news.mc.duke.edu: In 1999, Duke researchers led by Laura Niklason, M.D., reported in the journal Science on experiments in which they grew pig arteries in a novel "bioreactor" system that mimics the fetal environment, and then successfully implanted these bioengineered arteries back into the pig. Unfortunately, researchers found that human artery cells did not possess enough life cycles to be grown into functional arteries.

The key to overcoming this hurdle was found in a cancer research lab. Every time a cell divides, the ends of its chromosomes, or telomeres, erode until they become so short that the cell receives a signal to stop growing. While at the Massachusetts Institute of Technology, current Duke researcher Chris Counter, Ph.D., had previously cloned the hTERT (human telomerase reverse transcriptase subunit) component of the enzyme telomerase that stops telomeres from shortening, and had shown that expression of hTERT permitted some human cells to continue to divide indefinitely, in effect making them immortal. [...]

This is the first time arteries have been grown from non-neonatal vascular cells, the researchers said. This achievement is important, they continued, since the goal is to engineer arteries that will resist immunological attack, so they must be grown from cells taken from the actual patients who will ultimately receive the arteries. [...]

"Telomeres are present in all normal dividing cells and act as a built-in check against unwanted cellular proliferation," Counter explained. "In this case, telomere shortening worked against us, preventing the cells from dividing long enough to form an artery in the laboratory. So we stole a trick cancer cells use to keep dividing; namely we turned on hTERT to stop telomerase shortening."

The researchers did not detect any signs of unwanted cellular proliferation in their bioengineered arteries, although Counter did emphasize that before these arteries can be implanted into humans, the researchers must "turn off" hTERT. It is expected that the implanted arteries would then "age" as would native arteries.