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A Dendritic Cell–Based Vaccine Elicits T Cell Responses Associated with Control of HIV-1 Replication

Therapeutic DC vaccines elicit HIV-1–specific immune responses that change viral set point in patients of cART. Putting the Vaccine Before the cART Combination antiretroviral therapy has turned HIV infection from a death sentence to a manageable disease. However, current treatment requires “cART for life,” a less than ideal situation for HIV-infected individuals because of drug cost and worries about resistance. New vaccine strategies are attempting to control viral replication after infection, thus allowing discontinuation of cART and a “functional cure.” Garcia et al. report a dendritic cell (DC)–based vaccine that elicits an HIV-1–specific immune response and may change the setpoint of viral load. The authors pulsed the patient’s own DCs with heat-inactivated whole HIV and then used these DCs as a therapeutic vaccine. The vaccine was safe and well tolerated. They observed a decrease in viral setpoint after cART interruption in vaccinated patients with a concomitant increase in HIV-1–specific T cell responses. Although not yet a functional cure, these results support future studies optimizing a therapeutic vaccine to maintain HIV-1–infected patients. Combination antiretroviral therapy (cART) greatly improves survival and quality of life of HIV-1–infected patients; however, cART must be continued indefinitely to prevent viral rebound and associated disease progression. Inducing HIV-1–specific immune responses with a therapeutic immunization has been proposed to control viral replication after discontinuation of cART as an alternative to “cART for life.” We report safety, tolerability, and immunogenicity results associated with a control of viral replication for a therapeutic vaccine using autologous monocyte-derived dendritic cells (MD-DCs) pulsed with autologous heat-inactivated whole HIV. Patients on cART with CD4+ >450 cells/mm3 were randomized to receive three immunizations with MD-DCs or with nonpulsed MD-DCs. Vaccination was feasible, safe, and well tolerated and shifted the virus/host balance. At weeks 12 and 24 after cART interruption, a decrease of plasma viral load setpoint ≥1 log was observed in 12 of 22 (55%) versus 1 of 11 (9%) and in 7 of 20 (35%) versus 0 of 10 (0%) patients in the DC–HIV-1 and DC-control groups, respectively. This significant decrease in plasma viral load observed in immunized recipients was associated with a consistent increase in HIV-1–specific T cell responses. These data suggest that HIV-1–specific immune responses elicited by therapeutic DC vaccines could significantly change plasma viral load setpoint after cART interruption in chronic HIV-1–infected patients treated in early stages. This proof of concept supports further investigation of new candidates and/or new optimized strategies of vaccination with the final objective of obtaining a functional cure as an alternative to cART for life.

Glutamate Released by Dendritic Cells as a Novel Modulator of T Cell Activation

Adaptive immune responses begin after productive immunosynaptic contacts formation established in secondary lymphoid organs by dendritic cells (DC) presenting the Ag to T lymphocytes. Despite its resemblance to the neurosynapse, the participation of soluble small nonpeptidic mediators in the intercellular cross-talk taking place during T cell–DC interactions remains poorly studied. In this study, we show that human DC undergoing maturation and in contact with T cells release significant amounts of glutamate, which is the main excitatory neurotransmitter in mammalians. The release of glutamate is nonvesicular and mediated by the DC-expressed Xc− cystine/glutamate antiporter. DC-derived glutamate stimulating the constitutively expressed metabotropic glutamate receptor 5 impairs T cell activation. However, after productive Ag presentation, metabotropic glutamate receptor 1 is expressed in T cells to mediate enhanced T cell proliferation and secretion of Th1 and proinflammatory cytokines. These data suggest that, during T cell–DC interaction, glutamate is a novel and highly effective regulator in the initiation of T cell-mediated immune responses.

Distinct Gene Expression Profiling after Infection of Immature Human Monocyte-Derived Dendritic Cells by the Attenuated Poxvirus Vectors MVA and NYVAC

