Attenuated Acute Graft-Versus-Host Disease Following Allogeneic Stem Cell Transplantation In the Absence of RORγt.

Haplotype matched and complete MHC mismatched murine HSCT models were used. For the haploidentical model C57BL/6 (H-2^b, B6) mice served as donors while C57BL/6 × DBA2 F1 (H-2^bxd, B6D2) mice functioned as recipients. Effector T cells (T_effs) were isolated from the spleens of wild type (WT) B6 and RORgt knockout mice backcrossed 7–8 generations onto a B6 background. B6D2 mice were lethally irradiated with 900 rads on day -1 and injected intravenously with 4 × 10⁶ T_effs from WT or RORgt^−/− mice supplemented with 3 × 10⁶ WT T cell depleted bone marrow cells (TCD BM) on day 0. For the completely MHC mismatched model, BALB/c mice (H-2^d) were lethally irradiated with 800 rads on day -1 and administered 5 × 10⁵ WT or RORgt^−/− T_effs supplemented with 5 × 10⁶ B6 TCD BM on day 0.

B6D2 mice that received RORgt^−/− T_effs displayed significantly attenuated GvHD, recovering from weight loss by day +31 and demonstrating 100% survival on day +60. Conversely, mice that received WT T_effs showed intense disease progression with 100% mortality by day +31 (Figure A, p<0.0001 for survival comparison between WT and RORgt^−/− recipients using Fisher's exact test). Similar results were seen using the completely MHC mismatched model, with superior overall survival noted in those animals receiving RORgt ^−/− T_effs (put in p value here). Recipients of RORgt ^−/− T cells demonstrated statistically significant decreased TNF in serum compared to WT recipients (Figure B, p=0.001 comparing WT and RORgt^−/− recipients using student's t test). Interestingly, despite the decreased severity of GvHD, serum concentrations of IFN-g were increased in recipients transplanted with RORgt ^−/− T cells. Chimerism studies post-transplant revealed complete donor reconstitution in recipients of both RORgt^−/− and WT T_effs. Donor T_effs isolated from recipient livers post-transplant consistently demonstrated an activated phenotype, with low L selectin and high CD25 expression.

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T cell expression of the Th17 transcription factor, RORgt, is critical for the development of lethal GvHD following allogeneic stem cell transplantation in both the haploidentical and MHC complete mismatch models. GvHD attenuation in the absence of RORgt is not the result of an inability for donor T cells to undergo activation or to engraft in vivo. Interestingly, the absence of RORgt from donor T cells led to enhanced IFN-g in serum. Thus, in vivo, the Th17 pathway is critical for the induction of GvHD.

No relevant conflicts of interest to declare.