Endogenously Expressed nef Uncouples Cytokine and Chemokine Production from Membrane Phenotypic Maturation in Dendritic Cells

Abstract

Immature dendritic cells (DCs), unlike mature DCs, require the viral determinant nef to drive immunodeficiency virus (SIV and HIV) replication in coculture with CD4+ T cells. Since immature DCs may capture and get infected by virus during mucosal transmission, we hypothesized that Nef associated with the virus or produced during early replication might modulate DCs to augment virus dissemination. Adenovirus vectors expressing nef were used to introduce nef into DCs in the absence of other immunodeficiency virus determinants to examine Nef-induced changes that might activate immature DCs to acquire properties of mature DCs and drive virus replication. Nef expression by immature human and macaque DCs triggered IL-6, IL-12, TNF-α, CXCL8, CCL3, and CCL4 release, but without up-regulating costimulatory and other molecules characteristic of mature DCs. Coincident with this, nef-expressing immature DCs stimulated stronger autologous CD4+ T cell responses. Both SIV and HIV nef-expressing DCs complemented defective SIVmac239 delta nef, driving replication in autologous immature DC-T cell cultures. In contrast, if DCs were activated after capturing delta nef, virus growth was not exacerbated. This highlights one way in which nef-defective virus-bearing immature DCs that mature while migrating to draining lymph nodes could induce stronger immune responses in the absence of overwhelming productive infection (unlike nef-containing wild-type virus). Therefore, Nef expressed in immature DCs signals a distinct activation program that promotes virus replication and T cell recruitment but without complete DC maturation, thereby lessening the likelihood that wild-type virus-infected immature DCs would activate virus-specific immunity, but facilitating virus dissemination.

HIV-Infected Langerhans Cells Preferentially Transmit Virus to Proliferating Autologous CD4+ Memory T Cells Located within Langerhans Cell-T Cell Clusters

“…We hypothesize that virion production by CD4 ϩ T cells is efficient and rapid in the presence of HIV-infected LC and SEB, inducing apoptosis of infected T cells before significant proliferation can occur. HIV-infected LC may have produced pro-apoptotic factors in the presence of SEB, because HIV-infected APCs have previously been reported to produce pro-apoptotic factors, including TNF-␣ (20,21,25), Fas ligand (25), and TNF-related apoptosis-inducing ligand (26,27).…”

“…Recent reports have shown that HIV infection of DC induces expression of chemokines in these cells that differentially attract certain T cell subsets. HIV Tat or Nef protein expression within monocyte-derived DC increased production of IFNinducible protein-10 and monokine induced by IFN-␥ (18,19) or macrophage inflammatory protein-1␣ and -␤, respectively (20,21). These chemokines are ligands for either CXCR3 or CCR5, which are more highly expressed on memory CD4…”

Intravenous Injection of a Lentiviral Vector Encoding NY-ESO-1 Induces an Effective CTL Response

“…To evade the immune response, wild-type HIV-1 has been reported to modulate DC function by a number of strategies, including Nef and Tat induction of cytokine and chemokine production in the absence of maturation (50,51). It has been proposed that this serves to attract T cells, permitting HIV-1 transmission from DC without stimulating an immune response.…”

The Effects of HIV-1 Nef on CD4 Surface Expression and Viral Infectivity in Lymphoid Cells Are Independent of Rafts

“…Direct effects are particularly visible in lymphocytes activated a few days after infection, in which replication of nef-deleted HIV (HIV⌬nef) is barely detectable. Nef also indirectly impacts lymphocytes, when expressed in macrophages or in dendritic cells: HIV-infected macrophages or dendritic cells release paracrine factors (chemokines, soluble CD23, and soluble ICAM), which permit the infection of resting T cells (32)(33)(34). The capacity of HIV to replicate in non-activated lymphocytes is likely linked to the numerous described effects of Nef on T cell activation.…”