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Scientists have found that people infected with HIV-2 who do not develop AIDS mount a strong immune response against a specific HIV protein. The research could help develop vaccines against HIV.

HIV-2 infection, unlike HIV-1, rarely progresses to full disease, with 80 per cent of HIV-2 patients never showing clinical symptoms.

Researchers from the Republic of The Gambia, the Republic of Guinea Bissau and the United Kingdom analysed a group of 64 symptom-free HIV-2 patients in Guinea Bissau.

They found that patients' immune systems — notably their immune cells called T cells — responded particularly to a viral protein called 'Gag', helping them control viral replication. Gag is also a component of HIV-1.

The stronger the response to Gag, the lower the level of HIV-2 in patients' blood. Those with the strongest responses had undetectable levels of virus in their blood.

The study was published in the Journal of Clinical Investigation this month (6 September).

It shows that in HIV-2 patients, the T cell response is enough to control infection. This is important because, when designing vaccines, researchers must decide which part of the immune system (antibodies or T cells) should be activated against HIV.

"The knowledge that HIV-positive patients who mount a Gag-specific T cell response can control viral replication can now be used for the development of preventative and therapeutic T cell-based vaccines," Aleksandra Leligdowicz, researcher at the UK-based Human Immunology Unit and lead author on the paper, told SciDev.Net.

This is the first time that HIV-2 has been studied in symptom-free patients, allowing their 'protective' immune response to be analysed.

Assan Jaye, a Gambian researcher on the study, told SciDev.Net that because HIV-1 also has a Gag gene, we now have "greater insight about how to best design a vaccine against HIV". 

Some symptom-free HIV-1 patients also show a strong immune response against the protein.

Jaye adds that the research is important as it shows that it is the quality of the immune response, not its overall quantity, that makes all the difference. 

Guinea Bissau has the highest HIV-2 infection rate in the world, with up to 20 per cent of all adults above 40 years of age infected. HIV-2 is largely restricted to West Africa and is rarely deadly.

Link to full paper in the Journal of Clinical Investigation

Reference: Journal of Clinical Investigation doi 10.1172/JCI32380 (2007)

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