In 2017, Professor Liu Pengtao made a major breakthrough by capturing stem cells at the earliest stage ever, before they started to differentiate into different cell types. He called his discovery expanded potential stem cells (EPSCs) and it opened up the field to various new explorations. Recently, his team has reaped some of the benefits from those explorations. Last year, the US National Academy of Medicine (NAM) awarded Professor Liu, Managing Director of the Centre for Translational Stem Cell Biology (CTSCB) and his team a Healthy Longevity Catalyst Award (Hong Kong), for using EPSC technology to develop a new system for studying normal ageing that is based on human trophoblast cells – the first time a ‘normal’ developmental process has been captured for this purpose. Trophoblast cells are present in the placenta, nourish the foetus and protect it from the mother’s immune system. ‘Functional trophoblasts are produced from progenitor cells in the placenta, and they gradually become old and aged throughout the pregnancy. They are understudied, but their ageing process is unique since it represents an accelerated ageing of normal human cells,’ he said. But his achievements with trophoblast cells do not stop there. Prompted by concerns in the early days of the COVID-19 pandemic that babies could perhaps be infected by their mothers, Professor Liu and his collaborators were able to show that trophoblast cells can indeed be infected with the SARS-CoV-2 virus and other coronaviruses early in their development – in particular, the synctiotrophoblasts (STBs), which express high levels of the protein ACE2, a receptor for the virus. However, the good news was that ACE2 expression is strong only in the first few days of embryo development, before the embryo implants in the placenta and trophoblast progenitors start to differentiate to mature STBs. ‘In general, there is rarely direct vertical transmission of the virus from the mother to the foetus, so babies are safe,’ he said. ‘But we don’t know at the moment whether very early embryos are infected or whether they can develop normally. If the embryo is lost, it would not be noticed by the patients because there are only about 100 cells in a free-floating embryo. We are using a 3D model of a human embryo to study this further.’ The use of EPSC technology in this discovery not only gave scientists a ‘window’ to the womb – it would be difficult and unethical to do such a study in a pregnant patient – but also identified a new platform for drug screening. STBs are at least 1,000 times more sensitive to anti-viral drugs than other cells used by the pharmaceutical industry, and could be used to help identify molecules that might otherwise be missed using less sensitive drug targets. The drugs could then be FEATURE ↓Professor Liu Pengtao, Managing Director of CTSCB and his team garnered the Healthy Longevity Catalyst Award (Hong Kong) from the US NAM for using EPSC technology to develop a new system for studying normal aging. New Directions for Stem Cell Innovator 16
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