CD45 is a family of transmembrane protein tyrosine phosphatases exclusively expressed by hematopoietic cells and critically involved in the regulation of T cell activation signals, We now demonstrate that three 100-mu g doses of antiCD45RB mAb MB23G2 can induce long-term engraftment of islets into major histcompatibility complex-disparate chemically diabetic mice, Long-term graft survivors (>120 days) were tolerant to new islet allografts from the original donor strain, MB23G2 induced a temporary decrease in number circulating leukocytes but had no effect on leukocyte number in other lymphoid compartments, Histologic examination...