Macrophage Internal HIV-1 Is Protected from Neutralizing Antibodies

In macrophages, HIV-1 accumulates in intracellular vesicles designated virus-containing compartments (VCCs). These might play an important role in the constitution of macrophages as viral reservoirs and allowHIV-1 to evade the immune system by sequestration in an internal niche, which is difficult to access from the exterior. However, until now, evidence of whether inter-nal virus accumulations are protected from the host’s humoral immune response is still lacking. In order to be able to study the formation and antibody accessibility of VCCs, we generated HIV-1 with green fluorescent protein (GFP)-tagged Gag replicating in primary macrophages. Live-cell observations revealed faint initial cytosolic Gag expression and subsequent large intracellular Gag accumulations which stayed stable over days. Taking advantage of the opportunity to study the accessibility of intracellular VCCs via the cell surface, we demonstrate that macrophage internal HIV-1-containing compartments cannot be targeted by neu-tralizing antibodies. Furthermore, HIV-1 was efficiently transferred from antibody-treated macrophages to T cells. Three-dimensional reconstruction of electronmicroscopic slices revealed that Gag accumulations correspond to viral particles within enclosed compartments and convoluted membranes. Thus, although some VCCs were connected to the plasmamembrane, the complex membrane architecture of the HIV-1-containing compartment might shield viral particles from neutralizing antibod-ies. In sum, our study provides evidence that HIV-1 is sequestered into a macrophage internal membranous web, posing an ob-stacle for the elimination of this viral reservoir. Macrophages are important HIV-1 target cells in vivo (26, 40).They can have a lifespan of several weeks to months, patro