News (Updated October 1,
2005)
[Home]
[Previous
news]
| Friday, September 23, 2005 - Sunday, September 25, 2005 |
||
|
||
Merck's MRKAd5 HIV vaccine candidate elicited a stronger-than-expected immune response in trials among healthy volunteers, say researchers. The good news has led Merck to double enrollment in the trial to 3,000. The trial began in January. MRKAd5 is an adenovirus-based vaccine containing three engineered genes based on North and South American HIV strains. The HIV genes are designed to provoke a "killer" T-cell response that would destroy HIV-infected human cells. The strong response occurred even among volunteers who already had adenovirus antibodies from previous infection by the common-cold virus. MRKAd5 boosted the number of killer T-cells by 50- to 100-fold, an immune response comparable to that of successful vaccines against smallpox or measles, says Lawrence Corey, principal investigator of the HIV Vaccine Trials Network. The Seattle-based research group, supported by the National Institutes of Health, is overseeing 15 active vaccine trials. The MRKAd5 trial is a collaboration of Merck, HIVTN, and the National Institutes of Allergy and Infectious Diseases. [This summary provided by the CDC National Center for HIV, STD, and TB Prevention | The Wall Street Journal | September 23, 2005 | Marilyn Chase] |
||
US-based doctors monitored infection rates for the AIDS virus among more than 10,500 Ugandan women, about a fifth of whom were pregnant or breast-feeding.
The volunteers were all routinely tested for the human immunodeficiency virus (HIV) during the study period, and gave details about their social background, sexual activity, use of condoms and relationship with men to the researchers.
After taking behavioural and socio-economic factors into account, the investigators found that women who were pregnant were more than twice as likely to become infected as women who were not pregnant.
Two previous studies conducted in Africa have also come to roughly the same result but this is the first to take the important step of factoring in poverty and safe-sex practises, which influence the risk of infection.
The authors, led by Ronald Gray of Johns Hopkins University in Maryland, say the reason why pregnant women appear to be especially vulnerable to HIV is unclear, and call on other researchers to verify their results.
They theorise that pregnancy causes hormonal changes which may thin the protective mucous lining of the vagina or may affect a woman's immune system, making it more susceptible to takeover by HIV.
"It would be prudent to warn women of this potential risk of HIV acquisition during pregnancy, and to promote safe sex (i.e. monogamy and condom use), or sexual abstinence where feasible," the study says.
The virus which causes Aids may be getting less powerful, researchers say.
A team at the Institute of Tropical Medicine, in Antwerp, compared HIV-1 samples from 1986-89 and 2002-03.
They found the newer samples appeared not to multiply as well, and were more sensitive to drugs - some other studies argue they are becoming more resistant.
The researchers, writing in the journal Aids, stressed their work in no way meant efforts to prevent the spread of HIV should be scaled down.
Story from BBC NEWS:
Keith Alcorn
They were only able to compare 12 samples from each time period, and they were unable fully to tease out any effect that drug therapy may have had on the virus.
Hope for future
Researcher Dr Eric Artz said: "This was a very preliminary study, but we did find a pretty striking observation in that the viruses from the 2000s are much weaker than the viruses from the eighties.
"Obviously this virus is still causing death, although it may be causing death at a slower rate of progression now. Maybe in another 50 to 60 years we might see this virus not causing death."
Keith Alcorn, senior editor at the HIV information charity NAM, said it had been thought that HIV would increase in virulence as it passed through more and more human hosts.
But the latest study suggested the opposite is actually true.
"What appears to be happening is that by the time HIV passes from one person to another, it has already toned down some of its most pathogenic effects in response to its host's immune system," he said.
"So the virus that is passed on is less 'fit' each time.
"This would suggest that over several generations, HIV could become less harmful to its human hosts.
"However, we are still far from that point - HIV is still a life-threatening infection."
Similar trend
Dr Marco Vitoria, an HIV expert at the World Health Organization, said other diseases - such as smallpox, TB and syphilis - had shown the same tendency to weaken over time.
"There is a natural trend to reach an 'equilibrium' between the agent and the host interests, in order to guarantee concomitant survival for a longer time," he said.
However, Dr Vitoria stressed that the latest findings should not lull people into a false sense of security.
"This kind of change cannot be adequately measured in years, but in generations," he told the BBC News website.
He also questioned whether it was possible to draw firm conclusions from such a small study.
Will Nutland, of the charity Terrence Higgins Trust, said: "This latest study adds to the debate on an apparently confusing and contradictory issue.
"Some studies suggest recent strains of HIV are more sensitive to drugs while others claim strains are becoming more resistant.
"The study adds to the body of evidence but HIV is showing no signs of dying out in the near future."