HIV-1 cell-to-cell infection of macrophages escapes type I interferon and host restriction factors, and is resistant to antiretroviral drugs.

HIV-1-infected macrophages participate in viral transmission, dissemination, and establishment of tissue virus reservoirs. Despite counteracting viral proteins (Vif, Vpu, Vpr and Nef), cell-free virus macrophage infection is restricted by host cell factors, including those induced by interferons. Here, we show that these viral proteins and type I interferon do not influence HIV-1 cell-to-cell transfer to macrophages by cell-cell fusion with infected T cells, still leading to the formation of multinucleated giant cells (MGCs). Accordingly, depletion of SERINC5 and APOBEC3G do not alter virus spreading and formation of virus-producing MGCs. We further show that the nuclei derived from infected T cells remains transcriptionally active in MGCs and may explain resistance to restriction factors and antiretroviral drugs. Unexpectedly, we detect viral DNA in myeloid nuclei shortly after the initial fusion with macrophages. Together, these findings unravel how HIV-1 macrophage infection by cell-cell fusion escapes type I interferon and cellular restriction factors independently of the viral auxiliary proteins, while displaying resistance to antiretroviral drugs.