In 1975, Peter Doherty and Rolf Zinkernagel identified human leukocyte antigens (HLA). HLA are proteins found everywhere in the body except red blood cells. They are especially prevalent in white blood cells. Many types of HLA exist, often varying greatly from person to person. Doherty and Zinkernagel were awarded the 1996 Nobel Prize in Physiology or Medicine for this discovery.
Since many types of HLA exist, scientists can use HLA typing for genetic identification. They are able to compare the types of HLA in different people and determine if the people are related based on similarities between these proteins. HLA have become increasingly important for identifying positive matches between donors and recipients of bone marrow transplants.
The degree of variation among HLA in different people provides for fairly accurate paternity testing, with a power of exclusion from 80 to 90% when combined with blood typing and serological testing. The accuracy of HLA typing increases with the rarity of a tested person's HLA. However, this procedure is normally performed serologically, requiring a relatively large amount of fresh (no more than a few days old) blood. Additionally, the collection process can be considered uncomfortable, especially for children, and cannot be performed on infants under the age of 6 months.