While the use of animal organs or cloned human organs is still a long way off, the next big target for surgeons is to develop reliable techniques for transplanting nerves.

In particular, they are interested in the neural material that makes up the brain and spine.

Connecting nerves has always been the hardest technical part of a transplant operation, and it is this difficulty that makes neural transplantation such a challenge.

Results offer hope

There are clinical trials being carried out around the world where nerve cells are transplanted into patients.

Nerves set challenge for transplant surgeons

Doctors hope the process can be used to treat brain diseases such as Parkinson's, Huntington's, Alzheimer's and multiple sclerosis, as well as spinal injuries.

Most of the research so far has focussed on Parkinson's Disease, and the results of such experimental treatment have been promising.

When diseased nerve cells are replaced with healthy ones, patients show improvement and reduce their medication.

Embryo tissue

The healthy cells come from the neural tissue of aborted embryos or animals because adult brain cells will not survive the transfer.

In the US, there is a four-year project under way at the University of Florida to investigate the use of nerve cells in treating spinal injuries.

Last year, the researchers became the first team to perform a nerve transplant to treat a man paralysed with a spine injury.

But the most urgent research being carried out aims to make the operations that already exist more widely available.

Not everyone who needs a transplant can get one because there are not enough organs available.

This means researchers focus their efforts on addressing the shortfall and maximising the benefits offered by a transplant.

Fiona Gravette, of the National Transplant Information Service, said: "Research aims to make the things we have work better and longer."

Relatives' donations

Normally organs are taken from dead bodies, so, in the absence of more deaths, gaining an increase in the number of donor organs available requires more live donation.

Family members are ideal for live transplants

Live donations are usually made by a blood relative of the patient, and the most common organ donated is a kidney as it is possible to lead a normal life with only one.

However, the British are often reluctant to donate.

Ms Gravette said: "It is something we do not do a lot of in this country.

"In Norway, nearly 40% of all transplants are done this way. In the US, the figure is 25% while it is 10% in the UK."

The reason for this might be because operating on a well patient goes against doctors' training, she said, but the success rate of the procedure was good and getting better.

Double value

Other research aims to make the most of donated organs.

Split-liver transplants take advantage of the organ's unique ability to regenerate.

A liver can be divided and given to two patients, doubling the value of the donated organ.

Researchers are developing a technique whereby a living parent can donate a piece of liver to their child.

And there is promising work on split-lung transplants.

Although the lung cannot regenerate, two donors can each give a small piece of lung to a third person with a respiratory disease such as cystic fibrosis.

Beating side-effects

The donors will have reduced breathing capacity, but remain healthy while the quality of life will be greatly improved for the recipient.

Once the organ has been transplanted, there is the danger of rejection, so another key area of research is in improving the drugs that control a patient's immune system.

"Doctors have to juggle the drug cocktail to be immunosuppressive without being toxic," Ms Gravette said.