Background: Dendritic cells (DCs) are potent antigen-presenting cells, and their physiological localization in tissues which interact with the external environment is important as an initial barrier against pathogens such as human immunodeficiency virus type I (HIV-1). Therefore, DCs are a key step in infection of individuals by HIV-1. Several models have been proposed to explain the possible role of DCs as a reservoir for HIV-1 in patients on virally suppressive, highly active antiretroviral therapy (HAART). However, the low yield of cell isolates and the lack of specific markers on DCs have made this evaluation a difficult task.

Methods: The present study analyzes whether HIV-1 pro-virus occurs in peripheral blood DCs or HIV-1 virions occurs on peripheral blood DCs from HIV-1-infected individuals on suppressive HAART, with plasma viral RNA levels <50 copies/mL.  Peripheral blood DCs were isolated from a cohort of HIV-1-seropositive men taking suppressive HAART, via a column separation technique. Viral out-growth assays were performed in vitro, as well as gag and R/U5 polymerase chain reaction (PCR) amplification of viral RNA and DNA respectively, from DC and peripheral blood mononuclear cell (PBMC) extracts.

Results: Fluorescence-activated cell sorting (FACS) data revealed cellular yields from 85.90 - 92.18% of relatively pure DCs isolated from patients' PBMCs.  Although RNA gag and DNA RU/5 were detected in all PBMC samples isolated from these patients, these proviral and virion or viral unspliced RNA forms were not detected in the DC isolates.  In addition, no replication-competent virus was demonstrated in the DC fraction, while virus was isolated from each patient's CD8+ T-lymphocyte-depleted PBMCs.

Conclusions: The current study suggests that, in infected individuals treated with suppressive HAART, HIV-1 is not actively being transmitted from peripheral blood DCs to T-cells, the DCs are not an internal reservoir for replication-competent HIV-1, and viral particles are not attached to the surface of the peripheral blood DCs. Therefore, these populations of DCs are not a major reservoir site for HIV-1 in patients on HAART with undetectable (< 50 copies/mL) plasma viral RNA.