TNFSF9 and cancer: These events were dependent on increasing CD8 T lymphocytes.22, 23 Expression of CD137 ligand (CD137L) has been found on activated T cells, B cells, dendritic cells, and macrophages.24, 25 Furthermore, CD137L is constitutively expressed on cancer cell lines, and, when T cells were cocultured with carcinoma cells, the expression of CD137L resulted in higher levels of IFN‐γ production by the activated T cells.26