Preliminary findings indicate the new test may provide HIV-positive
patients with a more accurate prognosis than current methods,
which can tally the numbers of T4 cells but cannot distinguish
them from other lymphocytes in terms of actual potency, said Dr.
Mark Holodniy, Acting Assistant Professor of Medicine at Stanford
University School of Medicine.
The usefulness of the test should extend to many immunologic diseases,
he added. Measuring the infection fighting power of individual
types of lymphocytes "would revolutionize how immunology
is done," Holodniy said. "We will need to go back and
look at other diseases."
Scientists developed the new technique at Becton Dickinson Immunocytometry
Systems in San Jose, California. To test its application in AIDS
patients, they collaborated with Holodniy, who directs the AIDS
Research Center at the Stanford-affiliated Veterans Affairs Medical
Center in Palo Alto, California.
Results from the group's preliminary studies were recently presented
in a poster session at the National Conference on Human Retroviruses
and Related Infections, held in Washington, DC.
HIV-positive patients with the same T4 levels can have vastly
different clinical courses. Some successfully fight off opportunistic
infections for years, while others succumb quickly. The new test
may help to predict which path a patient is likely to take by
measuring the functional ability of the remaining T4 cells as
they decline below a critical number, Holodniy said.
He and his colleagues took blood from approximately 30 HIV-positive
patients and mixed each sample in a test tube with a bacterial
toxin. If potent, the surfaces of the T4 lymphocytes become studded
with a particular protein, signaling the initiation of an immune
To measure the amount of this protein, thereby gauging the cells'
potency, the researchers add a fluorescent chemical that tags
the protein and then put the sample through a flow cytometer.
In general, the team found that T4 cells from asymptomatic HIV-positive
patients produced more of the early activation marker than those
from patients with more advanced disease. However, among AIDS
patients with severe disease-as measured by opportunistic infections-the
researchers found great variation in the amount of the activation
"Even if you have the same classification of AIDS clinically,"
Holodniy said, "you can have markedly different functional
T4 capacity." The ability to measure a patient's remaining
immune function "may help predict disease progression more
accurately," he said.
Currently available tests of white cell function cannot evaluate
the critical T4 cells independently of other lymphocytes, he noted.
Moreover, these tests take several days to complete and involve
working with radioactivity. The new flow cytometry test uses fluorescent
rather than radioactive tags and takes only 5 hours, Holodniy
While the test is not yet FDA-approved for clinical use, Becton
Dickinson will soon be marketing it to researchers, Holodniy said.