New antibody suppresses spread of HIV-1 in infected individuals
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Shalini Saxena
Since its discovery and rapid spread in the
1980s, scientists and physicians have desperately tried to understand
the HIV virus and develop effective treatments. Unfortunately, HIV is a
tricky virus that evades typical immune responses.
During a successful immune system response to a
foreign body, white blood cells produce antibodies that target the
invader. These antibodies then flag the foreign body for destruction by
other immune cells. For the most part, HIV evades these immune defenses,
but rare individuals develop antibodies that effectively block multiple
strains of the virus. Researchers are now showing that these antibodies
can also act as treatments in other HIV patients.
HIV has several ways of avoiding the immune
response. Unlike most viruses, HIV specifically attacks a type of white
blood cell that is critical to our immune system. During replication,
the HIV virus also picks up many new mutations, which often change it
enough that any antibodies produced earlier during the infection no
longer recognize it. There are very few parts of the virus where changes
due to mutations would cause it to be unable to enter cells; even fewer
antibodies have been identified that bind to these locations.
These rare antibodies can also keep the virus
from infecting new cells, which could make them an effective therapy.
In animal studies, injection of low concentrations of these antibodies
could act as a vaccine and provide protection against infection.
Injections can even control active infections when combined with
additional antibodies that target other molecules on the the HIV
surface. These preclinical findings led to humans phase 1 clinical
trials to evaluate a specific antibody that targets HIV. This study
revealed that a single intravenous injection of the antibody typically
reduced the presence of HIV in the blood of patients who have viruses
that were sensitive to the antibody.
These promising results come from an
international team of scientists and physicians that has investigated
the safety and clinical efficacy of one of the most potent anti-HIV-1
neutralizing antibodies. Known as monoclonal antibody 10-1074, it
targets a specific HIV protein called the v3 glycan. This target is
different from the one recognized by the antibodies used in earlier
studies.
After performing test-tube studies
demonstrating the efficacy of the antibody, the researchers evaluated
its safety in humans in a small trial. The study included two groups of
participants: 14 uninfected individuals and 19 individuals with an HIV-1
infection. The participants received a single intravenous infusion of
the antibody at one of following doses: 3, 10, or 30 mg/kg.
The researchers then tracked the clearance of
the antibody by following its levels in the participants’ serum.
Consistent with previous studies, HIV-1 infected individuals exhibited
faster elimination of the antibody, with a half-life of 12.8 d compared
to 24.0 d for uninfected participants. Despite the fast clearance,
however, the antibody appeared to be effective.
Three HIV-1 infected individuals on the trial
were undergoing a specific type of treatment (antiretroviral therapy)
and exhibited no changes in the level of HIV in their system due to the
antibody infusion. Thirteen HIV-1 infected participants with the highest
levels of virus received the highest dose of the antibody (30 mg/kg).
Eleven of them showed a rapid decline in HIV levels. Tracking the
infection through the first weeks after treatment revealed the
evolution of multiple viruses that were no longer affected by the
antibody. However, these new variants generally remained sensitive to
antibodies targeting other virus surface molecules.
Overall, this investigation demonstrates the
safety of infusions of antibody 10-1074 in humans. While the virus
quickly evolved resistance to these treatments, the resulting viruses
remained susceptible to other antibodies. Thus, researchers may be able
to build a cocktail of antibodies that effectively block active HIV
infections.
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