Hybrid Hearts for Transplant: Could Stem Cells Solve Rejection Problems
Andy Coghlan, New Scientist Magazine
Human organs for transplant are scarce
"It's amazing, absolutely beautiful," says
The rat hearts beat just as if there were inside a live animal, but even more remarkable is how each one has been made: by coating the stripped-down "scaffolding" of one rat's heart with tissue grown from another rat's stem cells.
Taylor, a stem cell scientist at the
This could lead to a virtually limitless supply of organs for transplantation that are every bit as intricate as those that grow naturally, except that they don't provoke the catastrophic immune response that obstructs the use of traditional "xenotransplants."
"We're already working with heart, kidney, liver, lung, pancreas, gallbladder and muscle," Taylor says. Rival groups are using similar procedures to create new livers and muscle, too.
Human organs for transplant are scarce. One option is to engineer organs from scratch in the lab, using artificial scaffolds. While bladders and skin can be grown in the lab, growing more complex organs and their intricate blood-vessel networks, has proved tricky.
Xenotransplants from pigs are another possibility, though fraught with problems. You have to prevent the recipient's immune system from destroying the organ, and also ensure the transplant is free of pig viruses that could be passed on.
Taylor's organs avoid these problems. For starters, building an intricate scaffold from scratch is unnecessary. "It's letting nature do most of the work," she says. What's more, because the stem cells that "clothe" the naked scaffold are taken from the patient, the organ stands a higher chance of being accepted by their immune system.
The idea is fairly simple: Take an organ from a human donor or animal, and use a mild detergent to strip away flesh, cells and DNA so that all is left is the inner "scaffold" of collagen, an "immunologically inert" protein. Add stem cells from the relevant patient to this naked shell of an organ and they will differentiate into all the cells the organ needs to function without inducing an immune response after transplant, or any new infections.
The idea has already worked with simple organs. In 2008,
Taylor's team is using the same technique to create much more complex organs such as hearts, and extending it to using animal, as well as human, scaffolds.
A big challenge with complex organs is ensuring that all their cells are infused with blood. Without blood, cells in the center of the organ would be starved of oxygen and die after transplantation. Taylor says her method overcomes this problem.
A big breakthrough came in
Since then, Taylor says they have managed to "pretty much repopulate the whole vascular tree" with cells, which includes veins, arteries and capillaries. "Because we've retained the blood vessels, we can take the plumbing and hook it up to the recipient's natural blood supply," says Taylor. "That's the beauty of this."
Although Taylor only added stem cells to the hearts, these cells differentiated into many different cells, in all the correct places, which is the best part of using decellularised scaffolds. The stem cells transformed into endothelial cells in the ventricles and atria, for example, and into vascular and smooth-muscle cells in the spaces for blood vessels, just as in a natural heart. Taylor thinks this happened because she pumped blood and nutrients through the organ, producing pressure in each zone, which helps to determine how cells differentiate there.
But chemical, as well as mechanical, cues seem to have guided differentiation. Taylor has evidence that growth factors and peptides remained anchored to the scaffold even after the flesh was washed off. These chemicals likely signaled to the stem cells, indicating how many should migrate to which areas and what to change into in each zone. "Our mantra is to give nature the tools and get out of the way," she says.
Her team has implanted the reclothed hearts into the abdomens of rats, where they survived temporarily and were not rejected. The next step is to see if the transplants can replace an existing heart and keep the animal alive and healthy. To do this, Taylor says they will need to come up with ways to grow more muscle tissue on the hearts. "We've built the vasculature but we don't think we've built enough muscle to keep animals alive."
She's also gearing up to repeat the rat experiments with pig hearts and livers. This could be easier because pig organs are larger and easier to handle than tiny rat hearts. Decellularised livers could also appear in humans before hearts because it may not be necessary to recreate entire livers for them to be useful.
Others are also working on livers.
Not everyone believes that turning decellularised tissue into a complex, functional organ is as simple as it sounds.
"We're a long way from being able to make functional tissues and organs," says
Taylor says people who find the idea of pig parts unacceptable should consider their current uses in humans. "We're not ready for prime time yet, but we're moving in the right direction," she says.
