HIV-1 Vpu complements HLA-A downregulation by Nef and impairs TCR-mediated recognition of HIV-infected cells through distinct mechanisms
Many viruses, including HIV-1, target the human leukocyte antigen (HLA) class I molecules HLA-A, HLA-B, and HLA-C to evade immune surveillance. HIV-1 Nef selectively downregulates HLA-A and HLA-B, whereas Vpu variants from primary strains reduce cell-surface HLA-C expression. Whether HIV-1 also uses Vpu to target other HLA molecules has remained unclear. Here, we show that Vpu from primary strains reduces HLA-A, including the globally prevalent HLA-A2, on infected cells. Although Nef is the principal modulator of these molecules, Vpu acts independently of Nef and impairs TCR-mediated recognition of infected cells in co-culture systems. However, the reduction in TCR signaling is also dependent on the presence of BST2/tetherin, a restriction factor that retains nascent virions and targets them for degradation. HLA-A2-restricted, HIV-specific CTL responses were lowest when both Nef and Vpu were present. Vpu variants from chronic and transmitted/founder strains, but not from the prototypical recombinant strain NL4.3, were sufficient to reduce cell-surface HLA-A2, although activity varied widely among variants and appears to have arisen independently in different hosts. Coimmunoprecipitation and immunofluorescence analyses showed that Vpu interacts with HLA-A2 and redirects it to a perinuclear compartment which is probably the trans-Golgi network through a mechanism governed by the Vpu N-terminus/transmembrane domain. Overall, our findings reveal a previously unrecognized function of Vpu and show how HIV-1 uses Nef and Vpu to limit HLA-A-mediated viral antigen presentation and promote immune evasion.