AAPS, American Association of Plastic Surgeons
AAPS, American Association of Plastic Surgeons
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89th Annual Meeting Abstracts


Vascularized Bone Marrow Permits Long-Term Rejection Free Survival of Facial Composite Tissue Allografts in Non-Human Primates
Helen G. Hui-Chou, MD, Gerhard S. Mundinger, MD, Arthur J. Nam, MD, Jay E. Sulek, BA, Amir H. Dorafshar, MBChB, Luke S. Jones, BS, Cinthia B. Drachenberg, MD, Debra L. Kukuruga, PhD, Steven T. Shipley, DVM, Stephen T. Bartlett, MD, Rolf N. Barth, MD, Eduardo D. Rodriguez, MD, DDS.
University of Maryland School of Medicine, Baltimore, MD, USA.

PURPOSE:
Composite tissue allotransplantation (CTA) utilizes components of vascularized skin, muscle, and bone to reconstruct complicated defects. All clinical CTA cases have been characterized by reversible rejection responses requiring additional immunosuppressive treatments. We developed a non-human primate facial CTA model to study immunosuppressive strategies and outcomes dependent on the presence or absence of vascularized bone marrow (VBM).

METHODS:
Seven donor/recipient pairs of Cynomolgus macaques were screened pre-operatively against a panel of human monoclonal MHC class I antibodies to identify selectively donor only cross-reactive reagents. Specificity for donor cells was confirmed via flow cytometry. We were able to identify donor-specific monoclonal antibodies in all 7 facial CTA pairs. Facial CTA grafts were transplanted into recipient’s left lower abdomen and microsurgical anastamosis performed to femoral vessels. One group of 4 recipients received facial CTA grafts consisting of skin, muscle, bone and bone marrow included in the angle of mandible. A second group of 3 recipient animals received a facial CTA graft consisting of skin and muscle without VBM. All recipients received combined tacrolimus/mycophenolate mofetil (MMF) therapy. Recipients were monitored weekly for evidence of macrochimerism by flow cytometry and biopsied at scheduled intervals.

RESULTS:
We have performed 35 CTA experiments including facial and fibula allografts. Facial CTAs with skin, muscle and VBM that received tacrolimus (FK) monotherapy (n=6) demonstrated rejection-free graft survival (POD 60-177) but developed Post Transplant Lymphoproliferative Disorder (PTLD). Facial CTA with VBM converted from FK to rapamycin (n=3) rejected the allografts (POD 37-107). Fibular CTA with VBM (n=5) on FK monotherapy demonstrated skin loss from technical and immunologic causes, but demonstrated bone union by endpoint between POD 185-205 without PTLD.
Mycophenolate mofetil (MMF) therapy was added to reduce FK levels. Facial CTA with skin, muscle, and VBM and treated with FK/MMF chronic therapy showed long-term rejection-free graft survival (POD 462, 250+, 229+, 194+). Two animals demonstrated both transient and sustained evidence of macrochimerism; nonetheless, weaning off immunosuppression resulted in acute and chronic rejection and graft loss (n=1).
Facial CTA with skin, muscle and no VBM treated with FK/MMF therapy demonstrated early acute rejection as well as complete rejection of all tissues in 2 animals on POD 23 and 42. One animal lost the skin component on POD 9, and has demonstrated chronic inflammation and fibrosis of muscle at POD 159+.

CONCLUSION:
Long-term rejection-free CTA survival was permitted by FK/MMF therapy and the presence of VBM. Grafts treated with matching protocols deficient of VBM rejected without additional immunosuppressive therapies. Additional immunosuppressive approaches of FK monotherapy or rapamycin conversion were associated with the development of PTLD and rejection. These data support a protocol combining vascularized bone marrow and simplified immunosuppressive therapy as a method to achieve prolonged graft survival without rejection episodes. This does not appear to translate to immunologic tolerance.


 

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