R-5780, a SagA-engineered Lactococcus lactis, is a safe oral synthetic-biology microbial therapy that potentiates PD-1 blockade.

Immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1) have transformed cancer therapy, yet response rates remain limited across solid tumors. Modulation of the gut microbiome has emerged as a promising strategy to enhance immunotherapy efficacy. R-5780 is an engineered Lactococcus lactis strain expressing the peptidoglycan hydrolase Secreted Antigen A (SagA), which generates muramyl dipeptide (MDP), a natural ligand of the nucleotide-binding oligomerization domain 2 (NOD2) receptor involved in innate immune activation and antigen-presenting cell maturation. Therapeutic potential of R-5780 was assessed in vivo murine models. Using the CT26 murine colorectal carcinoma model, oral administration of R-5780 with anti-PD-1 significantly inhibited tumor growth in both prophylactic and therapeutic settings compared to ICI therapy alone. Mechanistic studies revealed that R-5780 enhanced dendritic-cell activation and promoted a pro-inflammatory tumor microenvironment characterized by elevated interleukin-1 beta (IL-1β). Multiplex cytokine profiling and flow cytometry further showed that R-5780 reduced CD8+ T-cell exhaustion, with decreased expression of PD-1, LAG-3, and TIM-3 on intratumoral T cells. In murine toxicology studies, R-5780 was well tolerated, with no adverse events or systemic inflammation observed following oral administration. Together, these results identify R-5780 as a safe and potent NOD2 activator that synergizes with PD-1 blockade to enhance antitumor immunity and support its advancement toward clinical evaluation.