Natural Killer Cells and Cancer Immunity

Natural killer cells visualized under a microscope

Natural killer cells are aggressive cells of the immune system that play an important role in fighting cancer as well as viral-infected cells. While T cells are also important in cancer, natural killer cells are the "first responders" that are on the scene before the T cells are summoned. Not yet in use with other immunotherapy drugs researchers are looking at ways to harness the actions of natural killer cells as they have T cells.

NK cells are a type of lymphocyte, which in turn are one of the types of white blood cells in the body. It's thought that NK cells make up 10 percent or less of the white blood cells in the body.

How NK Cells Work for Immunity

As part of the innate immune system, natural killer cells don't have to recognize a specific abnormality (antigen) on viral-infected cells or cancer cells. This is in contrast to some functions of immune cells which result from immunologic memory (the kind of functions for which immunizations are designed). If a cell is not recognized as being a normal part of the body, the NK cell can perform one of two functions:

Cytotoxic (Cell Killing)

NK cells may be cytotoxic. In this process, the NK cell penetrates the cell and releases toxic granules into the abnormal cells. These granules then create holes in the cell membrane, allowing them to swell and burst and killing the cell on contact. Instead of bursting, the cell may instead be directed in a process of controlled death called apoptosis.


Natural killer cells may also be used as a form of immunoregulation. In this process, the NK cells regulate the function of the immune system by producing substances known as cytokines. You can visualize cytokines as the "hormones of the immune system" which stimulate other parts of the immune system. It is these other parts of the immune system that, once stimulated, resulting in the death of the cancer cell or viral-infected cell.

Cancer Research

Since natural killer cells are able to kill tumor cells by recognizing the difference between cancer cells and normal cells scientists are studying ways to increase the number or enhance the function of these cells in the body, as a way to treat cancer more effectively.  

Research on T cells has advanced tremendously, and now researchers are optimistic that they may be able to use the function of natural killer cells as well. NK cells work directly to detect and destroy cancer cells. In contrast, T cells have to be "told" there is a cancer cell present (presented with an antigen) before going to work.

Since people with cancer don't have enough NK cells to do enough to fight the tumor, researchers are looking at ways to provide more by using another person's NK cells (allogenic adoptive NK cell therapy). Unlike T cells that induce a graft vs. host reaction and attack the host's tissues, NK cells appear to be safe when obtained from another person and then injected.

Looking at NK cells may help advance our knowledge of cancer in other ways as well. For example, many people have wondered if "alternative" therapies such as music therapy or meditation may have an effect on cancer, and if so, how. A small study found that music therapy was associated with both an increased number and increased activity of natural killer cells. What this means is still unknown, but is an interesting finding going forward.

Can You Improve the Function of Your Natural Killer Cells?

In one study promoting the benefit of exercise, researchers found that moderate exercise may improve the function of natural killer cells in people with cancer. On the other side of the equation, cigarette smoking appears to interfere with the function of natural killer cells, and smoking cessation is one way to ensure that your body’s natural killer cells are working as well as possible.

A Word From Verywell

Natural killer cells are a critical part of your immune system, especially with the roles they play in eliminating both viral-infected cells and cancer cells. Research is in progress looking at ways to both boosts the function of these cells and increase their numbers as a method of fighting cancers.

Of note is that there are things you can do yourself that may affect your natural killer cells. Exercise appears to increase their numbers and smoking lowers them. As we learn about the immunology of cancer we are learning not only new methods to fight tumors but the ways that we can support our own immune system in fighting these cancers for us.

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