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Objectives:  Immune activation is the result of cell activation and proliferation; it allows HIV replication, and plays a key pathogenic role in HIV infection. To assess whether cell activation is sufficient to sustain HIV replication, the effects of mycophenolic acid (MPA) and hydoxyurea (HU) (cytostatic drugs inhibiting cell proliferation but not activation) on HIV replication were studied in latently infected cells.

Methods:  CD4 cells were positively selected from peripheral blood mononuclear cells (PBMC) with magnetic beads. Infection was carried out with HIV-1_IIIB at 0.001 TCDI₅₀/cell or HIV-1_MN at 4.2 ng/10⁶ CD4. Cells were stained with carboxy-fluorescein diacetate, succinimidyl ester (CFSE) to evaluate proliferation. They were cultured for 5 days, then stimulated with phytohemagglutinin (PHA), and 48 hours later IL-2 was added. At day 10 or 14 supernatants from the infection were collected to evaluate p24 Ag production, and cells were stained with an anti-CD69 antibody to evaluate cellular activation. Treatment with 10 mM MPA and 100 mM HU was either continued for 10 days, interrupted at day 5, or added to the culture at day 5.

Results:  Results (medians of multiple replicates) are all expressed as percentage of the positive controls (untreated samples). MPA or HU treatment for 10 days prevented viral replication (percentage p24 Ag production, 0.8% and 0.3%, respectively), and cell proliferation (percentage of CFSE positive cells, 7.23% and 13.3%, respectively), while CD69 expression did not change in the MPA samples (percentage CD69 positive cells, 91.26%) and increased in the HU samples (170.9%). Viral replication was effectively controlled also at day 14. Similar results (at day 10, HIV replication 1.2% and 2.7%, proliferation 5.2% and 11.5%, activation 134.2% and 157.8%, for MPA and HU, respectively) were obtained when treatment was initiated at day 5—that is before PHA stimulation. Therapy interruption at day 5 resulted in limited control of viral replication at day 10 (67.9%) in the MPA samples, and delayed viral rebound in the HU samples (1.2% at day 10, and 71.5% at day 14), while cell proliferation and activation were comparable to that observed in the untreated samples.

Conclusion:  Inhibition of cell proliferation, in the presence of maintained cell activation, is sufficient to limit viral replication in cells latently infected with HIV. One implication is that modulation of cell proliferation without suppression of cell activation may inhibit HIV without major interference with the ability of T cells to mount a proper immune response.

Keywords: HIV suppression; cell proliferation; cell activation