The studies, one led by John W. Mellors, M.D., of the University of Pittsburgh School of Medicine, and Alvaro Munoz, Ph.D., of the Johns Hopkins School of Public Health, the other by Michael D. Hughes, Ph.D., of the Harvard School of Public Health, and Richard T. D'Aquila, M.D., of Massachusetts General Hospital and Harvard Medical School, appear in the June 15 issue of the Annals of Internal Medicine. An editorial by NIAID grantee Michael D. Saag, M.D., of the University of Alabama at Birmingham, accompanies these reports.
"These studies help refine our understanding of prognostic markers for HIV infection and underscore the value of routinely using both viral load measurements and CD4+ T cell counts in the care and management of individuals with HIV/AIDS," says NIAID Director Anthony S. Fauci, M.D.
Last year, Dr. Mellors and his colleagues in NIAID's Multicenter AIDS Cohort Study (MACS) reported that measuring the amount of HIV RNA in the bloodstream, commonly referred to as viral load, is the single best way to predict an HIV-infected person's risk for developing AIDS or dying. The current MACS study confirms and extends those findings.
"Our study showed that, while viral load is the most powerful single predictor of outcome in HIV-infected individuals, combining it with CD4+ T cell counts allows a more precise estimation of prognosis," explains Dr. Mellors.
The researchers measured HIV viral load in baseline blood samples obtained from more than 1,600 HIV-infected men who enrolled in the MACS study between March 1984 and April 1985. Physicians measured the participants' CD4+ T cell counts at study entry and monitored the men for signs of HIV disease progression over a 10-year period. Nearly 1,000 participants developed AIDS during this period.
Using a technique known as regression tree analysis, the researchers divided study participants into 12 categories defined by discrete intervals of viral loads and CD4+ T cell counts and determined how many persons in each category had developed AIDS within three, six and nine years of their entry into the study.
The researchers found that CD4+ counts provided important information for discriminating the relative risk for disease progression among individuals with similar viral load levels. For example, only 3.6 percent of study participants with 500 or fewer copies of HIV RNA per milliliter (ml) of blood and more than 750 CD4+ T cells per cubic millimeter (mm3) of blood progressed to AIDS within nine years. By comparison, 22.3 percent of persons with the same viral load but 750 or fewer CD4+ cells/mm3 progressed to AIDS within the same period. At the other end of the risk spectrum, 97.9 percent of persons with baseline viral loads greater than 30,000 copies/ml and less than 200 CD4+T cells/mm3 progressed to AIDS within six years, compared with 66.8 percent who had the same viral load but greater than 500 CD4+ T cells/mm3.
The MACS study was initiated prior to the availability of anti-HIV drugs. Therefore, only 60 percent of the participants were treated with antiretrovirals during the 10-year study period. Those who were treated received monotherapy with AZT or other nucleoside analogue drugs.
"Our results were not confounded by subsequent therapy because there were no baseline differences in the values of the markers between treated and untreated individuals," says Dr. Mellors. "These markers," he adds, "were highly predictive of outcome independent of subsequent treatment with nucleoside monotherapy. The value of this study is that it accurately estimates prognosis for the HIV-infected individual considering therapy."
In a study of the use of these measures during combination antiretroviral therapy, Drs. Hughes, D'Aquila and colleagues in NIAID's AIDS Clinical Trials Group (ACTG) found that prediction of disease progression can be optimized by measuring viral load and CD4+ T cells before, and viral load shortly after, treatment begins. The researchers measured baseline viral load and CD4+ T cell counts in 198 HIV-infected individuals participating in ACTG study 241, which compared treatment with AZT and didanosine (ddI) to treatment with AZT, ddI and nevirapine. These measurements were repeated eight and 48 weeks after treatments started. Over a one-year treatment period, the investigators monitored study participants for signs of disease progression.
A total of 34 individuals developed opportunistic infections, malignancies or died during the treatment period. There was no significant difference in the number of these events between the two treatment groups. The researchers found that low CD4+ T cell counts and high viral loads at baseline independently predicted the risk of disease progression and death. However, they also found that the combined use of these measures improved their predictive value: individuals with high viral loads and low CD4+ T cell counts were more likely to develop AIDS than were those with high viral loads and relatively higher CD4+ T cell counts.
Measuring viral load eight weeks after treatment started provided still more prognostic information -- there was a 52 percent reduction in risk of disease progression for every 10-fold decrease in viral load at this point.
"We also found that a 2.5-fold or greater change in viral load probably indicates a true biological change in an individual patient, rather than a random fluctuation," says Dr. D'Aquila. "Our results, and those of other studies, suggest that clinicians might consider alternate treatments if a patient's viral load is not decreased by at least 2.5-fold within several weeks after a new antiretroviral regimen is initiated."
NIAID, a component of the National Institutes of Health (NIH), supports research on AIDS, tuberculosis and other infectious diseases, as well as allergies and immunology. NIH is an agency of the U.S. Department of Health and Human Services.
NIAID press releases, fact sheets and other materials are available on the Internet via the NIAID home page at http://www.niaid.nih.gov.
Note: MACS investigators measured viral load with a branched DNA assay manufactured by Chiron Corporation (Emeryville, Calif.). In the ACTG study, researchers measured viral load with a quantitative reverse transcription-polymerase chain reaction assay made by Roche Molecular Systems (Alameda, Calif. and Branchburg, N.J.). Supplemental support for viral load testing in ACTG 241 was provided by Boehringer Ingleheim Pharmaceutical, Inc. (Ridgefield, Conn.). Boehringer Ingleheim, Bristol-Myers Squibb Co. (Wallingford, Conn.) and Glaxo Wellcome Co. (Research Triangle Park, N.C.) provided study medications for ACTG 241.