Molecular relapse monitoring reveals the domination of impaired NK cell education over impaired inhibition in missing KIR‐ligand recognition in patients after unrelated hematopoietic stem cell transplantation for malignant diseases

Abstract

Transplantation of HLA and/or KIR mismatched allogeneic hematopoietic stem cells can lead NK cells to different states of activation/inhibition or education/resetting and change anti‐tumor immunosurveillance. In this study, we used molecular relapse monitoring to investigate a correlation between either missing ligand recognition or variation of the cognate iKIR‐HLA pairs with clinical outcomes in patients with hematological malignancies requiring allogeneic hematopoietic stem cell transplantation (allo‐HSCT). Patients (N = 418) with acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), myelodysplastic syndrome (MDS), or lymphoma receiving T‐cell repleted graft from HLA‐matched or partly mismatched unrelated donors between 2012 and 2020 in our center were included in this study. Missing‐ligand recognition was assessed through the presence or absence of recipients' HLA ligand for a particular inhibitory KIR (iKIR) exhibited by the donor. Inhibitory KIR‐HLA pair number variation was defined by loss or gain of a new cognate pair of HLA‐KIR within the new HLA environment of the recipient, compared with the donor's one. Considering the results of our research, we drew the following conclusions: (i) loss of iKIR‐HLA cognate pair for C1, C2, and/or Bw4 groups led to significant deterioration of disease‐free survival (DFS), molecular relapse, overall survival (OS) and non‐relapse mortality (NRM) for patients undergoing allo‐HSCT in the standard phase of the disease. This phenomenon was not observed in patients who underwent transplantation in advanced hematological cancer. (ii) The missing ligand recognition had no impact if the proportion of HLA mismatches was not considered; however, adjustments of HLA mismatch level in the compared groups highlighted the adverse effect of the missing ligand constellation. (iii) The adverse effect of adjusted missing ligand suggests a predominance of lost NK cell education over lost NK cell inhibition in posttransplant recipients' new HLA environment. Our results suggested that donors with the loss of an iKIR‐HLA cognate pair after transplantation should be avoided, and donors who provided an additional iKIR‐HLA cognate pair should be preferred in the allo‐HSCT donor selection process.