Impact of Donor Activating KIR Genes on HSCT Outcome in C1-Ligand Negative Myeloid Disease Patients Transplanted with Unrelated Donors—A Retrospective Study

Natural Killer cells (NK) are lymphocytes with the potential to recognize and lyse cells which escaped T-cell mediated lysis due to their aberrant HLA expression profiles. Killer cell immunoglobulin-like receptors (KIR) influence NK-cell activity by mediation of activating or inhibitory signals upon interaction with HLA-C (C1, C2) ligands. Therefore, absence of ligands for donor inhibitory KIRs following hematopoietic stem cell transplantation (HSCT) may have an influence on its outcome. Previous studies showed that C1 negative patients have a decreased HSCT outcome. Our study, based on a cohort of 200 C1-negative patients, confirmed these findings for the endpoints: overall survival (OS: HR = 1.41, CI = 1.14-1.74, p = 0.0012), disease free survival (DFS: HR = 1.27, CI = 1.05-1.53, p = 0.015), treatment related mortality (TRM: HR = 1.41, CI = 1.01-1.96, p = 0.04), and relapse incidence (RI: HR = 1.33, CI = 1.01-1.75, p = 0.04) all being inferior when compared to C1-positive patients (n = 1246). Subsequent analysis showed that these findings applied for patients with myeloid malignancies but not for patients with lymphoproliferative diseases (OS: myeloid: HR = 1.51, CI = 1.15-1.99, p = 0.003; lymphoblastic: HR = 1.26, CI = 0.91-1.75, p = 0.16; DFS: myeloid: HR = 1.31, CI = 1.01-1.70, p = 0.04; lymphoblastic: HR = 1.21, CI = 0.90-1.61, p = 0.21; RI: myeloid: HR = 1.31, CI = 1.01-1.70, p = 0.04; lymphoblastic: HR = 1.21, CI = 0.90-1.61, p = 0.21). Interestingly, within the C1-negative patient group, transplantation with KIR2DS2 resulted in better OS (9/10 matched: HR = 0.24, CI = 0.08-0.67, p = 0.007) as well as DFS (9/10 matched: HR = 0,26, CI = 0.11-0.60, p = 0.002), and transplantation with KIR2DS1 positive donors was associated with a decreased RI (HR = 0.30, CI = 0.13-0.69, p = 0.005). TRM was increased when the donor was positive for KIR2DS1 (HR = 2.61, CI = 1.26-5.41, p = 0.001). Our findings suggest that inclusion of KIR2DS1/2/5 and KIR3DS1-genotyping in the unrelated donor search algorithm of C1-ligand negative patients with myeloid malignancies may prove to be of clinical relevance.