Microorganism delivery of cancer vaccines

Cancer immunotherapeutic vaccines offer a promising approach which can activate the immune system to target and kill cancer cells. Despite great progresses, challenges still exist in clinical practice, including immunosuppressive tumor microenvironment, tumor heterogeneity as well as low delivery efficiency. Microbe-based cancer vaccines, leveraging the abilities of bacteria and viruses to target hypoxic tumor regions/infect cancer cells as well as enhance the immunogenicity of tumor microenvironment, have attached prominent attention for the potential to revolutionize vaccine designing. Particularly, advances in synthetic biology enable precise expression of tumor antigens or immune checkpoint inhibitors in microbial cancer vaccines, furthermore facilitating personalized immunotherapeutic potential. This review describes the interactions between microorganisms and the host immune system, and systematically introduces the tumor-targeting mechanisms of microorganisms. Specifically, we provide a comprehensive describe about advantages and applications of bacteria, as a type of microbial vaccines, for antitumor treatment. We also delve into multiple kinds of viral vaccines and virus-like particles for cancer therapy. Recent examples of combining microbial vaccines with other therapeutic modalities designed to combat tumors are highlighted. Last but not least, we address the underlying challenges of microbial cancer vaccines. Meanwhile, this review prospects that microbial cancer vaccines represents a transformative immunotherapy strategy with tumor-targeting and immune-activating potential.