Aids e Células-tronco / Stem cells for Aids

Cientistas anunciam uma novidade no tratamento da Aids com um método pioneiro que emprega células-tronco, protegendo o sistema imunológico do vírus causador da doença.

Resultados de testes preliminares despertaram esperanças em uma nova forma de terapia para doentes que sofrem de Aids, patologia que surge nos últimos estágios da infecção pelo Vírus da Imunodeficiência Humana, o HIV.

Novas pesquisas deverão ser feitas para estabelecer se os pacientes poderão até mesmo se livrar totalmente da infecção por HIV. A técnica consiste no isolamento de genes que impedem a disseminação do HIV pelo organismo, introduzindo os genes em células-tronco humanas em laboratório, e depois as transplantando para a medula óssea do paciente.

No primeiro teste com humanos, as células-tronco anti-HIV foram transplantadas em cinco pacientes com Aids que receberam transplante de medula no tratamento linfoma, umtipo de câncer.

Pequenas quantidades das células transplantadas conseguiram crescer e produzir novas células brancas, leucócitos, resistentes ao HIV, melhorando as condições dos pacientes.

No entanto, poderá levar ainda dez anos até que a técnica esteja disponível para uso corriqueiro, enquanto 40 milhões estão infectados pelo HIV em todo o mundo, e três milhões morrem anualmente. A intenção é que apenas um transplante possa vir a proteger os pacientes pelo resto da vida., porque células resistentes têm se mantido nos pacientes com linfoma.

O HIV ataca as células chamadas linfócitos-T, que desempenham papel fundamental no sistema imunológico porque atacam outras formas de infecção. Com o tempo, o número de linfócitos-T no sangue cai, à medida que o vírus se espalha e sistema imune para de funcionar, conduzindo à situação conhecida como Deficiência Auto-imune, a Aids, o que significa que os doentes não conseguem mais combater as infecções secundárias por si mesmos. A maioria morre de pneumonia ou cânceres como o linfoma. A medula óssea contém células-tronco (CT) que são capazes de formar todos os tipos de células sanguíneas. É nela que são produzidas as plaquetas, as células vermelhas e as brancas. Os cientistas descobriram que podem importar três genes que protegem as células conta o ataque pelo HIV para dentro dessas células-tronco, em laboratório. Administrando aos pacientes CT com esses genes, o organismo deles consegue produzir novas células, resistentes ao HIV, logo, capazes de defender o otganismo contra outras formas de infecção.

Existe também a intenção de desenvolver um tratamento intermediário que permitirá ao pacientes receber uma injeção para potencializar as células sanguíneas resistentes ao HIV de modo a melhorar sua capacidade de combater infecções. Como os transplantes de medula são procedimentos caros e arriscados, este pode ser método eficaz de tratar os milhões de pessoas com Aids, às quais bastaria receber uma injeção.

Uma combinação de múltiplos genes poderia acabar com a habilidade de o vírus sofrer mutações para escapar às terapias.

Scientists have claimed a breakthrough in the fight against Aids with a pioneering stem cell treatment that protects the immune system from the virus that causes the disease.

Results of a preliminary trial have raised hopes of a new form of therapy for people suffering from Aids, which occurs in the latter stages of infection with Human Immunodeficiency Virus (HIV). The scientists are planning further research to establish whether the treatment could even rid patients of HIV infection altogether.

The technique involves isolating genes which curb the spread of HIV inside the body, introducing the genes into human stem cells in a laboratory, then transplanting the stem cells into a patient's bone marrow.

In the first human trial, anti-HIV stem cells were transplanted into five Aids patients undergoing bone marrow replacement as part of treatment for a form of cancer known as lymphoma.

Small quantities of the transplanted stem cells were able to grow and produce new white blood cells resistant to HIV, resulting in an improvement in the patients' conditions.

Findings from the trial will be presented this week at the Stem Cell World Congress in Palm Springs, California. It could take up to ten years before an effective clinical treatment could be put into widespread use.

Around 40 million people worldwide are infected with HIV and an estimated three million die each year with the virus.

"We are trying to prevent the immunodeficiency that is a result of HIV infection," said Dr David DiGiusto, director of haematopoietic cell therapies at City of Hope Medical Centre in Duarte, California, where the research was carried out.

"It is still an experimental treatment at the moment, but we hope that eventually we will be able to give Aids patients just one transplant and that would then protect them for life. "We have data to show that the resistant cells are persisting in our lymphoma patients." HIV, which is a sexually-transmitted infection, attacks white blood cells known as T-lymphocytes, which play a central role in the immune system by fighting other forms of infection.

Over time the number of T-lymphocytes in the body decreases as the virus spreads and the immune system stops working, leading to the condition known as Auto-Immune Deficiency, or Aids, meaning patients are no longer able to fight off infections themselves. Most Aids patients die from pneumonia or cancers such as lymphoma.

Bone marrow contains stem cells that are capable of forming all types of blood cells including the white blood cells that form part of the immune system. The scientists have found they can import three genes that protect cells against attack from HIV into these blood stem cells in the laboratory.

By giving patients stem cells that carry these anti-HIV genes, the patients' bodies are able to produce new white blood cells that are resistant to attack from HIV and so able to defend the body from other forms of infection.

They are due to begin a larger trial where patients will be given greater concentrations of the anti-HIV stem cells in a bid to fight off their condition.

The researchers also hope to develop an intermediate treatment that will allow Aids patients to be given booster injections of HIV resistant white blood cells that would help to improve their ability to fight off infections.

While the ultimate hope is that the pioneering treatment could rid patients of HIV infection entirely, this might not happen if the virus, once it has been prevented from infecting white blood cells, proves able to persist elsewhere in the body.

"What we are doing is genetically modifying a fraction of the patient's stem cells with genes that target three different aspects of HIV that allow it to get into the immune cells and replicate. "When those stem cells are transplanted into patients, they create mature immune cells that circulate in the patient and protect against HIV."

"Bone marrow operations are both risky and expensive so for it to be an effective way of treating the millions of people who have Aids, it would need to be something that could be given more like an injection.

Dr Marilyn Robertson, network director of the Scottish Stem Cell Network and an Aids expert, said: "This potentially looks very interesting and the combination of multiple genes could tackle the ability for the virus to mutate and get around therapies.

"The research is still in its early stages so clearly there needs to be more work done before it could be used as an effective treatment."