Immunological properties of bone marrow microenvironment 1 year after allogeneic hematopoietic stem cell transplantation.

Regeneration of the bone marrow microenvironment after transplantation of allogeneic hematopoietic stem cells is poorly explored. The goal of our study was to investigate this process focusing on immunologic factors: concentrations of selected cytokines, expression of immunosuppressive proteins CD47 and CD274 on hematopoietic stem cells, and frequency of T regulatory lymphocytes (Tregs). Bone marrow samples were collected before transplantation, on the day of transplantation, and at the 1-year follow-up. As a control group, we used bone marrow from healthy donors. Prior to the conditioning, the percentage of Tregs and concentration of interleukin-10 were higher in the bone marrow of patients than in healthy donors. The conditioning regimen resulted in increased concentrations of interferon-γ and expression of CD274 on hematopoietic stem cells. Twenty-eight days after transplantation, level of Tregs, expression of CD47, and concentration of interleukin-10 and latency-associated peptide 1 were increased compared with the period before conditioning. Starting from day 100 after transplantation, the microenvironment tended to normalize; the level of Tregs and concentrations of most cytokines were similar to values in the bone marrow of healthy donors.