CD137-mediated signals costimulate T cells and protect them from activation-induced apoptosis; they induce curative antitumor immunity and enhance antiviral immune responses in mice. In contrast, anti-CD137 agonistic mAbs can suppress T-dependent humoral immunity and reverse the course of established autoimmune disease. These results have provided a rationale for assessing the therapeutic potential of CD137 ligands in human clinical trials. In this study, we report that a single 200-μg injection of anti-CD137 given to otherwise naive BALB/c or C57BL/6 mice led to the development of a series of immunological anomalies. These included splenomegaly, lymphadenopathy, hepatomegaly, multifocal hepatitis, anemia, altered trafficking of B cells and CD8 T cells, loss of NK cells, and a 10-fold increase in bone marrow (BM) cells bearing the phenotype of hemopoietic stem cells. These events were dependent on CD8 T cells, TNF-α, IFN-γ, and type I IFNs. BM cells up-regulated Fas, and there was a significant increase in the number of CD8+ T cells that correlated with a loss of CD19+ and Ab-secreting cells in the BM. TCR Vαβ usage was random and polyclonal among liver-infiltrating CD8 T cells, and multifocal CD8+ T cell infiltrates were resolved upon termination of anti-CD137 treatment. Anti-CD137-treated mice developed lymphopenia, thrombocytopenia, and anemia, and had lowered levels of hemoglobin and increased numbers of reticulocytes.

Systemic lupus erythematosus (SLE) is a CD4+ T cell–dependent, immune complex–mediated, autoimmune disease that primarily affects women of childbearing age. Generation of high-titer affinity-matured IgG autoantibodies, specific for double-stranded DNA and other nuclear antigens, coincides with disease progression. Current forms of treatment of SLE including glucocorticosteroids are often inadequate and induce severe side effects. Immunological approaches for treating SLE in mice using anti-CD4 mAb’s or CTLA4-Ig and anti-CD154 mAb’s have proven to be effective. However, like steroid treatment, these regimens induce global immunosuppression, and their withdrawal allows for disease progression. In this report we show that lupus-prone NZB × NZW F1 mice given three injections of anti-CD137 (4-1BB) mAb’s between 26 and 35 weeks of age reversed acute disease, blocked chronic disease, and extended the mice’s lifespan from 10 months to more than 2 years. Autoantibody production in recipients was rapidly suppressed without inducing immunosuppression. Successful treatment could be traced to the fact that NZB × NZW F1 mice, regardless of their age or disease status, could not maintain pathogenic IgG autoantibody production in the absence of continuous CD4+ T cell help. Our data support the hypothesis that CD137-mediated signaling anergized CD4+ T cells during priming at the DC interface

No abstract

CD137 (4-1BB), 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 CD137 is 4-1BB ligand, a member of the TNF superfamily that is weakly expressed on naïve or resting B cells, macrophages, and DCs. Upon activation, the level of 4-1BBL 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 4-1BB 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 4-1BBL-deficient mice failed to demonstrate any loss of essential immunological function, or other noteworthy deficits, we have found that 4-1BBL-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.

No abstract