But the treatment is too risky to help most who are infected with the virus ... A man may have been cured of both HIV and leukaemia after receiving a stem-cell transplant from a donor who is genetically resistant to HIV. About two years after the procedure, there is still no sign of the virus, even though the patient no longer takes antiretroviral drugs. Nature News takes a look at the promises and limitations of the experimental treatment.

Infection with the human immunodeficiency virus type 1 (HIV-1) requires the presence of a CD4 receptor and a chemokine receptor, principally chemokine receptor 5 (CCR5). Homozygosity for a 32-bp deletion in the CCR5 allele provides resistance against HIV-1 acquisition. We transplanted stem cells from a donor who was homozygous for CCR5 delta32 in a patient with acute myeloid leukemia and HIV-1 infection. The patient remained without viral rebound 20 months after transplantation and discontinuation of antiretroviral therapy. This outcome demonstrates the critical role CCR5 plays in maintaining HIV-1 infection.

Doctors have succeeded in ridding a man of the HIV virus by giving him a bone marrow transplant in what they claim is the closest treatment yet to a cure for the disease. The remarkable case gives new impetus to the development of gene therapy for HIV which could ultimately replace the need for expensive and toxic antiretroviral drugs. Instead of taking drugs for life, HIV sufferers might instead have a one-off treatment that would leave them virus-free. The 42-year-old American had been infected with HIV for a decade. He was treated with antiretroviral drugs in Berlin, where he lives, for four years to hold the disease in check, but then developed leukaemia. Since being given a bone marrow transplant two years ago, he has not taken antiretroviral drugs to control HIV and has had no resurgence of either disease. He is believed to be the longest HIV-free survivor who was previously treated with antiretroviral drugs. Full details of the case are published for the first time today in The New England Journal of Medicine. An editorial in the journal says it "places further emphasis on gene therapies" for HIV, adding: "The case paves the way for innovative approaches that provide long-lasting viral control with limited toxicities for persons with HIV infection." The man's treatment began with a search by doctors at Berlin's Charité Hospital for a bone marrow donor with a genetic resistance to HIV. One of the strangest features of the disease is the way some people who have been exposed to the virus on many occasions remain uninfected. Twenty years ago, it was noticed that certain prostitutes in Nairobi remained uninfected despite exposure to the virus through thousands of sexual contacts. It has since emerged that some people carry a mutation of a gene (CCR5) that confers protection against HIV. In Western populations an estimated one to three per cent have the mutation. Dr Gero Hutter, a haematologist at the Berlin Charité Hospital, and colleagues tested 61 potential donors before they found one with the CCR5 genetic mutation, who agreed to the operation.

The spread of the Roman Empire through Europe could help explain why those living in its former colonies are more vulnerable to HIV. The claim, by French researchers, is that people once ruled by Rome are less likely to have a gene variant which protects against HIV. This includes England, France, Greece and Spain, New Scientist reports. Others argue the difference is linked to a far larger event, such as the spread of bubonic plague or smallpox.

Researchers at the University of Pennsylvania School of Medicine and collaborators are using minute, naturally occurring proteins called zinc fingers to engineer T cells to one day treat AIDS in humans. The Penn researchers and colleagues from Sangamo Biosciences (Nasdaq:SGMO), Richmond, CA, who developed the zinc finger technology, report in an advanced online issue of Nature Biotechnology the first steps towards the goal of using modified T cells from an HIV-infected person for their own treatment. They showed that, using the zinc fingers, they could reduce the viral load of immune-deficient mice transplanted with engineered T cells. "By inducing mutations in the CCR5 gene using zinc finger proteins, we've reduced the expression of CCR5 surface proteins on T cells, which is necessary for the AIDS virus to enter these immune system cells," explains first author Elena Perez, MD, PhD, Assistant Professor of Pediatrics at Penn. "This approach stops the AIDS virus from entering the T cells because it now has an introduced error into the CCR5 gene." Some people are born with a mutation on their CCR5 gene and therefore do not have a working CCR5 receptor on the surface of their T cells. These rare individuals are immune to HIV infection and seemingly are not affected by the non-functional CCR5 protein. The zinc finger approach aims to mimic this natural immunity.

Homozygosity for the naturally occurring Delta32 deletion in the HIV co-receptor CCR5 confers resistance to HIV-1 infection. We generated an HIV-resistant genotype de novo using engineered zinc-finger nucleases (ZFNs) to disrupt endogenous CCR5. Transient expression of CCR5 ZFNs permanently and specifically disrupted approx50% of CCR5 alleles in a pool of primary human CD4+ T cells. Genetic disruption of CCR5 provided robust, stable and heritable protection against HIV-1 infection in vitro and in vivo in a NOG model of HIV infection. HIV-1-infected mice engrafted with ZFN-modified CD4+ T cells had lower viral loads and higher CD4+ T-cell counts than mice engrafted with wild-type CD4+ T cells, consistent with the potential to reconstitute immune function in individuals with HIV/AIDS by maintenance of an HIV-resistant CD4+ T-cell population. Thus adoptive transfer of ex vivo expanded CCR5 ZFN–modified autologous CD4+ T cells in HIV patients is an attractive approach for the treatment of HIV-1 infection.

By creating a custom-designed enzyme that can sever a gene, researchers have made a key type of human blood cell more resistant to the HIV virus. They hope to use the technique to create disease-fighting infusions of a patient’s own genetically-altered cells. The advance is a key test of a technique that could, in theory, allow scientists to design enzymes that bind to the human genome at any spot of choice and cut or correct sequences involved in other diseases.