Anti-CD137 antibodies in the treatment of autoimmune disease and cancer

CD137 (4-IBB), is an inducible T-cell costimulatory receptor and a member of the tumor necrosis factor receptor (TNFR) superfamily. It is expressed on activated T cells and activated natural killer (NK) cells, but is constitutively expressed on a population of splenic dendritic cells (DCs). The natural counter receptor for CD 137 is 4-IBB ligand, a member of the TNF superfamily that is weakly expressed on naive or resting B cells, macrophages, and DCs. Upon activation, the level of 4-IBBL expression increases on these cells. In T cells CD137-induced signals lead to the recruitment of TRAF family members and activation of several kinases, including ASK-1, MKK, MAPK3/ MAPK4, p38, and JNK/SAPK. Kinase activation is then followed by the activation and nuclear translocation of several transcription factors, including ATF-2, Jun, and NF-kappaB. CD137-mediated T-cell costimulation as measured by enhanced proliferation and cytokine production can be induced by anti-CD137 monoclonal antibodies (MAbs) or by employing immobilized 4-IBB ligand. In addition to augmenting suboptimal TCR-induced proliferation, CD137-mediated signaling protects T cells, and in particular, CD8(+) T cells from activation-induced cell death (AICD). Although studies with CD137-deficient or 4-IBBL-deficient mice failed to demonstrate any loss of essential immunological function, or other noteworthy deficits, we have found that 4-IBBL-deficient mice failed to generate a strong antiviral immune response following lymphocytic choriomeningitis virus (LCMV) peptide vaccination. We further found that although compromised, the immune response to LCMV vaccination in these mice could be fully restored by injecting them with anti-CD137 MAbs at the time of vaccination. Finally, we have found that injecting normal mice with anti-CD137 MAbs had profound effects on their ability to develop immune responses to allo- and autoantigens. The results of these studies discussed in this article provide a rationale for assessing the potential use of anti-CD137 MAbs for therapeutic purposes.