Objectives: The goal of this study was to examine the impact of various immunosuppressive regimens on an early NK cell recovery following haematopoietic cell transplantation (alloHCT).
Methods: The number of peripheral blood NK cells was analysed with the use of flow cytometry on day +30 (+/-2) after alloHCT from an HLA identical sibling (n=43) or an unrelated (n=34) donor.
Results: Patients receiving prednisolone as a prophylaxis of acute graft-versus-host disease had lower number of NK cells compared to those not given steroids prophylactically (110(10-694) vs. 212(33-890) x106/L, p=0.005). In contrast, administration of anti-thymocyte globulin (ATG) (7.5- 15 mg/kg) as a part of preparative regimen was not found to influence the NK cell recovery. Similarly, no effect on the number of peripheral blood NK cells was observed with regard to other analysed factors: cell dose, type of myeloablative conditioning, source of stem cells, patient and donor characteristics, number of post-transplant methotrexate doses.
Conclusions: Immunosuppressive therapy may affect NK cell recovery following alloHCT. Since NK cells are considered a potential tool for cellular therapy of haematological malignancies, our findings should be taken into account when planning this kind of treatment in the context of allotransplantation.

Keywords: NK cells, allogeneic hematopoietic cell transplantation, Immunosuppression