Mesenchymal Stem Cells (MSCs) Intensify the Impact of KIR Ligand-Mismatching on Acute Graft-Versus-Host Disease Post HSCT in Patients with Acute Myeloid Leukemia but Not with Acute Lymphocytic Leukemia

Objectives: Mesenchymal stem cells (MSCs) and killer cell immunoglobulin-like receptor (KIR) ligand-mismatch, which can trigger the alloreactivity of natural killer (NK) cells, have been shown to be protective for severe acute and chronic graft-versus-host disease (aGVHD, cGVHD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, there are no prospective or retrospective studies exploring their relationship. Here, we investigated the potential influence of KIR matching, MSCs and their coaction on GVHD prophylaxis, overall survival (OS) and relapse rate (RR) of allo-HSCT.

Methods：Data from 154 patients with acute myeloid and lymphocytic leukemia treated with allo-HSCT between May 2015 and May 2020 in the transplantation unit of the Fujian Medical University Union Hospital were retrospectively analyzed. The cohort included 93 male patients (60.3%) and 61 female (39.7%), with a median age of 24 years (1-59 years), 104 cases of acute myeloid leukemia (AML; 67.5%) and 50 cases with acute lymphocytic leukemia (ALL; 32.5%). Eighty-one patients (52.6%) underwent MSCs infusion on day+1. The sources of MSCs were human placenta or human bone marrow. MSCs infusion dose ranged from 0.5 to 3x10⁶/kg of recipient weight. 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. Cox proportional hazards model and Kaplan-Meier survival curves were used for analysis.

Results：At the time of transplantation, 65 cases (42.2%) were in remission, while 89 (57.8%) had active disease. aGVHD occurred in 31 patients (20.1%) and recurrence arose in 21 patients (13.6%), but no significant cGVHD was observed. After adjusting for age, disease-risk, HLA-match, donor gender, conditioning regimen intensity and type of post-grafting GVHD prophylaxis, Cox regression analysis revealed that KIR ligand-matching was associated with an increased risk of aGVHD compared to KIR ligand-mismatching (p=0.023) in AML patients, but KIR ligand-mismatching had no significant effect on aGVHD in ALL patients, and on OS and RR in both AML and ALL patients. MSCs was associated with much lower recurrence rate (RR) (p=0.049), even when the recipients were not in remission at the time of HSCT. Furthermore, MSCs reduced the incidence of aGVHD in both AML and ALL patients, although it did not reach statistical significance (p=0.19). The combination of KIR ligand-mismatching and MSCs infusion significantly suppressed aGVHD occurrence in AML patients (p=0.033). More importantly, MSCs infusion intensified the suppression effect of KIR ligand-mismatching on aGVHD in AML patients (p=0.047). In the KIR ligand-mismatch group, the incidence of aGVHD was 10.3% when patients received MSCs, compared to 25.6% in those who did not. However, combining KIR ligand-mismatch and MSCs injection had no significant effect on aGVHD in ALL patients, or on OS and RR in both AML and ALL patients.

Conclusions: KIR ligand-mismatch, MSCs infusion and their combination significantly reduced the risk of aGVHD after allo-HSCT in AML patients. It confirms the relationship between MSCs injection and lower RR. These data provide a clinically applicable strategy where co-transplantation with MSCs and triggering of allo-NK cells by KIR ligand-mismatching can ameliorate aGVHD, thus improving allo-HSCT outcome in AML patients.