Microbiota collectively refers to all microorganisms living in a defined environment such as on the skin or in the intestinal tract, mouth, vagina, and eyes, including bacteria, archaea, fungi, and viruses. The largest population of microorganisms in the human body locates in the intestine and is called the gut or intestinal microbiota. Intestinal microbes are involved in a variety of physiological functions to maintain the health of the host, including providing nutrients and vitamins, catabolic drugs, and toxins, protecting the body from pathogens, promoting the development of the immune system, and maintaining epithelial mucosal homeostasis. The microbiota plays an important role in the physiology and pathology of the human body.

Cancer is a leading cause of death in the world. According to the World Health Organization (WHO), 10 million people died from cancer in 2020. It is estimated that 10-20% of cancers can be attributed to microbial infections. Many studies have demonstrated that the intestinal microbiota plays an important role in tumorigenesis. Microbes and their products can either have a direct carcinogenic effect or prevent the occurrence and development of cancer by regulating the production of circulating metabolites, inflammation, and immune responses. Cancer immunotherapy is a very promising therapy by boosting the immune system to kill cancer cells and suppress tumor growth. Microbiota on or in the human body can influence immune responses affecting immunotherapy.

This Special Issue invites original research and review articles which contribute to the understanding of the roles of microbiota in cancer immune responses and immunotherapy which may provide novel approaches in treating cancer.

Potential topics include but are not limited to the following:

• Research and development of microbe-associated cancer immunotherapy
• Mechanisms of microbiota disturbance in cancer immune responses
• Correlation of microbiota with tumorigenesis
• Screening and application of biomarkers of microbiota in cancer immune responses
• Mechanisms of bacterial translocation causing cancer
• Relationship between microbiota and mucosal immunity and its anticancer mechanism
• Signaling pathways of microbiota regulating tumorigenesis
• Mechanisms and applications of probiotic bacteria in immunotherapy