More than 35 years after it was invented, a therapy that uses immune cells extracted from a person’s own tumour is finally hitting the clinic. At least 20 people with advanced melanoma have embarked on treatment with what are called tumour-infiltrating lymphocytes (TILs), which target and kill cancer cells.

What are the side effects?

Most of the therapy’s side effects, such as anaemia and fevers, come from the chemotherapy and IL-2 treatments used to prepare patients for TIL infusion. But Sarnaik says that there is a risk of “friendly fire” if TILs also attack normal cells alongside the tumour cells. This can cause autoimmune conditions such as vitiligo, in which TILs cause skin discolouration by attacking pigment cells.