Trackable Tolerogenic Macrophages Integrate PD‐L1 and Rapamycin Signaling to Suppress Alloimmune Responses in Transplantation

ABSTRACT Cell‐based immunotherapies represent a promising strategy for transplant tolerance, yet challenges remain in graft targeting, in vivo tracking, and comprehensive regulation of alloreactive T cells. Here, we developed trackable tolerogenic macrophages ( TTMs ), engineered to overexpress PD‐L1, incorporate azide groups for bioorthogonal labeling, and encapsulate rapamycin nanoparticles (RAPA NPs). Following intravenous administration in murine allografts, TTMs preferentially homed to inflamed grafts and were visualized in vivo. TTMs reduced graft inflammation and prolonged allograft survival up to 35 days, significantly longer than PD‐L1 or RAPA monotherapy groups. Mechanistic studies showed that PD‐L1 ligation of PD‐1 suppressed Th1 differentiation and CD8 ⁺ T‐cell activation, reducing IFN‐γ/TNF‐α and thereby attenuating complement activation and PI3K/Akt/mTOR signaling. This enhanced rapamycin‐mediated mTOR inhibition and promoted Foxp3 ⁺ Treg induction with increased IL‐10 production. The elevated IL‐10 further strengthened PD‐1/PD‐L1 signaling, forming a feedback loop that maintained a tolerogenic microenvironment. Together, these findings highlight TTMs as multifunctional therapeutic cells that integrate graft homing, real‐time tracking, and dual‐pathway immunoregulation to advance precision immunotherapy in transplantation.