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

PLoS One. 2019 Jan 24;14(1):e0210914. doi: 10.1371/journal.pone.0210914. eCollection 2019.


Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Composite Tissue Allografts* / drug effects
  • Composite Tissue Allografts* / immunology
  • Composite Tissue Allografts* / pathology
  • Drug Implants
  • Forelimb / transplantation
  • Graft Rejection / immunology
  • Graft Rejection / prevention & control
  • Graft Survival / drug effects
  • Graft Survival / immunology
  • Hydrogels
  • Immunosuppressive Agents / administration & dosage
  • Immunosuppressive Agents / pharmacokinetics
  • Models, Animal
  • Proof of Concept Study
  • Swine
  • Swine, Miniature
  • Tacrolimus / administration & dosage*
  • Tacrolimus / pharmacokinetics
  • Vascularized Composite Allotransplantation / methods*


  • Drug Implants
  • Hydrogels
  • Immunosuppressive Agents
  • Tacrolimus

Grants and funding

The studies were supported by intramural grant funding from the US Air Force Medical Service Agency (59MDW Office of Science and Technology) and in part by extramural funding from Department of Defense Grant W81XWH-15-2-0047 Log MR141085 (Reconstructive Transplant Research Program). CAF was funded by a fellowship from the United Kingdom Ministry of Defence. J.M.K. and N.J. were financially supported by Department of Defense (DOD) award W81XWH-14-1-0229, a Disease Targeted Innovative Research Grant from Rheumatology Research Foundation, a grant from King Abdulaziz City for Science and Technology through the Center of Excellence for Biomedicine (CEBM) and with the support of the Football Players Health Study at Harvard. The Football Players Health Study is funded by a grant from the National Football League Players Association. The content is solely the responsibility of the authors and does not necessarily represent the official views of Harvard Medical School, Harvard University or its affiliated academic health care centers, the National Football League Players Association, or the Brigham and Women’s Hospital.