Actym’s lead program, ACTM-838, a STACT strain that encodes an engineered IL-15 (IL-15plex) cytokine and an engineered, constitutively active STING variant (eSTING), is rapidly advancing to the clinic. In preclinical studies, the IL-15plex + eSTING payload combination delivered by STACT resulted in primary human and mouse M2 macrophage production of type I interferon, and repolarization into a novel hybrid M1/M2 phenotype capable of tumor cell phagocytosis and priming of CD8+ T-cells. Complete tumor responses were observed in metastatic, checkpoint refractory tumors (IV dosing), that were dependent on CD8+ T-cells. In primates, STACT was well tolerated, rapidly cleared, and elicited minimal cytokine responses after IV dosing. In February of 2022, Actym signed a global manufacturing contract with Wacker Biotech, a leading CDMO for production of live bacterial products, for ACTM-838 clinical supply.