Factors controlling successful islet engraftment. The successful engraftment of transplanted islets is determined by both the ability to form new blood vessels and the capacity to limit apoptosis induced by both extrinsic (induced by extracellular inducers, such as inflammatory cytokines) and intrinsic (induced by intrinsic factors, such as hypoxia and nutrient deprivation) pathways. Proangiogenic factors such as VEGF, Ang-1, and ephrin promote angiogenesis. By contrast, antiangiogenic factors such as TSP-1 reduce this process.
