Consistent survival in consecutive cases of life-supporting porcine kidney xenotransplantation using 10GE source pigs

The critical shortage of donor organs necessitates innovative solutions, and xenotransplantation, using porcine organs, presents a promising avenue. The Food and Drug Administration (FDA) has recently provided guidance on a regulatory pathway for solid organ xenotransplantation, emphasizing the need for consistent results, standardized procurement and preservation methods, and the use of FDA-approved immunosuppression. While previous studies have shown long-term survival in NHP models, inconsistent results and the use of non-FDA-approved medications like CD40/CD154 costimulatory blockade agents have raised concerns regarding clinical translation. Furthermore, the impact of cold ischemic time, a necessity for off-site procurement in clinical settings, on xenograft survival has not been fully elucidated. This study aims to address these challenges by demonstrating consistent long-term survival in consecutive pig-to-NHP kidney xenotransplantation cases, employing FDA-approved preservation and immunosuppression strategies and tolerating significant cold preservation time.

Numerous studies have demonstrated the potential of xenotransplantation, particularly using genetically modified pigs, to overcome the organ shortage. However, challenges remain, such as inconsistent graft survival rates across studies, often with significant early graft loss due to hyperacute rejection or other complications. Most studies have excluded recipients experiencing early rejection, hindering the comprehensive assessment of safety and efficacy. Furthermore, the reliance on non-FDA-approved immunosuppression, particularly CD40/CD154 blockade, hinders the clinical translation of these promising results. This study aims to overcome these limitations by focusing on consecutive cases, including those with adverse outcomes, and using only FDA-approved immunosuppression strategies. Existing literature highlights the complexities of xenotransplantation, including the impact of cold ischemic time and the need for refined recipient selection and immunologic screening methodologies.

This study utilized six baboons (*Papio anubis*) as recipients, receiving kidneys from 10GE pigs (with 10 genetic modifications) sourced from a designated pathogen-free (DPF) facility. Kidneys were preserved using FDA-approved hypothermic machine perfusion (XVIVO or Lifeport) for 3-5 hours. Recipients underwent a standardized immunosuppression induction protocol involving B and T cell depletion, and were then randomized into two groups: one received conventional, clinically available immunosuppression (CNI-based with CD28/CTLA4 costimulation blockade), and the other received CD40/CD154 costimulatory blockade-based maintenance immunosuppression. Pre-transplant screening was rigorously performed to identify recipients at low risk for hyperacute rejection. Graft function was monitored through serum creatinine levels and regular biopsies. Histological analyses were conducted at various time points to assess rejection mechanisms and potential infections. The primary endpoint was kidney failure (creatinine >10 mg/dL).

This study achieved a mean survival of 220 days and a median survival of 261 days across six consecutive NHP recipients. One recipient with high levels of preformed anti-pig antibodies experienced hyperacute rejection. Among the five low-risk recipients, mean survival was 263 days, with four surviving beyond six months and three beyond nine months. Grafts maintained normal electrolyte levels until the onset of irreversible renal failure. Causes of graft failure included antibody-mediated rejection (AMR), acute cellular rejection, and adenovirus infection. This study is the first to demonstrate long-term xenograft survival (up to 285 days) using a CNI-based immunosuppression regimen without CD40/CD154 costimulatory blockade. Furthermore, the study successfully demonstrated long-term survival with a clinically relevant 3-5 hour cold ischemic time, showing the feasibility of off-site procurement from a DPF facility.

The results of this study address the critical need for consistent and clinically translatable results in xenotransplantation. The consistent long-term survival achieved in consecutive cases, using FDA-approved immunosuppression and tolerating extended cold ischemia time, provides strong evidence supporting the safety and feasibility of clinical kidney xenotransplantation. The successful application of a conventional CNI-based immunosuppression regimen, without CD40/CD154 blockade, bridges a significant gap between preclinical NHP models and the clinical reality of human allotransplantation. The findings suggest that careful recipient selection based on rigorous pre-transplant screening, reliable transgene expression in the source pigs, and optimized immunosuppression protocols are crucial for achieving successful outcomes. This study highlights the potential for minimizing the reliance on experimental immunosuppressive agents, accelerating the clinical translation of xenotransplantation.

This study provides compelling evidence for the feasibility of clinical kidney xenotransplantation. Consistent, long-term survival in consecutive cases, using FDA-approved methods, including overcoming a significant cold ischemic time, and demonstrating success without CD40/CD154 blockade, strongly supports clinical translation. Future research should focus on refining recipient selection criteria, optimizing immunosuppression regimens, and investigating the mechanisms of adenovirus-induced graft loss to further improve the success and longevity of xenotransplantation.

The relatively small sample size limits the generalizability of the findings. The study population was limited to baboons, and the results may not perfectly translate to human recipients. While this study used FDA-approved preservation methods, further investigation is needed to fully understand the effects of prolonged cold ischemic time and explore strategies for minimizing ischemic reperfusion injury. Finally, the impact of potential zoonotic transmission beyond adenovirus requires continued monitoring.