Abstract
Although spontaneous kidney transplant acceptance/tolerance occurs in mice and occasionally in humans, mechanisms remain unclear. Herein we test the hypothesis that EPO, a hormone predominantly produced by the adult kidney, has immunomodulating properties that are required for spontaneous kidney graft acceptance. In vitro, in a manner dependent on the EPO receptor and CD131 on antigen-presenting cells, EPO induced the secretion of active TGFβ by antigen-presenting cells, which in turn converted naïve CD4+ T cells into functional Foxp3+ regulatory T cells (Treg). In murine transplant models, pharmacologic downregulation of kidney-derived EPO prevented spontaneous Treg generation. In a controlled, prospective cohort clinical study, EPO administration at doses used to correct anemia augmented the frequency of peripheral CD4+CD25+CD127lo T cells in humans with CKD. Furthermore, EPO directly inhibited conventional T cell proliferation in vitro via tyrosine phosphatase SHP-1-dependent uncoupling of IL-2Rβ signaling. Conversely, EPO-initiated signals facilitated Treg proliferation by augmenting IL-2Rγ signaling and maintaining constitutively quenched IL-2Rβ signaling. In additional murine transplant models, recombinant EPO administration prolonged heart allograft survival, whereas pharmacologic downregulation of kidney-derived EPO reduced the expression of TGFβ mRNA and abrogated kidney allograft acceptance. Together, our findings delineate the protolerogenic properties of EPO in inhibiting conventional T cells while simultaneously promoting Treg induction, and suggest that manipulating the EPO/EPO receptor signaling axis could be exploited to prevent and/or treat T cell-mediated pathologies, including transplant rejection.