A Johns Hopkins expert in HIV and how the AIDS virus
hides in the body says antiretroviral
drugs have stopped HIV from replicating, the first of three
key steps needed to rid people of the
virus.
In an address delivered Aug. 6 at the 17th
International Conference on AIDS, held in Mexico
City, infectious disease specialist Robert Siliciano said that current
drug-combination therapies can
stop HIV in its tracks, with some combos suppressing its
ability to make copies to less than one in a
billion.
But, he said, progress is still needed in identifying
where viral reservoirs persist and in finding
ways to eliminate these HIV hiding places.
Indeed, it was Siliciano's team at Johns Hopkins that
in 1995 confirmed the existence of these
reservoirs in immune system CD4 memory T-cells —
those left behind, after an initial infection, to fight
recurrences. The CD4s concentrate in the lymph nodes and
spleen. Siliciano suggests that other as yet
unverified viral pools could exist, citing previous studies
at Johns Hopkins that, in 2006, identified
adult stem cells and progenitor cells as potential
hideaways for HIV.
According to Siliciano, a professor at the Johns
Hopkins School of Medicine and a Howard
Hughes Medical Institute investigator, laboratory models
that mimic HIV infection in these reservoir
cells are key to finding drugs that can eliminate them.
"We know now that HIV can be stopped," Siliciano said
before the presentation. "Our next
steps are to go after these reservoirs of HIV. And although
much work needs to be done to find and
eliminate them, infected people who have access to
antiretroviral drugs and who take them as
prescribed stand a good chance of leading normal lives."
Siliciano points out that if antiretroviral drugs can
be made more accessible, affordable and
less toxic, then infected people who take the drugs
correctly will not develop AIDS.
Included in Siliciano's presentation are recent data
from his team and researchers at the
National Cancer Institute and the University of Pittsburgh,
which show that adding a fourth, more
potent anti-HIV drug to existing antiviral combinations
does not further suppress the number of HIV
viral copies in the blood.
"Adding more drugs to current regimens will not
further reduce the amount of virus in the
blood," Siliciano said. "We have already reached rock
bottom in using drugs to stop HIV from
replicating. The trace amounts of virus that remain are
coming from viral reservoirs, not active
replication of the virus."
In 15 HIV-positive study participants already using
highly active antiretroviral therapy, or
HAART, to suppress the virus, researchers added either a
protease inhibitor or a non-nucleoside
reverse transcriptase inhibitor. They found no greater
suppression in viral blood levels than seen
before the fourth drug was added.
Hundreds of thousands of the more than 1 million
Americans infected with HIV are currently
using HAART, a combination usually of three of 25 potent
antiviral medications. These drugs almost
eliminate the amount of virus in the blood, lowering the
number to fewer than 50 copies per cubic
milliliter of blood.
Siliciano also described the progress of four
laboratory models for testing HIV reservoirs,
including one developed at Johns Hopkins, in identifying
all viral reservoirs and in penetrating them
with antiretroviral drugs.
There are more than 33 million people in the world
living with HIV, including at least 1 million in
the United States and 23,000 in the state of Maryland.
Funding for the latest study was provided by the
Howard Hughes Medical Institute, National
Institute of Allergy and Infectious Diseases and Doris Duke
Charitable Foundation.
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