PURPOSE: Previously we have shown that MHC class I-mismatched recipient miniature swine (n=3) experienced rejection (from POD42 onwards) of the epidermal component of fasciocutaneous vascularized composite allografts (VCAs), despite stable mixed chimerism. We sought to extend and optimize this protocol with a combination of CTLA4-Ig, a vascularized bone marrow compartment and donor bone marrow transplantation in order to induce tolerance and/or full VCA survival.

METHODS: Prior to VCA, all animals received non-myeloablative conditioning with 300 cGy total body and 700 cGy thymic irradiation on day -2. Tacrolimus was initiated on the morning of day 0 (and continued to POD30 before tapering to stop on POD45; target trough level 10–15 ng/mL) before osteomyocutaneous hind limb VCAs were transplanted into MHC class I-mismatched recipient animals (n=4). CTLA4-Ig was administered on POD 0, 2, 4 and 6 in Group I (n=2) and on POD 0, 2, 4, 6, 20 and 50 in Group II (n=2). Surveillance biopsies of the VCA were performed on POD 14, 30 and 50, or whenever clinical rejection was suspected. The development of mixed chimerism was evaluated across a variety of cell lineages by flow cytometry. Systemic immune status and function were assessed by standard in vitro assays.

RESULTS: Three animals had to be removed from study on POD9, POD33 and POD39, due to major complications. All three VCAs remained rejection-free (clinically and on histology) up to experimental end-point. At time of this report, animal 23693 (Group I) has been successfully weaned off all immunosuppression for more than 8 weeks, without any evidence of rejection or graft-versus-host disease thus far. Establishment of mixed chimerism was detected in peripheral blood. Additional in vitro analyses are ongoing at this time.

CONCLUSIONS: The addition of CTLA4-Ig and vascularized bone marrow (as part of an osteomyocutaneous VCA) may confer additional protection against the development of acute skin rejection episodes in MHC class I-mismatched recipients through mechanisms that remain to be determined. Further follow-up of 23693 will be required for confirmation of multi-lineage stable mixed chimerism and to determine whether long-term VCA tolerance will be achieved. Successful results will bring us one step closer towards clinical application in VCA patients.

CITATION INFORMATION: Schol I, Ng Z, Lellouch A, Gama A.-R, Kurtz J, Cetrulo C. CTLA4-Ig, Vascularized Bone Marrow and Donor Bone Marrow Cells Successfully Negate the Development of Acute Skin Rejection of Vascularized Composite Allografts in MHC Class I Mismatched Recipients. Am J Transplant. 2017;17 (suppl 3).

« Back to 2017 American Transplant Congress