Research Article: Graft-implanted, enzyme responsive, tacrolimus-eluting hydrogel enables long-term survival of orthotopic porcine limb vascularized composite allografts: A proof of concept study

Date Published: January 24, 2019

Publisher: Public Library of Science

Author(s): C. Anton Fries, Shari D. Lawson, Lin C. Wang, Kai V. Slaughter, Praveen K. Vemula, Ashish Dhayani, Nitin Joshi, Jeffrey M. Karp, Rory F. Rickard, Vijay S. Gorantla, Michael R. Davis, Stanislaw Stepkowski.


Currently, patients receiving vascularized composite allotransplantation (VCA) grafts must take long-term systemic immunosuppressive therapy to prevent immunologic rejection. The morbidity and mortality associated with these medications is the single greatest barrier to more patients being able to receive these life-enhancing transplants. In contrast to solid organs, VCA, exemplified by hand or face transplants, allow visual diagnosis of clinical acute rejection (AR), directed biopsy and targeted graft therapies. Local immunosuppression in VCA could reduce systemic drug exposure and limit adverse effects. This proof of concept study evaluated, in a large animal forelimb VCA model, the efficacy and tolerability of a novel graft-implanted enzyme-responsive, tacrolimus (TAC)—eluting hydrogel platform, in achieving long-term graft survival.

Orthotopic forelimb VCA were performed in single haplotype mismatched mini-swine. Controls (n = 2) received no treatment. Two groups received TAC hydrogel: high dose (n = 4, 91 mg TAC) and low dose (n = 4, 49 mg TAC). The goal was to find a dose that was tolerable and resulted in long-term graft survival. Limbs were evaluated for clinical and histopathological signs of AR. TAC levels were measured in serial blood and skin tissue samples. Tolerability of the dose was evaluated by monitoring animal feeding behavior and weight.

Control limbs underwent Banff Grade IV AR by post-operative day six. Low dose TAC hydrogel treatment resulted in long-term graft survival time to onset of Grade IV AR ranging from 56 days to 93 days. High dose TAC hydrogel also resulted in long-term graft survival (24 to 42 days), but was not well tolerated.

Graft-implanted TAC-loaded hydrogel delays the onset of Grade IV AR of mismatched porcine forelimb VCA grafts, resulting in long term graft survival and demonstrates dose-dependent tolerability.

Partial Text

The life-changing reconstructive benefits and routine clinical utilization of VCA have been hampered by the risks related to lifelong, high-dose, multi-drug immunosuppression [1]. To date, uncontrolled acute rejection (AR) or chronic rejection (CR) has led to numerous graft losses [2,3]. Medication non-compliance is also a major contributor to preventable graft failure [4]. Tacrolimus (TAC), the mainstay drug in VCA, has a very narrow therapeutic range, with variable diurnal peaks and troughs after oral delivery [5]. Unlike solid organs, VCA offers unique opportunities for visual graft surveillance for clinical rejection as well as access to directed biopsies and graft targeted drug delivery [3,6,7].

All experiments were performed at the Tri-Service Research Laboratories, United States Army Institute for Surgical Research, Fort Sam Houston, San Antonio, Texas. These were in accordance with a protocol independently reviewed and approved by the Institutional Animal Care and Use Committee (IACUC) of the Tri-Service Research Laboratory.

Despite evolving clinical experience and progress in the understanding of the biology of VCA, one of the main factors preventing wider acceptance and routine clinical application are the associated adverse effects of long-term immunosuppression [22]. Since most VCA are non-life-saving procedures, the risks and toxicity of immunosuppression must be carefully balanced against their potential life enhancing benefits [23].




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