The scientists are attempting to bolster the own body's defenses. With CRISPR, all you need is a simple snip. After drawing blood from the patient, the team targeted a specific gene in their T cells, a type of white blood cell that protects the body by attacking dangerous cells. Cancer spreads, in part, because cancerous cells are often ignored by T cells since they're made by the host's own body. The team switched off the programmed cell death protein 1 (PD-1), which normally suppresses a T cell's drive to eliminate cells with reckless abandon. The hope is that switching it off will unleash the T cells on their cancerous targets.