Requirements for Prolongation of Allograft Survival with Regulatory T Cell Infusion in Lymphosufficient Hosts

Abstract

Background For the clinical applicability of regulatory T cells (Tregs) in transplantation, it is critical to determine if donor antigen specificity is required for their immunosuppressive function. We developed an allospecific CD4+ T cell receptor transgenic (TCR-tg) mouse as a source for large numbers of Tregs with defined allospecificity and tested whether they are more effective than polyclonal Tregs at suppressing allograft rejection. Materials and Methods CD4+CD25+CD62Lhi T cells were sorted from the spleen and peripheral lymph nodes of wild-type (WT-Tregs) and TCR-tg (Allo-Tregs) mice, and expanded using IL-2 and anti-CD3/anti-CD28 conjugated magnetic beads. Tregs were tested for their ability to suppress the proliferation and cytokine production of alloreactive CD4+CD25- T cells in mixed leukocyte assays. Syngeneic WT hosts were adoptively transferred 5×106 Tregs and transplanted with allogeneic hearts. Results Using anti-CD3/anti-CD28 conjugated beads, Tregs were expanded in vitro 100-fold and maintained their suppressor phenotype and function. Allo-Tregs were 6-8 times more potent on a cell-for-cell basis than WT-Tregs in suppressing allospecific proliferation in vitro. Allo-Tregs were unable to suppress in the absence of allo-antigen. Adoptive transfer of expanded Allo-Tregs into WT recipients prolonged the graft survival in a F1 heart transplant model compared to WT-Treg or no treatment [20.0±4.4 d (n=6) vs. 10.4±1.2 (n=8) and 9.7±1.6 d (n=6)]. Conclusions Unlike polyclonal Tregs, allospecific Tregs are able to prolong allograft survival. However, large numbers of Allo-Tregs were unable to induce tolerance, suggesting that Treg therapy in immunocompetent recipients will require conditioning and/or additional immunomodulation for the induction of tolerance.

Thymus-Derived Regulatory T Cells Infiltrate the Cardiac Allograft Before Rejection

“…28,29 Studies in a humanized mouse model of skin transplantation as well as studies in a heart transplantation model in mice demonstrated that donor-antigen-specific Tregs more effectively suppress the alloresponse than polyclonal Treg. 43,44 Also in humans, the generation of donor-specific Treg after kidney transplantation has been reported. 45 All these studies demonstrate that donor antigen specificity is crucial for suppression of the antidonor-directed immune response, but the origin and relative contribution of different Treg subsets are unclear.…”

CD45 ligation expands Tregs by promoting interactions with DCs

“…The transfer of ex vivo-expanded Tregs in solid organ transplantation and autoimmunity faces practical limitations, including a requirement for large numbers of cells, possibly infused repeatedly, to try to effect a significant increase in Tregs (6,(43)(44)(45)(46). In comparison, a reagent-based therapeutic approach for in vivo expansion of Tregs would be more practical.…”

Allogeneic Mature Human Dendritic Cells Generate Superior Alloreactive Regulatory T Cells in the Presence of IL-15

“…Alloantigen-specific Tregs with a much greater specificity can be generated by expansion in the presence of allogeneic PBMCs (18,19) or B cells (10,20). The potential benefit of these alloantigen-specific Tregs is targeted suppression rather than general immunosuppression and increased suppressive potency (9,(21)(22)(23)(24)(25)(26). This may translate in fewer Tregs needed to have a therapeutic effect in the patient.…”