The Immune System Can Restrain Cancer Growth

The immune system has been shown in the past to destroy cancer cells, but in a study with mice models of primary chemical carcinogenesis, it has been shown that immunity can also control cancer for an extended period of time in what has been termed an "equilibrium". The researchers induced cancer in mice by giving them methylcholanthrene, which is a tar much like that found in cigarette smoke. After a first wave of deadly tumors, the mice that survived did not have any growing tumors; only dormant tumors remained. The mice appeared healthy, and their tumors were kept dormant by the immune system. These tumors only developed into active tumors after T cells were depleted or interleukin-12 or interferon gamma, both cytokines, were neutralized. This indicated that adaptive immunity provided by T cells was the component of the immune system that maintained the tumors in a dormant state. If the mice immune systems were suppressed, the tumors would begin to grow again.

This "equilibrium" state also appears to exist in humans, as evidenced by clinical observations. There are cases where the recipient of an organ transplant developed cancer that their organ donor previously had and was assumed to be cured. After the organ transplant, the recipient was highly immunosuppressed, allowing the cancer that had been held in check by the immune system of the donor to begin growing again.

News article:http://www.nature.com/nature/journal/vaop/ncurrent/full/nature06363.html
Paper:http://www.nature.com/nature/journal/vaop/ncurrent/full/nature06309.html