Abstract 2778: Discovery and preclinical characterization of BAY 1905254 a novel immune checkpoint inhibitor for cancer immunotherapy targeting the immunoglobulin-like domain containing receptor 2 (ILDR2)

ILDR2 is a type I transmembrane protein belonging to the B7 family of immunomodulatory receptors with 98 % sequence identity between the extracellular domains of human and murine orthologues. The exact physiological role of ILDR2 is still unclear, but it has been implicated in the development of type 2 diabetes and the formation of tri-cellular junctions. Our detailed analyses reveal that ILDR2 is expressed in kidney, testis, liver, and lymph node fibroblastic reticular cells (FRC). The latter is particularly interesting since FRC belong to the CD45 - stromal population, a specialized cell subset located in the T cell zone. These cells are essential for recruitment of naive T cells and activated dendritic cells to the lymph node and have been reported to exhibit immuno-regulatory properties. Due to its structural similarity to members of the B7 family and due to its expression in FRCs, we speculated that ILDR2 might play a role e.g. in T cell priming and the initiation of antigen-specific T cell responses. In line with this, we and our collaborators from Compugen were able to show that an ILDR2 -Fc fusion protein is able to a) bind to activated (but not naive) T cells, b) suppress TCR-stimulated cytokine secretion and c) exhibit immunomodulatory effects in several models of autoimmune diseases, i.e. multiple sclerosis, rheumatoid arthritis, and type 1 diabetes. As a consequence, we set out to generate antibodies against this novel immuno-oncology target and describe here for the first time the characterization of BAY 1905254, a human/mouse cross-reactive IgG2 antibody blocking the immunosuppressive activity of ILDR2. BAY 1905254 specifically binds to ILDR2 but not to the closely related family members ILDR1 and ILDR3/LSR. It enhances antigen-specific T cell proliferation in vivo in an ovalbumin vaccination model with OT-I transgenic T cells. BAY 1905254 exhibits anti-tumor activity in different syngeneic mouse models with efficacy correlating with increasing mutational load. Furthermore, additive/synergistic anti-tumor effects can be observed in combination with either an anti-PD-L1 Ab, an immunogenic cell death inducing chemotherapeutic (Docetaxel) or tumor antigen immunization. Ex vivo analysis reveal that BAY 1905254 treatment results in increased intra-tumoral IFN-y levels and enhanced infiltration of CD45 + cells, e.g. of CD8α + dendritic cells (DCs). Interestingly, this DC population is known to play a crucial role in cross-presentation, thus, in the initiation of CD8 + T cell responses. In summary, BAY 1905254 is a function-blocking Ab able to counteract the immuno-suppressive function of the newly discovered immuno-oncology target ILDR2. The Ab exhibits in vivo efficacy both in monotherapy as well as in combination with various other approaches, and it is planned to advance BAY 1905254 into FiM trials in 2018. Citation Format: Julia Huetter, Uwe Gritzan, Ilona Gutcher, Sven Golfier, Wolf-Dietrich Doecke, Merlin Verena Luetke-Eversloh, Helge Roider, John Hunter, Andrew Pow, Spencer Liang, Zurit Levine, Ofer Levy, Ilan Vaaknin, Bertolt Kreft, Lars Roese. Discovery and preclinical characterization of BAY 1905254 a novel immune checkpoint inhibitor for cancer immunotherapy targeting the immunoglobulin-like domain containing receptor 2 (ILDR2) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2778.