Reversible Human Immunodeficiency Virus Type-1 Latency in Primary Human Monocyte-Derived Macrophages Induced by Sustained M1 Polarization

We have reported that short-term stimulation of primary human monocyte-derived macrophages (MDM) with interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), i.e. M1 polarization, leads to a significant containment of virus replication. Here we show that M1-MDM restimulation with these cytokines 7 days after infection (M1(2) MDM) promoted an increased restriction of HIV-1 replication characterized by very low levels of virus production near to undetectable levels. In comparison to control and M1-MDM that were not restimulated, M1(2) MDM showed a stronger reduction of both total and integrated HIV DNA as well as of viral mRNA expression. M1(2) MDM were characterized by an upregulated expression of restriction factors acting at the level of reverse transcription (RT), including apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like 3A (APOBEC3A) and APOBEC3G, but not SAM domain and HD domain-containing protein 1 (SAMHD1). M1(2) MDM also showed an increased expression of Class II Transactivator (CIITA) and Tripartite Motif22 (TRIM22), two negative regulators of proviral transcription, whereas expression and phosphorylation of transcriptional inducers of HIV-1, such as nuclear factor kB (NF-kB) and signal transducer and activator of transcription 1 (STAT1), were not impaired in these cells. The almost quiescent state of the infection in M1(2) MDM was promptly reversed by coculture with mitogen-stimulated leukocytes or cell incubation with their filtered culture supernatant. M1(2) MDM harbored replication-competent HIV-1 as virus spreading following cell stimulation was fully prevented by the RT inhibitor lamivudine/3TC. Selective reactivation of proviral expression in M1(2) MDM, but not in control or in M1-MDM that were not restimulated, was confirmed in cells infected with single round Vesicular Stomatitis Virus-G-pseudotyped HIV-1. Thus, M1(2) MDM represent an in vitro model of reversible, almost quiescent HIV-1 infection of primary human macrophages that could be further exploited for "Cure" related investigations.