Stem cells used to grow blood vessels in mice

Human stem cells have been used to create networks of blood vessels in mice that functioned for nine months.

A team of scientists from Massachusetts
General Hospital started with human induced pluripotent stem (iPS) cells), and transformed
these into vascular precursor cells by adding a combination of protein molecules. These
precursor cells were then implanted onto the surface of the brains of 25 mice.

Within two weeks of implantation, the precursor cells had formed
networks of blood vessels that functioned as well as the existing vessels. The
researchers also found that the artificial vessels were durable, surviving for
up to 280 days.

'The discovery of ways to bring mature cells back to a "stem-like"
state that can differentiate into many different types of tissue has brought
enormous potential to the field of cell-based regenerative medicine, but the
challenge of deriving functional cells from these iPS cells still remains', said Dr Rakesh Jain, director of the Steele Laboratory for Tumor Biology at Massachusetts General Hospital and co-author of the study. 'Our team has developed an efficient method to generate
vascular precursor cells from human iPS cells and used them to create networks
of engineered blood vessels in living mice.'

The scientists also implanted vascular precursor cells under the skin of
mice. This experiment also generated functional blood vessels, but five times
more precursor cells were required and the vessels were short-lived.

The ability to repair or grow new blood vessels could be useful in
treating conditions such as cardiovascular
disease, a major health risk in the UK. Study coauthor Dr Rekha Samuel said: 'The
potential applications of iPS cell-generated blood vessels are broad - from
repairing damaged vessels supplying the heart or brain to preventing the need
to amputate limbs because of the vascular complications of diabetes'.

The technique may also be of use in tissue engineering, since providing a
vascular supply to artificial tissue is a major obstacle in the production of whole
organs. However, Dr Samuel noted that long term safety issues regarding the
use of these cells still need to be addressed.

Additionally, the researchers found that iPS cells derived from patients with
type 1 diabetes had the ability to generate functional, long-lasting blood
vessels. However, these stem cells showed differences in their cell-generating
potential, meaning that further research is needed to understand the underlying
mechanisms.

The study was published in the journal PNAS.