Impact of the Inhibitory KIR-HLA Receptor-Ligand Model on Unrelated Hematopoietic Stem Cell Transplantation in Patients with Leukemia.

The interaction between killer cell immunoglobin-like receptor (KIR) and HLA molecule has particular relevance to the unrelated hematopoietic stem cell transplantation (HSCT). The presence of KIR on donor’s NK cells and the absence of the corresponding KIR ligand in the recipient’s HLA repertoire as a receptor-ligand model can be used to predict the outcome of HSCT. To investigate the effect of KIR-HLA receptor-ligand mismatching and the expression of inhibitory KIR (iKIR) on the unrelated Allo-HSCT of leukemia, the following study has been carried out. The KIR genotypes of 36 patients of ALL (n=18), AML (n=10), and CML (n=8) as well as their unrelated donors were obtained from the Database of China Marrow Donor Program. KIR genotyping was performed with PCR-SSP. The KIR and HLA mismatching status (receptor-ligand mismatch model) between recipients and donors was analyzed thereafter. The expression of iKIR was determined by flow cytometry on recipients after HSCT. All cases were followed up closely until July, 2007. Among all the donor/recipient pairs analyzed, 15 pairs displayed the matched pattern with respect to the KIR genotyping though, graft-versus-host (GVH) KIR ligand-mismatched in 13 pairs, and host-versus-graft (HVG) KIR ligand-mismatched in 8 pairs. 26 recipients were lack of HLA-Cw2,4,5,6,15 ligands although iKIR/2DL1 was expressed on their corresponding donors. Similarly, 35 donors with iKIR/2DL2/L3 on their NK cells could recognized HLA- Cw1,3,7,8,12,14 ligands in their recipients. iKIR/3DL1 was expressed on 9 donors although the correlated HLA-Bw4 ligand was absent on the recipients. iKIR/3DL2 was expressed on 24 donors although the correlated HLA-A11 ligand was absent on the recipients. Except for one case, 35 patients were successfully transplanted, in which seven patients were dead, giving the survival rate of 80.0%. The cause of death was either acute/chronic GVHD or relapse. The frequency of acute GVHD (60.0%, 9/15), leading to death (26.7%, 4/15), was the highest in KIR receptor-ligand matched model. The incidence of acute GVHD and death was 30.8% (4/13) and 23.1% (3/13) in the GVH KIR ligand-mismatching, respectively; while the incidence of chronic GVHD was 37.5% (3/8) and no death happened in HVG KIR ligand-mismatching pattern. The expression of iKIR/2DL1 could be detected on ALL (13.0%∼16.6%) and CML (1.8∼6.2%) patients four month after HSCT. The expression of both iKIR/2DL1 (4%) and iKIR/2DL2 (12%) was found only in one patient with CML three month after HSCT, increased to 33.4% and 32.6% accompanied by cGVHD, and dropped to 7.6% and 10.3% one year after HSCT. These results suggested that the deficiency in iKIR/2DL1 based on the KIR-HLA receptor-ligand mismatching model together with the expression of a number of activating KIR in recipients increases the occurrence of GVHD, relapse, and death in unrelated HSCT. Analysis on KIR-HLA gene expression profiling could be useful in predicting the clinical outcome of unrelated Allo-HSCT in leukemia patients. The overall and disease-free survival after HSCT could be improved by preventing the development of GVHD.