The latest research looked at treating malignant melanoma

Here is how scientists were able to achieve this.

How it works

Dr Stephen Rosenberg and his team at the US National Cancer Institute isolated immune cells, called T cells, from the cancer patients.

T cells are white blood cells that can recognise and attack foreign invaders.

Next the scientists used a virus to carry receptor genes into the T cells.

These genes enable the T cell to make receptors. In turn, these receptors recognise specific cancers - in this case malignant melanoma.

The modified T cells are then transfused into the patients where they will attack the cancer cells.

Has this been done before?

Dr Rosenberg and his team are the first to demonstrate that engineered T cells can persist in the body and shrink large tumours in humans.

But many scientists have been looking at using gene therapy to treat different diseases, including cancer.

Scientists at Manchester University have also been looking at gene-modified t-cell therapy.

This technique is one of many. The possibilities offered by gene therapy are expanding all the time.

Generally, gene therapy is a way of treating disease by either replacing damaged or abnormal genes with normal ones or by providing new genetic instructions to help fight disease.

Scientists have already been looking at correcting faulty genes responsible for a condition by "smuggling" working copies into the cells and hoping they will replace the problem originals.

Again, they do this by using a virus to carry the replacement DNA into the cells.

The treatment has been successfully used, as in the case of the so-called "bubble boy" Rhys Evans, who suffered from a genetic condition which prevented him from developing a working immune system.

Are there safety concerns?

Yes. Authorities in the US have found that hundreds of experiments have failed and have caused a number of deaths.

French authorities suspended gene therapy trials after a child developed leukaemia after undergoing treatment.

What is the future for gene therapy?

Doctors and scientists working in the field are confident that gene therapy could provide the key to curing a wide range of major diseases.

They, however, acknowledge that much more study is needed before the technique can be used extensively.