Large-gap peripheral nerve repair using xenogeneic transplants in rhesus macaques.

Surgical intervention is required to successfully treat severe, large-gap (≥4 cm) peripheral nerve injuries. However, all existing treatments have shortcomings and an alternative to the use of autologous nerves is needed. Human and porcine nerves are physiologically similar, with comparable dimensions and architecture, presence and distribution of Schwann cells, and conserved features of the extracellular matrix (ECM). We report the repair of fully transected radial nerves in 10 Rhesus Macaques using viable, whole sciatic nerve from genetically engineered (GalT-KO), designated pathogen free (DPF) porcine donors. This resulted in the regeneration of the transected nerve, and importantly, recovery of wrist extension function, distal muscle reinnervation, and recovery of nerve conduction velocities and compound muscle action potentials similar to autologous controls. We also demonstrate the absence of immune rejection, systemic porcine cell migration, and detectable residual porcine material. Our preliminary findings support the safety and efficacy of viable porcine nerve transplants, suggest the interchangeable therapeutic use of cross-species cells, and highlight the broader clinical potential of xenotransplantation.

Immunological response in cynomolgus macaques to porcine α-1,3 galactosyltransferase knockout viable skin xenotransplants-A pre-clinical study.

BACKGROUND: Allogeneic skin recovered from human deceased donors (HDD) has been a mainstay interim treatment for severe burns, but unfortunately risk of infectious disease and availability limitations exist. Genetically engineered ɑ-1,3 galactosyltransferase knockout (GalT-KO) porcine source animals for viable skin xenotransplants may provide a promising clinical alternative. METHODS: Four cynomolgus macaque recipients received full-thickness surgical wounds to model the defects arising from excision of full-thickness burn injury and were treated with biologically active skin xenotransplants derived from GalT-KO, Designated Pathogen Free (DPF) miniature swine. Evaluations were conducted for safety, tolerability, and recipient immunological response. RESULTS: All skin xenotransplants demonstrated prolonged survival, vascularity, and persistent dermal adhesion until the study endpoint at post-operative day 30. No adverse outcomes were observed during the study. Varying levels of epidermolysis coincided with histologic detection of CD4+ and CD8+ T cells, and other cellular infiltrates in the epidermis. Recipient sera IgM and IgG demonstrated significant antibody immune response to non-α-1,3-galactose porcine xenoantigens. Separately, specific wound healing mediators were quantified. Neither porcine cell migration nor PERV were detected in circulation or any visceral organs. CONCLUSIONS: These results provide a detailed analysis of vital skin xenotransplants utilizing a non-human primate model to predict the anticipated immunological response of human patients. The lack of adverse rejection even in the presence of elevated Ig indicates this is a prospective therapeutic option. The findings reported here directly supported regulatory clearance for a first-in-man, Phase I xenotransplantation clinical trial.

Efficacy and safety of ex vivo cultured adult human mesenchymal stem cells (Prochymal™) in pediatric patients with severe refractory acute graft-versus-host disease in a compassionate use study.

Preliminary studies using directed-donor ex vivo expanded human mesenchymal stem cells (hMSCs) have shown promise in the treatment of acute graft-versus-host disease (aGVHD). However, their production is cumbersome and standardization is difficult. We describe the first experience of using a premanufactured, universal donor, formulation of hMSCs (Prochymal) in children (n = 12; 10 boys; 9 Caucasian; age range: 0.4-15 years) with treatment-resistant grade III and IV aGVHD who received therapy on compassionate use basis between July 2005 and June 2007 at 5 transplant centers. All patients had stage III or IV gut (GI) symptoms and half had additional liver and/or skin involvement. Disease was refractory to steroids in all cases and additionally to a median of 3 other immunosuppressive therapies. The hMSCs (8 × 10(6)cells/kg/dose in 2 patients and 2 × 10(6)cells/kg/dose in the rest) were infused intravenously over 1 hour twice a week for 4 weeks. Partial and mixed responders received subsequent weekly therapy for 4 weeks. HLA or other matching was not needed. The hMSCs were started at a median of 98 days (range: 45-237) posttransplant. A total of 124 doses were administered, with a median of 8 doses (range: 2-21) per patient. Overall, 7 (58%) patients had complete response, 2 (17%) partial response, and 3 (25%) mixed response. Complete resolution of GI symptoms occurred in 9 (75%) patients. Two patients relapsed after initial response and showed partial response to retreatment. The cumulative incidence of survival at 100 days from the initiation of Prochymal therapy was 58%. Five of 12 patients (42%) were still alive after a median follow-up of 611 days (range: 427-1111) in surviving patients. No infusional or other identifiable acute toxicity was seen in any patient. Multiple infusions of hMSCs were well tolerated and appeared to be safe in children. Clinical responses, particularly in the GI system, were seen in the majority of children with severe refractory aGVHD. Given the favorable results observed in a patient population with an otherwise grave prognosis, we conclude that hMSCs hold potential for the treatment of aGVHD, and should be further studied in phase III trials in pediatric and adult patients.

