Abstract PO-038: Unbiased discovery of novel antibody therapies that stimulate macrophage-mediated destruction of B-cell lymphoma
Authors: Ribeiro Juliano , Geli Carlota Pages , Velarde José , Meglan Anna , Blandin Jasmine , Vaccaro Kyle , Crespo Marta , Weiskopf Kipp 
Published: June 2024

Abstract
Monoclonal antibodies are among the most effective treatments for patients with blood cancers, and they primarily function by marking cells for destruction by the innate immune system. Macrophages are critical innate effectors of antibody therapies for lymphoma, but their anti-tumor capacity is limited by the CD47/SIRPa interaction. CD47 acts a “don’t eat me” signal that is highly expressed on the surface of many lymphomas, and it prevents phagocytosis by binding to the inhibitory receptor SIRPa expressed on macrophages. In multiple clinical trials, CD47-blocking therapies have demonstrated encouraging signs of efficacy for B-cell lymphomas, particularly when used in combination with rituximab, an opsonizing anti-CD20 antibody. However, the best antibodies and combination strategies to activate macrophages remains unknown. Here, we sought to define the repertoire of cell surface antigens that can be targeted to stimulate macrophage-mediated destruction of B-cell lymphomas. To achieve this goal, we developed a high-throughput functional screening platform to measure the ability of primary macrophages to attack B-cell lymphoma cells. We successfully applied this system to screen monoclonal antibody libraries targeting hundreds of distinct cell surface antigens across both mouse and human systems. We conducted screens using each antibody as a single agent, in combination with anti-CD20, or in combination with anti-CD47. From these efforts, we identified CD24, CD38, CXCR4, CD71, and multiple other novel and unique antigens that could be targeted alone or in combination to exert maximal macrophage-mediated destruction of B-cell lymphoma. Of note, some of the identified targets are predominantly expressed by the lymphoma cells, whereas others are expressed by the macrophages and act as unappreciated immune checkpoints. In validation studies, we defined a multitude of new antibody combinations that robustly stimulate macrophages to attack and eliminate lymphoma cells. Since some anti-CD47-antibodies have been limited by on-target hematologic toxicity, we also used the identified targets to engineer a collection of novel bispecific antibodies that induce macrophage phagocytosis without causing hematologic toxicity. We generated 156 bispecific antibodies, produced them recombinantly, and demonstrated they can maximize macrophage-mediated cytotoxicity of human B-cell lymphoma cells while minimizing binding to healthy blood cells. In mouse xenograft models, these bispecific antibodies exhibited significant single-agent activity in a model of aggressive B-cell lymphoma. Thus, our study has led to the development of a multitude of novel therapeutic candidates and combination strategies that can be developed further to maximize anti-tumor function and benefit patients with lymphoma. Furthermore, our approach can be rapidly applied to other hematologic malignancies to create innovative bispecific agents that maximize anti-tumor responses by macrophages or other innate immune cells.
Citation Format: Juliano Ribeiro, Carlota Pages Geli, José Velarde, Anna Meglan, Jasmine Blandin, Kyle Vaccaro, Marta Crespo, Kipp Weiskopf. Unbiased discovery of novel antibody therapies that stimulate macrophage-mediated destruction of B-cell lymphoma [abstract]. In: Proceedings of the Fourth AACR International Meeting on Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2024 Jun 19-22; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(3_Suppl):Abstract nr PO-038.