Most skin cancer drugs that activate the immune system work by triggering immune cells, called T cells, to attack tumors, but when T cells are activated for too long, they can wear out and cease to function. A new study led by Penn State College of Medicine scientists finds that another type of immune cell – natural killer cells – can be harnessed to pick up the slack when T cells no longer work and may also reinvigorate T cells to attack melanoma tumors.