PDCD1 and rheumatoid arthritis: However, despite the development of irAE following PD-1 pathway blockade,28 PD-1 may yet serve as a therapeutic target in the early stages of autoimmunity through pathway agonism.6 Our demonstration here of PD-1hi Tph cells in early RA indicates that compared with existing therapeutics, targeting T cells agonistically through PD-1 may inhibit both T cell-mediated and autoreactive B cell-mediated tissue damage during early RA disease progression.