TNF and neoplasm: In human leukemia cells, the CD137/CD137L interaction can also result in bidirectional signaling to suppress NK cell-mediated responses; CD137 recognition of CD137L on leukemic cells transmits inhibitory signals into the NK cell to impair cytokine production and cytotoxicity responses and CD137L engagement by CD137 induces the production of TNF and immunosuppressive interleukin (IL)-10 by the tumor cells (119).