PDCD1 and Arthritis: While the PD-1/PD-L1 pathway is not the only pathway implicated in autoimmunity, peptides optimized from the MN1.4 scaffold could be used to treat several common diseases shown to have deficient PD-1/PD-L1 signaling, such as diabetes and arthritis, in addition to autoimmune diseases, such as those caused by conventional mAb-based immunotherapies (31, 32).