Unlike visceral solid-organ transplants, composite tissue allografts (CTA) are modules composed of various tissues, each with differing antigenicity, and therefore differing potential for rejection.1 Skin and muscle (and perhaps synovium) are the most antigenic and appear to be most susceptible to rejection, while bone, tendon, cartilage, and neurovascular tissue appear to be less immunogenic and evoke rejection responses of lower magnitude. Although CTA have tremendous potential clinical application for functional and structural reconstruction of major congenital and acquired peripheral tissue defects, these transplants, until recently, have remained one of the last frontiers in clinical organ transplantation because of concerns regarding their risk/benefit ratio.2,3 Two questions address the key issues involved: (1) Can rejection of these highly antigenic tissues be prevented using currently available immunosuppressive regimens with acceptable drug-specific and generalized toxicity? and (2) Will function be restored to a significant degree so as to justify the surgical and immunosuppressive risks involved? The information presented at the Second International Symposium on Composite Tissue Allotransplantation (Louisville, May, 18–19, 2000) has begun to shed some light on the answers to these questions. The recipients of hand transplants in Lyon (two patients), Louisville (one patient), and Guangzhou (two patients) all received a form of antilymphocyte antibody for induction (antithymocyte globulin and/or an interleukin-2 receptor [IL-2R] antagonist), and tacrolimus (FK506), mycophenolate mofetil, and prednisone therapy for maintenance immunosuppression. Despite this clinically acceptable but nonetheless intensive immunosuppressive regimen, akin to that currently utilized for rejection-prone, nonuremic, insulin-dependent diabetics who receive a pancreas transplant,4 the first Lyon patient sustained an episode of acute rejection at 8 weeks and the Louisville recipient developed moderate acute cellular rejection at 6, 20, and 27 weeks posttransplant.5,6 Although all these episodes resolved completely after combination systemic pulse steroid and topical FK506-clobetasol treatment, the transient increase in oral with or without intravenous (IV) prednisone and FK506 doses during and after each rejection episode further increased the already elevated immunosuppressive burden in these patients. Along these lines, the Louisville recipient developed tissue-invasive cytomegalovirus disease at 15 weeks posttransplant, requiring subsequent long-term ganciclovir prophylaxis. These preliminary results suggest that clinical application of CTA is more likely to gain widespread acceptance if the systemic immunosuppressive burden and its attendant long-term risks of infection, malignancy, and drug-specific side effects could be reduced while simultaneously preventing rejection and maintaining function.
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