PDCD1 and autoimmune thrombocytopenic purpura: In vitro studies have proved that PD-L1-Fc recombinant fusion protein (PD-L1-Fc, linking the extracellular domains of PD-1) increased T cell apoptosis and inhibited the activation and proliferation of T cells in ITP, suggesting the important role of PD-1 pathway in the pathogenesis of ITP (17).