SAMHD1 Limits HIV-1 Antigen Presentation by Monocyte-Derived Dendritic Cells

Abstract

Monocyte-derived dendritic cells (MDDC) stimulate CD8؉ cytotoxic T lymphocytes (CTL) by presenting endogenous and exogenous viral peptides via major histocompatibility complex class I (MHC-I) molecules. MDDC are poorly susceptible to HIV-1, in part due to the presence of SAMHD1, a cellular enzyme that depletes intracellular deoxynucleoside triphosphates (dNTPs) and degrades viral RNA. Vpx, an HIV-2/SIVsm protein absent from HIV-1, antagonizes SAMHD1 by inducing its degradation. The impact of SAMHD1 on the adaptive cellular immune response remains poorly characterized. Here, we asked whether SAMHD1 modulates MHC-I-restricted HIV-1 antigen presentation. Untreated MDDC or MDDC pretreated with Vpx were exposed to HIV-1, and antigen presentation was examined by monitoring the activation of an HIV-1 Gag-specific CTL clone. SAMHD1 depletion strongly enhanced productive infection of MDDC as well as endogenous HIV-1 antigen presentation. Time-lapse microscopy analysis demonstrated that in the absence of SAMHD1, the CTL rapidly killed infected MDDC. We also report that various transmitted/founder (T/F) HIV-1 strains poorly infected MDDC and, as a consequence, did not stimulate CTL. Vesicular stomatitis virus glycoprotein (VSV-G) pseudotyping of T/F alleviated a block in viral entry and induced antigen presentation only in the absence of SAMHD1. Furthermore, by using another CTL clone that mostly recognizes incoming HIV-1 antigens, we demonstrate that SAMHD1 does not influence exogenous viral antigen presentation. Altogether, our results demonstrate that the antiviral activity of SAMHD1 impacts antigen presentation by DC, highlighting the link that exists between restriction factors and adaptive immune responses. IMPORTANCEUpon viral infection, DC may present antigens derived from incoming viral material in the absence of productive infection of DC or from newly synthesized viral proteins. In the case of HIV, productive infection of DC is blocked at an early postentry step. This is due to the presence of SAMHD1, a cellular enzyme that depletes intracellular levels of dNTPs and inhibits viral reverse transcription. We show that the depletion of SAMHD1 in DCs strongly stimulates the presentation of viral antigens derived from newly produced viral proteins, leading to the activation of HIV-1-specific cytotoxic T lymphocytes (CTL). We further show in real time that the enhanced activation of CTL leads to killing of infected DCs. Our results indicate that the antiviral activity of SAMHD1 not only impacts HIV replication but also impacts antigen presentation by DC. They highlight the link that exists between restriction factors and adaptive immune responses.

Lack of ADCC Breadth of Human Nonneutralizing Anti-HIV-1 Antibodies

“…Virus stocks were prepared by the transfection of 293T cells (obtained from the ATCC) along with vesicular stomatitis virus G (VSV-G) to normalize infectivity (88). Cells were infected with NL4.3, NLAD8, and transmitted-founder HIV-1 strains (CH040, CH058, CH077, CH106, RHPA, THRO, REJO, and WITO; obtained from the NIH AIDS Reagent Program) as described previously (89). Viral inocula (25 to 100 ng of p24/10 6 cells) were adjusted to achieve similar levels of Gag ϩ cells (around 40 to 50%) at 48 h postinfection.…”

Triggering of TLR‐3, ‐4, NOD2, and DC‐SIGN reduces viral replication and increases T‐cell activation capacity of HIV‐infected human dendritic cells

“…). Note that for DCs loaded with HIV for 24 h in the presence of RT inhibitors (AZT+NVP), HIV Ags are derived solely from incoming viral particles (so‐called exogenous presentation) ; in contrast, upon 3 days of infection, the source of HIV Ags corresponds mainly to newly synthetized HIV proteins (so‐called endogenous presentation) . A representative IFN‐γ ELISpot, using MDDCs from a single donor, is presented in Supporting Information Fig.…”

“…B). However, 3‐day p.i., the main source of Ags is derived from newly synthetized Gag Ags . We thus examined T‐cell activation relative to the infection rates (Fig.…”

SAMHD1: Recurring roles in cell cycle, viral restriction, cancer, and innate immunity

“…Why this is the case is not entirely understood, but it has been proposed that by using Vpx to degrade SAMHD1 and enable productive infection of macrophages and dendritic cells, which serve as the sentinel cells of the immune system, HIV-2 may in fact be alerting the host’s natural defenses to its presence. HIV-1 restriction in non-dividing immune cells may enable it to maintain an undetectable reservoir of latent virus, while avoiding activation of the host’s immune systems (154–156). Evidence supporting this model shows that SAMHD1 restriction of HIV-1 limits the innate and adaptive immune responses by preventing the activation of the cGAS/STING pathway (157).…”