Influence of KIR Genes and HLA Class I Ligands on Overall and Event-Free Survivals after Allogeneic Hematopoietic Stem Cell Transplantation in Patients with Acute Myelogenous Leukemia

Acute myelogenous leukemia (AML) is the most sensitive to natural killer (NK)-cell reactivity among blood malignancies treated with allogeneic hematopoietic stem cell transplantation (allo-HSCT). Function of NK cells is regulated by their inhibitory and activating surface receptors, including killer-cell immunoglobulin-like receptors (KIRs). KIRs with specificity to different HLA class I-encoded ligands seem to play a major role in allorecognition: HLA-C allotypes with asparagine at position 80 (HLA-C1ligands) are recognized by KIR2DL2/3, HLA-C allotypes with lysine at position 80 (HLA-C2 ligands) are recognized by KIR2DL1and KIR2DS1, and HLA-B allotypes with a polymorphic sequence motif at position 77-83 (Bw4 ligands) are recognized by KIR3DL1.There are numerous but sometimes contradictory data about the role of KIR genes and genes of their HLA ligands in outcomes after HLA-identical related and HLA-matched unrelated HCST in patients with AML.

The goal of our prospective study was to evaluate the influence of KIR genes and HLA class Iligands on overall survival (OS) and event-free survival (EFS) after allo-HSCT in adult patients with AML.

35 patients with AML (median age 36 years, range 19-60) treated with allogeneic HSCT in our transplant center from HLA-identical related (n=19) and HLA-matched (10/10) unrelated (n=16) donors were included in the study. Median follow-up was 18 months (range, 5-56). The pre-transplantation risk category included standard or high risk. Patients in complete remission 1 (CR1) were categorized as standard risk (n=22), whereas patients in > CR1 were considered as high risk (n=13). In case of HLA-identical related HSCT donor KIR genotyping was performed simultaneously with HLA-typing. In case of HLA-matched unrelated HSCT donor KIR genotyping was performed in time of confirmatory HLA-testing or in day of HSCT. KIR genotyping was done using a PCR-SSP kit (Olerup, Sweden). Overall survival (OS) and event-free survival (EFS) were calculated by Kaplan-Meier method, and compared with log-rank test. OS was defined as survival without lethal event from any cause, EFS was defined as survival in complete remission without lethal event from any cause.

The 3-year estimated OS and EFS in all patients were 66 and 43%, respectively. 10 patients died (29%), relapse (hematological and/or molecular) was diagnosed in 18 patients (51%). The pre-transplantation risk category was the main factor affecting OS and EFS after HSCT. The probability of the 3-year OS and EFS for standard-risk patients was 86 and 57%, respectively. Nobody of our patients with high risk lived more than18 months. Conditioning regimen, graft source and donor/patient gender combination had no significant effect on OS and EFS. The patients with unrelated HLA-matched donors had better (not significantly) EFS in comparison with recipients of related HLA-identical grafts (p=0.12).

The influence of KIR and HLA- ligand genes on EFS after allo-HSCT was investigated in patients with standard risk. We did not find the immunogenetic factors (presence of B- haplotypes in donors, donor KIR B content, presence of centromeric or telomeric B- motifs in donors, presence of missing HLA ligand for any inhibitory KIR of donor), which significantly affected EFS, but we found two obvious tendencies. The patients with HLA-C1/C1 homozygosity had a tendency to improved EFS compared with patients having either HLA-C1/C2 or HLA-C2/C2 ligands (p=0.09). There was a tendency to better EFS in HLA-C1/x recipients of KIR2DS1 -positive allografts (p=0.09).

Our data suggest that KIRs and their HLA class I ligands play role in the graft versus leukemia effect in AML. It seems that HLA-C1 homozygosity improves EFS in patients after allo-HSCT, and KIR2DS 1-positive donors are preferable for HLA-C1/x patients.