Interferon gamma (IFN-g) continuous infusion affects engraftment in a murine transplant model

Effects of Interferon gamma (IFN-g) on hematopoiesis have been reported as both stimulatory and suppressive. In humans, IFN-g appears to be deleterious in conditions such as chronic neutropenia, anemia of chronic disease, and aplastic anemia, suggesting some level of bone marrow suppression. Inborn errors of immunity often have an inflammatory component as part of their phenotype, and this inflammation may impact on their transplant outcomes leading to increased graft failure. We thus developed a murine model using implanted pumps to assess the impact of exogenous IFN-g administered by continuous infusion during transplantation. Murine model and IFN-g administration: Bone marrow nucleated cells (BMNCs) were collected from femurs and tibias of 8- to 10-week-old B6. SJL-Ptprca-Pep3b-/BoyJ donors (CD45.1+) and 5 million cells were injected via tail vein into 10- to 12-week-old recipient C57BL6 mice (CD45.2+) after 400cGy irradiation. Micro-osmotic pumps (Alzet®1007D/2001) were surgically implanted 2 days before transplant to provide continuous infusion of recombinant mouse IFN-g at 5ug/day for 7 days. %CD45.1 + engraftment inT, B, NK, and myeloid cells was determined in peripheral blood every 2 weeks (from 4 to 16 weeks) post-transplant using cell specific monoclonal antibodies. 16 weeks after transplant, mice were euthanized, and %CD45.1+ engraftment was measured in spleen and bone marrow. Although the absolute peripheral blood numbers were similar (Fig.1A), the infusion of IFN-g in this non myeloablative transplant resulted in lower donor engraftment as compared to control transplants (Fig.1B). Myeloid engraftment appeared to be most affected, with a statistically significant reduction of engraftment (p < 0.005) in monocytes and granulocytes. The quantitative reduction was higher than 70% as compared to control transplants worsening over time, suggesting that the long-term repopulating cells were most affected (Fig.1C). Bone marrow was affected in a similar pattern (Fig.1D).Download : Download high-res image (169KB)Download : Download full-size imageFigure 1. A. Peripheral blood Leukocyte absolute count and B. CD45.1+ peripheral blood engraftment, 16 weeks after transplant. C. Granulocytes CD45.1+ engraftment every 2 weeks. D. CD45.1+ Bone marrow engraftment Figure 1. A. Peripheral blood Leukocyte absolute count and B. CD45.1+ peripheral blood engraftment, 16 weeks after transplant. C. Granulocytes CD45.1+ engraftment every 2 weeks. D. CD45.1+ Bone marrow engraftment We established a mixed-chimera model to assess the impact of exogenous IFN-g on engraftment. Our results provide evidence that continuously elevated IFN-g levels are deleterious for engraftment and may help explain the clinical phenomena of graft loss in this patients. Further analysis of other inflammatory pathways and IFN-g blockers are ongoing.