KIR Ligand Incompatibility in HLA-Identical Sibling Nonmyeloablative Hematopoietic Stem Cell Transplantation for Hematologic Malignancies.

Natural killer (NK) cell alloreactivity based on inhibitory killer immunoglobulin-like receptor (KIR)-ligand incompatibility (i.e., missing KIR ligand) in the graft-vs-host (GVH) direction has been described to favorably influence engraftment, GVHD, and graft-vs-tumor (GVT) effect following haploidentical or matched unrelated HSCT in patients with hematologic malignancies. The degree and effect of KIR-ligand incompatibility has recently been explored following HLA-identical sibling HSCT (Hsu et al., Blood2005;105:4878). Based on a murine model, we developed a clinical trial with a goal of deliberately inducing a GVHD-free mixed chimeric platform following nonmyeloablative conditioning (consisting of equine ATG, cyclophosphamide, thymic irradiation, and a brief course of cyclosporine) and HLA-matched sibling HSCT. Donor leukocyte infusions (DLI) were given as early as five weeks post-HSCT to patients without GVHD in an attempt to achieve a conversion to full donor chimerism (FDC) with the goal of fully capturing GVT effect with little or no GVHD. In this study we hypothesized that KIR-ligand incompatibility in the GVH direction and KIR-ligand compatibility in the host-vs-graft (HVG) direction would reduce the rate of graft failure, decrease the incidence of GVHD, and improve overall survival following HLA-matched sibling HSCT. Fourteen transplant recipients (bone marrow, n=9; peripheral blood stem cell, n=5) with refractory hematologic malignancies (NHL, n=7; HD, n=3; MM, n=2; CLL, n=1; AML, n=1) were analyzed. KIR typing was accomplished using PCR amplified DNA from both donor and recipient patient samples. Typing of the amplified DNA was performed using the Lifecodes KIR-SSO typing kits (Tepnel Lifecodes Corporation). By using the SSO (sequence-specific oligonucleotides) technology in conjunction with the Luminex Instrument, KIR loci were identified for each patient and donor sample. KIR-ligand (HLA) incompatibility in the GVH and HVG directions were assessed based on HLA and KIR genotyping (KIR2DL1, KIR2DL2, KIR2DL3 and KIR3DL1) of 14 donors and 12 of the 14 recipients. Six of the 14 patients eventually lost their grafts despite DLI. Seven patients spontaneously achieved FDC and one converted to FDC following DLI. The missing KIR ligand analysis showed 12 patients (86%, n=12/14) with KIR-ligand incompatibility in the GVH direction (1 missing ligand, n=9; 2 missing ligands, n=3) and 10 patients (83%, n=10/12) with KIR-ligand incompatibility in the HVG direction (1 missing ligand, n=9; 2 missing ligands n=1). The presence or the degree of KIR-ligand incompatibility in GVH or HVG direction was not found to be predictive of spontaneous FDC or graft rejection. There was no significant relationship between the number of missing KIR ligands in either direction and the development of acute or chronic GVHD. This study shows a higher rate of KIR-ligand incompatibility in the GVH (86%) and HVG (83%) directions in the setting of HLA-matched sibling HSCT than previously reported. Although the small number of patients does not allow for statistically meaningful conclusions regarding clinical outcome, the observation of a high incidence of KIR-ligand incompatibility in this population justifies the study of larger patient cohorts to determine the influence of NK cell alloreactivity on transplant outcomes.