When tumors like melanoma form, the immune system mobilizes for war. White blood cells called lymphocytes rush to assault the tumor — but cancer has ways of disabling the immune system. Once the immune cells penetrate the area in and around the tumor, they can be caught in chemical snares that render them inert or exhausted, so they cease working.
But those immune cells still have the potential to kill cancer cells. For decades, scientists have been working on a therapy that harvests the immune cells from a patient’s tumor, grows an army of them in the billions in a lab, and releases them back into the patient. It’s called TIL, or tumor infiltrating lymphocyte therapy. The technique has long shown promise, but only in small observational studies.