When T cells encounter antigens presented by pathogens or tumor cells, they become activated; OX40 is upregulated on these T cells and binds to its ligand [OX40L (CD134L; TNFSF4; CD252)], which is typically found on antigen-presenting cells, including but not limited to dendritic and B cells. This evidence concerns the gene TNFSF4 and neoplasm.