CD137-Mediated T Cell Co-Stimulation Terminates Existing Autoimmune Disease in SLE-Prone NZB/NZW F1 Mice

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Abstract
T cell receptor recognition of antigen and major histocompatibility complex (signal 1) and T cell co-stimulation (signal 2) are essential for full T cell activation, differentiation, and survival of naïve and activated T cells. The proto-typical T cell co-stimulatory receptor, CD28, is a constitutively expressed type I integral transmembrane protein and member of the Ig superfamily. Since its discovery, additional T cell co-stimulatory receptors have been identified, a number of which belong to the tumor necrosis factor receptor superfamily. Included within this group is CD137 (4-1BB), an activation-inducible, type I transmembrane protein. Co-stimulation of T cells through CD137 effectively up-regulates CD8 T cell activation and survival. Although CD4(+) T cells are efficiently activated through the T cell receptor and CD137 receptor, it provokes CD4(+) T cell anergy and blockade of T-dependent humoral immune responses. Therefore, we tested whether agonistic anti-CD137 monoclonal antibodies (mAbs) would be effective in blocking the induction or progression of B cell dependent autoimmune disease. Herein, we demonstrate the protective effect of agonistic anti-CD137 mAbs in blocking systemic lupus erythematosus (SLE) disease progression in NZB/W F1 mice. Protection from SLE following anti-CD137 mAb treatment is not confined to rescuing mice from disease progression; rather, it fully protects young mice from developing any symptoms of disease. We further found that treatment of proteinuric mice with anti-CD137 blocks ongoing anti-dsDNA autoantibody production.