Preservation and transplantation of the small intestine. Physiological and immunological studies in the rat

Abstract

Small bowel transplantation is evolving as a therapeutic alternative for patients suffering from short bowel syndrome. The outcome of intestinal transplantation has recently improved, but several problems still remain. This thesis is based on rat experiments with the aims to - evaluate continuous in vitro perfusion of the rat small intestine as a method to study ischemia/reperfusion injury and to minimise its adverse effects. - determine the integrated functional capacity of the graft and the nutritional status of the host. - analyse migrational patterns of host and donor T lymphocytes preceding graft rejection. - evaluate blockade of the B7-CD28/CTLA4 pathway by CTLA4-Ig as a means to induce graft specific tolerance in small bowel transplantation. Continuous in vitro perfusion was performed in a system with the possibility of regulating temperature, flow rate and oxygenation of the perfusate, which was delivered to the intestinal lumen and/or the vasculature. The effect of ischemia/reperfusion injury on the intestinal graft was evaluated by studies of mucosal morphology, microvascular immunocytochemistry and gut barrier function after preservation, as well as by macroscopic appearance of the graft and survival of the host posttransplantation. In functional and metabolic studies of intestinal transplantation weight gain of the host and wet weight of muscle groups and intraabdominal fat depots were compared between control, transplanted, sham and short bowel operated animals. T cell migrational patterns were studied by flow cytometry, determining the proportion of host/graft CD4+ and CD8+ T cells in graft and recipient mesenteric lymph nodes of an allogeneic and physiological transplant model. Treatment with CTLA4-Ig and administration of IgG were compared in transplanted animals by determining survival rate of the host, degree of inflammation analysed by histology and the presence of macrophages and CD4+ T cells in the graft. Continuous in vitro perfusion of the intestinal graft with concomitant oxygenation at 6°C minimised mucosal damage and gut barrier dysfunction and is a valuable tool to study the pathophysiology of hypoperfusion. However, damage to the graft circulation is a limitation in intravascular perfusion and no long-term survival of animals transplanted with grafts preserved for 20 h was recorded. In the functional studies, the transplanted animals had a normal weight gain, but when fed high fat diet there was a reduction in wet weight of fat depots. Thus, small bowel transplantation is capable of overcoming the short bowel syndrome of the host and only when challenged by high fat diet an altered fat metabolism was seen. Preceding graft rejection there was a shift from host to graft T cell predominance in the transplant on postoperative day four, a T lymphocyte migrational pattern possible to develop for diagnostic purposes. Administration of CTLA4-Ig to the transplanted animal induced increased survival, reduced the degree of inflammation in the graft, but did not result in long-term graft specific tolerance.