Separation of Graft-Versus-Host Disease and Graft-Versus-Leukemia Effects by Targeting T-Bet and RORγt Transcription Factors
Authors: Yu Yu , Wang Dapeng , Semple Kenrick , Anasetti Claudio , Yu Xue-Zhong 
Published: October 2019

Abstract
Abstract 728

Background:
Allogeneic hemopoietic stem cell transplantation (HCT) is an effective therapy with potential cure of hematological malignancies through T cell-mediated graft-versus-leukemia (GVL) effects. However, beneficial GVL effects are frequently offset by the development of destructive graft-versus-host disease (GVHD) also induced by donor T cells. Recent studies including ours have demonstrated that donor T cells differentiated into type 1 or type 17-subset contribute to GVHD. Thus, we hypothesize that blocking both Th1 and Th17 lineage via disrupting Th1-specific (T-bet) and Th17-specific (RORγt) transcription factors can significantly reduce GVHD after allo-HCT.

Method:
Two murine models of bone marrow transplantation (BMT) that represent clinical GVHD and GVL were used: C57BL/6 (B6)→BALB/c and B6→(B6 × DBA2)F1. To mimic clinical residual hematological malignant disease, B cell lymphoma (A20) and mastocytoma (p815) were infused into BALB/c and (B6 × DBA2)F1 mice, respectively.

Results:
We first compared the ability of WT, T-bet−/−, RORγt−/−, and T-bet−/−/RORγt−/− T cells in the induction of GVHD, and found that RORγt−/− T cells had a comparable ability to cause GVHD as WT T cells, whereas T-bet−/− T cells were less pathogenic. The T-bet−/−/RORγt−/− T cells failed to induce acute GVHD but caused minor to modest chronic GVHD in some of recipients at the doses tested. To investigate whether recipients of T-bet−/−/RORγt−/− T cells had less severe target organ GVHD damage, we analyzed GVHD associated organ damage in liver, lung and bowel. Fourteen days after adoptive transfer of WT, T-bet−/−, RORγt−/−, and T-bet−/−/RORγt−/− T cells, recipients which received T-bet−/−/RORγt−/− donor T cells showed markedly reduced T cell infiltration and tissue damage in liver, lung, and bowel. Mechanistic studies revealed that T-bet−/−/RORγt−/− T cells produced significantly less IFNγ (Th1 cytokine) and IL-17 (Th17-cytokine) but significantly more IL-4 and IL-5 (Th2-cytokines) as compared to WT T cells. In addition, T-bet−/−/RORγt −/− donor T-cells express significantly less CXCR3 and CCR6, chemokine receptors required for infiltration of alloreactive T cells into GVHD targeted organ, which could be the reason that significantly fewer T-bet−/−/RORγt−/− T cells were accumulated in recipient liver and lung than WT T cells. Furthermore, we tested the ability of WT and T-bet−/−/RORγt−/− T cells in mediating GVL effect. Although T-bet−/−/RORγt−/− T cells failed to induce acute GVHD, their ability to reject A20 or p815 cells was comparable to that of the WT T cells at the dose tested.

Conclusions:
These results indicate that blocking T-bet and RORγt prevents acute GVHD by suppressing donor T cell differentiation towards Th1 and Th17 and promoting differentiation towards Th2, and inhibiting donor T cell expansion and infiltration into GVHD target organs. Furthermore, blocking T-bet and RORγt could preserve GVL effect. Thus, the current study validates new targets for the separation of donor T cell–mediated GVHD and GVL activity, which could eventually be beneficial to patients with hematological malignancies.

Disclosures:
No relevant conflicts of interest to declare.