Restriction of in vitro T cell-mediated cytotoxicity in lymphocytic choriomeningitis within a syngeneic or semiallogeneic system.

Doherty and Zinkernagel discovered how a class of white blood cells known as T cells kill virus-infected cells in the body, and so present the spread of viruses. 

In 1998 Zinkernagel and Doherty were awarded the Nobel Prize in Physiology or Medicine "for their discoveries concerning the specificity of the cell mediated immune defence."