Stem cells may not heal liver disease

Author:  Katrina Outland
Institution:  Hawaii Pacific University
Date:  August 2004

Bone marrow stem cells may not directly solve liver disease problems, according a report published by researchers at the Oregon Health & Science University. Published in the recent issue of Nature Medicine, the study showed that macrophages, a certain type of white blood cell, are what actually heal diseased liver cells.

"This is probably the best way to establish in the far future a therapeutic strategy," said lead author Dr. Holger Willenbring. "It might be worthwhile figuring out if [macrophage transplants] could be established."

Previously, scientists had thought that stem cells cure diseases by ‘transforming’ into liver, brain, lung, or other organ cells. However, this study suggests that this notion isn’t entirely true.

"We found out that the bone marrow cells were not turning into liver cells directly, but that they were fusing with pre-existing liver cells instead," said Dr. Markus Grompe, co-author and director of the Oregon Stem Cell Center. "The liver cells were turning the [macrophages] into their own kind."

Willenbring explained that stem cells in bone marrow create many types of blood cells, one of which is the macrophage. These macrophages can travel to many different organs, where they differentiate, or specialize. Usually, macrophages clean debris and perform various other tasks, but Willenbring and colleagues found that they can fuse with diseased liver cells and ultimately cure them.

"It’s pretty promising because it means you can reprogram a [macrophage] for your own needs," said Willenbring. "It’s very valuable."

Grompe added, "The most important discovery is you don't need to transplant stem cells at all. If you transplant only macrophages, you'll get liver cells that correct liver disease in mice."

Macrophage transplants don’t require irradiation treatments, an advantage over stem cell transplants. Also, a few stem cells can produce many thousands of macrophages, eliminating extra cells that don’t need to be transplanted.

Though human macrophage transplants may be far in the future, Willenbring is optimistic about this contribution to curing liver disease. "It is a refinement, clarifying the mechanism," he said. "It might be worthwhile figuring out if this could be established."