HIV-1 Gag-virus-like particles induce natural killer cell immune responses via activation and maturation of dendritic cells.

Despite the extensive efforts that have been made to combat acquired immune deficiency syndrome (AIDS), the number of people infected each year with human immunodeficiency virus type 1 (HIV-1) is still increasing worldwide, and a safe and effective vaccine to control HIV infection is urgently needed. Recently, the natural killer (NK) cell-mediated innate immune response, which represents the first line of defense against infections, has attracted attention for its role in combating HIV infection and disease progression. In the present study, we investigated the immunogenic ability of HIV-1 Gag-virus-like particles (Gag-VLPs) to induce NK cell immune responses in vitro and in vivo. Gag-VLPs efficiently activated human monocyte-derived dendritic cells (MDDCs), eliciting MDDC maturation with an associated increase in the surface expression of CD80, CD86 and MHC classes I and II, MDDC proliferation and proinflammatory cytokine production. Gag-VLP-treated MDDCs subsequently activated autologous NK cells, leading to their proliferation and production of interferon-γ and to the upregulation of NK cell cytotoxicity against YAC-1 cells and HIV-1-infected CD4(+) T cells. In addition, we introduced a 2-phase immunization strategy in BALB/c mice to assess the role of DCs in the induction of NK cell immune responses by Gag-VLPs in vivo. Our findings reveal that Gag-VLPs efficiently activate DCs, which in turn induce innate and Gag-specific immune responses in NK cells.