Salmonella Breaks Tumor Immune Tolerance by Downregulating Tumor Programmed Death-Ligand 1 Expression

Area of Science:

• Oncology
• Immunology
• Microbiology

Background:

• Cancer immunotherapy utilizes the host immune system to fight tumors.
• Some bacteria, like Salmonella, exhibit immunomodulatory properties beneficial in cancer treatment.
• Tumor cells often evade immune detection through mechanisms like programmed death-ligand 1 (PD-L1) expression.

Purpose of the Study:

• To elucidate the molecular mechanisms by which Salmonella influences tumor immunity.
• To investigate Salmonella's effect on PD-L1 expression and T cell activity in cancer.
• To evaluate Salmonella's therapeutic potential in inhibiting tumor growth.

Main Methods:

• Tumor-T cell coculture systems were used to assess Salmonella's impact on T cells.
• Western blotting analyzed the involvement of the AKT/mTOR pathway in Salmonella-mediated PD-L1 downregulation.
• Systemic Salmonella administration was performed in tumor-bearing mice models.

Main Results:

• Salmonella accumulation in tumors reduced PD-L1 expression on tumor cells.
• The AKT/mTOR pathway (P-AKT, P-mTOR, P-p70s6K) was implicated in PD-L1 downregulation.
• Salmonella increased T cell numbers, reduced T cell apoptosis, inhibited tumor growth, and enhanced T cell infiltration in vivo.

Conclusions:

• Salmonella effectively reduces PD-L1 expression, a key immune checkpoint in cancer.
• The study identifies the AKT/mTOR pathway as crucial for Salmonella's immunomodulatory effects.
• Salmonella demonstrates significant potential as an oncolytic immunotherapy agent by enhancing anti-tumor T cell responses.