Rhys Evans life could have been very different.

He could have been a bubble boy, forced to walk around in a protective see-through plastic canopy. You see, he was born with an immune system that barely worked. The slightest infection could have proved fatal. But Rhys is now 14years old and doing fine.

So how did Rhys avoid living in a bubble?

The simple answer is that Rhys got lucky his condition was diagnosed when he was a baby. Even more fortunately, doctors at Great Ormond Street Hospital were able to do something about it. They understood that Rhyss condition was caused by a genetic flaw and they thought that if they could correct this flaw then they could restore his immune system. That is exactly what happened, and why Rhys is now no different to any other young teenager.

Rhyss treatment is an example of gene therapy, which was the subject of a fascinating lecture that I attended last month. Leonard Seymour, professor of gene therapies in the Department of Oncology at Oxford University, gave four reasons why 2014 has been a breakthrough year for this revolutionary, but controversial, approach.

Let me begin by describing these successful trials.

Rhys Evans is not the only boy (it does not affect girls) to have received gene therapy for this syndrome 20 were given it at about the same time as Rhys. But he was lucky. In the trial, one in four ended up with leukaemia.

This year has seen the results of a new trial. In this, nine boys were treated and eight have been reported as still alive, 16 to 43 months after treatment. The ninth died from an infection already present when he began the gene therapy. Overall, the outcome is hugely promising and suggests that gene therapy could provide a permanent cure for patients who would otherwise receive a bone marrow transplant from a donor, with all the consequent risks of rejection.

HIV is a virus that weakens the immune system by destroying the white blood cells that fight disease and infection. In order to destroy the cells it has to enter them, and it does this via a protein called CCR5, found on the cell surface. Researchers have noticed that about 1% of patients contract HIV and yet come to no harm. The reason is that their cells have a rare genetic mutation which prevents them from displaying the CCR5 protein on their surface.

Now researchers have managed to engineer white blood cells so that they have this same rare mutation. They have injected billions of these genetically modified cells into 12 trial patients, and there is evidence that this procedure is safe and could suppress the virus.

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Why 2014 has been a breakthrough year for gene therapy