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 response.
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 marker.
"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 said.
While the test is not yet FDA-approved for clinical use, Becton Dickinson will soon be marketing it to researchers, Holodniy said.