While an immune system booster called IL-12p70 helps people fight cancer, this protein is toxic when injected into people systemically. Now, a new study shows how to boost levels of this protein in melanomas safely. The researchers developed a vaccine that includes immune system cells from the bodies of people with melanoma. These cells then stimulate production of the immune system booster IL-12p70 in tumors. In a phase I clinical trial, the vaccine increased IL-12p70 levels in six of seven people with melanoma, and one of them was in complete remission more than 4 years later. This trial is currently accepting new participants.