STAT1 Deficiency Fails to Protect Against Murine Chronic GVHD

Abstract

Donor Th1 cells, which play a key role in promoting acute GVHD, may also contribute to chronic GVHD. To further characterize the role of Th1 cells in cGVHD, we used a model developed by the Drobyski Lab whereby acute GVHD is initiated (B6 ⇒ BALB/c BMT; 21-day transplant interval), with subsequent adoptive transfer of post-BMT B6 T cells into syngeneic, immune-deficient hosts (B6129s7-Rag1; 45-day observation interval) for induction of auto-reactive, cGVHD. Because STAT1 is the signaling pathway for the Th1-polarizing cytokines IFN-α and IL-12, we used STAT1-deficient (KO) donor T cells to assess whether Th1 cell deficiency might yield reduced cGVHD; other transplant cohorts received T cells that were either wild-type (WT), STAT3-KO (loss of Th17 function), or STAT6-KO (loss of Th2 function). Clinical signs of acute GVHD (weight loss, hunched posture) was severe in WT, mild in STAT3-KO, and STAT6-KO T cells; in contrast, STAT1-KO T cell recipients showed no signs of acute GVHD. Chronic GVHD, which was manifested by weight loss and extensive skin disease (erythematous, scaling rash with alopecia; > 50% body surface area), occurred in 100% of recipients of WT and STAT1-KO T cells (5/5 and 10/10 cases, respectively); by comparison, extensive skin disease was not observed in recipients of STAT3-KO or STAT6-KO T cells (0/9 and 0/5 cases, respectively). As such, STAT1-deficiency appeared to reduce acute GVHD but not chronic GVHD. Further experiments were performed at the end of the cGVHD observation interval to confirm that recipients of STAT1-deficient T cells were indeed deficient in Th1 cells post-BMT. Relative to recipients of WT T cells, recipients of STAT1-KO T cells had reduced capacity to secrete IFN-γ (4661±664 vs. 2656±281; p < 0.03) and TNF-α (3154±269 vs. 1872±84; p < 0.001) and reduced absolute numbers of splenic CD4+IFN-γ+ T cells (14±1.9 vs .07±.02; p < 0.05) and CD8+IFN-γ+ T cells (4.1±1.2 vs. 0.8±.1; p < 0.05). As such, recipients of STAT1-deficient T cells were indeed deficient in Th1-polarization post-BMT during cGVHD. Remarkably, relative to WT T cell recipients, recipients of STAT-1 deficient T cells had increased absolute numbers of post-BMT splenic CD4+IL-17± T cells (0.2±0.05 vs 13.2±6.5.; p < 0.05). These data indicate that long-term post-BMT deficiency of Th1-type cells does not protect against chronic GVHD, perhaps in part due to expansion of alternative pathogenic T cells such as the Th17 subset.