DURHAM, N.C. -- Researchers at Duke University Medical
Center have developed a highly sensitive test for identifying
which drug-resistant strains of HIV are harbored in a patient's
bloodstream.

The test may provide physicians with a tool to guide patient
treatment by predicting if a patient is likely to become
resistant to a particular HIV drug, said one of its developers,
Feng Gao, M.D., associate professor of medicine. Drug
resistance is one of the most common reasons why therapy for
HIV, the virus that causes AIDS, fails.

The test, which detects genetic changes, or mutations, in
HIV, also may help scientists understand how the constantly
evolving virus develops drug resistance, Gao said. He said such
knowledge ultimately may result in the development of new
treatments designed to evade resistance.

The findings will appear online on Sunday, Jan. 7, 2007, in
the journal Nature Methods, as well as in the journal's
February 2007 print edition. The work was supported by the
National Institutes of Health and the Duke Center for AIDS Research.

Duke has filed for a provisional patent on the technology,
and the Duke Office of Licensing & Ventures is considering
various options to commercialize this technology.

Because HIV genes mutate so easily and the virus reproduces
so rapidly, most people who are infected have many different
forms of the virus in their bodies. In some cases, mutated
strains take on new properties that make them more resistant to
the drugs used in antiretroviral therapy, the primary means of
treatment for HIV infection.

During antiretroviral therapy that does not fully suppress
the virus, a strain that develops drug resistance will grow
more quickly than strains lacking such resistance, and the
resistant strain will replicate to become the most prominent
virus in the person's body.

"The viral populations found in the blood of one patient can
be very different from the populations present in another," Gao
said. "Which resistant viruses are at hand can have important
implications for the successful treatment of that patient."

More than 20 drugs currently are available for treating HIV
infection. All but one of the drugs target two of the genes
that serve as blueprints for vital protein components of HIV:
reverse transcriptase and protease.

The Duke test examines the genes of HIV strains for
mutations at certain positions that are known to be linked to
drug resistance. For example, a change at a specific spot along
the genetic code -- position 46 -- of the protease gene results
in resistance to the drug indinavir.

To assess the test, the researchers analyzed blood samples
from three different groups of HIV patients: those who had
never received antiretroviral treatment, those who had received
treatment but were not currently being treated and those who
were receiving treatment but the treatment was not completely
successful.

After processing the blood samples and isolating the genetic
material in each of them, the researchers added tiny
fluorescent tags designed to stick to HIV genes in particular
ways. Tags designed to stick to mutated gene locations known to
produce drug resistance were labeled to appear green, while
tags designed to stick to the same gene locations but where the
genes had not mutated were labeled to appear red.

The researchers used a sophisticated computer program to
count the number of molecules with green or red fluorescent
tags in each sample. The test proved sensitive enough to detect
a single mutated virus out of 10,000 nonmutated viruses in the
patient samples, Gao said.

"This level of sensitivity makes the assay about 1,000 times
more sensitive than the most widely used assays on the market
for detecting drug-resistant HIV viruses" Gao said. "Thus, the
assay may permit more accurate prediction of treatment
outcomes."

The test also can detect when a virus molecule has more than
one mutation, a capability that no commercially available test
has achieved, Gao said. This capability may prove critical for
detecting HIV strains that have become resistant to multiple
drugs, a condition that occurs often as many patients are
treated with many drugs at the same time.

The test may find broader medical application as well, Gao
said. He said it has the potential to detect mutations that
confer drug resistance in infectious agents that cause other
diseases besides HIV, such as hepatitis B, hepatitis C and
tuberculosis.

Other researchers participating in the study were Fangping
Cai, Haifeng Chen, Charles B. Hicks, John A. Bartlett and Jun
Zhu.