Whether myeloid cells are latently infected remains to be firmly established. In this regard, we have previously reported that short-term exposure of primary MDM to pro-inflammatory cytokines (IFN-γ plus TNF−α), i.e. "M1 polarization", partially prevented productive virus infection and reduced proviral transcription. Methods: M1-polarized MDM were restimulated with M1 cytokines R5 HIV-1 (M1 2 protocol). Cell cultures were monitored for supernatant-associated RT activity, HIV-1 DNA load,

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... /3A expression, and for cell reactivation by co-culture with T cell blasts. Results: We observed a significant, further reduction of virus replication down to near undetectable levels by RT activity over 30 days of culture. HIV-1 DNA levels were ca. 100-and 1,000-fold lower in M1-MDM and M1 2 -MDM vs. control, unpolarized cells, respectively. APOBEC3A, but not APOBEC3G, was significantly upregulated by the M1 2 protocol protocol 15 days post-infection. No effect of T cell blast co-culture on control, infected MDM was observed, whereas significant levels of RT activity were induced in M1 2 -MDM by this approach. Conclusions: Stimulation of already infected M1-MDM with proinflammatory, M1-cytokines counterintuitively resulted in a further, significant inhibition of virus replication down to "near-latency" levels in terms of RT activity and viral DNA levels and upregulation of APOBEC3A expression. Recovery of virus production was achieved by cocultivation of M1 2 -infected MDM with allogeneic T cell blasts, indicating the existence of a pool of infected cells carrying inducible proviruses. Additional experiments are ongoing to define the levels of integrated proviruses vs. total HIV-1 DNA by Alu-PCR, the reproducibility of the M1 2 protocol with a VSV-g pseudotyped single round virus, and the panel of stimuli capable of reactivating virus expression.