Israeli researchers discover method to neutralize tumor growth in embryonic stem cell therapy

JERUSALEM, May 6 (Xinhua) -- Researchers at the Hebrew University of
Jerusalem discovered a method to potentially eliminate the tumor-risk factor in
utilizing human embryonic stem cells, said the university on Wednesday.

The researchers' work paves the way for further progress in the promising
field of stem cell therapy, said the press release of the university sent to
Xinhua.

According to the release, human embryonic stem cells are theoretically
capable of differentiation to all cells of the mature human body (and are hence
defined as "pluripotent").

This ability, along with the ability to remain undifferentiated
indefinitely in culture, make regenerative medicine using human embryonic stem
cells a potentially unprecedented tool for the treatment of various diseases,
including diabetes, Parkinson's disease and heart failure.

However, a major drawback to the use of stem cells remains the demonstrated
tendency of such cells to grow into a specific kind of tumor, called teratoma,
when they are implanted in laboratory experiments into mice.

It is assumed that this tumorigenic feature will be manifested upon
transplantation to human patients as well. The development of tumors from
embryonic stem cells is especially puzzling given that these cells start out as
completely normal cells.

A team of researchers at the Stem Cell Unit in the Department of Genetics
at the Silberman Institute of Life Sciences at the Hebrew University has been
working on various approaches to deal with this problem.

In their latest project, the researchers analyzed the genetic basis of
tumor formation from human embryonic stem cells and identified a key gene that
is involved in this unique tumorigenicity.

This gene, called survivin, is expressed in most cancers and in early stage
embryos, but it is almost completely absent from mature normal tissues.

The survivin gene is especially highly expressed in undifferentiated human
embryonic stem cells and in their derived tumors. By neutralizing the activity
of survivin in the undifferentiated cells as well as in the tumors, the
researchers were able to initiate programmed cell death (apoptosis) in those
cells.

This inhibition of this gene just before or after transplantation of the
cells could minimize the chances of tumor formation, but the researchers caution
that a combination of strategies may be needed to address the major safety
concerns regarding tumor formation by human embryonic stem
cells.