ILDR2 is a member of the Ig superfamily, which is implicated in tricellular tight junctions, and has a putative role in pancreatic islet health and survival. We recently found a novel role for ILDR2 in delivering inhibitory signals to T cells. In this article, we show that short-term treatment with ILDR2-Fc results in long-term durable beneficial effects in the relapsing-remitting experimental autoimmune encephalomyelitis and NOD type 1 diabetes models. ILDR2-Fc also promotes transplant engraftment in a minor mismatch bone marrow transplantation model. ILDR2-Fc displays a unique mode of action, combining immunomodulation, regulation of immune homeostasis, and re-establishment of Ag-specific immune tolerance via regulatory T cell induction. These findings support the potential of ILDR-Fc to provide a promising therapeutic approach for the treatment of autoimmune diseases.

The B7-like protein family members play critical immunomodulatory roles and constitute attractive targets for the development of novel therapies for human diseases. We identified Ig-like domain-containing receptor (ILDR) 2 as a novel B7-like protein with robust T cell inhibitory activity, expressed in immune cells and in immune-privileged and inflamed tissues. A fusion protein, consisting of ILDR2 extracellular domain with an Fc fragment, that binds to a putative counterpart on activated T cells showed a beneficial effect in the collagen-induced arthritis model and abrogated the production of proinflammatory cytokines and chemokines in autologous synovial-like cocultures of macrophages and cytokine-stimulated T cells. Collectively, these findings point to ILDR2 as a novel negative regulator for T cells, with potential roles in the development of immune-related diseases, including autoimmunity and cancer.

Abstract B7 proteins play critical immunomodulatory roles and provide attractive targets for development of novel therapies for cancer and autoimmunity, both of which involve improper immune tolerance. A major medical need in autoimmunity is restoration of immune tolerance to self-antigens. CGEN-15001, an Fc fusion protein of a novel B7-like protein that we identified, regulates immune homeostasis by inhibiting Th1/Th17 responses while enhancing Th2 and anti-inflammatory cytokines such as IL-10, and promoting iTreg differentiation. This was observed in vitro using murine cells and in PBMCs of healthy donors and MS patients, as well as in vivo in R-EAE model and in HY transplantation model. Short-term administration of CGEN-15001 in R-EAE model of MS and in NOD model of T1D resulted in durable therapeutic effects which lasted long after cessation of treatment, suggestive of restoration of immune tolerance. Treg blockade with anti-IL-10 or anti-TGFβ, and transient Treg neutralization with anti-CD25 abolished these therapeutic effects. Importantly, transferring CD4+ T cells from CGEN-15001-treated mice to naïve recipients protected them from R-EAE induction in Ag-specific manner, demonstrating induction of Ag-specific tolerance. In contrast, tolerance transfer was not achieved following CTLA4-Ig treatment in spite of the remission it induced in the donor mice. In summary, CGEN-15001 has a unique mode of action, combining immunomodulation and regulation of immune homeostasis, as well as re-establishment of Ag-specific tolerance via enhancing Treg differentiation, leading to durable disease amelioration. These findings support the potential of CGEN-15001 to provide a promising therapeutic approach across autoimmune diseases.

Meeting abstracts The past few years have witnessed a renaissance in the field of immuno-oncology largely due to the clinical success in targeting the immune checkpoints CTLA-4 and PD-1. Towards identification of novel immune checkpoint drug targets we developed a dedicated predictive discovery

We discovered a novel immune checkpoint protein based on characteristics of the B7/CD28 family. CGEN-15001 is a fusion protein composed of the extracellular domain of this protein fused to IgG Fc. CGEN-15001 inhibits T cell activation, demonstrates immunomodulation by inhibiting pro-inflammatory Th1 and Th17 responses while promoting anti-inflammatory IL-10 and Th2 responses, and enhances iTreg differentiation. CGEN-15001 is efficacious in animal models of autoimmunity such as multiple sclerosis (MS), rheumatoid arthritis, type1 diabetes (T1D) and psoriasis. In the EAE model of MS and in the NOD model of T1D, short 2-week treatment with CGEN-15001 resulted in long term inhibition of disease. In the T1D model, mice treated with CGEN-15001 retained normal blood glucose levels18 weeks after cessation of treatment. To further study tolerance induction, the H-Y minor Ag mismatch bone marrow transplantation model was used. CGEN-15001 treatment resulted in graft survival and increase in Tregs, indicating donor specific tolerance induction. The prolonged therapeutic responses in models of autoimmunity and the prevention of graft rejection, imply establishment of immune tolerance by CGEN-15001. Taken together, the mode of action of CGEN-15001 that combines inhibition of autoreactive cells, immunomodulation and restoration of immune tolerance, suggests it should provide long standing and safe therapy for autoimmune diseases.

Meeting abstracts Members of the B7/CD28 family of immune checkpoints, such as CTLA4, PD1 and PDL-1, play critical roles in T cell regulation and have emerged as promising drug targets for cancer immunotherapy. We hypothesize that additional novel members of the B7/CD28 family play a role as

Abstract Immune checkpoints, such as CTLA4 and PD-1, have emerged as promising drug targets for cancer immunotherapy. We hypothesize that additional novel members of the B7/CD28 family play a role in T cell regulation and thus may serve as targets for therapeutic mAbs. However, the discovery of novel family members is challenging since proteins of the immune system, including proteins of the B7 protein In order to identify novel members of the B7/CD28 protein family, Compugen has developed a discovery approach integrating gene and protein information with extensive expression data, and has identified nine novel membrane proteins that possess characteristics of the B7/CD28 protein family members and are therefore predicted to play a role in T cell co-stimulation. In order to validate our predictive discovery findings, we evaluated the effect of our proteins on immune cells, particularly T cells. For that goal, we expressed the proteins on the cell surface upon ectopic expression, and also produced fusion proteins consisting of the extracellular domain of the predicted proteins, fused to an IgG Fc domain. Here we present results obtained for two of our novel proteins, CGEN-15001T and CGEN-15022. Both display robust inhibition of T cell activation. Interestingly, CGEN-15001, one of the Fc-fused proteins, leads to increased levels of anti-inflammatory cytokines such as IL-4 and IL5, while reducing pro-inflammatory cytokines such as IFN-γ and IL-17. In addition, CGEN-15001 was found to enhance iTregs differentiation. Furthermore, these molecules showed therapeutic efficacy in mouse models of multiple sclerosis and rheumatoid arthritis. To investigate the potential of these membrane proteins as drug targets for treatment of cancer we have performed extensive IHC studies, on a variety of healthy and malignant tissues. Both CGEN-15001T and CGEN-15022 were found to be expressed in numerous types of cancers, each showing a unique pattern of expression. CGEN-15001T, in addition to its expression on tumor cells, was found to be expressed on tumor infiltrating immune cells, especially on Macrophages and Mast cells. Based on the immunomodulatory activities and the expression pattern on malignant and immune cells, CGEN15001T and CGEN15022 may serve as mAb targets for cancer immunotherapy. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B291. Citation Format: Gady Cojocaru, Ofer Levy, Amir Toporik, Liat Dassa, Iris Hecht, Ilan Vaknin, Sergey Nemzer, Tania Pergan, Amit Novik, Shirley Sameah-Greenwald, Anat Oren, Zohar Tiran, Peter Steinberger, Joseph Podojil, Nora Tarcic, Eyal Neria, Galit Rotman, Zurit Levine. Identification of novel immune checkpoints and their implementation as mAb targets for cancer immunotherapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B291.