In a joint study, South Korean and US scientists have isolated the first human embryonic stem cell lines specifically tailored to match the nuclear DNA of patients.

This achievement, published in the May 19 on-line issue of the Science journal, pushes the stem cell research closer to the goal of transplanting healthy cells into humans to replace cells damaged by diseases such as Parkinson's and diabetes, scientists said.

Each of the 11 new human embryonic stem cell lines was created by transferring the nuclear genetic material from a non- reproductive cell of a patient into a donated egg, or "oocyte," whose nucleus had been removed.

Next, oocytes with the patient's genetic material were allowed to grow to the blastocyst stage, an early stage of embryo development. Stem cells were then derived from the inner cell mass of the blastocyst.

The researchers, led by Woo Suk Hwang from Seoul National University, yielded the first embryonic stem cell line from a cloned human blastocyst in year 2004.

In the new study, they replaced the nuclei from donated oocytes with nuclei from skin cells from male and female patients, aged between 2 to 56, who had spinal cord injuries, juvenile diabetes and the genetic disease "congenital ypogamma-globulinemia."

From the 185 donated oocytes, endowed with the genetic material from a different person, the researchers reported development of 31 hollow balls of cells called "human nuclear-transfer blastocysts," from which they derived 11 stem cell lines.

Researchers said the cells are chromosomally normal, self- renewing and "pluripotent," meaning they have the ability to form the three major types of cells in the early embryo that give rise to all other cells in the body.

For example, the stem cells can differentiate into cells that display characteristics of skin and retina cells, muscle cell bundles, bone matrix cells and cells of the gastrointestinal and respiratory lining.

One of the next preclinical steps, according to the researchers, is to evaluate differentiated patient-specific human embryonic stem cell lines for immune-system tolerance, therapeutic efficacy and safety.

Initial laboratory experiments showed immune system compatibility between the stem cell lines and the cells of the people who supplied each line's nuclear DNA, suggesting that the patient's body might tolerate the cells after transplantation.

But before patient-specific stem cells can potentially be used in clinic, a variety of issues must be addressed, the researchers noted.

The stem cell lines produced from patients with disease will likely display characteristics of the disease, and so they will probably not be appropriate for treating patients directly.

In addition, scientists must develop methods to efficiently direct the differentiation of embryonic stem cells to specific stable cell types.

They must also find a way to remove the remaining animal components from the laboratory procedures. Currently, the procedure for isolating non-reproductive cells for the nuclear transfer involves animal enzymes and serum.

The researchers cautioned that work with human embryonic stem cells and studies of stem cells in animal model systems indicate that serious abnormalities in human development would result if the cells were used in reproductive cloning.

Any attempts at reproductive cloning would be dangerous and should not be attempted under any conditions, they noted.

Source: Xinhua