BackgroundAllogeneic hematopoietic cell transplantation (HCT) can be curative for many hematologic diseases. However, complications such as graft-versus-host disease (GVHD) and relapse of primary malignancy remain significant and are the leading causes of morbidity and mortality. Effects of killer Ig-like receptors (KIR)-influenced NK cells on HCT outcomes have been extensively pursued over the last decade. However, the relevance of the reported algorithms on HLA matched myeloablative HCT with rabbit antithymocyte globulin (ATG) is used for GVHD prophylaxis remains elusive. Here we examined the role of KIR and KIR-ligands of donor-recipient pairs in modifying the outcomes of ATG conditioned HLA matched sibling and unrelated donor HCTMethods and FindingsThe study cohort consisted of 281 HLA matched sibling and unrelated donor-recipient pairs of first allogeneic marrow or blood stem cell transplantation allocated into ‘discovery’ (135 pairs) and ‘validation’ (146 pairs) cohorts. High resolution HLA typing was obtained from the medical charts and KIR gene repertoires were obtained by a Luminex® based SSO method. All surviving patients were followed-up for a minimum of two years. KIR and HLA class I distributions of HCT pairs were stratified as per applicable definitions and were tested for their association with cause specific outcomes [acute GVHD grade II-IV (aGVHD), chronic GVHD needing systemic therapy (cGVHD) and relapse] using a multivariate competing risks regression model as well as with survival outcomes [relapse-free survival (RFS), cGVHD & relapse free survival (cGRFS) and overall survival (OS)] by multivariate Cox proportional hazards regression model. A significant association between KIR genotype mismatching (KIR-B/x donor into KIR-AA recipient or vice versa) and cGVHD was found in both discovery (p = 0.001; SHR = 2.78; 95%CI: 1.50–5.17) and validation cohorts (p = 0.005; SHR = 2.61; 95%CI: 1.33–5.11). High incidence of cGVHD associated with KIR genotype mismatching was applicable to both sibling and unrelated donors and was specific to recipients who had one or two C1 bearing HLA-C epitopes (HLA-C1/x, p = 0.001; SHR = 2.40; 95%CI: 1.42–4.06). When compared with KIR genotype mismatched transplants, HLA-C1/x patients receiving grafts from KIR genotype matched donors had a significantly improved cGRFS (p = 0.013; HR = 1.62; 95%CI: 1.11–2.39). Although there was no effect of KIR genotype matching on survival outcomes, a significantly reduced incidence of relapse (p = 0.001; SHR = 0.22; 95%CI: 0.10–0.54) and improved relapse-free survival (p = 0.038; HR = 0.40; 95%CI: 0.17–0.95) was observed with one or more missing ligands for donor inhibitory KIR among the recipients of unrelated donor transplants.ConclusionsThe present study for the first time presents the beneficial effects of KIR genotype matching in reducing cGVHD in myeloablative transplant setting using HLA matched (sibling and unrelated) donors. The findings offer a clinically applicable donor selection strategy that can help control cGVHD without ...

BACKGROUND Uncontrolled reactivation of Epstein-Barr virus (EBV) leading to post-transplant lymphoproliferative disorder (PTLD) is one of the major complications after T-cell depleted HCT. Recovering within weeks after HCT, natural killer (NK) cells are deemed important in the immunopathogenesis of EBV complications. Their role however remains elusive. NK cell responses are regulated by a series of activating and inhibitory cell surface receptors, central to which are the Killer Ig-like Receptors (KIR). Here we hypothesized and tested whether diverse NK cell receptor repertoires can titrate NK cell functional responses to EBV and can potentially modify the risk of developing PTLD. METHODS KIR genotypes, centromeric and telomeric motifs and their variants were determined for 356 allo-HCT donors through next generation sequencing of KIR locus. PBMNCs from KIR typed healthy volunteers were co-cultured with EBV-transformed cells and degranulation and IFNγ producing NK cells were enumerated using multi-parameter flow cytometry. Effect of donor KIR profile on PTLD was tested using competing risks regression statistics. Segregation of NK cell response to EBV across various KIR repertoires was tested by Mann-Whitney U statistics RESULTS At least one copy of Donor tA01 motifs was required for a strong protection against PTLD (p=0.0001, SHR=0.17). The number of EBV induced NK cells increased with increasing tA01 motifs. There was no influence of recipients’ KIR repertoire on the risk of developing PTLD. CONCLUSIONS KIR-regulated NK cells have a profound effect on the risk of PTLD. KIR gene profile based identification of HCT recipients at high risk of PTLD will enable closer monitoring of EBV DNAemia and facilitate prompt therapy.

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