Engineered Bacteria Enhance Bladder Cancer Immunotherapy with Tumor-Specific Antibodies

The intratumoral microbiome has recently emerged as a new hallmark of cancer, with implications for response or resistance to therapy. While bacteria can either promote or inhibit cancer growth, intratumoral bacteria can also be engineered using synthetic biology to remodel the tumor microenvironment. Here, we engineered the probiotic bacterium E. coli Nissle 1917 (EcN) to express the human chemokine CXCL13, a critical component of germinal center (GC) formation. The GC reaction is a fundamental aspect of adaptive immunity by which antibody affinity develops in secondary lymphoid organs for defense against pathogens. Using orthotopic models of bladder cancer, engineered CXCL13-expressing EcN colonized bladder tumors and elicited GC responses in bladder tumor-draining lymph nodes after intravesical delivery. Furthermore, when combined with PD-1 blockade, engineered EcN amplified the antitumor antibody response and promoted long-term survival and protective immunity upon tumor rechallenge. Thus, we demonstrate that synthetically engineered CXCL13-expressing EcN can enhance the efficacy of PD-1 checkpoint blockade immunotherapy by amplifying tumor-specific humoral immunity. Citation Format: Mathieu Rouanne, Noah Chen, Dylan Mariuzza, Zaofeng Yang, Fangda Li, Thomas Savage, Kenia de los Santos-Alexis, Rosa Vincent, Cathy L. Mendelsohn, Tal Danino, Nicholas Arpaia. Tumor-specific antibodies elicited by engineered bacteria promote bladder cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1348.