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This article was originally published in The Gray Sheet

Executive Summary

GENELABS' QC-PCR QUANTITATIVE HIV-I TEST STUDY RESULTS demonstrate that the diagnostic technology "may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative," M. Piatak, Jr., PhD, Genelabs, et al., report in the March 19 edition of Science. The researchers comment that "there is currently a widely recognized need for new markers that allow timely assessment of the in vivo antiviral activity of new therapeutic approaches and agents and that better predict the ultimate clinical efficacy of new treatments." The study data suggest "that determination of virion-associated HIV-1 RNA levels in plasma by QC-PCR represents a marker of viral replication with potential for widespread applicability in assessment of the activity of antiretroviral therapy," the researchers conclude. Genelabs' "quantitative competitive" method incorporates polymerase chain reaction gene amplification technology developed by Hoffmann-La Roche. The QC-PCR method works by comparing amplified counts of naturally occurring HIV-I RNA to levels of synthetic, modified RNA in patient blood samples. The ratio of natural to synthetic product "consistently reflects the starting amounts of each," according to a March 23 Genelabs release. In the study, a collaboration between researchers at Genelabs and the Department of Medicine at the University of Alabama- Birmingham, performance of the QC-PCR method was compared to p24 antigen and virus culture assays in testing of 66 blood samples from HIV-positive patients at various stages of infection. "Whereas the QC-PCR method quantified virion-associated HIV- 1 RNA in all 66 patients tested, virus culture and standard p24 antigen assays were much less sensitive," the researchers found. For example, when testing samples from the 20 patients in the study with CD4+ cell counts greater than 500 per cubic millimeter, virus culture identified only four positive samples, and standard p24 antigen assays identified five positive samples. When testing samples from the 18 individuals with CD4+ cell counts of 200 to 500 per cubic millimeter, virus culture identified six as positive, and standard p24 antigen assays provided seven positive results. Virus culture identified 22 out of 28 positive samples from patients with CD4+ cell counts lower than 200 while the p24 antigen assays identified 24 of the positive samples. Compared to QC-PCR, standard PCR methods contain "potential sources of variability" in reverse transcription and amplification steps, Piatak et al. note. Typical PCR techniques "do not provide the level of stringent internal control that is a central feature of QC-PCR," the authors conclude. The QC-PCR test was originally developed by Redwood City, California-based Genelabs to measure viral load in ongoing clinical studies of its alpha-trichosanthin GLQ223 candidate anti- AIDS drug, and currently is available for research use only. Genelabs "plans to make the method available for wider use once additional data are gathered," according to the firm. Enzo Biochem also is working on a quantitative HIV test method, and results of a 246-sample study of the company's technique, called the Enzo microplate assay for HIV DNA, are reported in the current issue of Clinical Chemistry. Jennifer Rapier, National Center of Infectious Diseases, Centers for Disease Control and Prevention, et al., reported that the Enzo technique was able to accurately identify 104 seronegative samples and identified 141 of 142 (99.3%) seropositive samples. In addition, the researchers claim that the technique "can be combined with PCR for quantitative assessment of viral copies. Thus, this procedure provides the potential for direct assessment of viral loads in patient samples." In a March 24 press release, Enzo says that "one major application of the Enzo test would be to identify earlier the HIV virus among donors." In addition, the technique may "have value in monitoring therapeutic results in HIV-infected patients," the company claims. Enzo says the test "is undergoing further evaluation in order to establish the full scope of its applications."

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