Human heart valve from stem cells

Tissue for transplants could be available within three years if trials are successful.

Human heart valve from stem cells

A British research team led by the world's leading heart surgeon has grownpart of a human heart from stem cells for the first time. If animal trialsscheduled for later this year prove successful, replacement tissue could beused in transplants for the hundreds of thousands of people suffering fromheart disease within three years.

Sir Magdi Yacoub, a professor of cardiac surgery at Imperial College London,has worked on ways to tackle the shortage of donated hearts for transplant formore than a decade. His team at the heart science centre at Harefield hospitalhave grown tissue that works in the same way as the valves in human hearts, asignificant step towards the goal of growing whole replacement hearts from stemcells. 

According to the World Health Organisation, 15 million people died ofcardiovascular disease in 2005; by 2010, it is estimated that 600,000 peoplearound the world will need replacement heart valves. "You can see thecommon pathway of death and suffering is heart failure," said Prof Yacoub."Reversing heart failure could have a major impact."
Growing replacement tissue from stem cells is one of the principal goals ofbiology. If a damaged part of the body can be replaced by tissue that isgenetically matched to the patient, there is no chance of rejection. So far,scientists have grown tendons, cartilages and bladders, but none of these hasthe complexity of organs, which are three-dimensional structures of dozens ofdifferent types of cells.

To crack the problem, Prof Yacoub assembled a team of physicists,biologists, engineers, pharmacologists, cellular scientists and clinicians.Their task - to characterise how every bit of the heart works - has so fartaken 10 years. The progress of his team and that of colleagues around theworld will be published in August in a special edition of the journalPhilosophical Transactions of the Royal Society.

Prof Yacoub said his team's latest work had brought the goal of growing awhole, beating human heart closer. "It is an ambitious project but notimpossible. If you want me to guess I'd say 10 years. But experience has shownthat the progress that is happening nowadays makes it possible to achievemilestones in a shorter time. I wouldn't be surprised if it was some day soonerthan we think."

Currently, many people suffering from heart valve disease have artificialreplacement valves. Though they save lives, the artificial valves are far fromperfect. They perform none of the more sophisticated functions of livingtissue, children need their valves replaced as they grow, and patients need alifetime of drugs to prevent complications after surgery.

"The way a living valve functions, it anticipates haemodynamic eventsand responds and changes its shape and size. It's completely different from anartificial valve which will just open and shut. The heart muscle itself willappreciate something which will make it free to contract properly," saidProf Yacoub.

Adrian Chester, one of the lead scientists at the Harefield centre, hasfocused on characterising the valves in the heart. "You have mediators inblood or released locally in the valve that can make parts of the valvecontract and relax. That work has then extended into looking at the incidenceof nerves in the valve - these can cause the types of contractions andrelaxations in a very specific way."

By using chemical and physical nudges, the scientists first coaxed stemcells extracted from bone marrow to grow into heart valve cells. By placingthese cells into scaffolds made of collagen, Dr Chester and his colleaguePatricia Taylor then grew small 3cm-wide discs of heart valve tissue. Laterthis year, that tissue will be implanted into animals - probably sheep or pigs- and monitored to see how well it works as part of a circulatory system.

If that trial works well, Prof Yacoub is optimistic that the replacementheart tissue, which can be grown into the shape of a human heart valve usingspecially-designed collagen scaffolds, could be used in patients within threeto five years.

Growing a suitably-sized piece of tissue from a patient's own stem cellswould take around a month but he said that most people would not need suchindividualised treatment. A store of ready-grown tissue made from a widevariety of stem cells could provide good matches for the majority of thepopulation.

Prof Yacoub's inspiration has come not only from other scientists but alsofrom an unexpected source - the celebrated British artist, Antony Gormley, whohas donated a sculpture to the heart science centre. "We need a lot ofexperts from different fields but we also need a lot of imagination and a lotof understanding of how form interacts with function," said Prof Yacoub."Art gives a lot of inspiration and beauty. And beauty is part ofscience."

Mr Gormley, who has also contributed to the upcoming special issue of thePhilosophical Transactions of the Royal Society with an article on therelationship between form and function in sculpture, said he admired theuniversalism with which Prof Yacoub approached his work. "He manages to dothe Robin Hood job in a very important way for the benefit of all humanity. Ifound in him a fellow traveller in terms of trying to do things at the fringesof the possible with the highest levels of input in terms of technology andintelligence. Everybody breathes air, everybody pumps blood."


Güncelleme Tarihi: 20 Eylül 2018, 18:16