Background: : Despite the promise of pancreatic islet allotransplantation for diabetes treatment, its clinical application is limited by the shortage of suitable human donors. Genetically modified porcine islets offer a viable alternative. While immunosuppressive therapies that block the CD40/CD154 pathway have shown efficacy in preclinical xenotransplantation studies, their translation to clinical practice remains challenging due to safety concerns, particularly with anti-CD154 agents. In this study, we explore the use of clinically applicable immunomodulatory regimens that exclude anti-CD154, alongside immune monitoring, in a pig-to-nonhuman primate islet xenotransplantation model.
Methods: Cynomolgus monkeys were rendered diabetic with streptozotocin and received an intraportal infusion of 50,000 ~ 100,000 IEQ/kg of islets from GGTA/CMAH/4GalNT2/ iGb3s gene knockout (QKO) pigs. All recipients received a base immunosuppressive regimen of anti-thymocyte globulin (ATG) induction and tacrolimus, sirolimus and mycophenolate mofetil (MMF) maintenance. Cohort 1 received the base regimen only; Cohort 2 also received abatacept; Cohort 3 additionally received crovalimab and rituximab.
Results: Islet graft survival were 35 and 25 days in Cohort 1, 140 days in Cohort 2, and 217 days in Cohort 3. All recipients exhibited a significant decrease in peripheral blood T lymphocytes following transplantation. T cells began to recover early by post-transplantation day (POD) 14, with effector memory CD8⁺ T cells increasing more prominently than other T cell subsets. In addition, no significant elevations in plasma IL-6 or TNF levels were observed. Recipients in Cohort 1 and Cohort 2 showed significantly elevated levels of membrane attack complex (MAC) and C5a, along with substantial infiltration of CD3⁺ T cells and CD68⁺ macrophages in the xenografts. In contrast, Cohort 3 recipients showed no significant changes in MAC or C5a levels and exhibited reduced infiltration of CD3⁺ and CD68⁺ cells. The proportion of xenograft-derived cell-free DNA (xdcfDNA) was markedly elevated at POD 7 and declined to low, by day 28 in Cohorts 1 and 2. In Cohort 3, xdcfDNA levels remained consistently baseline and stable.
Conclusions: Our experience demonstrates that the effector memory CD8+ T cells and activated macrophages may be detrimental to long-term graft survival, and the need for sustained immunosuppression to prevent immune responses in islet xenografts. These findings suggest the clinical applicability of a CD154-free immunomodulatory strategy in islet xenotransplantation using QKO porcine islets.