CD34⁺ progenitor cells from asymptomatic patients are not a major reservoir for human immunodeficiency virus-1

Controversy exists as to whether hematopoietic progenitor cells are infected by human immunodeficiency virus-1 (HIV-1) in vivo. Most studies have focused on patients with acquired immunodeficiency syndrome (AIDS)/AIDS- related complex, and little data are available on asymptomatic patients with well preserved CD4⁺ T-cell counts. To determine if CD34⁺ hematopoietic progenitor cells are infected early in the course of HIV-1 disease, we evaluated 10 asymptomatic HIV-1 seropositive (HIV-1⁺) patients. The CD34⁺ cell fraction was purified by a two-step procedure consisting of both affinity chromatography and fluorescence-activated cell sorting that resulted in a median purity of over 99%. Using conventional and nested polymerase chain reaction (PCR) assays, we evaluated the presence and frequency of HIV- 1 proviral DNA. Both bone marrow mononuclear cells and CD34^- cells from all 10 patients were strongly positive for the HIV-1 pol and/or gag gene sequences. In contrast, sorted CD34⁺ cells from only two of 10 patients were positive, and the number of copies of proviral DNA in these samples was estimated to be from 2 to 5 per 250,000 cells. To test the in vitro functional capacity of CD34⁺ progenitors, these cells were assayed in both methylcellulose and long-term stromal culture. We found no significant reduction in the number of colony-forming unit-erythroid (CFU-E), burst- forming unit-erythroid (BFU-E), or colony-forming unit-granulocyte macrophage (CFU-GM) colonies, or in the frequency of cobblestone area forming cells from limit dilution analysis in HIV-1⁺ asymptomatic patients. Pooled methylcellulose colonies generated from CD34⁺ cells were HIV-1^- in nine of 10 samples. All progeny from long-term cultures of CD34⁺ cells were HIV-1^- . We conclude that the CD34⁺ hematopoietic progenitor compartment is not infected in the majority of asymptomatic HIV-1⁺ patients, and that these cells may represent a suitable target for strategies designed to protect developing CD4⁺ T cells from infection.