Although NK cells are recognized as effector lymphocytes of the innate immune system, they also regulate the adaptive immune response by releasing inflammatory cytokines and developing immunological memory. Unlike other lymphocytes such as T or B cells, NK cells do not express rearrangeable, antigen-specific receptors. 

During the last few decades, immunotherapy is considered to be an important approach to help our immune system to fight various kinds of diseases, such as tumor. Sometimes, it works very well for some types of cancers, for example: bladder cancer, colorectal cancer, breast cancer and lymphoma.

The gut microbiome or gut flora is a vast community of microorganisms such as bacteria, viruses, protozoa, and fungi that inhabit the digestive tract of the human and other animals. In the human body, bacterial species colonize into the oral cavity, skin, vagina, and placenta, however, the largest population of microorganisms resides in the intestine. The majority of gut microbiota belong to the phyla Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria.

The immune system developed certain checks and balance to control or inhibit the reactivity against normal cells of the body. Uncontrolled immune responses to the non-self entities such as bacteria, viruses, parasites, or mutated self-antigens can cause an inflammatory reaction and autoimmune diseases.

Cancer nanomedicine was originally developed for more efficient delivery of chemotherapeutic agents into tumor, and has been extensively employed as a therapeutic for cancer treatment owing to its unique features in drug delivery, diagnosis and imaging, as well as the therapeutic nature of some nanomaterials themselves.