The roles of the new negative T cell costimulatory pathways in regulating autoimmunity

The B7 family of T cell costimulatory molecules has recently acquired several new members. Some of these are activating while others are inhibitory. In this review, we will focus on the novel inhibitory pathways with particular emphasis on the PD-1:PD-L pathway. Understanding the mechanisms of these pathways has implications for development of novel treatment strategies for autoimmune disease, transplantation, tumor immunotherapy, and vaccine development.