Abstract 6082: Enhanced NK cell reactivity with Fc-optimized B7-H3 antibody for colorectal and non-small cell lung cancer

Abstract Colorectal cancer (CRC) and non-small cell lung cancer (NSCLC) are among the deadliest cancers worldwide, especially in advanced stages with limited treatment options. While immune checkpoint inhibitors (ICIs) targeting PD-1/PD-L1 have shown significant potential, their efficacy is limited to a small subset of CRC patients with microsatellite instability-high (MSI-H) tumors, and their use in NSCLC is often limited by severe side effects, further restricting their applicability. This underscores the urgent need for alternative immunotherapeutic approaches employing novel targets to expand clinical benefit. Here, we present a novel strategy exploiting natural killer (NK) cell mediated antibody-dependent cellular cytotoxicity (ADCC) using a monoclonal antibody (mAb) targeting B7-H3 (CD276). B7-H3, a B7 family immune checkpoint protein, is overexpressed in several tumor types, including CRC and NSCLC, but minimally expressed in normal tissues, making it an ideal target for cancer immunotherapy. Our engineered B7-H3 mAb, 8H8, was modified by introducing amino acid substitutions (S239D/I332E) in the Fc region to create the Fc-optimized variant 8H8-SDIE. This variant shows increased affinity for CD16 on NK cells, thereby enhancing ADCC potential. Preclinical characterization demonstrated robust B7-H3 expression and specific binding of 8H8-SDIE to CRC (n=5) and NSCLC (n=3) cell lines, with saturation at approximately 1 µg/mL. Co-culture of allogeneic peripheral blood mononuclear cells (PBMCs) with B7-H3-positive CRC and NSCLC cells confirmed that 8H8-SDIE significantly activated NK cells, as evidenced by increased expression of CD69 and CD25. Upregulation of CD107a further indicated NK cell degranulation. Additional analyses showed that 8H8-SDIE treatment promoted the secretion of IFNγ, TNF, and effector molecules such as granzyme A, granzyme B, granulysin, and perforin, thereby enhancing NK cell-mediated cytotoxicity. In short-term, mid-term and long-term cytotoxicity assays, 8H8-SDIE induced potent target cell-restricted lysis of CRC and NSCLC cell lines, while the iso-SDIE control showed no effect. In conclusion, 8H8-SDIE is a potent immunotherapeutic candidate that effectively induces NK cell anti-cancer reactivity and represents a promising treatment option for CRC and NSCLC. Citation Format: Sylwia Anna Stefanczyk, Xenija Kaiser, Samuel J. Holzmayer, Ilona Hagelstein, Latifa Zekri, Susanne Jung, Melanie Märklin. Enhanced NK cell reactivity with Fc-optimized B7-H3 antibody for colorectal and non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6082.