In 1997, Juha Kononen, a postdoctoral fellow at the National Human Genome Research Institute, was pondering the significance of the recently developed DNA microarray. He was studying genetically altered genes in cancerous cells using fluorescence in situ hybridization and immunostaining of individual tissue sections. The process was, he says, "very laborious." Kononen wondered whether a technology based on DNA biochips could aid in his research. "I thought why could you not invert the concept? Instead of laying down hundreds or thousands of probes, how about laying down hundreds or thousands of tissue spots and probing them one antibody or gene probe at a time." Kononen ap-proached his advisor, Olli Kallioniemi, NHGRI section head for the cancer genetics branch, who gave the green light to proceed.
What Kallioniemi and Kononen developed was the tissue microarray (TMA), an ordered array of tissue cores--up to 1,000 of them--on a single glass slide.1 The ...
