How the switch actually works inside the cell
PD-1 was first found in the research team's mice experiments for this type of lymphoma. In these experiments, they were able to find explanations to how this special protein works. PD-1 is signaled to activate when defective genes for cell growth start to surface, which happens during the development of cancer. Its role is actually to suppress the effects of these growth genes by recruiting other suppressive genes to help. That's why it's such a potent growth deterrent for defective T cells - it's the main stop switch that can help turn off other switches too.