Casey O. Lightbourn

Marked in Vivo Donor Regulatory T Cell Expansion via Interleukin-2 and TL1A-Ig Stimulation Ameliorates Graft-versus-Host Disease but Preserves Graft-versus-Leukemia in Recipients after Hematopoietic Stem Cell Transplantation

Regulatory T cells (Tregs) are critical for self-tolerance. Although adoptive transfer of expanded Tregs limits graft-versus-host disease (GVHD) after hematopoietic stem cell transplantation (HSCT), ex vivo generation of large numbers of functional Tregs remains difficult. Here, we demonstrate that in vivo targeting of the TNF superfamily receptor TNFRSF25 using the TL1A-Ig fusion protein, along with IL-2, resulted in transient but massive Treg expansion in donor mice, which peaked within days and was nontoxic. Tregs increased in multiple compartments, including blood, lymph nodes, spleen, and colon (GVHD target tissue). Tregs did not expand in bone marrow, a critical site for graft-versus-malignancy responses. Adoptive transfer of in vivo-expanded Tregs in the setting of MHC-mismatched or MHC-matched allogeneic HSCT significantly ameliorated GVHD. Critically, transplantation of Treg-expanded donor cells facilitated transplant tolerance without GVHD, with complete sparing of graft-versus-malignancy. This approach may prove valuable as a therapeutic strategy promoting transplantation tolerance.

Superior immune reconstitution using Treg-expanded donor cells versus PTCy treatment in preclinical HSCT models

Posttransplant cyclophosphamide (PTCy) has been found to be effective in ameliorating acute graft-versus-host disease (GVHD) in patients following allogeneic hematopoietic stem cell transplantation (aHSCT). Adoptive transfer of high numbers of donor Tregs in experimental aHSCT has shown promise as a therapeutic modality for GVHD regulation. We recently described a strategy for in vivo Treg expansion targeting two receptors: TNFRSF25 and CD25. To date, there have been no direct comparisons between the use of PTCy and Tregs regarding outcome and immune reconstitution within identical groups of transplanted mice. Here, we assessed these two strategies and found both decreased clinical GVHD and improved survival long term. However, recipients transplanted with Treg-expanded donor cells (TrED) exhibited less weight loss early after HSCT. Additionally, TrED recipients demonstrated less thymic damage, significantly more recent thymic emigrants, and more rapid lymphoid engraftment. Three months after HSCT, PTCy-treated and TrED recipients showed tolerance to F1 skin allografts and comparable immune function. Overall, TrED was found superior to PTCy with regard to weight loss early after transplant and initial lymphoid engraftment. Based on these findings, we speculate that morbidity and mortality after transplant could be diminished following TrED transplant into aHSCT recipients, and, therefore, that TrED could provide a promising clinical strategy for GVHD prophylaxis.