People waiting for liver transplants may soon have a new option. Vital Therapies, a medical device company based in San Diego, CA, is testing a system made up of human liver cells that mimics the function of the organ, giving time for an ailing liver to regenerate or for a donor liver to become available. About 2500 people in the U.S. die every year waiting for a donor

While the overall approach is similar to kidney dialysis, mimicking liver function is far more complicated. In addition to filtering blood, the liver makes thousands of proteins and other molecules. At the heart of the device, called an Extracorporeal Liver Assist Device (ELAD), are human cells derived from a liver tumor--unlike typical liver cells, these so-called immortalized cells can be grown successfully outside the body.

The cells are grown around a series of hollow fibers, through which the patients' plasma flows.