Background: Patients on prolonged and effective HAART have been demonstrated the persistence of infected CD4+ T cells that harbor latent replication-competent virus. To investigate the phenotypic features of these infected lymphocytes, we examined 4 highly purified subsets of memory and naïve CD4+ T cells for the presence of replication-competent virus .

Methods: In 11 highly adherent patients on long-term HAART with undetectable plasma virus, using a magnetic bead-based procedure, we isolated highly purified CD4+ CD45RO+, CD4+ CD45RA+ T cells. Then CD62L cells were separated. We quantified total viral DNA in freshly isolated T cell subsets by means of quantitative PCR. To verify whether HIV DNA was competent for replication, HIV RNA was measured in supernatants following 21 days of cell activation.

Results: HIV DNA was detectable in the CD45RO+ CD4+ and CD45RA+ CD4+ T-cell subsets in 100% and  90% of the patients tested. In central memory CD45RO+CD62L+, effector CD45RO+CD62L, truly naïve CD45RA+CD62L+, and CD45RA+CD62L- CD4 T cells, HIV DNA was found in 100%, 55%, 88%, and 50% of the patients tested, respectively. HIV DNA amounts were significantly higher in the CD45RO+ fraction as compared to the CD45RA+ subset (p< 0.01, Wilcoxon test) and in the CD45RO+CD62L+ fraction as compared to the 3 other CD45RA/RO CD62L± subsets (p<0.01). Detectable HIV RNA was found in the culture supernatants of CD45RO+ CD4+ and CD45RA+ CD4+ T-cell subsets in 80% and 66% of the patients tested and in CD45RO+CD62L+, CD45RO+CD62L,  CD45RA+CD62L+, and CD45RA+CD62L- CD4 T cells in 100%, 100%, 100% and 50% of the patients tested.

Conclusions: In patients on prolonged and effective HAART, the pool of infected CD4+ T lymphocytes includes a predominant part of memory cells but also cells of naïve phenotype. This should be taken into account in the therapeutic strategies to reduce the pool of HIV-reservoir cells.