Association of Ikir-Mismatching and Donor Akirs with Better Outcomes in Haploidentical Hematopoietic Stem Cell Transplantation for Acute Myeloid Leukemia

Objectives: Natural killer (NK) cells are the first donor-derived lymphocytes to be reconstituted after transplantation and play a critical role in improving transplantation outcomes. Their surface receptor, killer cell immunoglobulin like receptor (KIR), can trigger the alloreactivity of NK cells and have been shown to be protective for acute and chronic graft-versus-host disease (aGVHD, cGVHD) while retaining graft-versus-leukemia (GVL) effect. However, different results have been reported about KIR matching models and KIR alleles based on patient, donor and transplant characteristics, resulting in significant controversy about the best donor selection strategy. Here, we investigated the potential influence of KIR matching and KIR alleles on GVHD prophylaxis, overall survival (OS) and relapse rate (RR) of haploidentical hematopoietic stem cell transplantation (haplo-HSCT) in acute myeloid leukemia (AML) patients. Methods：Data from 79 patients with AML treated with haplo-HSCT between May 2015 and May 2021 in the transplantation unit of the Fujian Medical University Union Hospital were retrospectively analyzed. The cohort included 49 male patients (62.0%) and 30 female (38.0%), with a median age of 25 years (1-68 years). KIR genotyping was performed by the PCR-SSO method. The amplicons were quantified on the Luminex 200 flow analyzer and analyzed using the Quick-Type for Lifecodes software for generating KIR data. HLA-A and -B alleles were typed by polymerase chain reaction using sequence-specific primers (PCR-SSP) (TBG, Taipei, Taiwan). HLA-C genotyping was determined by reverse hybridization with sequence specific oligonucleotides probes (rSSO) Line probe assay. Cox proportional hazards model and Kaplan-Meier survival curves were used for analysis. Results：At the time of transplantation, 49 cases (62.0%) were at CR1, while 30 (38.0%) were not. aGVHD occurred in 16 patients (20.3%) and recurrence arose in 10 patients (12.7%), 4 (5.1%) cases cGVHD was observed. After adjusting for age, disease-risk, disease-status, HLA-match, donor gender, conditioning regimen intensity and type of post-grafting GVHD prophylaxis, Cox regression analysis revealed that both KIR ligand-ligand mismatching (KLM) and KIR receptor-ligand matching (RLM) was associated with an decreased risk of aGVHD and relapse compared to KIR ligand-ligand matching and receptor-ligand matching group, respectively (aGVHD: KLM: p=0.047, RLM: p＜0.001; RR: KLM: p=0.049, RLM: p=0.017). Furthermore, RLM shows more accurate in prediction of relapse and aGVHD compared with KLM in both aGVHD and relapse. (aGHVD: p=0.009; RR: p=0.039). After taking activating KIR (aKIR) into consideration to compensate the defect of only inhibitory KIR (iKIR) dominant model, we found that patients with more donor activating KIRs can reach the lower incidence of aGVHD and relapse, and the benefit can gradually increase parallel with the increase in donor activating KIRs. (aGVHD：p=0.019；RR：p=0.037). Patients with both receptor-ligand mismatch and the most donor aKIRs can reach the lowest relapse, lowest incidence of aGVHD and best overall survival (OS). Conclusions: KIR-mismatch, both KLM and RLM significantly reduced the risk of aGVHD and relapse after halpo-HSCT in AML patients and RLM show more superiority in the prediction of HSCT outcome. The synergistic effects of receptor-ligand mismatch and more donor aKIRs can provide a better clinically applicable donor selection strategy to improve haplo-HSCT outcome in AML patients.