Live attenuated bacterium limits cancer resistance to CAR-T therapy by remodeling the tumor microenvironment

Abstract

The tumor microenvironment (TME) is characterized by the activation of immune checkpoints, which limit the ability of immune cells to attack the growing cancer. To overcome immune suppression in the clinic, antigen-expressing viruses and bacteria have been developed to induce antitumor immunity. However, the safety and targeting specificity are the main concerns of using bacteria in clinical practice as antitumor agents. In our previous studies, we have developed an attenuated bacterial strain (Brucella melitensis 16M ∆vjbR, henceforth Bm∆vjbR) for clinical use, which is safe in all tested animal models and has been removed from the select agent list by the Centers for Disease Control and Prevention. In this study, we demonstrated that Bm∆vjbR homed to tumor tissue and improved the TME in a murine model of solid cancer. In addition, live Bm∆vjbR promoted proinflammatory M1 polarization of tumor macrophages and increased the number and activity of CD8+ T cells in the tumor. In a murine colon adenocarcinoma model, when combined with adoptive transfer of tumor-specific carcinoembryonic antigen chimeric antigen receptor CD8+ T cells, tumor cell growth and proliferation was almost completely abrogated, and host survival was 100%. Taken together, these findings demonstrate that the live attenuated bacterial treatment can defeat cancer resistance to chimeric antigen receptor T-cell therapy by remodeling the TME to promote macrophage and T cell-mediated antitumor immunity.

A metabolically engineered bacterium controls autoimmunity by remodeling the pro-inflammatory microenvironment

“…BmΔ vjbR or BmΔ vjbR::tnaA were cultivated and prepared for experimentation as previously described 8 .…”

“…Cell staining and flow cytometric analysis were performed as described previously 8 using the described labeling reagents. Briefly, surface and intracellular staining was performed on the single-cell suspensions and analyzed using LSR Fortessa cell analyzer (BD).…”

“…Importantly, BmΔ vjbR has been shown to be safe in immunocompetent and immunocompromised mice 9 , goats 10 , sheep 11 , and non-human primates 12 . We also have shown that BmΔ vjbR can combat cancer in a murine model by remodeling the tumor microenvironment (TME) to a pro-inflammatory state 8 . Moreover, when BmΔ vjbR treatment was combined with adoptive cell transfer (ACT) of tumor antigen (Ag)-specific CD8 + T cells, tumor growth and proliferation were dramatically impaired 8 .…”

“…We also have shown that BmΔ vjbR can combat cancer in a murine model by remodeling the tumor microenvironment (TME) to a pro-inflammatory state 8 . Moreover, when BmΔ vjbR treatment was combined with adoptive cell transfer (ACT) of tumor antigen (Ag)-specific CD8 + T cells, tumor growth and proliferation were dramatically impaired 8 . Conversely, in the current studies, we engineered BmΔ vjbR to express tryptophanase (tnaA); i.e., BmΔ vjbR::tnaA , to produce the tryptophan metabolite indole, a molecule that modulates the fate and function of T regs 13 .…”

“…For the bacterial vector, we selected an attenuated strain of Brucella melitensis that harbors a deletion in vjbR , a master regulator of virulence ( BmΔ vjbR ) 8 . Like other Gram-negative organisms, Brucella strains express a lipopolysaccharide (LPS) lacking endotoxin activity.…”