As an example, transforming growth factor-β1 (TGF-β1) increases the expression of the programmed cell death-1 (PD-1) receptor by enhancing antigen-driven PD-1 gene transcription through Smad3 transcriptional activation in T cells in vitro and in tumor-infiltrating lymphocytes in vivo (23). The gene discussed is PDCD1; the disease is neoplasm.