Cell-Associated HIV Cross-Presentation by Plasmacytoid Dendritic Cells Is Potentiated by Noncognate CD8+ T Cell Preactivation

Identification of macaque dendritic cell precursors in blood and tissue reveals their dysregulation in early SIV infection

Distinct dendritic cell (DC) subsets play important roles in shaping immune responses. Circulating DC precursors (pre-DCs) are more susceptible to HIV infection in vitro, which may explain the inefficiency of immune responses against HIV. However, the interplay between HIV and pre-DC is not defined in vivo. We identify human pre-DC equivalents in the cynomolgus macaque and then analyze their dynamics during simian immunodeficiency virus (SIV) infection to illustrate a sharp decrease of blood pre-DCs in early SIV infection and accumulation in lymph nodes (LNs), where they neglect to upregulate CD83/CD86 or MHC-II. Additionally, SIV infection attenuates the capacity of stimulated LN pre-DCs to produce IL-12p40. Analysis of HIV cohorts provides correlation between costimulatory molecule expression on pre-DCs and T cell activation in spontaneous HIV controllers. These findings pinpoint certain dynamics and functional changes of pre-DCs during SIV infection, providing a deeper understanding of immune dysregulation mechanisms elicited in people living with HIV.

Toll-like receptor agonists enhance HIV-specific T cell response mediated by plasmacytoid dendritic cells in diverse HIV-1 disease progression phenotypes

BACKGROUND

Plasmacytoid dendritic cells (pDCs) sense viral and bacterial products through Toll-like receptor (TLR)-7 and -9 and translate this sensing into Interferon-α (IFN-α) production and T-cell activation. The understanding of the mechanisms involved in pDCs stimulation may contribute to HIV-cure immunotherapeutic strategies. The objective of the present study was to characterize the immunomodulatory effects of TLR agonist stimulations in several HIV-1 disease progression phenotypes and in non HIV-1 infected donors.

METHODS

pDCs, CD4 and CD8 T-cells were isolated from 450 ml of whole blood from non HIV-1 infected donors, immune responders (IR), immune non responders (INR), viremic (VIR) and elite controller (EC) participants. pDCs were stimulated overnight with AT-2, CpG-A, CpG-C and GS-9620 or no stimuli. After that, pDCs were co-cultured with autologous CD4 or CD8 T-cells and with/without HIV-1 (Gag peptide pool) or SEB (Staphylococcal Enterotoxin B). Cytokine array, gene expression and deep immunophenotyping were assayed.

FINDINGS

pDCs showed an increase of activation markers levels, interferon related genes, HIV-1 restriction factors and cytokines levels after TLR stimulation in the different HIV-disease progression phenotypes. This pDC activation was prominent with CpG-C and GS-9620 and induced an increase of HIV-specific T-cell response even in VIR and INR comparable with EC. This HIV-1 specific T-cell response was associated with the upregulation of HIV-1 restriction factors and IFN-α production by pDC.

INTERPRETATION

These results shed light on the mechanisms associated with TLR-specific pDCs stimulation associated with the induction of a T-cell mediated antiviral response which is essential for HIV-1 eradication strategies.

FUNDING

This work was supported by Gilead fellowship program, the Instituto de Salud Carlos III (Fondo Europeo de Desarrollo Regional, FEDER, "a way to make Europe") and the Red Temática de Investigación Cooperativa en SIDA and by the Spanish National Research Council (CSIC).

Cross-presentation by the others

The critical role of conventional dendritic cells in physiological cross-priming of immune responses to tumors and pathogens is widely documented and beyond doubt. However, there is ample evidence that a wide range of other cell types can also acquire the capacity to cross-present. These include not only other myeloid cells such as plasmacytoid dendritic cells, macrophages and neutrophils, but also lymphoid populations, endothelial and epithelial cells and stromal cells including fibroblasts. The aim of this review is to provide an overview of the relevant literature that analyzes each report cited for the antigens and readouts used, mechanistic insight and in vivo experimentation addressing physiological relevance. As this analysis shows, many reports rely on the exceptionally sensitive recognition of an ovalbumin peptide by a transgenic T cell receptor, with results that therefore cannot always be extrapolated to physiological settings. Mechanistic studies remain basic in most cases but reveal that the cytosolic pathway is dominant across many cell types, while vacuolar processing is most encountered in macrophages. Studies addressing physiological relevance rigorously remain exceptional but suggest that cross-presentation by non-dendritic cells may have significant impact in anti-tumor immunity and autoimmunity.

IgG-Complexed Adenoviruses Induce Human Plasmacytoid Dendritic Cell Activation and Apoptosis

Following repeat exposure to many human adenoviruses (HAdVs), most adults harbour long-lived B- and T-cell responses. Combined, this response typically protects us for years from re-infection by the same HAdV type. In spite of these immune responses, some HAdV types are associated with persistent infections that constitute a life-threatening risk when an individual's T-cell response is compromised. By contrast, patients with B-cell deficiencies do not appear to be at a greater risk of HAdV disease. This dichotomy begs the question of the secondary role of anti-HAdV antibodies during host defence. In this study, we explored IgG-complexed (IC)-HAdV5 and primary human plasmacytoid dendritic cell (pDC) interactions. We found that IC-HAdV5 are efficiently internalized in pDCs, stimulate their activation through TLR9 signalling, and cause apoptosis. These data may help reconcile the enigma of robust immune response to HAdVs, while concurrently allowing persistence.