Vital, Porcine, Gal-Knockout Skin Transplants Provide Efficacious Temporary Closure of Full-Thickness Wounds: Good Laboratory Practice-Compliant Studies in Nonhuman Primates.

Vital, genetically engineered porcine skin transplants have long been regarded as a promising treatment option for severe burn wounds. The objective of this two-part, preclinical study was to evaluate the ability of vital, split-thickness skin xenotransplants derived from designated pathogen-free, alpha 1,3 galactosyltransferase knockout miniature swine to provide temporary wound closure of full-thickness wound defects intended to model severe and extensive, deep partial- and full-thickness burn wounds. In part 1 of the study, four full-thickness wound defects were introduced in four cynomolgus macaques recipients and, then engrafted with two xenografts and two allografts to achieve temporary wound closure. On POD-15, autografts were used to achieve definitive wound closure and were observed until POD-22. In part 2 of the study, four additional subjects each received two full-thickness wound defects, followed by two xenografts to achieve temporary wound closure, and were observed postoperatively for 30 days without further intervention. All grafts were assessed for signs of adherence to the wound bed, vascularity, and signs of immune rejection via gross clinical and histological methods. Xenograft and allograft comparators were equivalent in part 1, and later autografts were otherwise indistinguishable. In part 2, all xenotransplants demonstrated adherence, vascularity, and survival until POD-30. These were unexpected results that exceed previously published findings in similar models. Furthermore, the ensuing GLP-study report directly supported regulatory clearance, permitting a phase I clinical trial. This solution holds great promise as an alternative to human cadaver allograft, the current standard of care for the treatment of severe burns.

Clinical Impact of Cryopreservation on Split Thickness Skin Grafts in the Porcine Model.

Vital, genetically engineered, porcine xenografts represent a promising alternative to human cadaveric allografts (HCA) in the treatment of severe burns. However, their clinical value would be significantly enhanced if preservation and long-term storage-without the loss of cellular viability-were feasible. The objective of this study was to examine the direct impact of cryopreservation and the length of storage on critical in vivo and in vitro parameters, necessary for a successful, potentially equivalent substitute to HCA. In this study, vital, porcine skin grafts, continuously cryopreserved for more than 7 years were compared side-by-side to otherwise identically prepared skin grafts stored for only 15 minutes. Two major histocompatibility complex (MHC)-controlled donor-recipient pairs received surgically created deep-partial wounds and subsequent grafting with split-thickness porcine skin grafts, differentiated only by the duration of storage. Clinical and histological outcomes, as well as quantification of cellular viability via a series of 3-4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) assays, were assessed. No statistically significant differences were observed between skin grafts cryopreserved for 15 minutes vs 7 years. Parametric distinctions between xenografts stored for short- vs long-term durations could not be ascertained across independent clinical, histological, or in vitro evaluative methods. The results of this study validate the ability to reliably preserve, store, and retain the essential metabolic activity of porcine tissues after cryopreservation. Plentiful, safe, and readily accessible inventories of vital xenografts represent an advantageous solution to numerous limitations associated with HCA, in the treatment of severe burns.

Adult human mesenchymal stem cells added to corticosteroid therapy for the treatment of acute graft-versus-host disease.

The unique immunomodulatory properties of mesenchymal stem cells (MSCs) make them a rationale agent to investigate for graft-versus-host disease (GVHD). Human MSCs were used to treat de novo acute GVHD (aGVHD). Patients with grades II-IV GVHD were randomized to receive 2 treatments of human MSCs (Prochymal(R)) at a dose of either 2 or 8 million MSCs/kg in combination with corticosteroids. Patients received GVHD prophylaxis with tacrolimus, cyclosporine, (CsA) or mycophenolate mofetil (MMF). Study endpoints included safety of Prochymal administration, induction of response to Prochymal, and overall response of aGVHD by day 28, and long-term safety. Thirty-two patients were enrolled, with 31 evaluable: 21 males, 10 females; median age 52 years (range: 34-67). Twenty-one patients had grade II, 8 had grade III, and 3 had grade IV aGVHD. Ninety-four percent of patients had an initial response to Prochymal (77% complete response [CR] and 16% partial response [PR]). No infusional toxicities or ectopic tissue formations were reported. There was no difference with respect to safety or efficacy between the low and high Prochymal dose. In conclusion, Prochymal can be infused safely into patients with aGVHD and induces response in a high proportion of GVHD patients.