Targeting IRE1α/XBP1 signaling synergizes with cyclosporine A to ameliorate skin allograft rejection

This study investigated the synergistic effect and immunomodulatory mechanism of combining IRE1α/XBP1 pathway inhibition with cyclosporine A (CsA) against acute rejection in a murine allogeneic skin transplant model. BALB/c-to-C57BL/6 skin allograft recipients were treated with the IRE1α/XBP1 inhibitor 4µ8C, alone or combined with perioperative short-term CsA. Graft survival and histopathology were monitored. Flow cytometry was employed to analyze immune cells in lymphoid organs and to measure serum donor-specific antibodies (DSA). Intragraft mRNA expression was quantified by RT-qPCR and serum cytokine levels were determined using multiplex immunoassays. Pharmacological IRE1α/XBP1 inhibition downregulated endoplasmic reticulum stress-related genes in allografts, delayed rejection, and reduced systemic inflammation. The combination therapy (4µ8C + CsA) further prolonged allograft survival and reduced inflammatory infiltration. Mechanistically, the combined treatment achieved its dual immunomodulatory effect by reducing the frequency of CD8⁺ T cells and suppressing the generation of effector memory T cells and follicular helper T cells, while promoting the expansion of regulatory T cells (as evidenced by increased CD4⁺Foxp3⁺ Treg frequencies among CD3⁺ T cells). It also suppressed DSA production and intragraft pro-inflammatory cytokine expression. Inhibition of the IRE1α/XBP1 pathway synergizes with CsA to enhance efficacy through coordinated regulation of T-cell differentiation and mitigation of inflammatory responses. This presents a novel combinatorial strategy that has the potential to improve transplant outcomes.