Loss of IFNγR1 Signaling on Donor Bone Marrow Abrogates GVHD but Maintains Immunocompetence.
Authors: Capitini Christian M. , Herby Sarah , Mackall Crystal L. , Fry Terry J. 
Published: April 2020

Abstract
BACKGROUND: Acute graft versus host disease (GVHD) remains as the major complication after allogeneic bone marrow transplant (BMT) resulting in organ toxicity and immune dysfunction. Indeed, we have previously demonstrated that GVHD impairs responses to dendritic cell vaccines. The pathophysiology of GVHD involves preparative regimen-induced inflammation of target organs, release of inflammatory mediators such as gamma interferon (IFNg), and subsequent activation of alloreactive T cells. Given that IFNg can both contribute to GVHD and provide beneficial immune responses, we explored the potential role of IFNg on GVHD and post-transplant immunocompetence.
METHODS: We utilized a minor histocompatibility antigen mismatched, T cell-depleted BMT model, with delayed donor lymphocyte infusions (DLIs) as a means of controlling the induction of acute GVHD and to provide a source of immunocompetence in a thymectomized mouse. To study the role of IFNg on GVHD, we chose either IFNg receptor 1 (IFNgR1) −/− marrow or DLI to permit the normal production of IFNg in GVHD while influencing which cells that can respond to the cytokine. Normal C57BL/6 (B6) or IFNgR1 −/− B6 mice were used as bone marrow donors on day 0 into lethally irradiated, thymectomized B6 × C3H.SW (F1) mice. Normal B6 or IFNgR1 −/− DLIs given with or without a dendritic cell vaccine were introduced at days 14 and 28 post-BMT both to control the induction of GVHD and to provide a population of vaccine-responding cells. F1 recipients were observed for signs of GVHD. ELISPOT of the number of antigen-reactive IFNg-producing splenocytes were also performed to measure functional response to vaccine.
RESULTS: The absence of IFNgR1 in the DLI abrogates GVHD as shown by % change in weight (B6 DLI = −6.3 +/− 4.7 vs. IFNgR1−/− DLI = 6.6 +/− 6.1, p=0.001) and allows for greater doses of DLI to be tolerated by the host, however, there is also decreased vaccine responses by ELISPOT (B6 DLI = 1631 vs. IFNgR1−/− DLI = 72, p=0.03). Surprisingly, using IFNgR1−/− bone marrow also abrogates GVHD as shown by % change in weight (B6 marrow = −6.3 +/− 4.7 vs. IFNgR1−/− marrow = 4.4 +/− 4.2, p less than 0.05) and splenocyte count (B6 marrow = 31.48 +/− 12.54 vs. IFNgR1−/− marrow = 63.54 +/− 15.92, p=0.008), but vaccine responses by ELISPOT can be restored to levels that are equivalent of syngeneic control mice, even in the presence of a normal B6 DLI (B6 marrow = 1631 vs. IFNgR1−/− marrow = 9283, p=0.0002). The abrogation of GVHD by IFNgR1−/− marrow does not appear to be a dominant effect since mixtures of IFNgR1 −/− and normal B6 bone marrow still cause GVHD.
CONCLUSIONS: Recipients of allogeneic bone marrow and T cells developed GVHD and had decreased vaccine responses by ELISPOT. Loss of IFNgR1 on allogeneic donor lymphocytes abrogates their ability to cause GVHD, but also diminished their ability to respond to vaccine. Surprisingly, loss of IFNgR1 on a donor bone marrow-derived, non T cell results in equivalent abrogation of GVHD, while restoring immunocompetence through favorable responses to a vaccine. Further studies will attempt to identify the phenotype of the responsible bone marrow-derived cell. These results demonstrate a strategy of providing higher doses of DLIs to enhance anti-tumor activity without exacerbating GVHD, and thus, have implications for immune modulation post-allogeneic BMT.