MTOR signaling regulates protective activity of transferred CD4^-/-Foxp3^-/- T cells in repair of acute kidney injury

CD4^-/-Foxp3^-/- regulatory T cells (Tregs) are required for normal immune homeostasis. Recent studies suggested that Treg transfer facilitates recovery from acute kidney injury (AKI), but the molecular events that maintain Treg function after adoptive transfer remain unclear. This study aimed to investigate the regulation of mammalian target of rapamycin (mTOR) signaling in the Tregmediated therapeutic effect on ischemic AKI. We noted significant Treg expansion in C57BL/6 mouse kidney, with enhanced immunosuppressive capacity after renal ischemia/reperfusion. mTOR inhibition significantly increased the frequency of Tregs in cultured CD4^-/- T cells, with enhanced production of anti-inflammatory cytokines, which, conversely, was reduced by mTOR activation. Rapamycin, an inhibitor of mTOR, was transiently administered to C57BL/6 mice before ischemia/reperfusion surgery. No beneficial effect of rapamycin treatment was seen in the early recovery of AKI as a result of its inhibitory effect on tubular regeneration. However, rapamycin markedly enhanced the expansion of kidney Tregs, with increased mRNA expression of anti-inflammatory cytokines. Adoptive transfer of rapamycin-treated Tregs markedly suppressed conventional T cells, responder myeloid cells, and reactive myofibroblasts; however, it promoted host Tregs and alternative macrophages, leading to better renal function and less kidney fibrosis. Taken together, Treg transfer with mTOR inhibition markedly improves outcomes of ischemic AKI. These findings reveal an important role for mTOR signaling in maintaining Treg activity after adoptive transfer and highlight the therapeutic potential of targeting Tregs in acute and chronic kidney disease.