The progress toward developing an HIV vaccine may be hindered by
the results of a new study by UCLA researchers, which found
differences in the way identical twins’ immune systems
responded to the virus.
The study, led by Dr. Otto Yang, an associate professor in the
departments of medicine and microbiology, immunology and molecular
genetics, tracked a pair of male twins first infected with HIV via
blood transfusions from the same donor just after they were born in
1983.
Researchers have only been studying the twins since 2000, but
did research on the twins’ prior histories, including a study
of blood samples from 1995. Both of the twins have very similar
medical histories, from taking most of the same medications to
treat HIV and having similar illnesses and HIV complications at
about the same times throughout their lives.
However, when it comes to their bodies’ reactions to HIV,
the similarities end.
To protect the body from viruses, cells in the immune system
have receptors on their surfaces which bind to proteins on the
viruses. This binding keeps the viruses from damaging the body. HIV
harms the body by avoiding the immune system’s attacks
through mutations that change the shape of its proteins so that
they cannot fit into the receptors of the cellular immune
system.
“If the virus mutates the protein being bound, then that
receptor becomes useless in clearing the virus … The reason
that’s important is there’s a degree of randomness in
the way the immune system reacts which we can’t
control,” Yang said.
The immune system responds through the generation of randomly
shaped receptors, which can bind to various proteins of different
viruses. Therein lies the difference between the twins, whose
immune systems generated different receptors in response to HIV.
Researchers said this difference between identical twins is an
indication of how difficult it will be to create a vaccine to
accommodate the masses of infected people across the world.
“The implication of our study for vaccine research (is
that it) helps show our inability to predict the immune responses
that people will have in attempting to control HIV growth within
the body,” said Paul Krogstad, professor of pediatrics and
pharmacology and another researcher for the study.
“Identical twins (are) as identical as two people can be.
These data help demonstrate even identical twins are, in more than
one way, obviously distinct human beings,” he said.
Both Krogstad and Yang said this study is just one part of a
larger study on how HIV affects patients and does not yet indicate
the end of the search for a vaccine.
In the study, researchers said, “Sterilizing immunity
against HIV is considered an unlikely, and possibly unattainable,
goal for vaccine development, but protection against disease may be
possible if persistently effective immune responses can be
generated.”
Yang said there have not been any significant steps taken toward
developing a vaccine, so this should not be viewed as a step
backwards.
“We need to be careful about making conclusions abroad
about one pair of twins … The twins are a good example of
something that theoretically would be predicted by theories about
how the immune system works,” he said.
Krogstad said the fact that the twins are even alive today is a
sign of hope for the future of HIV research.
“(That they are alive) by itself is remarkable and
something that wouldn’t be expected 15 years ago. Their
survival into adulthood is a testament in advances in our ability
to monitor and treat HIV infections both in adults and
children,” he said.
Krogstad also said there is no reason to be pessimistic about
the future.
“I see progress. I see hope in seeing so many kids who
were infected making it into adulthood, many of them in good
health, many with the opportunity to look forward to long
life.”