Microbiome-mediated immune modulation in tumor microenvironment.

This chapter explores the complex interplay between the tumor microenvironment (TME), the microbiome, and the immune system. It focuses on how microbes and their metabolites influence tumor development, progression, and the subsequent immune responses. The TME is a highly complex environment made up of cancer cells, immune cells, and the extracellular matrix, where immune cells can either inhibit or promote tumor growth depending on the context. The chapter highlights several key mechanisms of interaction, including microbial metabolites, the presentation of microbial antigens by tumor or immune cells, and the role of immune checkpoints, such as PD-L1, in modulating immune responses. Certain bacteria, viruses, and fungi can trigger immune responses that lead to the destruction of cancer cells, often through processes such as immunogenic cell death (ICD). Conversely, dysbiosis, or an imbalance in microbial communities, can create a pro-tumorigenic environment, aiding in tumor progression through chronic inflammation, immune suppression, and metabolic alterations. The chapter categorizes microbial interactions with cancer into three areas: microbes directly causing cancer (e.g., Epstein-Barr virus and HPV), cancers that induce infections (e.g., obstructing the respiratory or digestive systems), and tumors located in organs with natural microbiomes, such as the gastrointestinal tract. In addition to these mechanisms, the chapter also illuminates how microbial antigens can serve as potential identifiers and tools for cancer diagnosis and treatment, offering new avenues for personalized medicine. The insights gained from this exploration are important for advancing microbial-based therapies and improving the effectiveness of immunotherapies in cancer treatment.