ROCHESTER, June 26 -- For decades, immunologists have thought of the thymus as a finishing school, a place where the immune system graduates its soldiers before sending them into the bloodstream to begin training for war. Zhiming Mao, a researcher at the Mayo Clinic Graduate School of Biomedical Sciences, spent years inside that assumption. On Thursday, his team published a paper in Nature Communications that dismantles it.

The study shows that CD8+ T cells, the cytotoxic cells the immune system deploys against tumors and infected tissue, begin acquiring cancer-fighting capacity while they are still maturing inside the thymus, long before they enter circulation. More precisely, the research identifies PD-1, the protein at the center of o...