Biologics and Donor Bone Marrow Cells for Targeted Immunomodulation in Composite Tissue Allotransplantation – A Large Animal Translational Trial

Eric Wimmers¹, Galen Wachtman², Vijay Gorantla², Cheng-Hung Lin¹, Stefan Schneeberger¹, Rishi Jindal², Jignesh Unadkat², Xin Xiao Zheng², Gerald Brandacher^1,2, W.P. Andrew Lee^1,2.

¹Department of Plastic and Reconstructive Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA; ²Division of Plastic and Reconstructive Surgery, University of Pittsburgh, Pittsburgh, PA, USA.

Introduction: Bone marrow (BM) infusion following organ transplantation is a prerequisite for potential donor-antigen specific tolerance induction. We developed a preclinical swine model to determine the optimal dose of BM cells to achieve microchimerism. Furthermore, induction therapy was optimized by augmenting the BM infusion with biologics in the form of co-stimulatory blockade (CTLA4Ig).

Materials and Methods: Yucatan miniature swine (n=12) underwent total body and thymic irradiation for cytodepletion. Animal groups received 15, 30 or 60 million cells/kg of whole unmodified BM. The optimal dose of BM cell infusion was then applied to subsequent experiments evaluating the addition of CTLA4Ig. Yucatan miniature swine (n=9) underwent heterotopic hind limb transplantation and received 30 days of FK506 treatment. Group I (control) received irradiation and BM infusion; Group II received irradiation, BM infusion, and CTLA4Ig; Group III received CTLA4Ig only.

Results: Microchimerism was established in all animals after BM cell infusion; at POD 9 it was significantly increased for 60 million cells/kg (p=0.0001). Transplanted animals in Group I rejected the skin portion of the allograft at 50, 52, and 53 days post-transplant. Remaining allograft components (muscle, bone, nerve, vessel) survived indefinitely. Group II animals had complications (unexplained weight loss) leading to sudden death (n=1) or were euthanized at 28 and 35 days post-transplant. Group III animals demonstrated significantly prolonged graft survival beyond 150 days post-transplant. Skin and muscle histology in all long-term surviving animals were normal.

Conclusions: Bone marrow cell infusion with 60 million cells/kg results in stable levels of microchimerism. The addition of co-stimulatory blockade (CTLA4Ig) enabled us to optimize induction therapy, reduce maintenance immunosuppression, and prolong graft survival. Such targeted immunomodulatory protocols that combine BM cell-based strategies and biologics might facilitate immune tolerance and eliminate the need for multi-drug immunosuppression to maintain graft survival after CTA.