Purpose: Our goal for this study was to determine the relative fates of endogenous Foxp3^– conventional (Tconv) and Foxp3⁺ regulatory T cells (Tregs) specific for alloantigens as compared to non-antigen-specific T cells in the context of murine allotransplantation.

Methods: To selectively study alloreactive endogenous Tregs, donor hearts from F1 (BALB/cxC57BL/6) mice expressing the model antigen 2W were transplanted into C57BL/6 recipients, and 2W:I-A^b tetramers were used to track peripheral 2W:I-A^b-specific Tregs and Tconv cells. Long-term graft survival was induced in two groups of mice with co-stimulation blockade (CoB) comprising either anti-CD154 (D0, 7 and 14) + donor splenocytes (D0), or CTLA-4Ig (D0 and 2). Mice were sacrificed at D7 and D30, and their splenic T cells were phenotyped.

Results:Whereas the percentages or total numbers of 2W-reactive Tregs in secondary lymphoid organs were similar at d7 in naïve, acutely rejecting, and CoB-treated mice, at 30d post-transplant, recipients treated with transient CoB demonstrated increased Tregs (~40%) within the 2W:I-A^b T cell population, compared to 5-10% in naïve or acutely rejecting controls. However, no significant difference in the percentages of bulk Tregs was observed between CoB-treated and control recipients. In contrast, acutely rejecting animals saw a large increase in 2W:I-A^b-binding Tconv cells both at D7 and D30 post-transplantation, with CoB-treated mice experiencing a much smaller increase.

Conclusions: These results demonstrate that enrichment of donor-specific Tregs is not an early biomarker that predicts tolerance versus rejection, but may accurately mark established tolerance. In contrast, CoB prevented the early (d7) expansion of 2W-reactive Tconv observed in acute rejection, and maintained them at frequencies comparable to naïve controls at day 30 post-transplant. These observations are consistent with the restriction in the frequency of alloreactive Tconv being a prerequisite for successful transplant tolerance induction. Taken together, the ability to track the fate of endogenous donor-reactive Tregs is a powerful approach to gain insights into their fate in tolerance induction and maintenance, as well as in rejection.

CITATION INFORMATION: Young J, Chen J, Miller M, Yin D, Moon J, Alegre M.-L, Chong A. Tracking of Endogenous Graft-Reactive Tregs Reveals Their Peripheral Enrichment During Transplantation Tolerance. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress