Macropinosomes are a site of HIV-1 entry into primary CD4+ T cells

HIV-1 has been observed to enter target cells at both the plasma membrane and endosomes. However, which pathways mediate its entry into primary CD4+ T cells, the major targets of this virus, remains unclear. Here, we show that HIV-1 can enter primary CD4+ T cells through macropinocytosis, a form of endocytosis. We found that HIV-1 can enter primary CD4+ T cells at both the plasma membrane and internal compartments, while entry into common T cell lines occurred primarily at the plasma membrane. Inhibition of macropinocytosis suppressed HIV-1 internalization into and subsequent fusion with primary CD4+ T cells regardless of the viral coreceptor usage. Microscopic analysis of viral contents exposed to the cytosol confirmed that HIV-1 fusion occurs at the macropinosomal membrane. Finally, the inhibition of macropinocytosis blocked HIV-1 infection of primary CD4+ T cells. Altogether, this study identifies macropinocytosis as one pathway for HIV-1 entry into primary CD4+ T cells. Significance statementHIV-1 entry is an important therapeutic target. However, the exact subcellular location of HIV-1 entry into primary CD4+ T cells, a major in vivo host for HIV-1, remains undetermined. The current study shows that macropinosomes serve as a site for productive HIV-1 entry into the cytoplasm of primary CD4+ T cells. Supporting the role for macropinosomes, inhibition of macropinocytosis prevents HIV-1 internalization into, fusion with, and infection of primary CD4+ T cells. By contrast, HIV-1 infection of a CD4+ T cell line commonly used in HIV-1 research is insensitive to macropinocytosis inhibition. Altogether, this study highlights the primary-T-cell-specific dependence of HIV-1 on macropinocytosis for productive entry and therefore suggests the macropinosome-mediated HIV-1 entry as a potential target for antiviral strategies.