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08-01-2006 | Biotecnologia |
Fonte: BBC News
Scientists are proposing to use the hormone which triggers puberty to make organ transplants safer.
Transplant patients currently have to take drugs for the rest of their lives to prevent rejection of the organ.
But a team from Massachusetts General Hospital hope to use the hormone to activate the thymus gland, which plays a key role in «priming» immune cells.
However, a UK expert cast doubt on the theory, which is outlined in New Scientist magazine.
Immunosuppressant drugs prevent the body rejecting a transplanted organ, but they increase the risk of infections and cancers.
The US team are focusing on the thymus, a small organ beneath the breastbone, which prompts T cells in the immune system to attack foreign cells without harming the body's own tissue.
Once children reach adolescence, the sex hormones testosterone and oestrogen which are produced start to «stunt» the thymus - a process that continues throughout adulthood.
David Sachs, who is leading the research, told the magazine: «It's big and juicy in childhood, but starts to get fatty and to wither away after puberty.
«Although it keeps ticking over, it is never again as active in priming T cells.»
He suggests temporarily shutting down sex hormone activity using Lupron, a synthetic version of gonadotrophin-releasing hormone (GnRH).
Hormone levels
GnRH is released from the hypothalamus in the brain to trigger puberty.
Dr Sachs plans to give the treatment to pigs.
Once their thymus gland is revived, each animal will receive a kidney transplant and immunosuppressant drugs for a fortnight.
During this time, it is believed that the T-cells in the thymus will be exposed to cells and proteins from the new kidney, which they should be primed to treat as being part of the body.
After a few months, the hormone treatment would be stopped allowing the pigs to «return» to their normal hormonal adult state.
The hope is there would not be any need for immunosuppressant drugs because the body would by then recognise the organ.
The team have previously shown in tests on young pigs - at a stage of development similar to a 10-year-old child - that the animals can tolerate transplanted organs after just two weeks of immunosuppressive drug treatment.
However, this was not true for adult pigs or those which had had their thymus removed.
Tolerance
But Dr Maggie Dallman, of Imperial College London, was sceptical that the procedure would work in humans.
«When you transplant organs into even small children, they reject their organs without immunosuppression, just like adults.»
Dr Sachs said that was true, but that not all teenage transplant patients who stop taking their drugs rejected the organ, showing tolerance can develop naturally.
He hopes to have results from his experiments on pigs in a year's time.
If they are successful, he will seek approval for a study on humans.
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