Important note: Information in this article was accurate in February 1999. The state of the art may have changed since the publication date.AIDSWEEKLY Plus; Monday, February 22, 1999
Daniel J. DeNoon, Senior Editor
Genotypic tests look for specific HIV mutations that confer resistance to various antiretroviral drugs. HIV is so notoriously susceptible to mutation, however, that an infected person harbors not a single strain but a swarm of viral subspecies. The tests are able to detect drug-resistant strains when they comprise 5 to 10 percent of the viral swarm.
This might not be good enough, warn CDC researcher B. Roberts and colleagues. In their initial experiment Roberts et al. mixed drug- sensitive and drug-resistant HIV stocks at various concentrations and used them to infect target cells in the presence of the drugs.
"Cultures infected with less than 1 percent drug-resistant virus showed emergence of HIV-1 in the presence of drug treatment," Roberts reported in a poster presentation to the 6th Conference on Retroviruses and Opportunistic Infections, held January 31-February 4, 1999, in Chicago, Illinois.
In another experiment, Roberts et al. isolated HIV strains from patients who recently had seroconverted and who had never received antiretroviral drugs. They were able to find viral strains resistant to zidovudine (AZT).
The researchers then independently isolated HIV from CD4 and CD14 subsets of the patients' peripheral blood mononuclear cells (PBMC). CD4(+) T cells, but not monocytes, harbored AZT-resistant virus.
"Phenotypic analysis of HIV-1 isolated from T-cell and monocyte subsets suggests different viral genotypes are harbored in these cell populations," they wrote in their presentation abstract. "Virus harbored in monocytes may not reflect the viral population in plasma."
Roberts et al. suggested that it will be important to identify the different drug-resistant viral strains associated with different PBMC subsets.
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