse (P = .82).