Functional Human Blood Vessels Grown in Lab Mice

Author: Madeline Ellis

Imagine being able to replace failing heart blood vessels without surgery! That is the ultimate goal of a research team at Harvard Medical School and Children's Hospital Boston who have, for the first time, grown functioning blood vessels in laboratory mice using cells taken from human bone marrow, blood and umbilical cords. Juan M. Melero-Martin, a research fellow at Harvard and co-author of the study, said they envision a day when "a patient has need to vascularize ischemic tissue, we can get cells from the patient ahead of time, grow them and inject them back into the patient."

Instead of stem cells, the research team is using progenitor cells, which are similar to stem cells but can only differentiate into specific cells, while stem cells have the ability to differentiate into practically any cell in the body. Two different kinds of progenitor cells were used in the study; the endothelial progenitor cells (EPCs), which become the lining of the blood vessels, and mesenchymal progenitor cells (MPCs), which wrap around the endothelial cells and provide stability. "What's really significant about our study is that we are using human cells that can be obtained from blood or bone marrow rather than removing and using fully developed blood vessels," said Harvard's Joyce Bischoff, Ph.D., associate professor and senior author of the study.

The cells were mixed with nutrients and growth factors in a culture dish and then implanted into the cells of mice with weakened immune systems. After one week, the cells grew into a network of vessels that connected to each other and the blood vessels of the mice, without genetic alteration or manipulation to improve their growth. They continued to transport blood during the four-week study. "It's kind of a self-assembly process; they do the job on their own," Dr. Bischoff said in a telephone interview with Bloomberg. "We mix them together and they talk to each other and give directions on how to form a blood vessel."

Dr. Bischoff said there is still much work ahead and many more animal studies to be done before the concept could be used in humans. Their current goal is to shorten the growth time for the blood vessels from seven days to 24 to 48 hours in order to restore blood flow to the starving tissue, such as a heart after a heart attack. However, the technique could also be used to treat a number of conditions where new blood vessels are needed, such as wound healing and other acute injuries.

According to the American Heart Association's Heart Disease and Stroke Statistics 2008 Update, 469,000 cardiac revascularizations (also known as coronary artery bypass graft or CABG operations) were done in the United States in 2005. This procedure normally involves using a piece of vein, such as an artery from a patient's leg, to divert blood around a blocked section. But the grafts are difficult to find and have a high failure rate after 10 years.

The study was published in the July 18 issue of the journal Circulation Research.