Naïve CD4+ T Cells Harbor a Large Inducible Reservoir of Latent, Replication-Competent HIV-1.

Background: The latent HIV-1 reservoir represents a major barrier to a cure. Based on the levels of HIV-1 DNA in naïve (TN) versus resting memory CD4+ T cells, it is widely hypothesized that the latent reservoir resides primarily within memory cells. Here, we compared virus production from TN and central memory (TCM) CD4+ T cells isolated from HIV-1-infected individuals on suppressive therapy.

Methods: CD4+ TN and TCM cells were purified from the blood of seven HIV-1-infected individuals on suppressive therapy for ≥ 5 years. Real-time PCR was used to quantify total HIV-1 DNA, and extracellular virion-associated HIV-1 RNA or viral outgrowth assays were used to assess latency reversal following treatment with anti-CD3/CD28 mAbs, phytohaemagglutinin/interleukin-2, phorbol 12-myristate 13-acetate/ionomycin, prostratin, panobinostat, or romidepsin.

Results: HIV-1 DNA was significantly higher in TCM compared to TN cells (2,179 versus 684 copies/10 6 cells, respectively). Following exposure to anti-CD3/CD28 mAbs, virion-associated HIV-1 RNA levels were similar between TCM and TN cells (15,135 versus 18,290 copies/mL, respectively). In 4/7 donors, virus production was higher for TN cells independent of the latency reversing agent used. Replication-competent virus was recovered from both TN and TCM cells.

Conclusions: Although the frequency of HIV-1 infection is lower in TN compared to TCM cells, as much, if not more, virus is produced from the TN population after exposure to latency reversing agents. This finding suggests that quantifying HIV-1 DNA alone may not predict the size of the inducible latent reservoir, and that TN cells may be an important reservoir of latent HIV-1.