New Test May Predict Course of AIDS

Preliminary findings indicate the new test may provide HIV-positivepatients with a more accurate prognosis than current methods,which can tally the numbers of T4 cells but cannot distinguishthem from other lymphocytes in terms of actual potency, said Dr.Mark Holodniy, Acting Assistant Professor of Medicine at StanfordUniversity School of Medicine.

The usefulness of the test should extend to many immunologic diseases,he added. Measuring the infection fighting power of individualtypes of lymphocytes "would revolutionize how immunologyis done," Holodniy said. "We will need to go back andlook at other diseases."

Scientists developed the new technique at Becton Dickinson ImmunocytometrySystems in San Jose, California. To test its application in AIDSpatients, they collaborated with Holodniy, who directs the AIDSResearch Center at the Stanford-affiliated Veterans Affairs MedicalCenter in Palo Alto, California.

Results from the group's preliminary studies were recently presentedin a poster session at the National Conference on Human Retrovirusesand Related Infections, held in Washington, DC.

HIV-positive patients with the same T4 levels can have vastlydifferent clinical courses. Some successfully fight off opportunisticinfections for years, while others succumb quickly. The new testmay help to predict which path a patient is likely to take bymeasuring the functional ability of the remaining T4 cells asthey decline below a critical number, Holodniy said.

He and his colleagues took blood from approximately 30 HIV-positivepatients and mixed each sample in a test tube with a bacterialtoxin. If potent, the surfaces of the T4 lymphocytes become studdedwith a particular protein, signaling the initiation of an immuneresponse.

To measure the amount of this protein, thereby gauging the cells'potency, the researchers add a fluorescent chemical that tagsthe protein and then put the sample through a flow cytometer.

In general, the team found that T4 cells from asymptomatic HIV-positivepatients produced more of the early activation marker than thosefrom patients with more advanced disease. However, among AIDSpatients with severe disease-as measured by opportunistic infections-theresearchers found great variation in the amount of the activationmarker.

"Even if you have the same classification of AIDS clinically,"Holodniy said, "you can have markedly different functionalT4 capacity." The ability to measure a patient's remainingimmune function "may help predict disease progression moreaccurately," he said.

Currently available tests of white cell function cannot evaluatethe critical T4 cells independently of other lymphocytes, he noted.Moreover, these tests take several days to complete and involveworking with radioactivity. The new flow cytometry test uses fluorescentrather than radioactive tags and takes only 5 hours, Holodniysaid.

While the test is not yet FDA-approved for clinical use, BectonDickinson will soon be marketing it to researchers, Holodniy said.