The Innate Immune Sensor Sting Promotes CD8+ T Cell-Mediated Gvhd after Preclinical Allogeneic Hematopoietic Stem Cell Transplantation

Abstract

Graft-versus-host disease (GVHD) remains a significant cause of morbidity and mortality in patients receiving allogeneic hematopoietic stem cell transplants (aHSCTs). Pre-HSCT conditioning typically consists of irradiation and drug administration resulting in the death of rapidly dividing cells. Damage to host tissues initiates a cytokine storm, promoting activation and expansion of donor anti-host alloreactive T cells. Cell death following conditioning has promoted the hypothesis that sensors of cytoplasmic DNA damage in GVHD target tissues contribute to cytokine production. We identified a role for Stimulator of Interferon Genes (STING), an innate immune sensor, in GVHD using pre-clinical MHC-matched (MUD) aHSCT models. Here, we show that the STING pathway promotes CD8+ T cell-mediated GVHD after MHC matched and MHC-mismatched aHSCT. To assess a role for STING after MHC-matched aHSCT, we transplanted C3H.SW BM + unfractionated T cells into irradiated B6-WT or STING−/− recipients. STING−/− recipients developed reduced weight loss, GVHD scores and skin pathology 6 wks post-HSCT. Chimeric studies demonstrated that the absence of STING in non-hematopoietic cells was responsible for the amelioration of GVHD. Therefore, to test STING signaling in non-hematopoietic intestinal cells, we generated intestinal organoid cultures which upregulated IFNβ, TNFα, IL-6, CXCL10 and MHC class I mRNA 6 hrs after stimulation with the highly specific STING agonist DMXAA, supporting the notion that STING can contribute to GI inflammation in vivo (Fig. 1A). To evaluate the potential impact of STING in the clinical setting, we examined MHC-matched recipients homozygous for a human allele associated with diminished STING activity and found STINGHAQ/HAQ mice exhibited diminished GVHD vs WT. Since MHC-matched GVHD is primarily mediated by CD8+ T cells, we next asked if CD4+ T cells were dispensable for the reduction of GVHD in STING−/− recipients. Indeed, GVHD was reduced in STING−/− recipients after transplant of C3H.SW BM and CD8+ T cells (Fig. 1B,C). Notably, STING deficiency was recently reported to worsen GVHD after MHC-mismatched aHSCT (Fischer J, et al, Sci. Transl. Med. 2017). Since CD4+ T cells are dominant during MHC-mismatched GVHD, we transplanted BALB/c BM + CD8+ T cells into B6-WT and STING−/− mice. Again, STING−/- recipients developed lower GVHD clinical scores, reduced skin pathology and had lower frequencies of activated T cells 8 wks post-HSCT vs WT, supporting a role for STING in the promotion of CD8+ T cell-mediated GVHD – consistent with this pathways upregulation of MHC class I (Fig. 1D,E). In total, these studies demonstrate that STING plays an important role in regulating aHSCT and promotes CD8+ T cell-mediated GVHD regardless of the genetic disparity between donor and recipient. The findings support the notion that this pathway may provide a target for new strategies to ameliorate GVHD.