Because cancer arises from a person's own cells, it's often overlooked by the immune system. In the past decade, however, scientists have discovered that some immune system cells do indeed recognize tumor cells. There's still a problem: Being few in number, these cells are typically ineffective in fighting cancer.
Scientists can extract these potential fighters from cancer patients. Then they culture the rare cells, which are a type of T cell, to greatly expand their number. Two new studies indicate that when these multiple copies, or clones, of T cells are injected into the patients, they sometimes put the brakes on cancer.