A non-pathogenic strain of Escherichia coli (E. coli) bacteria that has been engineered to express stimulator of interferon genes (STING; transmembrane protein 173; TMEM173) protein, with potential immunoactivating and antineoplastic activities. Upon intratumoral administration, STING-expressing E. coli SYNB1891 are engulfed by antigen presenting cells (APCs) within the tumor. STING-mediated pathways within the APCs are then activated resulting in a type I interferon (IFN) response which promotes initiation and propagation of tumor-specific T-cell responses. In addition, the bacterial component of SYNB1891 may further stimulate the innate immune system via Toll-like receptors (TLRs) which may enhance the magnitude of the overall immune response. STING, a transmembrane protein that activates immune cells in the tumor microenvironment (TME), plays a key role in the activation of the innate immune system.