A sensitive, rapid test can be used to monitor the amount of HIV in a patient's bloodstream. In the future, this procedure may help clinicians both decide when to give anti- HIV therapy and also gauge its effectiveness, according to researchers at the National Institute of Allergy and Infectious Diseases (NIAID), Georgetown University and Chiron Corporation.
The test, called the branched DNA assay for HIV-1 infection, also may help investigators determine more quickly if experimental HIV therapies are effective. Currently, clinical trials can take years as scientists often rely on the development of AIDS-related infections or death to judge new treatments.
The research report, describing the use of the assay to monitor the virologic status of 102 HIV-infected patients at the NIAID HIV Clinic, appears in the November 1994 Journal of Infectious Diseases. The paper is the first publication to discuss the use of the assay to measure changes in the amount of HIV in a person's blood -- his or her viral burden -- in response to antiviral drugs or immune-boosting therapy.
Many physicians think monitoring a patient's HIV viral burden is important because of the apparent correlation between viral burden and the severity of disease: sicker patients generally have more virus than those with less advanced disease. Within the last year, research by several groups has suggested that reducing viral burden with antiretroviral drugs delays the progression of HIV disease.
The ability to measure levels of HIV in the blood is critical because changes in the amount of circulating virus may predict a patient's clinical course," says H. Clifford Lane, M.D., NIAID clinical director and senior NIAID author of the study. "The branched DNA assay is a sensitive, reproducible and rapid method for evaluating HIV viral burden at all stages of infection."
The assay, developed by Mickey S. Urdea, Ph.D., and colleagues of Chiron Corp. of Emeryville, Calif., is currently available only for research use. The test offers certain advantages over other measures of viral burden such as blood culture techniques and the p24 antigen capture assay. Culturing is labor intensive and results can vary from laboratory to laboratory. The p24 assay, a measure of HIV-produced proteins, may not accurately gauge the amount of viable HIV in a person's blood.
The branched DNA assay, on the other hand, yields reproducible results and is relatively simple to perform. The assay measures the amount of RNA, the genetic material of HIV, in virus particles in patient's blood.
Using the branched DNA assay, the investigators found virus- associated RNA in 74 percent of 102 patients studied at the NIAID HIV Clinic. In contrast, the p24 assay detected viral protein in 60 percent of these patients. In a subset of 56 patients tested by blood culture and the branched DNA assay, 89 percent were positive by the branched DNA assay, but only 61 percent by culture. The branched DNA assay revealed HIV levels in half the 18 patients with more than 400 CD4+ T cells per cubic millimeter of blood. CD4+ T cells are the crucial immune system cells depleted during HIV infection.
These results suggest that the assay could be used to monitor patients at all stages of disease," says Dr. Lane.
Of the patients, 23 had received a combination of the drugs zidovudine (AZT), didanosine (ddI) and U-90152S as part of a clinical trial. An average five-fold decrease in viral burden was noted in these patients within one week of starting therapy.
"By measuring changes in virus levels, it may prove possible to plan effective, individualized treatment strategies for patients, and to rapidly determine the minimal effective doses of new drugs," says Dr. Lane. "With virologic measurements such as the branched DNA assay, clinicians may be able to distinguish between patients likely to remain stable and thus not in need of immediate therapy, and patients whose increasing viral loads suggest that therapy is indicated.
"For patients already on therapy, the branched DNA assay reveals changes in virus levels in response to therapeutic intervention," he adds. "An increase in viral load might show that the therapy is losing effectiveness, and that a switch to another therapy is indicated."
Dr. Lane emphasizes, "Additional work is needed to validate these ideas before such approaches can become part of routine clinical practice."
Dr. Lane's co-authors include Richard T. Davey, M.D., of NIAID; Joseph A. Kovacs, M.D., of NIH's Warren Grant Magnuson Clinical Center; Robin L. Dewar, Ph.D., Helene C. Highbarger, Marinella D. Sarmiento, M.B. Vasudevachari, Ph.D., and Norman P. Salzman, Ph.D., of Georgetown University; and John A. Todd, Ph.D., and Dr. Urdea of Chiron Corp. Drs. Dewar and Salzman, and Ms. Highbarger are now with Program Resources, Inc., Frederick, Md.
NIAID supports investigators and scientific studies at universities, medical schools, hospitals and research institutions in the United States and abroad aimed at preventing, diagnosing and treating illnesses such as AIDS, tuberculosis, and asthma as well as allergies. The NIAID HIV Clinic, a component of the Institute's Division of Intramural Research, conducts clinical trials of innovative therapies against HIV infection in the Warren G. Magnuson Clinical Center on the campus of the National Institutes of Health. Other NIAID-supported trials of AIDS therapies are conducted at clinical sites around the country by AIDS Clinical Trials Group, the Terry Beirn Community Programs for Clinical Research on AIDS and the Division of AIDS Treatment Research Initiative.