Gene therapy to treat HIV shows promise

The success of a new gene therapy trait represents a significant step towards a 'functional cure' for HIV, human immunodeficiency virus, US researchers announced this week. By mimicking the effects of a naturally occurring gene mutation that makes an individual resistant to infection, this therapy aims to reduce or eliminate the dependency of HIV patients on antiretroviral drugs.

Out of the six HIV patients treated with the new therapy, which works by stopping the virus from getting inside the white blood cells it normally infects, one patient had completely cleared the virus and a further two saw a ten-fold drop in virus levels, despite not taking any antiretroviral drugs.

'We're over the moon to have seen that in this small phase one study', said Jeff Nichol, the executive president of research at Sangamo BioSciences, the company that funded the trial.

The treatment involves isolating white blood cells called T-cells from patients and then genetically modifying them with a specially designed enzyme which inactivates the CCR5 gene. This gene codes for a receptor that is required for HIV to get inside and infect the T-cells, effectively making them HIV-resistant. These cells can then be transfused back into the body.

We inherit two copies of the CCR5 gene, one from each parent. The patient that responded best in the trial, becoming 'virus-free', already carried one mutated copy of the gene, making it easier to produce T-cells where both copies were defective. Researchers believe this is the key to its success — the treatment worked best in those patients who had the largest number of doubly defective T-cells.

Earlier this year, Timothy Brown from Berlin became the first, and so far the only, person to be cured of HIV after he received multiple blood transfusions from an individual who carried a defective copy of the CCR5 gene. According to WebMD, five percent of the general population carry two mutated copies of the CCR5 gene, while ten percent carry one mutated copy.

Dr Pablo Tebas, the infectious disease clinician who headed up one of the clinical trials, believes the trial 'shows a path forward'. Referring to the Timothy Brown case he said: 'The Berlin patient is only one patient, and it changed research priorities'.

It is likely that the results of this trial will lead to increased research into disrupting the CCR5 gene to treat HIV, but Dr Tebas cautions: 'This is a very small experiment, and I don't think it's a cure by any means'.

The results of the trial were reported at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago, Illinois, but are yet to be published or undergo peer review.