Transient Detection of Microchimerism Using Quantitative RT-PCR for Insertion/Deletion Polymorphysms After Full Face Transplant.

Transplantation of vascularized composite allografts (VCA) containing vascularized bone marrow (VBM) may be permissive of improved immunologic outcomes. We developed and reported on a non-human primate model that supported this hypothesis and was associated with transient evidence of macrochimerism detected in the peripheral blood. We performed a full face transplant in March of 2012 consisting of a total face and double jaw segment. The recipient received T cell depletion with Alemtuzumab (30 mg) and post-operative therapy with tacrolimus, mycophenolate mofetil, and steroids. Macrochimerism was monitored for by both short tandem repeat (STR) analysis and selective anti-HLA antibodies. A novel RT-PCR assay based on insertion/deletion (In/Del) polymorphisms (sensitivity 0.01%) was utilized to analyze microchimerism in stored peripheral blood specimens. Peripheral blood chimerism was not detected by either flow cytometry or STR-based techniques at any time post-operatively (20 months). RT-PCR analysis of peripheral blood specimens was performed on samples from post-operative days (POD) 3 to 49 to examine for microchimerism. On POD 3 and 7 the recipient demonstrated 0.05% microchimerism. This subsequently decreased to 0.015% on POD 21, 0.001% on POD 35, and 0.0% on POD 49. Analysis of late samples from 6 and 11 months post-operatively demonstrated 0.0% chimerism.Figure: No Caption available.Full face transplant with large volume VBM to a recipient treated with T cell depletion did not demonstrate macrochimerism. Additional analysis with a novel RT-PCR technique using In/Del polymorphisms demonstrated transient evidence of low-level microchimerism that disappeared after 21 days. Peripheral blood chimerism is unlikely to be the mechanism by which VCA with VBM achieved a good immunologic outcome in our patient with standard immunosuppression. Ongoing studies of recipient and donor bone marrow will analyze for the presence of donor cell populations that may serve as the mechanism for good immunologic outcomes.