Long-term vagus nerve stimulation synergized with rapamycin elicits neuroimmune modulation to prolong skin allograft survival

Vagus nerve stimulation (VNS) has been reported to suppress inflammation and autoimmune diseases; however, its role in transplantation rejection remains poorly defined. We developed a model for long-term VNS (L-VNS) and evaluated its efficacy, alone and combined with immunosuppressant rapamycin (L-VNS&Rapa), in a major-mismatch skin transplant model. L-VNS prolonged allograft survival, while L-VNS&Rapa enhanced this effect. Mechanistically, L-VNS&Rapa was superior in restraining T cell/macrophage infiltration, and systemic and local Th1 cytokine IFN-γ levels. Furthermore, L-VNS elevated splenic neurotransmitter norepinephrine (NE) and lowered splenic and systemic IFN-γ levels. In vitro, NE inhibited antigen-specific CD4⁺ T cell proliferation and IFN-γ secretion, an effect augmented by Rapa. Additionally, L-VNS&Rapa increased Treg infiltration and IL-10 level in the graft while expanding Treg and reducing effector T cell populations in draining lymph nodes. These findings indicate that neuroimmune modulation by L-VNS and pharmacological immunosuppression by Rapa act synergistically to promote allograft survival, offering a combination strategy for intervening in transplant rejection.