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Experimental mRNA HIV vaccine safe, shows promise in animals

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New York, Dec 10 (IANS) An experimental HIV vaccine based on mRNA — the same platform technology used in two highly effective Covid-19 vaccines — has shown promise in mice and non-human primates, according to scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the US National Institutes of Health.

The results, published in the journal Nature Medicine, show that the novel vaccine was safe and prompted desired antibody and cellular immune responses against an HIV-like virus.

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Rhesus macaques receiving a priming vaccine followed by multiple booster inoculations had a 79 per cent lower per-exposure risk of infection by simian-human immunodeficiency virus (SHIV) compared to unvaccinated animals.

“Despite nearly four decades of effort by the global research community, an effective vaccine to prevent HIV remains an elusive goal,” said co-author and NIAID Director Anthony S. Fauci.

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“This experimental mRNA vaccine combines several features that may overcome shortcomings of other experimental HIV vaccines and thus represents a promising approach,” he added.

The experimental vaccine works like mRNA Covid-19 vaccines. However, instead of carrying mRNA instructions for the coronavirus spike protein, the vaccine delivers coded instructions for making two key HIV proteins, Env and Gag.

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In studies with mice, two injections of the VLP-forming mRNA vaccine induced neutralising antibodies in all animals. The Env proteins produced in the mice from the mRNA instructions closely resembled those in the whole virus, an improvement over previous experimental HIV vaccines.

The team then tested the Env-Gag VLP mRNA vaccine in macaques. Besides the prime vaccine, the boost vaccines, delivered over the course of a year, contained Gag mRNA and Env mRNA from two HIV clades other than the one used in the prime vaccine.

Although the doses of mRNA delivered were high, the vaccine was well tolerated and produced only mild, temporary adverse effects in the macaques, such as loss of appetite.

By week 58, all vaccinated macaques had developed measurable levels of neutralising antibodies directed against most strains in a test panel of 12 diverse HIV strains. In addition, the VLP mRNA vaccine also induced a robust helper T-cell response.

Beginning at week 60, immunised animals and a control group of unimmunised macaques were exposed weekly, via the rectal mucosa, to SHIV. Because non-human primates are not susceptible to HIV-1, scientists use a chimeric SHIV in experimental settings because that virus replicates in macaques. After 13 weekly inoculations, two out of seven immunised macaques remained uninfected.

The other immunised animals had an overall delay in infection, which occurred, on average, after eight weeks. In contrast, unimmunised animals became infected on average after three weeks.

–IANS

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