Sensitized recipients exhibit accelerated but not hyperacute rejection of vascularized composite tissue allografts

Technical, Immunological, and Ethical Similarities and Differences Between Vascularized Composite Allotransplantation and Solid Organ Transplantation in Current Practice

Solid organ transplantation (SOT) is a surgical method used as the gold standard in end-term organ failure. Following SOT, successful results have also been achieved in vascularized composite tissue transplantation, which improves the quality of life with the success of solid organ transplants and the development of modern immunosuppressive regimens. This review discusses the preoperative, operative, postoperative, and immunological differences between vascularized tissue transplantation and SOT.

Vascularized composite allograft-specific characteristics of immune responses

Vascularized composite allograft (VCA) transplantation, or reconstructive transplantation, has revolutionized the treatment of complex tissue and functional defects. Despite arriving during an age in which the immunology of solid organ transplant rejection has been investigated in much detail, these transplants have offered new perspectives from which to explore the immunobiology of transplantation. VCAs have a number of unique molecular, cellular, and architectural features which alter the character and intensity of the rejection response. While much is yet to be clarified, an understanding of these distinct mechanisms affords new possibilities for the control of immune responses in an effort to improve outcomes after VCA transplantation.

Anti-HLA sensitization in extensively burned patients: extent, associated factors, and reduction in potential access to vascularized composite allotransplantation

Extensively burned patients receive iterative blood transfusions and skin allografts that often lead to HLA sensitization, and potentially impede access to vascularized composite allotransplantation (VCA). In this retrospective, single-center study, anti-HLA sensitization was measured by single-antigen-flow bead analysis in patients with deep, second- and third-degree burns over ≥40% total body surface area (TBSA). Association of HLA sensitization with blood transfusions, skin allografts, and pregnancies was analyzed by bivariate analysis. The eligibility for transplantation was assessed using calculated panel reactive antibodies (cPRA). Twenty-nine patients aged 32 ± 14 years, including 11 women, presented with a mean burned TBSA of 54 ± 11%. Fifteen patients received skin allografts, comprising those who received cryopreserved (n = 3) or glycerol-preserved (n = 7) allografts, or both (n = 5). An average 36 ± 13 packed red blood cell (PRBC) units were transfused per patient. In sera samples collected 38 ± 13 months after the burns, all patients except one presented with anti-HLA antibodies, of which 13 patients (45%) had complement-fixing antibodies. Eighteen patients (62%) were considered highly sensitized (cPRA≥85%). Cryopreserved, but not glycerol-preserved skin allografts, history of pregnancy, and number of PRBC units were associated with HLA sensitization. Extensively burned patients may become highly HLA sensitized during acute care and hence not qualify for VCA. Alternatives to skin allografts might help preserve their later access to VCA.

A critical analysis of rejection in vascularized composite allotransplantation: clinical, cellular and molecular aspects, current challenges, and novel concepts

Advances in microsurgical techniques and immunomodulatory protocols have contributed to the expansion of vascularized composite allotransplantation (VCA) with very encouraging immunological, functional, and cosmetic results. Rejection remains however a major hurdle that portends serious threats to recipients. Rejection features in VCA have been described in a number of studies, and an international consensus on the classification of rejection was established. Unfortunately, current available diagnostic methods carry many shortcomings that, in certain cases, pose a great diagnostic challenge to physicians especially in borderline rejection cases. In this review, we revisit the features of acute skin rejection in hand and face transplantation at the clinical, cellular, and molecular levels. The multiple challenges in diagnosing rejection and in defining chronic and antibody-mediated rejection in VCA are then presented, and we finish by analyzing current research directions and novel concepts aiming at improving available diagnostic measures.

Composite tissue transplantation

Composite tissue transplantation is an emerging new era in transplant medicine and has become a viable reconstructive option for patients with large and devastating tissue defects. Advances in microsurgical techniques, transplant immunology and the development of potent immunosuppressive agents have enabled the realization of such types of transplants. Over the past decade, a rapidly growing number of face and upper extremity transplantations have been performed worldwide with highly encouraging outcomes. However, despite the fact that surgical, immunological and functional results are highly encouraging, the need for long-term and high-dose immunosuppression to enable graft survival and to treat/reverse acute skin rejection episodes remains a pace-limiting obstacle towards wide spread application. In this chapter we review the history and development of this novel field, the functional and immunological outcomes based on the world experience, unique biological features of such transplants, mechanisms and treatment protocols for acute skin rejection, as well as novel concepts for immune modulation and tolerance induction.