Abstract 5243: CAR B cells to accelerate antigen presentation in cancer

Abstract

Abstract Engineered B cells hold promise for multiple therapeutic applications. Walking Fish Therapeutics is engineering B cells to produce replacement proteins for deficiency diseases, antibodies of defined specificity and effector function, and Chimeric Antigen Receptor (CAR) B cells with and without therapeutic payloads for use in the oncology setting. B cells are professional antigen presenting cells (APCs) with the ability to present antigen to CD4+ T cells. Recent studies have found the presence of tumor infiltrating B cells are associated with favorable outcomes across multiple cancer types. Adoptive transfer of B cells has demonstrated antitumor activity in a syngeneic mouse model. B cells from OVA-vaccinated transgenic luciferase mice were adoptively transferred to mice bearing EG7.OVA-tumors. We observed B cells migrating to the tumor and tumor draining lymph node (TDLN), locations where B cells can engage with antigen. Further, we observed a strong anti-tumor response in mice receiving B cells from OVA-vaccinated donors. Based on these results, we hypothesized that B cells engineered to target tumor specific antigens may engage and activate the immune system leading to an enhanced antitumor immune response. We generated CAR B cells expressing synthetic BCRs with tumor-antigen specific scFvs fused to designated B cell signaling motifs. Expression of different CAR constructs were confirmed in both human and mouse B cells. Upon antigen engagement CAR B cells release pro-inflammatory cytokines. Importantly, we demonstrate in vitro that antigen-specific CAR B cells can recognize cognate cell surface antigen, leading to uptake, processing, and presentation on MHCII as detected by activation of peptide-specific CD4+ T cells. When administered in vivo by IV administration, we observed a significant increase in mouse CAR B cells at the tumor site compared to unengineered B cells. We are currently investigating additional CAR formats that may lead to enhanced anti-tumor activity. Citation Format: Mary Ellen Molloy, Jessica Balero, Ana Contreras-Sandoval, Mark Selby, Hangil Park, Srinivas Kothakota, Kathleen Boyle, Rosa Romano, Smrithi Rajendiran, Moises Hernandez, Ariel Pios, Rusty Williams. CAR B cells to accelerate antigen presentation in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5243.