Animal tissue rejection advance

[[R_H]]

BBC

Scientists have found a way to overcome the problem of the human body rejecting animal parts used in transplants.

The work, by the University of Leeds, means the use of animal tissue such as blood vessels, tendons and bladders may become common in surgery.

Human organs for transplant are constantly in short supply, meaning long waits for many patients.

Currently, the use of animal tissue for human transplant is restricted, and of limited effectiveness.

For instance, chemically treated heart valves from pigs have been transplanted into patients for more than a decade, but have a limited life span as they are inert and cannot be populated by the patient's own cells, and ruling out any possibility of repair to damage.

This poses a particular problem for young patients, as the valves do not grow with the child, and must be replaced frequently.

The Leeds team used a combination of freezing, chemical baths and ultrasound to strip the animal tissue of the cells and biological molecules that trigger a response from the immune system.

This left a biological scaffold which could then be populated by cells from a patient's own body, creating a tissue which carries no risk of rejection, which can be repaired, and which can grow with the body.

So far tests have only been carried out on animals, but researcher Professor John Fisher said it was hoped to begin clinical trials on humans next year.

Better alternative

Professor Fisher said: "We are talking about relatively simple tissues, such as blood vessels, heart valves, ligaments, tendons, surgical patches for internal repair.

"At the present time the surgeon has only got two choices, either sacrifice some tissue from somewhere else in the patient's body, or wait for a donor tissue from another human being, and clearly they are in short supply.

"This is a very attractive alternative, because it can be available off the shelf for the surgeon to use."

The scientists have formed a company, Tissue Regenix, and are working with the NHS Blood and Transplant Service to develop the technique so they can create new heart valves for children.

However, transplant expert John Forsythe, based at the Edinburgh Royal Infirmary, said much work was needed before the use of animal parts was routine in transplant surgery.

He said it was possible that the biological scaffold left behind after cells had been stripped away could still provoke a longer-term immune reaction, as it would still be different to that found in humans.

In addition, using tissue which was not inert carried a potential risk of infection.

However, he added: "If we have a means of stripping away the first, and most major cause of rejection that is certainly something that requires further investigation."

[dragon]

Nice to see mutiple fronts for over coming the same problem. I MIT have been working on a way to make self assembling cells out of the user's own tissue. And they been having some good breakthroughs.

These two topics brings to mind that episode in CSI New York where there was a human ear growing on a mouse's back

Tissue engineers are ambitious. If they had their way, a dialysis patient could receive a new kidney made in the lab from his own cells, instead of waiting for a donor organ that his immune system might reject. Likewise, a diabetic could, with grafts of lab-made pancreatic tissue, be given the ability to make insulin again. But tissue engineering has stalled in part because bioengineers haven't been able to replicate the structural complexity of human tissues. Now researchers have taken an important first step toward building complex tissues from the bottom up by creating what they call living Legos. These building blocks, biofriendly gels of various shapes studded with cells, can self-assemble into complex structures resembling those found in tissues.

"Living tissues have repeating functional units," says Ali Khademhosseini, a bioengineer at Harvard Medical School. The liver, for example, is made up of repeated hexagonal lobes. Each has a central branching vessel that brings in blood for filtration; the vessel and its branches are surrounded by toxin-filtering cells surrounded by canals that transport filtered blood to other vessels leading out of the organ. Traditional approaches to tissue engineering, says Khademhosseini, "rely on the cells to self-assemble and re-create structures found in the body." Bioengineers seed cells onto the outside of polymer scaffolds in the hopes that they will migrate inside and organize themselves. Cells do self-organize to some extent, but such top-down attempts have had limited success.

Khademhosseini is trying to re-create complex tissue structures by carefully controlling cell organization from the bottom up. He mixes cells into a solution of a biocompatible polymer called polyethylene glycol, then pours the mixture into molds shaped like blocks, stars, spheres, or any other shape. When exposed to a flash of light, the polymer blocks solidify. The living Legos can then be built up into more-complex structures and exposed to another flash of light that bonds them together. But assembly is painstaking: each block is only about a hundred micrometers across.

So Khademhosseini and a group of researchers at MIT and Harvard have come up with a simple two-step process to make the living Legos self-assemble. Their method, described in a paper published today in the Proceedings of the National Academy of Sciences, relies on the basic fact that water and oil don't mix. When water is dropped into a pool of oil, it will form a sphere, the shape that minimizes its interaction with the oil, says Khademhosseini. The polymer building blocks are hydrophilic--they easily absorb water and resist interacting with oil. But they can't change their shape, so when Khademhosseini places them in an agitating bath of mineral oil, the blocks clump together in order to minimize their contact with the oil. The polymer blocks, now assembled into branches, cubes, and other shapes, are bonded together with another flash of light. The organization of the resulting structures can be controlled by varying the shape and size of the building blocks and the agitation speed.

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