Human immunodeficiency virus type 1 (HIV-1) has evolved elaborate ways to evade immune cell recognition, including downregulation of classical HLA class I (HLA-I) from the surface of infected cells. Recent evidence identified HLA-E, a non-classical HLA-I, as an important part of the antiviral immune response to HIV-1. Changes in HLA-E surface levels and peptide presentation can prompt both CD8(+) T-cell and natural killer (NK)-cell responses to viral infections. Previous studies reported unchanged or increased HLA-E levels on HIV-1-infected cells. Here, we examined HLA-E surface levels following infection of CD4(+) T cells with primary HIV-1 strains and observed that a subset downregulates HLA-E. Two primary strains of HIV-1 inducing the strongest reduction in surface HLA-E expression were chosen for further testing. Expression of single Nef or Vpu proteins in T-cell lines as well as tail-swap experiments exchanging the cytoplasmic tail of HLA-A2 with HLA-E demonstrated that Nef modulated HLA-E surface levels in a cytoplasmic tail-dependent manner. Furthermore, infection of primary CD4(+) T cells with HIV-1 mutants showed that lack of functional Nef (and Vpu to some extent) impaired HLA-E downmodulation. Taken together, this study demonstrates for the first time that HIV-1 can downregulate HLA-E surface levels on infected primary CD4(+) T cells, potentially rendering them less vulnerable to CD8(+) T-cell recognition but at increased risk of NKG2A(+) NK-cell killing.IMPORTANCE For almost two decades, it was thought that HIV-1 selectively downregulated the highly expressed HLA-I molecules HLA-A and HLA-B from the cell surface in order to evade cytotoxic T-cell recognition, while leaving HLA-C and HLA-E molecules unaltered. It was stipulated that, thereby, HIV-1 infection maintains inhibition of NK cells via inhibitory receptors that bind HLA-C and HLA-E. This concept was recently revised when a study showed that primary HIV-1 strains reduce HLA-C surface levels, whereas the cell-line adapted HIV-1 strain NL4-3 lacks this ability. Here, we demonstrate that infection with distinct primary HIV-1 strains results in a significant downregulation of surface HLA-E levels. Given the increasing evidence for HLA-E as important modulator of CD8(+) T-cell and NKG2A(+) NK-cell function, this finding has substantial implications for future immunomodulatory approaches aimed at harnessing cytotoxic cellular immunity against HIV.< Réduire