A worldwide team of scientists has said the human immunodeficiency virus (HIV) was swiftly evolving to avoid the body's immune defences, a phenomenon that adds to the challenge of crafting an AIDS vaccine.
Mutations in HIV enable it to rapidly sidestep genetic variations
that offer a better natural shield against the deadly pathogen, they
said in a study published in the journal Nature.
"Even in the short time that HIV has been in the human population,
it is doing an effective job of evading our best efforts at natural
immune control of the virus," said Oxford University researcher Philip
"This is high-speed evolution that we're seeing in the space of just
a couple of decades."
Goulder's team analysed the genetic codes and viral strain of 2 800
infected people in North America, the Caribbean, Europe, sub-Saharan
Africa, Australia and Japan.
Their focus was on so-called human leukocyte antigen (HLA)
These control specialised proteins whose job is to act as a
signaller against intruders. The proteins present little pieces of HIV
to the body's heavy armour, T cells, which then seek out the virus and
Since HIV was identified as the cause of Aids, more than a quarter
of a century ago, doctors have learnt that even though no-one appears
to be naturally immune to the virus, people progress to the full-blown
disease at different rates.
Without antiretroviral drugs, some individuals may develop Aids as
little as a year after infection, while others take as long as two
The span depends largely on inherited luck, for there are variants
of HLA genes that are far better at combatting HIV than others. A tiny
difference in DNA can make a huge difference in holding back the virus.
Goulder's team came across some bad news. They found that the virus is able to mutate when facing the more successful variants of these genes.
This "escape mutation" is then transmitted on to the viral progeny
and then handed on to the human population when another person becomes
"Where a favourable HLA gene is present at high levels in a given
population, we see high levels of the mutation that enable HIV to
resist this particular gene effect," said co-author Rodney Phillips in
a press release issued by Oxford University.
"The virus is outrunning human variation, you might say."
The study adds a further complexity in the quest for an HIV vaccine,
say the authors.
Vaccine engineers will have to wrestle with different "escape
mutations" in HIV that exist in distinct pools of populations.
For instance, a highly favourable variant of HLA is called HLA-B*51.
It is common among people in Japan - and, as a result, two-thirds of
infected people there have a strain of HIV which features the "escape
mutation" for this variant.
In Britain and Africa, though, HLA-B*51 is far less common. As a
result, only between 15 to 25 percent of HIV-infected people have the
"escape mutation" in their version of the virus.
A moving target
So it means that a successful HIV vaccine may have to take these
geographical differences into account, as well as the stealthy,
slippery mutability of the virus itself.
"The implication is that once we have found an effective vaccine, it
would need to be changed on a frequent basis to catch up with the
evolving virus, much like we do today with the flu vaccine," said
Aids first emerged in 1981 as a novel disease that destroys immune
cells, exposing the body to opportunistic infections. HIV was
identified as its source in 1983. Twenty-five million people have died
of AIDS and an estimated 33 million people have HIV.
The new paper focuses only on HIV's ability to sidestep natural
immune systems. It did not address the virus' mutability towards
(Sapa-AFP, February 2009)