January 17, 2002	Thursday	Ziqa’ad 2, 1422

PARIS, Jan 16: Scientists are set to report encouraging progress but also a cruel setback in the quest for a vaccine to fend off HIV.

They have found that monkeys injected with an experimental vaccine can suppress the AIDS virus in their bodies to remarkably low levels — but the virus that survived can apparently mutate and sidestep the treatment.

The studies, conducted by a team led by Emilio Emini of Merck Research Laboratories in West Point, Pennsylvania, and another led by Dan Barouch of Harvard Medical School, Boston, are published in Nature, the British science journal.

Since it was first identified 20 years ago, AIDS has killed more than 20 million people and another 40 million are currently infected with HIV, yet the desperate search for a vaccine has borne no fruit.

One reason for this is the broad and shifting range of HIV strains, which makes it hard to generate a classic vaccine based on antibodies — the defensive proteins produced by B lymphocyte blood cells, which are trained to spot and destroy a known bacteria or protein.

The Emini team, reflecting widening interest in a parallel line of attack, tested three kinds of vaccines based on stimulating bigger defences — cytotoxic T lymphocytes (CTLs) that are able to home in on and destroy virus-infected cells.

The three vaccines used different transport systems to infiltrate cells around the body, each carrying tiny pieces of genetic material.

This DNA expressed a protein that, hopefully, would prime a response from the CTLs when macaque monkeys were injected with SHIV — a hybrid version of HIV and its simian relative, SIV.

One of the vaccines was a disabled virus, called adenovirus type 5 (Ad5), which carried the DNA in it like a Trojan horse; the second, based on the same principle, used a harmless virus once used in smallpox vaccination; the third, called a plasmid DNA vaccine, was a genetic chunk of the virus itself.

None of the monkeys was able to repel infection, which as in the famously effective case of the smallpox and polio vaccines, is the ultimate dream of vaccine engineers.

However, monkeys that were had been injected with the Ad5 vaccine or had received a booster jab of the DNA vaccine did astonishingly well.

Seventy days after they had been immunized, these animals had 10 times the number of CD4 immune system cells in their blood, and between 10 and 50 times fewer the number of viral copies, compared with control monkeys which had not been injected and fell sick with AIDS.

Reflecting excitement as well as scientific caution, Emini’s team declare themselves convinced that Ad5 is a “promising vaccine vector” for combating HIV-1, the most widespread form of the virus.

A gloomier note, however, was sounded by Barouch’s team, which found that out of eight vaccinated rhesus monkeys, the immune system in seven had successfully fought SHIV. Dismayingly, it failed in the eighth.

Examination of the virus in the eighth animal suggested that the strain had mutated, enabling it to dodge the vaccine.

“These data indicate that viral escape from CTL recognition may be a major limitation of the CTL-based AIDS vaccinations that are likely to be administered to human populations over the next several years,” Barouch’s team warns.

The research makes for mixed reading for vaccine designers, who entertain great hopes for DNA and Trojan horse vaccines but also deeply fear HIV’s cunning ability to become a shifting target.

“Sisyphus would be well suited to a career in AIDS vaccine research,” comment US researchers Jeffrey Lifson and Malcolm Martin.

That was the reference to the figure of Greek mythology, who was punished by the gods to roll a stone to the top of the hill, only to see it roll down once more after he reached the summit.—AFP