HIV-1 Infection of Trophoblasts Is Independent of gp120/CD4 Interactions but Relies on Heparan

Mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1) is the leading cause of HIV infection in infants. Direct infection of trophoblasts—cells forming the placental barrier—may cause this transmission. Entry of HIV-1 into trophoblasts is unusual for this retrovirus, because it is associated with endocytosis. However, given that trophoblasts express no or few receptors/coreceptors required for virus internalization, the mechanism underlying this event remains ambiguous. In the present study, we show that HIV-1 entry and infection of polarized trophoblasts are independent not only of CD4 but also of envelope (Env) glycoproteins gp120 and gp41. Virus internalization, cytoplasmic release, reverse transcription, integra-tion, and HIV-1 gene expression occurred with both fusion-incompetent and Env-deficient viruses. Importantly, fusion-independent infection was observed when we used viruses produced in a natural cellular reservoir (i.e., primary human cells). Finally, HIV-1 requires heparan sulfate proteoglycans for uptake in trophoblasts. To-gether, our findings illustrate that HIV-1 utilizes an unusual pathway for entering human polarized trophoblasts. More than 2 million children are living with HIV-1 worldwide, and 90 % of these infections resulted from transmission from the mother [1] occurring in utero