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On November 5, 1998, a major breakthrough in organ transplant was achieved by two independent teams of scientists from the University of Wisconsin in Madison and the John Hopkin's University School of Medicine in USA. From human embryos and foetuses, they cultured human embryonic stem cells which had the capacity to multiply rapidly and grow into any sort of tissue or organ that the body requires for transplants ( Down To Earth , Vol 7, No 14). However, the scientists warn that a lot has to be done before the findings are put into use. Doubts still persist whether they are able to grow these cells into the required or specific type of cells. According to Roger Pederson of the University of California, "No one knows how to make a stem cell differentiate to form a specific tissue. We do not know the magic words to create each tissue.'

Latest research reveals that these tissues may change in ways that may make them even more susceptible to cancer. Moreover, human cells that are cultured for long periods need to be thoroughly checked and screened before they are used as tissue grafts. So far, no problems have emerged with mouse stem cells, but this does not mean that the safety measures have to be neglected.

The two teams are still doubtful about the ability of the cells to form any tissue as they promised not to clone individuals or create a "human chimera', (a cross species hybrid that could be made by injecting human cells into an embryo of another species) due to ethical concerns.

But they believe that these cells have the right properties. They contain a high level of telomerase, an enzyme which is believed to be the precursor of organs and is required for cells to divide indefinitely. They also have the ability to form cells which are the representatives of the three main types of tissues: endoderm, mesoderm and ectoderm.

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