PIG PARTS ALREADY COMMONPLACE
Implanting organs made from the scaffold of a pig organ may sound off-putting and even dangerous, but millions of patients have already been treated with decellularised pig parts without being infected by stowaway pig viruses or suffering disastrous immunological reactions.
Pig heart valves are often used to replace faulty ones in people. In the past, patients who got such valves had to take immunosuppressive drugs. But this isn't necessary with newer pig valves, made by the company AutoTissue in
For years, companies have also been selling decellularised pig gut to produce patches that help the healing of diabetic ulcers, hernias and strained ligaments. Cook
Effectiveness of Laser Spine Surgery for Pain Relief Remains Unproven
H. Gordon Deen, M.D., Neurosurgery, Mayo Clinic
Spine surgery can be performed using several different tools, including a laser. Laser spine surgery has been around since the 1980s but it has never been studied in a controlled clinical trial to determine its effectiveness. Most neurosurgeons don't use lasers for spine surgery because there are no clear benefits to laser surgery over more well-established spine surgery techniques
Atril Fibrillation Treatment Involves Reducing Risk of Stroke
Stephen Hammill, M.D., Cardiovascular Diseases, Mayo Clinic
Atrial fibrillation is an irregular heart rhythm that involves the upper heart chambers (atria). During an episode of atrial fibrillation, the atria beat out of rhythm very quickly, up to 400 beats per minute. Fortunately, this rapid rate is slowed to about 70 to 150 beats per minute as the impulse travels to the lower chambers, the ventricles, which then pump blood to the body. The episode may last minutes to several days and individuals with atrial fibrillation should seek medical care promptly.
Surgery Not Only Option for Treating Spinal Stenosis
Mark Dekutoski, M.D., Orthopedic Surgery
Spinal stenosis is a common condition that results from changes to the spine as aging occurs. Symptoms vary in character and magnitude but can most often be effectively treated with nonsurgical therapies, such as medication and physical therapy. In severe cases, surgery may be necessary.
Managing Blood Pressure Crucial for Those With Aortic Dissection
Thoralf Sundt, M.D., Cardiovascular Surgery, Mayo Clinic
Aortic dissection, a tear in the inner layer of the aorta causes the inner and middle layers to separate, sometimes affecting the entire length of the aorta. Aortic dissection is the result of a weakness in the aortic wall. It's serious because the aorta, the largest artery in the body, is the main conduit of oxygenated blood from the heart.
Could Cigarette Smoking Ever Get Safer
Linda Geddes, New Scientist Magazine
Tobacco companies have begun "clinical trials" to assess whether a range of prototype "safer cigarettes" really do slash levels of toxic chemicals entering the body
Finding Effective Treatment For Chronic Pain
January W. Payne
Chronic pain is a problem that -- when healthcare, lost income, and lost productivity are taken into account -- is estimated to cost about $100 billion in the United States each year. More than a quarter of Americans age 20 or older, or about 76.5 million people, say they've experienced pain that lasted longer than 24 hours
Cholesterol - 10 Ways to Lower LDL and Raise HDL
January W. Payne
Your doctor tells you that your level of LDL -- the 'bad' type of cholesterol -- is too high, and, in a double whammy, he says that your level of HDL -- the 'good' cholesterol--is too low. Is there anything you can do to decrease the bad while increasing the good? There are steps you can take to accomplish this.
Principles of Conservative Prescribing: Do You Really Need All Those Pills
Harvard Health Letter
People who genuinely need medications should take them; indeed, getting people to take medications as prescribed is a persistent problem. But there's some questioning of prescribing practices these days, much of it inspired by a growing conviction that American health care has become too dependent on expensive medications.
Weight Loss Drugs & Diet Pills Have Many Drawbacks
Mary Pickett, M.D.
I wish we had a diet pill that could help people lose weight easily. None of the medicines on the market are worth using, if you ask me
Health, Nutrition & Diet: Getting Out the Gluten
Harvard Health Letters
Gluten seems to be the food ingredient non grata these days. Bakers are coming up with recipes for gluten-free cupcakes and baguettes. Anheuser-Busch sells Redbridge, a gluten-free beer made from sorghum. By some estimates, the sales of gluten-free foods have tripled since 2004. Gluten-free food has become more popular partly because doctors are diagnosing more cases of celiac disease, an autoimmune disorder whose symptoms are triggered by gluten, the protein content in wheat, barley, rye ...
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