SYNB1891

SYNB1891 is an investigational, intratumorally administered live biotherapeutic product developed by Synlogic. It consists of a non-pathogenic, engineered strain of *Escherichia coli* Nissle 1917 designed to produce a STING (Stimulator of Interferon Genes) pathway agonist, cyclic di-AMP, within the hypoxic tumor microenvironment. [1, 13, 14] Upon being engulfed by antigen-presenting cells (APCs), SYNB1891 releases the agonist, activating the STING pathway and promoting a type I interferon response. [1, 4] The bacterial chassis also provides a secondary immune stimulus via pattern recognition receptors like TLR4. [1, 2] This dual mechanism is intended to convert immunologically "cold" tumors into "hot" tumors, thereby stimulating an anti-tumor immune response. A Phase 1 trial evaluated it as a monotherapy and in combination with the checkpoint inhibitor atezolizumab for advanced solid tumors and lymphoma. [14] However, in February 2024, Synlogic announced it was ceasing operations and seeking strategic alternatives, effectively terminating further development of its pipeline, including SYNB1891. [5, 9]