Notch Signaling Is a Critical Regulator of Allogeneic T Cell Responses Mediating Graft-Versus-Host Disease.

Abstract 230

Allogeneic hematopoietic stem cell transplantation (HSCT) provides powerful therapeutic activity through elimination of cancer cells by donor T cells. However, its success is limited by life-threatening graft-versus-host disease (GVHD). Novel immunomodulatory approaches are needed to effectively control GVHD. Notch signaling is a highly conserved cell-cell communication that plays an essential role in T cell development and can influence differentiation and function of mature T cells in a context-dependent fashion. Using several mouse models of allogeneic HSCT, we report that inactivation of Notch signaling in donor T cells inhibits the induction of severe GVHD while preserving significant graft-versus-leukemia (GVL) activity. To block canonical Notch signaling in mature T cells without interfering with T cell development, we used conditional expression of the pan-Notch inhibitor DNMAML (ROSA^DNMAMLf × Cd4-Cre mice). DNMAML CD4⁺ T cells derived from donor C57BL/6 (B6) mice had normal initial activation, proliferation and expansion, but failed to differentiate into effector T cells mediating severe GVHD in lethally irradiated major histocompatibility complex-mismatched BALB/c recipient mice. Notably, Notch-deprived alloreactive T cells retained potent GVL activity, leading to improved overall survival of the recipients. Alloreactive DNMAML T cells showed impaired production of IL-2 and multiple inflammatory cytokines (e.g. TNFα, IFNγ and IL-17), as well as defective induction of selected effector molecules (e.g. granzyme B and perforin). The specificity of these findings was independently validated using donor CD4⁺ T cells with conditional inactivation of Rbpj, encoding CSL/RBP-Jk, a transcription factor that is absolutely required for Notch-mediated transcriptional activation. To further evaluate the effects of Notch signaling in both CD4⁺ and CD8⁺ alloreactive T cells, we infused control B6 or DNMAML B6 T cells into unirradiated haploidentical B6xDBA/2 F1 and irradiated minor histocompatibility antigen (miHA)-mismatched BALB/b recipients. Donor DNMAML CD4⁺ and CD8⁺ T cells both showed significantly reduced ability to induce severe GVHD in these CD4⁺ help-dependent CD8⁺ T cell-mediated GVHD mouse models. These results indicate that Notch is a novel critical signaling pathway regulating CD4⁺ and CD8⁺ T cell responses in multiple mouse models of allogeneic HSCT. Given the beneficial immunomodulatory effects of Notch inhibition in alloreactive donor T cells, Notch signaling appears as a promising therapeutic target to limit the harmful effects of GVHD while preserving beneficial GVL activity after allogeneic HSCT.