Stem cell scientists from the Commonwealth Scientific and Industrial Research Organisation or CSIRO (the Australian version of the NIH) have developed a test to identify unsafe pluripotent stem cells that can potentially cause tumors. This test is one of the first tests specifically designed for human induced pluripotent stem cells or iPSCs.
The development of this test marks a significant breakthrough in improving the quality of iPSCs and identifying unwanted stem cells that can form tumors. The test also directly assesses the stability of iPSCs when they are grown in the lab.
Andrew Laslett and his team have spent the last five years working on this research project and perfecting their test.
Laslett explained: “The test we have developed allows us to easily identify unsafe iPSC cells. Ensuring the safety of these cell lines is paramount and we hope this test will become a routine screen as part of developing safe and effective iPS-based cell therapies.”
Laslett’s research focused on comparing different types of iPS cells with human embryonic stem cells. Induced pluripotent stem cells are, at this time, the most commonly used type of pluripotent stem cell in research.
Laslett’s method has established that iPSCs made in certain ways are inherently less stable and riskier than those made by alternative means. For example, the classical way of making iPSCs, with genetically engineered retroviruses that insert their genes into the chromosomes of the cells they infect, can cause insertional mutations and are inherently more likely to cause tumors. In comparison, iPSCs made with viruses that do not integrate into the host cell’s DNA (that is, with genetically engineered adenoviruses), or made with plasmid DNA, mRNA or modified proteins, do not form tumors.
Laslett hopes the study and the new test method will help to raise the awareness and the importance of stem cell safety. He also predicts that tests like his will promote a kind of quality control over the production of iPSC lines.
“It is widely accepted that iPS cells made using viruses should not be used for human treatment, but they can also be used in research to understand diseases and identify new drugs. Having the assurance of safe and stable cells in all situations should be a priority,” said Laslett.
This test utilizes laser technology that activates fluorescent dyes attached to antibodies that are bound to specific cell surface proteins. If the cell has the cell surface protein bound by the antibody, the cell and its surface proteins fluoresce, and it is sent into the positive test tube. If it does not fluoresce, it is sent to the negative test tube. This technique is called fluorescence activated cell sorting or FACS. In order to identify proteins found the surfaces of iPSCs, Laslett’s team used dye-conjugated antibodies that bound to surface proteins TG30 (CD9) and GCTM-2. The presence of these specific cell-surface proteins provides a means to separate cells into safe and unsafe cell lines. Very early-stage differentiated stem cells that expressed TG30 (CD9) and GCTM-2 on their cell surfaces tend to dedifferentiate into pluripotent cells after differentiation and cause tumors, whereas those very early-stage differentiation stem cell lines that do not express TG30 (CD9) and GCTM-2 on their cell surfaces do not cause tumors. After separation of the stem cell lines by FACS, the iPSC lines were further monitored as they grew in culture. Unsafe iPS cell lines that form tumors usual clump together to make recognizable clusters of cells. However, the safe iPS cell lines do no such thing. This test can also be applied to somatic cell nuclear transfer human embryonic stem cells.
Professor Martin Pera, the Program Leader of Stem Cells, Australia said, “Although cell transplantation therapies based on iPS cells are being fast tracked for testing in humans, there is still much debate in the scientific community over the potential hazards of this new technology.”