Importance of Interleukin-7 in the Development of Experimental Graft-Versus-Host Disease

Interleukin (IL)-7 promotes both thymopoiesis and mature T lymphocyte survival and proliferation in experimental murine models of hematopoietic stem cell (HSC) transplantation. Because HSC products for transplantation also may contain IL-7–responsive mature T lymphocytes, we examined whether IL-7 is necessary for the induction of GVHD after allogeneic bone marrow transplantation (BMT). Lethally irradiated C57BL6J (B6) and B6.IL-7-/- (both H2Kb) recipient mice were co-transplanted with T cell–depleted (TCD) bone marrow cells and lymph nodes (LNs) from either congenic B6.SJL (CD45.1+) or allogeneic BALB/c (H2Kd) donor mice. After transplantation, the recipient mice were subcutaneously injected with either human recombinant IL-7 or phosphate-buffered saline (PBS) for 60 days. No evidence of GVHD was detected in the congenic recipients or in the allogeneic B6/IL-7-/- recipients treated with PBS; in contrast, significantly increased rates of GVHD-related mortality and morbidity were found in the allogeneic B6.IL-7-/- recipients treated with IL-7. The proliferation and number of donor T cells were significantly lower at day 30 post-BMT in the PBS-treated B6.IL-7-/- recipients compared with the IL-7–treated B6.IL-7-/- mice. These experiments demonstrate that IL-7 is an important factor in the development of GVHD, presumably by supporting the survival, proliferation, and possibly activation of alloreactive donor-derived T cells in the recipients.