CD56 natural killer regulatory cells in filgrastim primed donor blood or marrow products regulate chronic graft--host disease: the Canadian Blood and Marrow Transplant Group randomized 0601 study results.

Randomized trials have conclusively shown higher rates of chronic graft--host disease with filgrastim-stimulated apheresis peripheral blood as a donor source than unstimulated bone marrow. The Canadian Blood and Marrow Transplant Group conducted a phase 3 study of adults who received either filgrastim-stimulated apheresis peripheral blood or filgrastim-stimulated bone marrow from human leukocyte antigen-identical sibling donors. Because all donors received the identical filgrastim dosing schedule, this study allowed for a controlled evaluation of the impact of stem cell source on development of chronic graft--host disease. One hundred and twenty-one evaluable filgrastim-stimulated apheresis peripheral blood and filgrastim-stimulated bone marrow patient donor products were immunologically characterized by flow cytometry and tested for their association with acute and chronic graft--host disease within 2 years of transplantation. The immune populations evaluated included, regulatory T cells, central memory and effector T cells, interferon γ positive producing T cells, invariate natural killer T cells, regulatory natural killer cells, dendritic cell populations, macrophages, and activated B cells and memory B cells. When both filgrastim-stimulated apheresis peripheral blood and filgrastim-stimulated bone marrow were grouped together, a higher chronic graft--host disease frequency was associated with lower proportions of CD56 natural killer regulatory cells and interferon γ-producing T helper cells in the donor product. Lower CD56 natural killer regulatory cells displayed differential impacts on the development of extensive chronic graft--host disease between filgrastim-stimulated apheresis peripheral blood and filgrastim-stimulated bone marrow. In summary, while controlling for the potential impact of filgrastim on marrow, our studies demonstrated that CD56 natural killer regulatory cells had a much stronger impact on filgrastim-stimulated apheresis peripheral blood than on filgrastim-stimulated bone marrow. This supports the conclusion that a lower proportion of CD56 natural killer regulatory cells results in the high rate of chronic graft--host disease seen in filgrastim-stimulated apheresis peripheral blood. .