Vascularized composite allograft tolerance across MHC barriers in a large animal model.

Vascularized composite allograft (VCA) transplantation can restore form and function following severe craniofacial injuries, extremity amputations or massive tissue loss. The induction of transplant tolerance would eliminate the need for long-term immunosuppression, realigning the risk-benefit ratio for these life-enhancing procedures. Skin, a critical component of VCA, has consistently presented the most stringent challenge to transplant tolerance. Here, we demonstrate, in a clinically relevant miniature swine model, induction of immunologic tolerance of VCAs across MHC barriers by induction of stable hematopoietic mixed chimerism. Recipient conditioning consisted of T cell depletion with CD3-immunotoxin, and 100 cGy total body irradiation prior to hematopoietic cell transplantation (HCT) and a 45-day course of cyclosporine A. VCA transplantation was performed either simultaneously to induction of mixed chimerism or into established mixed chimeras 85-150 days later. Following withdrawal of immunosuppression both VCAs transplanted into stable chimeras (n=4), and those transplanted at the time of HCT (n=2) accepted all components, including skin, without evidence of rejection to the experimental end point 115-504 days posttransplant. These data demonstrate that tolerance across MHC mismatches can be induced in a clinically relevant VCA model, providing proof of concept for long-term immunosuppression-free survival.

Induction of tolerance to an allogeneic skin flap transplant in a preclinical large animal model.

Clinical composite tissue allotransplantation can adequately reconstruct defects that are not possible by other means. However, immunosuppressant toxicity limits the use of these techniques. Clinical attempts to reduce the amount of immunosuppression required by induction of an immunologically permissive state have so far been unsuccessful. The aim of this study was to induce tolerance in a preclinical large animal model. Donor hematopoietic stem cell (HSC) engraftment was induced by T-cell depletion, irradiation, and a short course of cyclosporine administered to the recipient, along with a hematopoietic cell infusion from a single haplotype major histocompatibility complex (MHC) mismatched donor. Skin was then allotransplanted from the donor. Both primarily vascularized skin flaps and secondarily vascularized conventional skin grafts were allotransplanted to investigate if the mode of transplantation affected outcome. Control animals received the skin allotransplants without conditioning. Tolerance was defined as no evidence of rejection at 90 days following transplantation. Conventional skin grafts only achieved prolonged survival (<65 days) in HSC-engrafted animals (P < .01). In contrast, there was indefinite skin flap survival with the achievement of tolerance in HSC-engrafted animals; this was confirmed on histology with donor-specific unresponsiveness on MLR and CML. Furthermore, a conventional skin donor graft subsequently applied to an animal tolerant to a skin flap was not rejected and did not trigger skin flap rejection. To our knowledge, this is the first time skin tolerance has been achieved across a MHC barrier in a large animal model. This is a significant step toward the goal of clinical skin tolerance induction.

Predictors of organ allograft tolerance following hematopoietic cell transplantation.

Using the miniature swine large animal model we have attempted to determine the relationship between tolerance and the presence of donor cells in the bone marrow, thymus and lineages of peripheral blood in a series of hematopoietic cell transplant recipients receiving delayed donor allografts without immunosuppression. Twenty-two animals receiving hematopoietic cell transplantation and a delayed organ allograft were analyzed. Assays for presence of donor CFUs in bone marrow (by PCR), thymic chimerism (by FACS and PCR/Southern Blot), peripheral blood chimerism (by FACS), and in vitro responsiveness to donor MHC were performed. Presence of donor BM CFUs, thymic chimerism and multilineage peripheral blood chimerism at the time of organ transplantation all correlated precisely with subsequent allograft tolerance (p < 0.001, p < 0.001, p < 0.005 respectively). These parameters were therefore accurate predictors (Positive Predictive Value (PPV) = 100% in all) of tolerance. In vitro assays of responsiveness were also highly associated (p < 0.002, p < 0.002 respectively), but were not as accurate predictors of subsequent organ tolerance (CML PPV = 80%). Engraftment, as indicated by the presence of donor derived CFU in the bone marrow, detectable thymic chimerism and multilineage peripheral blood chimerism are reliable predictors of subsequent donor allograft acceptance in hematopoietic cell transplant recipients.

Case-controlled study of patients with self-inflicted burns.

The main objectives of this study were to investigate whether patients with self-inflicted burns have larger burns, and a worse outcome, than patients with accidental burns. The secondary objective was to examine patient pre-injury characteristics to identify ways of preventing the burn occurring. A case-controlled study was performed: 36 deliberate self-burn patients were matched separately to two groups of accidental burn patients. The first group was used to compare burn severity. Patients were matched for age and sex; they were excluded if they had a psychiatric diagnosis, or a non-burn injury. The second group was used to compare outcome. The same matching and exclusion criteria were used as in the first group, with the addition of burn-size. Deliberate self-burn patients have significantly larger burns (p<0.01; median total body surface area (TBSA) 10% versus 1.5%) than accidental burn patients. They also stay in hospital longer, even when matched for burn-size (p<0.02; median stay 15 days versus 9 days). Self-inflicted burns occurred in supervised environments in 28% of cases. The number of deliberate self-burns could be reduced with simple interventions such as restricting smoking in hospitals and prisons, and also by identifying high-risk patients. The poor outcome from deliberate self-burns could be improved by well-coordinated multidisciplinary patient management with early psychiatric team involvement.

Don't miss HIT (heparin induced thrombocytopenia).

Thrombocytopenia following a burn injury can cause serious complications. There are several possible causes including the burn itself, drugs, sepsis and disseminated intravascular coagulation (DIC). A case report of a patient who developed heparin induced thrombocytopenia (HIT) whilst on haemofiltration for acute renal failure is presented. The aetiology of thrombocytopenia in a burns patient and its management is discussed. The key to effective treatment of thrombocytopenia is identification of the cause. HIT is an important diagnosis to include in the differential.

The hitch stitch: an obsolete neurosurgical technique?

The objective was to assess the efficacy of dural tenting sutures as a prophylactic measure against extradural haemorrhage following craniotomy. A comparison was made of postoperative extradural haemorrhage between a surgeon always using tenting sutures and a surgeon who never uses them. The subjects consisted of 130 adult patients, 44 with postoperative scans, with normal blood coagulation who underwent elective supratentorial craniotomy (September 1998 to December 2000). Outcome measures were haematoma volume and midline shift as measured on CT and reoperation due to extradural haematoma. The group using tenting sutures had larger median extradural haematoma (2.5 vs 2.0 ml) and midline shift (3 vs 0 mm) than the omitting group. These differences were not significant (P = 0.74 and 0.84). Reoperation due to extradural haemorrhage occurred in 3.6% of the group using tenting sutures and in 0% of the group omitting them. Prophylactic dural tenting sutures do not reduce the size of extradural haematomas in this study. A prospective, randomized trial is needed to eliminate surgeon bias.