Donor KIR-Haplotype B Improved Relapse-Free Survival After Allogeneic Stem Cell Transplantation for Multiple Myeloma

Abstract 2373

NK-cell alloreactivity determined by donor killer-cell immunoglobulin-like receptors (KIRs) has been shown to be predictive for relapse-free survival in myeloid leukemia after allogeneic stem cell transplantation. The role role of NK-cell allo reactivity in patients with multiple myeloma is unclear. Although the ligands for activating KIRs remain elusive, inhibitory KIRs on donor derived NK-cells and HLA class I molecules on the recipient cell determine NK cell alloreactivity. KIR genes on chromosome 19 segregate independently from HLA genes KIR haplotypes can be distinguished in two groups: group A has a fixed number of inhibitory receptors and only one activating receptor (KIR2DS4), while group B haplotype includes more activating receptor genes. Therefore individuals can be categorised as having A-KIR haplotype (A/A), or B-KIR haplotype which contains either A/B heterocygotes or B/B homocygotes KIRs. To analyse the effect of donor KIR-haplotype on outcome in multiple myeloma, we analysed 118 patients with a median age of 51 years (r: 29 – 68) who underwent allogeneic stem cell transplantation. Gender of the study population was predominantly male (n = 75, female: n = 33). Stem cell source was mainly peripheral blood stem cells (n = 105) and derived from unrelated donors (n = 81) or HLA-identical sibling (n = 37). 46 patients received graft from HLA-mismatched donor. The majority of the patients received a melphalan (100 – 140 mg/m²)/fludarabine-based reduced conditioning regimen (N = 106), either as part of an auto-allo-tandem protocol or as an allogeneic salvage protocol after relapse to an autograft. 46 patients had experienced relapse to an autograft prior to allogeneic stem cell transplantation. 79 patients were transplanted from KIR haplotype Bx and 39 from KIR haplotype A. Both groups were well balanced regarding age, HLA match, stem cell source, CMV seropositivity, remission status prior to transplantation, del 13q14, and relapse to prior autograft.

After a median follow-up of 5 years the 5-year estimated disease-free and overall survival was better for KIR haplotype B donors in comparison to KIR haplotype A donors (30 % vs. 14 %, p = 0.008, and 49 % vs. 36 %, p = 0.07). The disease-free survival benefit for KIR haplotype B was mainly seen in HLA-matched patients (4y DFS: 39 % vs. 18 %, p = 0.005), while in HLA mismatch transplantation no difference according to KIR haplotype could be detected (26 % vs. 18 %, p = 0.5).The difference in survival in the HLA-matched group was due to higher risk of relapse for KIR haplotype A in the HLA-matched group (cumulative incidence at 1 year 46 % vs. 17 %, p = 0.005).

In a multivariate Cox model KIR haplotype A remained a significant factor for worse disease-free (HR: 1.82, p = 0.008) and overall survival (HR: 1.69, p = 0.042). Other significant factors in the multivariate analysis were female donor sex (HR: 1.67, p = 0.04) and chemo-refractory disease at transplantation (HR: 1.76, p = 0.03) for OS and factors for DFS were unrelated donor (HR: 1.83, p = 0.02) and patient's age as continous variable (HR: 1.03, p =0.008) and donor female sex (HR: 1.62, p = 0.03).

We conclude that female donor sex and KIR haplotype A are important risk factors for outcome of allogeneic SCT in multiple myeloma and should be considered for donor selection.