Pretransplant targeting of TNFRSF25 and CD25 stimulates recipient Tregs in target tissues, ameliorating GVHD post-HSCT

The current approach to minimize transplant-associated complications, including graft-versus-host disease (GVHD) includes long-term pharmacological immune suppression frequently accompanied by unwanted side effects. Advances in targeted immunotherapies regulating alloantigen responses in the recipient continue to reduce the need for pan-immunosuppression. Here, in vivo targeting of the tumor necrosis factor superfamily receptor TNFRSF25 (also known as DR3) and the high-affinity interleukin-2 (IL-2) receptor with a TL1A-immunoglobulin (TL1A-Ig) fusion protein and low-dose IL-2, respectively, was used to pretreat recipient mice before allogeneic hematopoietic stem cell transplantation (aHSCT). Pretreatment induced regulatory T cell (Treg) expansion persisting 1 to 2 weeks after HSCT, leading to diminished GVHD and improved transplant outcomes. Expansion was accompanied by an increase in the frequency of stable and active Tregs, creating a suppressive tissue environment in the colon, liver, and eye. Importantly, pretreatment supported epithelial cell function/integrity, a diverse microbiome including reduction of pathologic bacteria outgrowth, and promotion of butyrate producing bacteria, while maintaining physiologic levels of obligate/facultative anaerobes. Notably, using a sphingosine 1-phosphate receptor agonist to sequester T cells in lymphoid tissues, it was found that the increased tissue Treg frequency included resident CD69⁺CD103⁺FoxP3⁺hepatic Tregs. In contrast to infusion of donor Tregs, the strategy developed here resulted in the presence of immunosuppressive target tissue environments in the recipient before the receipt of donor allogeneic-reactive T cells and successful perseveration of graft-versus-leukemia responses. We posit strategies that circumvent the need of producing large numbers of ex vivo manipulated Tregs may be accomplished through in vivo recipient Treg expansion, providing translational approaches to improve aHSCT outcomes.