Abstract LB001: Discovery of a monoclonal antibody that binds CD16a to inhibit the shedding and promote anti-tumor immunity

Abstract CD16a is the Fc receptor that triggers antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells. Several antibody therapies bind CD16a to induce anti-tumor immune responses. However, CD16a undergoes cleavage-mediated downregulation by ADAM17, a protease with broad specificity to over one-hundred different types of proteins. “CD16a shedding” is a therapeutic target because it decreases the number of CD16a molecules available for antibody engagement. To overcome the ADAM17’s broad specificity, we developed a monoclonal antibody (F9H4) that binds CD16a to inhibit the cleavage. F9H4 is extremely effective in inhibiting the shedding and retaining CD16a on the NK cell surface. When combined with cetuximab for CD16a engagement, F9H4 increased ADCC against human lung cancer cell lines. F9H4+cetuximab inhibited the development of tumors in the lungs of immunodeficient mice that were inoculated with human lung cancer cell line and NK cells. Notably, a major advantage of F9H4 is that it inhibits the shedding in a CD16a specific manner and thereby it enabled physiologically relevant studies in immunocompetent hosts. Consistent with that notion, we applied F9H4 to Fc gamma receptor-humanized (hFcR) mice, which are immunocompetent. F9H4+cetuximab inhibited tumor growth in hFcR mice, and such effect was NK cell mediated. Cetuximab induced the CD16a shedding by blood NK cells in vivo, but F9H4 inhibited it. To generate insights about the clinical significance of CD16a shedding, we applied the tissue explant technology to tumor samples from patients. Through that, we discovered that cetuximab induced whereas F9H4 inhibited the CD16a shedding by primary tumor-infiltrating leukocytes from untreated patients with early-stage non-small cell lung cancer. Finally, we developed an Fc-enhanced version of cetuximab, by point mutations in the Fc region, and discovered that it synergized with F9H4 to promote ADCC. Therefore, F9H4 represents a new means to promote NK cell-driven immunity and applicable to cancer immunotherapy pre-clinical research. Citation Format: Bruna Taciane da Silva Bortoleti, Sophia Quasem, Stefanie Maurer, Xiaoxuan Zhong, Ruan Pimenta, Luiza Ribeiro de Lima Brandão, Matthew Hernandez, Melanie Fraidenburg, Pedro Henrique Alves da Silva, Raymond Alvarez, Benjamin K. Chen, Thomas Marron, Lucas Ferrari de Andrade. Discovery of a monoclonal antibody that binds CD16a to inhibit the shedding and promote anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB001.