Untreated Individuals Show Increased HIV in Cells despite Stable Plasma Viral Load

The amount of viral genetic material in peripheral blood immune cells rises steadily over time in HIV positive people who are not taking antiretroviral therapy (ART), according to Dutch study described in the July 17, 2010 issue of AIDS. HIV levels in these cells increased even if blood plasma viral load remained stable, and was associated with decreases in CD4 cell count.

People with HIV often have a long asymptomatic stage of infection before developing overt AIDS-related illnesses or severe immune deficiency indicated by low CD4 T-cell count. While HIV levels in the blood are typically stable in this phase -- as production and elimination of virions (individual viral particles) is balanced -- a growing body of evidence shows that the virus nevertheless causes damage during this period.

Alexander Pasternak from the Center for Infection and Immunity in Amsterdam and colleagues performed a study to compare the dynamics of HIV-1 molecular markers in peripheral blood mononuclear cells (PBMCs) and in blood plasma during the asymptomatic phase of infection in individuals not on ART.

Investigators used real-time PCR assays to measure levels of HIV proviral DNA (genetic material integrated into the host cell genome), unspliced HIV RNA, and multiply spliced RNA in PBMCs from 10 untreated men with subtype B HIV at multiple time points during asymptomatic infection. A total of 53 measurements were taken over an average of 4.6 years (range 1.5 to 10.6 years), paired with plasma viral load and CD4 cell readings.

Results

• Plasma HIV RNA levels did not significantly change in any of the study participants during the asymptomatic period.
• Levels of unspliced HIV RNA increased significantly over time, however, in PBMCs from 6 out of 10 people.
• Levels of proviral DNA increased in peripheral blood cells from 4 people.
• Amounts of unspliced RNA in PBMCs increased significantly faster over time than either plasma RNA or proviral DNA.
• Rising levels of unspliced RNA and proviral DNA in PBMCs were significantly associated with decreasing CD4 cell counts (P = 0.006 and 0.02, respectively).
• In contrast, there was no significant correlation between plasma HIV RNA viral load and CD4 cell loss.

Based on these results, the study authors concluded, "During the asymptomatic phase of untreated HIV-1 infection, when virion production and clearance are balanced, resulting in stable plasma viremia, viral load in PBMCs steadily increases and is a sensitive and direct longitudinal virological marker of infection progression."

To explain these findings, they suggested that "progressive weakening of the antiviral immune response during the asymptomatic phase might be one of the factors defining the temporal increase in the relative numbers of HIV-producing cells, and, therefore, the increase in HIV-1 replication rates in PBMCs..." Alternatively, "cellular and/or viral factors might influence the rate of viral replication in PBMCs."

Levels of HIV in PBMCs are a more direct and sensitive marker of disease progression during the asymptomatic phase of infection and may be more useful than standard plasma HIV RNA viral load testing, the researchers added.

Investigator affiliations: Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity, Amsterdam, Netherlands; Laboratory of Clinical Virology, Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands.

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Reference

AO Pasternak, S Jurriaans, M Bakker, and others. Steady increase in cellular HIV-1 load during the asymptomatic phase of untreated infection despite stable plasma viremia. AIDS 24(11): 1641-1649. July 17, 2010.