Effect of cyclosporine A treatment in vitro on pancreatic islet allograft rejection.

Abstract SINCE significant progress has been made in the isolation and purification of islets of Langerhans, 1 several clinical trials of islet transplantation in type I (insulin-dependent) diabetic patients 2,3 have been performed worldwide. The success of islet transplantation depends on engraftment (prevention of primary nonfunction) and on the prevention of allograft rejection and recurrence of autoimmune aggression of the pancreatic beta cells. 4 In primary nonfunction, a critical role is thought to be played by inflammatory mediators such as locally produced cytokines and free radicals (nitric oxide, NO). It has been suggested that primary nonfunction results from a cell-mediated host-immune response of rapid onset caused by macrophages and their byproducts interleukin-1 and nitric oxide (NO). 5 Recently, it has been shown that during insulitis which produces the pancreatic beta-cell destruction associated with autoimmune diabetes in NOD (nonobese spontaneous diabetic) mice, the release of interleukin 1 (IL-1) by nonendocrine cells of the islet induces the expression of inducible nitric oxide synthase (iNOS) by beta cells which results in the inhibition of beta cell function by the production of NO. 6 Adhesion molecules are thought to influence the first interaction between host leukocytes which express very late activation antigen-4 (VLA-4) and leukocyte function associated antigen-1 (LFA-1), and graft vascular endothelial cells, with the expression of the counterreceptors vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). 7,8 It has been shown that in the inflammatory response, the cytokines TNFα and IL-1β induce the concurrent expression of VCAM-1, ICAM-1, and E-selectin in endothelial cells. 8 Furthermore, it has been suggested that cytokines by activating the inducible form of the enzyme iNOS and the production of nitric oxide (NO), could modulate the expression of adhesion molecules on endothelial cells and leukocytes. 9 By mediating the initial leukocyte/endothelial cell interactions, adhesion molecules may play an important role in graft rejection, mediation of infiltration into the graft, and dissemination of the antigenic message to the lymphoid tissues of the host. Many different adhesion molecules are up-regulated during rejection. Treatment of transplant recipients with monoclonal antibodies (MAb) against accessory adhesion molecules, such as LFA-1 and ICAM-1, has resulted in either a prolongation of transplant survival or the induction of tolerance in some animal models. 7 Treatments with monoclonal antibodies against VLA-4 and LFA-1 have produced a significant prolongation of rat islet allograft survival, 10 and the in vitro pretreatment of human islets with anti-human ICAM-1 inhibited xenograft rejection in nonimmunosuppressed diabetic mice. 11 We hypothesise that in vitro pretreatment of isolated pancreatic islets with cyclosporin-A (CsA), could exhibit a modulatory effect by inhibiting the adhesion molecules expression of ICAM-1, LFA-1, and VLA-4 of rat islet endocrine cells, endothelial cells, and passenger leukocytes present within the islets and, therefore, abrogate islet allograft rejection in a fully histoincompatible model. 9 We have, therefore, performed this study with the aim of preventing rat islet allograft rejection by the in vitro pretreatment of donor islets with Cs A. Furthermore, we have characterized the subpopulations of inflammatory cells infiltrating the rejected islets and the MHC class I antigens, II and adhesion molecules expression in infiltrating cells and in grafted islet cells.