PROJECT SUMMARY The engineering of immune cells such as chimeric antigen receptor (CAR)-T cells is driving a new era of cancer therapy. What makes this approach transformative is the ability to genetically program living cells to intelligently sense and respond to environments, adding specificity and efficacy that is not possible to obtain with molecular and antibody-based therapeutics. While CAR-T cell therapy has demonstrated remarkable success for hemato- logical malignancies, it has been faced with many challenges in solid tumor treatment including limitations in targeting safe tumor antigens, poor infiltration into tumors, and increased T cell dysfunction in the suppressive tumor microenvironment. Thus, there is a pressing need to develop technologies to enhance the safety and efficacy of this promising approach for solid tumors. Over the last few decades, microbiome and mechanistic studies have elucidated that bacteria selectively colonize tumor necrotic cores due to reduced immune surveil- lance. Where CAR-T cells struggle to target, locate, and infiltrate solid tumors, bacteria naturally home to, colo- nize, and remain indifferent to the antigenic profile of tumors. Due to advances in engineering capabilities from synthetic biology, microbes represent a natural platform for development as 'smart’ therapeutic delivery vehicles for cancer. In this way, probiotics can infiltrate tumors and be engineered as beacons for directing and enhancing CAR-T cell activities. This project proposal seeks to engineer a bridge between these two complimentary forms of cellular therapies for the treatment of triple negative breast cancer (TNBC). The objective of this proposal is to engineer bacteria and CAR-T cells together, developing a ProCAR (probiotic guided CAR-T cell) system that will improve the limitation of individual agents. Specifically, probiotics will be engineered to home to tumors and locally produce immune-stimulants to enhance CAR-T cell therapies – while CAR-T cells will be engineered to sense these molecules. The overarching innovation of this proposal is engineering communities of living medi- cines, where tumor colonizing bacteria are reengineered as beacons for directing and enhancing CAR-T cell cytotoxicity. This will be a fundamentally new approach to genetically engineering interactions between living medicines, combining the advantages of CAR-T cells and tumor-specific bacteria for cancer therapy, and further building the foundation for engineered communities.

PROJECT NARRATIVE The engineering of living cells is a transformative approach to cancer therapy, as cells can be genetically pro- grammed to intelligently sense and respond to environments potentially leading to improved safety and efficacy of therapies. However, approaches such as engineered chimeric antigen receptor (CAR)-T cells still face many challenges for the treatment of solid tumors including limitations in safe tumor antigen targeting, poor infiltration into tumors, and increased T-cell dysfunction. Leveraging synthetic biology tools to rapidly engineer tumor-hom- ing probiotics, the objective of this proposal is to program probiotic bacteria to produce therapeutics and immuno- stimulants inside of tumors that will enhance and guide CAR-T cell therapies for the treatment of solid tumors.