Saturday September 25, 2021 - 15:50 to 17:05
Long-term immunological response to viable xenogeneic nerve transplants in non-human primates – a preclinical study
Paul W. Holzer1,8, Elizabeth Chang2,8, Jamie Tarlton3, Diana Lu8, Jon Adkins8, Alan LaRochelle6, Curtis L. Cetrulo Jr.4,5, Linda Scobie3, Joan Wicks7, Rod Monroy8.
1Department of Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, United States; 2Department of Engineering, Northeastern University, Boston, MA, United States; 3Department of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow, United Kingdom; 4Reconstructive Transplantation Laboratory, Massachusetts General Hospital, Boston, MA, United States; 5Shriners Hospital for Children-Boston, Harvard Medical School, Boston, MA, United States; 6Biomere, Biomedical Research Models, Inc., Worcester, MA, United States; 7StageBio, Mt. Jackson, VA, United States; 8XenoTherapeutics, Inc., 501(c)3, Boston, MA, United States
Background: In this 12-month study, the safety and efficacy of viable, large-caliber, mixed-modal xenogeneic nerve transplants derived from genetically engineered, designated pathogen free porcine donors were evaluated as a potential method of reconstructing large-gap (≥4cm) peripheral nerve neurotmesis in non-human primates. Twenty million Americans suffer from peripheral nerve injury (PNI) resulting in nearly 50,000 surgeries annually.1 Successful early intervention improves the rate of nerve regeneration and reinnervation, but existing treatments have severe shortcomings.1,2 There is a critical need for high-quality surgical therapeutics. Candidate therapies should ideally contain viable Schwann cells and a matrix-rich scaffold.3–5 Porcine nerves share many physiological characteristics with human motor and sensory nerves1 and offer the potential for greater clinical availability. We thus hypothesized that viable porcine nerve transplants may be an effective alternative to existing surgical therapeutics. We published6 the study’s clinical outcomes (e.g. regain of function, electrophysiology). Here we specifically assess the histological and immunological responses to xenogeneic transplantation.
Methods: Bilateral, 4cm radial nerve neurotmesis, the complete physiological and anatomical transection of axons and connective tissue, was surgically introduced in ten Rhesus monkeys. For each subject, one limb was repaired with an autologous nerve transplant and the contralateral limb with xenogeneic in a blinded manner. Over a 12-month observational period, samples of nerve, spleen, liver, kidney, lung, and heart were evaluated for various macro-and-microscopic histomorphological characteristics. Subjects were iteratively assessed for anti-GalT-KO porcine IgG and IgM antibodies and the presence of porcine cells by qPCR.
Results: Previously reported1 functional recovery was observed in both autologous and xenogeneic treated limbs. Inflammation was greater at xenogeneic transplant sites, including infiltrating populations of lymphocytes, macrophages, and histiocytes, with the notable presence of tertiary lymphoid nodules along the exterior myelin sheath (Fig 1).
Anti-GalT-KO porcine IgG and IgM levels and trends were consistent with our previous experience,7 and our ongoing clinical trial8 (Fig 2).
Micro-chimerism was not detected in any tissues sampled, nor was there evidence of any systemic effects attributed to the xenogeneic transplant.
Conclusion: These long-term, in vivo data suggest promising safety and tolerability following reconstruction with viable, porcine nerve transplants. Key findings include the lack of systemic porcine cell migration over 12-months in subjects and complete elimination of the transplanted porcine tissue. Combined, these data are encouraging for neural xenotransplantation therapies and more broadly support the clinical feasibility of xenotransplantation.
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2. Althagafi A, Nadi M. Acute Nerve Injury. In: StatPearls. StatPearls Publishing; 2021. Accessed April 21, 2021. http://www.ncbi.nlm.nih.gov/books/NBK549848/.
3. Kornfeld T, Vogt PM, Radtke C. Nerve grafting for peripheral nerve injuries with extended defect sizes. Wien Med Wochenschr 1946. 2018;169(9-10):240-251. doi:10.1007/s10354-018-0675-6.
4. Ehretsman RLM, Novak CBP, Mackinnon SE. Subjective Recovery of Nerve Graft Donor Site. Ann Plast Surg. 1999;43(6):606-612.
5. IJpma FFA, Nicolai J-PA, Meek MF. Sural Nerve Donor-Site Morbidity: Thirty-Four Years of Follow-up. Ann Plast Surg. 2006;57(4):391-395. doi:10.1097/01.sap.0000221963.66229.b6.
6. Holzer PW, Chang EJ, Adkins J, et al. Viable Xenogeneic Nerve Transplants Demonstrates Regeneration and Functional Recovery Across Large-Gap Peripheral Nerve Injuries in Non-Human Primates. J Plast Reconstr Surg. 2021;Unpublished Manuscript.
7. Holzer PW, Chang E, Wicks J, Scobie L, Crossan C, Monroy R. Immunological response in cynomolgus macaques to porcine α-1,3 galactosyltransferase knockout viable skin xenotransplants—A pre-clinical study. Xenotransplantation. 2020;n/a(n/a):e12632. doi:10.1111/xen.12632.
8. XenoTherapeutics, Inc. An Open-Label Phase 1 Study to Evaluate the Safety and Tolerability of Xeno-SkinTM for Temporary Coverage of Severe and Extensive, Deep Partial and Full Thickness Burn Wounds. clinicaltrials.gov; 2021. Accessed April 29, 2021. https://clinicaltrials.gov/ct2/show/NCT03695939.
XenoTherapeutics, Inc., 501(c)3. Department of Defense (Grant number W18XWH-17-I-0454).