Soluble CD80 oral delivery by recombinant Lactococcus suppresses tumor growth by enhancing antitumor immunity

CD80 is an important co‐stimulatory molecule that participates in the immune response. Soluble CD80 can induce T cell activation and overcome PDL1‐mediated immune suppression. In this study, we aimed to construct recombinant Lactococcus lactis for oral delivery of the soluble CD80 (hsCD80) protein or the fusion protein containing the cholera toxin B subunit (CTB) and hsCD80 (CTB‐hsCD80) under the control of the nisin‐inducible expression system. The recombinant L. lactis expressed and secreted hsCD80 or CTB‐hsCD80 fusion proteins after induction by nisin in vitro and in the enteric cavity. Additionally, the CTB‐hsCD80 fusion protein showed uptake by intestinal epithelial cells, was cleaved by the furin protease, and was released as free hsCD80 protein into the blood circulation. Orally administered hsCD80 and CTB‐hsCD80 containing L. lactis increased the proportion of activated T cells in the spleen and intestinal epithelium, inhibited tumor growth, and prolonged the survival of tumor‐bearing mice. The hsCD80‐containing L. lactis showed greater therapeutic effects on primary colonic adenoma in APC(min/−) mice and completely suppressed tumor growth. Further, recombinant CTB‐hsCD80 in L. lactis was more efficient than hsCD80‐containing bacteria in inhibiting the growth of xenografted colon cancer and melanoma cells. hsCD80 engineered probiotics may serve as a promising new approach for antitumor immunotherapy, especially for colorectal cancer.