NK Cell Therapy: A Rising Star in Cancer Treatment

SIMPLE SUMMARY: A cancer treatment approach known as immunotherapy has become popular in the medical field. In this case, immune cells are boosted for effective response against cancer. A type of immune cell with significant potential for use in immunotherapy is the natural killer (NK) cell. The number of NK cells in the cancer tissues has been shown to be lower than normal, and this contributes to the growth of cancer cells. Besides, the immune function of the NK cells is compromised, thus interfering with anticancer immunity. Many research studies are being conducted to develop cancer treatment strategies based on increasing the number of NK cells and enhancing their activity. ABSTRACT: Immunotherapy has become a robust and routine treatment strategy for patients with cancer; however, there are efficacy and safety issues that should be resolved. Natural killer (NK) cells are important innate immune cells that have attracted increasing attention owing to their major histocompatibility complex-independent immunosurveillance ability. These cells provide the first-line defense against carcinogenesis and are closely related to cancer development. However, NK cells are functionally suppressed owing to multiple immunosuppressive factors in the tumor microenvironment; thus, releasing the suppressed state of NK cells is an emergent project and a promising solution for immunotherapy. As a result, many clinical trials of NK cell therapy alone or in combination with other agents are currently underway. This review describes the current status of NK cell therapy for cancer treatment based on the effector function and releasing the inhibited state of NK cells in the cancer microenvironment.