Relapse-free survival benefit from KIR B haplotype donors after HLA-matched and HLA-matched/KIR ligand–matched transplantation. The univariate Kaplan-Meier curves demonstrate the relapse-free survival (RFS) for patients receiving transplants from donors with or without KIR B haplotypes who were (A) 10/10 HLA matched, (B) HLA mismatched and KIR-ligand matched, or (C) HLA mismatched and KIR-ligand mismatched.