Abstract 2968: Development of anti-APP antibody targeting APP/CNTN4 axis as a novel cancer immunotherapy

Immunotherapeutic treatment has profoundly improved the clinical outcomes in patients with advanced cancers. However, most patients still have not responded to immune checkpoint inhibitor (ICI) treatment. Thus, it is still urgent to find novel treatments for patients who have no response to ICI and acquire ICI resistance. Amyloid precursor protein (APP) is a type I transmembrane protein expressed in various cell types. It has primarily been known as a key molecule in brain-related diseases such as Alzheimer’s. However, the function of APP in regulating T cell activity has yet to be elucidated. Previously, we identified that APP expressed in T cells is a binding partner protein of a novel immune checkpoint protein contactin 4 (CNTN4), and APP is a central molecule for conveying immunosuppressive signal of CNTN4 to T cells through the investigation using APP knocked-out T cells. Here we further confirmed that APP had a mechanism of action to weaken TCR signaling by reducing adhesion capacity to cancer cells even with extracellular domain regardless of intracellular domain. When APP was knocked out on CD4+ or CD8+ T cells, the conjugation of T cells with CT26 murine colorectal cancer cells was maintained better than APP WT T cells, and the increased conjugation induced improved T cell-mediated cytotoxicity on CT26 cancer cells. With the anti-APP monoclonal antibody generated by single B cell screening using rabbits, we also explored APP as a potential cancer immunotherapeutic target like CNTN4. Anti-APP antibody bound explicitly to APP recombinant protein without off-target binding and strongly bound to HEK293 overexpressing APP. Moreover, the anti-APP antibody, which inhibited the interaction between APP and CNTN4 more, showed better anti-tumor efficacy in the syngeneic mice model. However, the anti-APP antibody did not affect tumor growth in the immune-deficient mice model, suggesting that the anti-APP antibody shows anti-tumor activity by immunomodulation. To further investigate the immune modulatory function of T cell subsets in tumor-infiltrating lymphocytes by anti-APP antibody treatment, we analyzed the proportion of T cells, Treg cells, and CD8+ T cells expressing granzyme B and perforin in tumor tissues. Collectively, an anti-APP antibody, a therapeutic monoclonal antibody targeting the APP/CNTN4 axis, has the potential for a significant breakthrough in anticancer therapy. Citation Format: Mi Young Cha, Youngeun Ha, Bu-Nam Jeon, Hyunuk Kim, Yunyeon K