OP0197 CGEN-15001, A Novel Negative Co-Stimulator Fusion Protein is Effective in the Collagen-Induced Arthritis Mouse Model of Rheumatoid Arthritis

Background CGEN-15001 is a fusion protein composed of the extracellular domain of CGEN-15001T fused to IgG Fc. CGEN-15001T was recently identified as a novel member of the B7/CD28 costimulatory family based on shared bioinformatic characteristics with known members of this family. Objectives To study the effect of CGEN-15001 on T cell activation in vitro, and to evaluate its efficacy in the murine collagen-induced arthritis (CIA) model. Methods Murine naive CD4 + T cells were activated with anti-CD3 and either CGEN-15001 or control proteins. The effect of CGEN-15001 on activation marker expression and cytokine secretion was evaluated after 48hrs of incubation, while effects on cell division and apoptosis were evaluated after 96hrs. The effect of CGEN-15001T on human CD4 + and CD8 + T cells was studied using a similar experimental system. Furthermore, the effect of CGEN-15001T was tested utilizing HEK-293 stably transfected cells expressing CGEN-15001T. CIA was induced by immunizing DBA/1 mice with type II bovine collagen in CFA. Mice were injected i.p. with CGEN-15001, TNFR-Ig, CTLA4-Ig or Ig control at 4mg/kg, 3 times/ week for 10 days. Treatment started at disease onset and mice were scored daily for arthritis severity. On day 10 of arthritis, mice were sacrificed and paws and sera were collected. Alternatively, CIA was induced by boosting mice with type II collagen in CFA 21 days following immunization. Mice were treated i.p. with CGEN-15001, TNFR-Ig or control Ig, at 10mg/kg, Q2D on days 18-33 (“semi-established” treatment). Results Cell membrane expression of CGEN-15001T by HEK-293 inhibited the activation of Jurkat cells. In addition, CGEN-15001 inhibited murine CD4 + T cell activation, as manifested by inhibition of cell proliferation, IL-2 and IFNγ secretion, and expression of the early activation markers, CD69 and CD62L. CGEN-15001 also inhibited activation of human CD4 + and CD8 + T cells as demonstrated by reduction in CD69 expression. In the CIA model, CGEN-15001 demonstrated a potent therapeutic effect following administration to mice with existing disease, as shown by significant reduction in clinical score and joint swelling compared to mice treated with Ig control. In addition, CGEN-15001 treatment resulted in an increase in the collagen-specific IgG1/IgG2a ratio in the serum. This observation is in line with the Th1/Th17 to Th2 shift that was observed in vitro and in the RR-EAE model of MS. Furthermore, histological analysis of the arthritic joints showed reduced inflammation and joint erosion in CGEN-15001 treated mice compared to controls. Treatment with CGEN-15001 in a semi-established manner before disease onset resulted in inhibition of disease progression which was more pronounced than that of the positive control, TNFR-Ig. Conclusions CGEN-15001 has an immunomodulatory effect on T cell activation. The therapeutic impact of CGEN-15001 in the CIA model as well as previous data showing long term efficacy of CGEN-15001 in murine models of multiple sclerosis, support the therapeutic potential of CGEN-15001 in the treatment of rheumatoid arthritis and other autoimmune diseases. The therapeutic use of negative co-stimulators aimed at restoring and maintaining immune balance is a potential efficacious and safe approach for the treatment of autoimmune diseases. Disclosure of Interest I. Hecht Employee of: Compugen, K. McNamee Grant/research support from: Compugen, I. Vaknin Employee of: Compugen, A. Oren Employee of: Compugen, G. Rotman Employee of: Compugen, N. Tarcic Employee of: Compugen, E. Neria Employee of: Compugen, R. Williams Grant/research support from: Compugen