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Our findings indicate that the presence of particular activating KIRs in donor with their absence in recipient enhances GVHD, which is not accompanied by graft-versus-leukemia effect. Evaluation of activating KIR genotype may allow optimization of both donor selection and transplantation procedure in order to avoid GVHD.

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In a previous study we demonstrated that in case of KIR-ligand incompatibility, NK cells may mediate graft-versus-leukemia effect resulting in improved outcome in a setting of unrelated donor-hematopoietic stem cell transplantation (URD-HSCT). This effect, however, varies and depends on the preparative regimen including the use of pre-transplant antithymocyte globulin (ATG) as an in vivo T-depletion. On the other hand, the impact of ATG on NK cell recovery has not been determined so far. The goal of this study was to analyze the influence of various immunosuppressive modalities used for acuteGVHD prophylaxis or treatment on the early NK cell reconstitution after allogeneic HSCT. METHODS: We analyzed the number of peripheral blood NK cells with the use of flow cytometry on day +30 (+/−2) after alloHSCT. NK cells were defined as CD3-CD56+ cells. Eighty alloHSCT recipients were included in the study; 43 patients were given transplant from an HLA-identical sibling (sibHSCT) whereas in 37 cases the donor was an unrelated vulunteer. ATG (6–10 mg/kg) as a part of preparative regimen was used on days −3, −2, −1 in case of URD-HSCT, but not sibHSCT. Besides, acuteGVHD prophylaxis consisted of Cyclospirin A (3 mg/kg) since day −1 and short-course Methotrexate (three or four doses). For patients transplanted before year 2002 (38/80 analyzed cases) - prednisolone 0.5 mg/kg since day +1 until day +28 was additionally administered. Metylprednisolone (2 mg/kg) was used as a first-line therapy of acuteGVHD. RESULTS: We did not find any difference regarding the number of NK cells on day +30 after alloHSCT between patients given pre-transplant ATG and those in whom no form of T-depletion has been administered: 130 (11–841) x106/L vs. 116 (65–841) x106/L (p=NS). In contrast, the use of steroids for acuteGVHD prophylaxis was associated with significant impairment of the quantitative NK cell reconstitution: 106 (10–694) x106/L vs. 211 (32–890) x106/L NK cells on day +30 (p=0.004). The incidence of acuteGVHD as well as the use of steroids for acuteGVHD treatment had no impact on the number of circulating NK cells. None of the other factors analyzed including the number of methotrexate doses, source of stem cells, the number of CD34+ cells transplanted, and age was found to influence an early NK cell recovery. CONCLUSIONS: Although ATG used as a part of pre-transplant conditioning regimen circulates and remains active for several weeks after alloHSCT, it does not seem to have any impact on an early NK cell quantitative reconstitution. In contrast, prolonged administration of low-dose steroids may impair the NK cell recovery. Since NK cells are considered a potential tool for a cellular therapy of hematologic and other malignancies, our findings should be taken into account when planning this kind of treatment in the context of allotransplantation. In addition, our results support the earlier hypothesis that the preparative regimens containing ATG may enable elucidation of a potential benefit from KIR-ligand incompatibility.

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