Withdrawal of immunosuppression: implications for composite tissue allograft transplantation

Reepithelialization of Orthotopic Tracheal Allografts Prevents Rejection after Withdrawal of Immunosuppression

Prior work has demonstrated that immunosuppressed orthotopic tracheal allografts undergo progressive reepithelialization over a 48-day period with recipient-derived tracheal epithelium. We hypothesized that reepithelialization of tracheal allografts would prevent rejection after withdrawal of immunosuppression. BALB/c murine tracheal grafts were transplanted orthotopically into either syngeneic or allogeneic C57/BL6 recipients. The recipients were either not immunosuppressed, immunosuppressed with cyclosporine A (10 mg/kg per day) continuously, or immunosuppressed for 48 days and then withdrawn from immunosuppression. The grafts were assessed for acute and chronic rejection 10 days and 50 days after immunosuppression withdrawal. The immunosuppressed allograft recipients maintained a ciliated epithelium acutely and chronically after immunosuppression withdrawal. Ten days after immunosuppression withdrawal, there was a mild cellular infiltrate, which resolved 50 days after withdrawal. Electron microscopy, lymphocyte subpopulation assays, and lamina propria analysis demonstrated that immunosuppression withdrawal did not result in tracheal allograft rejection. In vitro and in vivo assessments did not demonstrate evidence of systemic or local immune tolerance. We conclude that reepithelialization of orthotopic tracheal allografts with recipient-derived mucosa prevents rejection of allograft segments. Tracheal transplantation may require only transient immunosuppression, which can be withdrawn after tracheal reepithelialization.

Experience with nerve allograft transplantation

Nerve allograft transplantation should be used for the repair of devastating peripheral nerve injuries that cannot be reconstructed through traditional means such as autologous nerve grafting or nerve transfer procedures. The risks of required systemic immunosuppression, although only temporary for nerve allograft recipients, preclude widespread use of this treatment modality. Translational research has led to several advancements in this field including the use of preoperative allograft cold preservation in University of Wisconsin organ preservation solution and inclusion of tacrolimus as part of the immunosuppressive regimen. Investigation of how to further diminish nerve allograft immunogenicity, speed neuroregeneration by use of agents such as tacrolimus, and promote preferential motor regeneration will further advance this field with the goal of restoring optimal function while minimizing patient morbidity.

Anatomic bases of vascularized elbow joint harvesting to achieve vascularized allograft

In order to later make precise the operative technique of free vascularized elbow allograft transfer, the anatomic conditions necessary for the success of such an operation are reviewed. The exact topography of the nutrient foramina of the humerus, radius, and ulna has been specified on 102 dry bones. The osseous resection at the recipient will have to be carried out on these aspects: nutrient foramina of the three bones of the elbow (at 9 cm from medial epicondyle for the humerus; at 8 cm for the two bones of forearm) in order to preserve diaphysary vascularization of the recipient. A study of arterial and venous vascularization carried out on 18 anatomic specimens showed that the osseous ends were irrigated by a periosteal arterial network and were drained in the centromedullary cavities. Systematization of the arteriovenous blood supply of the distal end of the humerus and proximal ends of the two forearm bones is proposed after dissection of 18 anatomic specimens. Arterial periosteal territories are defined. The importance of each peri articular arteriole is estimated according to the surface of its respective section. A radial, constant, and musculoperiosteal collateral artery from the brachial artery is described. It accounts for 12% (+/- 3%) of the total contribution. The recurrent radial artery is the most significant: 31% (+/- 9%) of the total contribution. The profunda brachii artery is negligible: 4% (+/- 2%) of the total contribution. As well for vascular as mechanical reasons, osteosynthesis will have to be carried out using screwed plates, the optimal location of which is specified according to the arterial periosteal cartography. Ulnar and radial nerves and, to a lesser extent, the median nerve can be harvested "en bloc" preserving their vascular supply in order to make vascularized grafts of them. Free vascularized elbow allograft transfer is technically possible, if one respects these anatomic bases.

Sirolimus: a comprehensive review

Sirolimus (Rapamune), Wyeth-Ayerst, Madison, NJ) is a new, potent, immunosuppressant that is emerging as a foundation for long-term immunosuppressive therapy in renal transplantation. The drug acts during both co-stimulatory activation and cytokine-driven pathways via a unique mechanism: inhibition of a multifunctional serine-threonine kinase, mammalian target of rapamycin (mTOR). Although there is no a priori reason to assume it, sirolimus displays a synergistic interaction to enhance the efficacy of cyclosporin A (CsA). In trials wherein the concentrations of CsA and sirolimus were tightly controlled, rates of acute rejection episodes were < 10%, despite markedly reduced exposures to each agent. In pivotal multi-centre blinded dose-controlled trials, the rates of acute rejection episodes within 12 months following administration of 2 or 5 mg/day sirolimus in combination with CsA and steroids were reduced to 19 and 14%, respectively. Since the inhibitory effect of sirolimus disables virtually all responses to cytokine mediators due to the widespread involvement of mTOR in multiple signalling pathways, the agent is likely also to retard proliferation of endothelial and vascular smooth muscle cells, an important component of the immuno-obliterative processes associated with chronic rejection. The advantages of this unique therapeutic action combined with an intrinsic lack of nephrotoxicity are counterbalanced by myelosuppressive and hyperlipidaemic side effects. Ongoing studies are assessing whether the long-term benefits of sirolimus to permit reduction in exposure to or elimination of calcineurin inhibitors ameliorate the progression of chronic nephropathy, the condition that erodes long-term renal transplant survival.

Potential of costimulation-based therapies for composite tissue allotransplantation

Clinical success has not been routinely achieved for composite tissue allotransplantation (CTA). Although most of the technical details of CTA have been overcome, the immunological aspects of these procedures have proved complex. Many traumatic conditions requiring CTA contraindicate acute global immunosuppression. Moreover, the risk of long-term immunosuppression is difficult to reconcile with non-life-threatening defects that can be adequately palliated. Recently, several successful immunomodulating strategies have been introduced for solid organ transplantation. They include therapies that alter costimulatory signals at engraftment. One approach, using treatment with a monoclonal antibody directed against CD154, has shown promise in rodent and nonhuman primate models and is discussed as a potential strategy for CTAs.

Anaesthesia for patients with a transplanted organ

Increasing numbers of individuals leading normal lives have transplanted organs. They may appear in any hospital for treatment of trauma or general diseases. Common anaesthesia methods can be used for these patients, but safe conduct of anaesthesia requires knowledge of the immunosuppression, risk factors, and altered physiology or drug actions. This article reviews the anaesthesia-related literature on patients with transplanted organs.