WASHINGTON (Reuters) - An AIDS vaccine that
helped keep monkeys from getting sick could show scientists how
to start fighting the HIV epidemic in people, researchers said
The vaccine did not prevent infection, but it did stop monkeys
from developing symptoms of HIV infection -- and it kept the
animals alive, the team at Massachusetts General Hospital and
Harvard University said.
Dr. Norman Letvin, the AIDS researcher who led the study, said
it showed that vaccine researchers can lower their sights a
bit, seeking not to prevent HIV infection entirely but to use a
vaccine to keep people from becoming so ill when they do become
"This study raises the possibility that, while we don't have
any approaches in hand that are likely to truly prevent
infection, we may have a number of approaches in hand that can
generate a killer T-cell response that can alter the course of
infection," Letvin said in a telephone interview.
AIDS researchers realize the only answer to the epidemic of
HIV, which infects 35 million people worldwide, is a vaccine.
But efforts to develop a preventive vaccine have been slow and
failure after failure have convinced experts that they need to
try for something a little less ambitious.
Letvin and colleagues have been working on a shot that might
not prevent infection but might stop people from becoming ill,
perhaps keeping them healthy without having to take expensive
drug cocktails that have extensive side-effects.
"Since most populations infected with HIV cannot afford drug
therapy, this would be of tremendous benefit," he said. He also
said the vaccine might make it less likely that an infected
person would pass the infection to someone else.
Writing in the journal Science, Letvin and colleagues said they
had devised a vaccine that used envelope proteins -- coming
from the outside of the virus -- from both SIV, the monkey
version of HIV, and human HIV.
This DNA vaccine was boosted with interleukin 2 (IL-2), an
immune system protein, and an antibody called IgG.
Working with a team at Merck Research Labs in West Point,
Pennsylvania, they tested 20 monkeys by giving them either a
fake or real vaccine and then infecting them with SHIV, an
engineered human-monkey virus that produces an especially quick
and deadly AIDS-like illness in monkeys.
Unvaccinated Monkeys Died Quickly
The monkeys who received the sham vaccine all became sick and
half died within 140 days.
"Monkeys that received the experimental vaccine, and there are
eight of those monkeys, became infected and early after
infection the virus replicated to very high levels. But ... the
vaccinated animals appear to be quite good at controlling the
level of viral replication," Letvin said.
Importantly, the vaccinated monkeys produced CD8 killer
T-cells, also known as cytotoxic T-lymphocytes or CTLs, that
attacked the virus.
Letvin said the study showed that producing this strong CTL
response is vital to create a working HIV vaccine.
"It is very, very important to remember that this was an
experiment done in monkeys, not in humans, and it was an
experiment done with a monkey virus," Letvin stressed.
Most vaccines produce antibodies that attach to viruses or
bacteria and help other immune cells find and kill them. This
does not work with HIV, perhaps because it mutates so quickly.
"The CTL response appears to be very important in controlling
AIDS virus infection," Letvin said. "CTL works by recognizing
cells that are infected with the AIDS virus and killing those
Letvin said any number of different vaccine formulations might
produce a CTL response and he hoped other researchers would now
be spurred to develop a formula to test in humans.
Dr. Robert Siliciano of Johns Hopkins University in Baltimore,
another HIV expert, called the study exciting.
"It changes the way people will look at what we are able to
achieve in the near-term in AIDS vaccines," he said in a
But Siliciano and other experts said the study suggested that
vaccines now being tested in people will not do the trick.
"Frankly, the current vaccines that have been tested already in
humans don't elicit quite as strong a response as seen in these
vaccines. So we have got to do better," he said.
Dr. Seth Berkley, president of the International AIDS Vaccine
Initiative (IAVI), said he was also encouraged. "Their
findings, combined with data on other vaccine approaches and
basic research studies, provide more evidence that a preventive
AIDS vaccine is possible," he said in a statement.