Targeted immunosuppression with a tissue-selective PD-1 agonist prevents rejection of transplanted hearts 2308742

Abstract Introduction Systemic immunosuppression to prevent allograft rejection or treat autoimmune disease can risk infection and malignancy. To uncouple therapeutic immunosuppression from systemic toxicity, we engineered Location-Specific T-cell Inhibitory Molecules (LoSTIMs), Fc-silent bispecific antibodies that activate PD-1 and inhibit T-cells only when they engage a predefined tissue surface antigen. We hypothesized that tissue-selective PD-1 agonism could protect allografts from rejection while sparing systemic immunity. Methods We profiled PD-1 agonism, epitope specificity, and binding kinetics of anti-PD-1 antibodies, then engineered Fc-silent bispecific LoSTIMs. We evaluated antigen-dependent PD-1 agonism in Jurkat reporter assays and inhibition of T-cell activation in primary T cells. We tested a donor MHC class I (H-2Kb)-specific LoSTIM in fully mismatched heterotopic cardiac transplant models, assessing graft survival and immune cell phenotype by flow cytometry and spatial transcriptomics. Results LoSTIMs acted as conditional PD-1 agonists, inhibiting T cells only when engaging target antigen, and were FcγR independent, enabling Fc-silent designs that do not deplete PD-1+ T-cells and preserve physiologic immunity outside the target tissue. Systemic treatment with H-2Kb-specific LoSTIM durably prevented rejection of C57BL/6 allografts in BALB/c recipients, whereas monospecific anti-PD-1 or anti-H-2Kb did not. Flow cytometry and spatial transcriptomics showed reduced donor-specific priming and graft infiltration, loss of effector function in graft-infiltrating CD8+ T cells, and a shift toward less inflammatory, regulatory/progenitor-like T-cell populations. Third-party C3H cardiac allografts (H-2Kk) lacking the H-2Kb surface antigen were not protected, consistent with tissue-selective immunosuppression. Conclusion LoSTIMs provide systemically administered, tissue-restricted PD-1 agonism that prevents allograft rejection without global immune suppression and may be generalizable to other immune diseases. Funding Source ASCO Young Investigator Award (JT), Claudia Adams Barr Fellowship in Innovative Basic Cancer Research (JT) Topic Categories Transplantation Immunology (TRAN)