ABSTRACT Although recombinants based on the attenuated poxvirus vectors MVA and NYVAC are currently in clinical trials, the nature of the genes triggered by these vectors in antigen-presenting cells is poorly characterized. Using microarray technology and various analysis conditions, we compared specific changes in gene expression profiling following MVA and NYVAC infection of immature human monocyte-derived dendritic cells (MDDC). Microarray analysis was performed at 6 h postinfection, since these viruses induced extensive cytopathic effects, rRNA breakdown, and apoptosis at late times postinfection. MVA- and NYVAC-infected MDDC shared upregulation of 195 genes compared to uninfected cells: MVA specifically upregulated 359 genes, and NYVAC upregulated 165 genes. Microarray comparison of NYVAC and MVA infection revealed 544 genes with distinct expression patterns after poxvirus infection and 283 genes specifically upregulated after MVA infection. Both vectors upregulated genes for cytokines, cytokine receptors, chemokines, chemokine receptors, and molecules involved in antigen uptake and processing, including major histocompatibility complex genes. mRNA levels for interleukin 12β (IL-12β), beta interferon, and tumor necrosis factor alpha were higher after MVA infection than after NYVAC infection. The expression profiles of transcription factors such as NF-κB/Rel and STAT were regulated similarly by both viruses; in contrast, OASL, MDA5, and IRIG-I expression increased only during MVA infection. Type I interferon, IL-6, and Toll-like receptor pathways were specifically induced after MVA infection. Following MVA or NYVAC infection in MDDC, we found similarities as well as differences between these virus strains in the expression of cellular genes with immunological function, which should have an impact when these vectors are used as recombinant vaccines.

A Therapeutic Dendritic Cell-Based Vaccine for HIV-1 Infection

A double-blinded, controlled study of vaccination of untreated patients with chronic human immunodeficiency virus type 1 (HIV-1) infection with 3 doses of autologous monocyte-derived dendritic cells (MD-DCs) pulsed with heat inactivated autologous HIV-1 was performed. Therapeutic vaccinations were feasible, safe, and well tolerated. At week 24 after first vaccination (primary end point), a modest significant decrease in plasma viral load was observed in vaccine recipients, compared with control subjects (P = .03). In addition, the change in plasma viral load after vaccination tended to be inversely associated with the increase in HIV-specific T cell responses in vaccinated patients but tended to be directly correlated with HIV-specific T cell responses in control subjects.

Human immature monocyte-derived dendritic cells produce and secrete α-defensins 1–3

Defensins are effector molecules of the innate immunity with a broad antimicrobial spectrum, including HIV. They also link innate and adaptive immunity, displaying chemotactic activity for monocytes, T cells, and dendritic cells (DCs). α‐Defensins 1–3 are mainly produced by neutrophils, but their production by other leukocyte subsets has also been reported. Herein, we studied whether monocyte‐derived DCs (MDDCs), which are regarded as a model for myeloid DCs, produce α‐defensins 1–3. We found that immature MDDCs (imMDDCs) produce α‐defensins 1–3 mRNA, but this production is undetectable or barely detectable following 48 h of maturation with the proinflammatory cytokine cocktail (IL‐1β+IL‐6+TNF‐α) or LPS. It is surprising that α‐defensins 1–3 production was up‐regulated when exposed to each one of the proinflammatory cytokines alone, especially IL‐1β. α‐Defensins 1–3 produced by imMDDCs were mainly secreted peptides. Production and secretion of α‐defensins 1–3 by imMDDCs can have biological relevance for the antigen processing of pathogens and can contribute to understanding differences in susceptibility to infections, an issue of special interest in the field of HIV infection.

Increased α-defensins 1-3 production by dendritic cells in HIV-infected individuals is associated with slower disease progression.

Background Defensins are natural endogenous antimicrobial peptides with potent anti-HIV activity and immuno-modulatory effects. We recently demonstrated that immature dendritic cells (DC) produce α-defensins1-3 and that α-defensins1-3 modulate DC generation and maturation. Since DC-HIV interaction plays a critical role during the first steps of HIV infection, we investigated the possible impact of α-defensins1-3 production by DC on disease progression. Methodology/Principal Findings Monocyte-derived DC (MDDC) were analyzed comparatively in healthy controls (HC) and HIV-infected patients, including untreated “elite” and “viremic” controllers, untreated viremic non-controllers and antiretroviral-treated patients. We found that production of α-defensins1-3 was significantly increased in MDDC from HIV-infected patients versus HC, and this increase was mainly due to that observed in controllers, while in non-controllers the increase was not statistically significant (controllers vs. HC, p<0.005; controllers vs. non-controllers p<0.05). Secreted α-defensins1-3 by immature MDDC positively correlated with CD4 T cell counts in controllers, but not in non-controllers. Moreover, independently of their clinical classification, HIV-infected patients with higher α-defensins1-3 secretion by immature MDDC showed slower disease progression, measured as no decrease in the number of CD4+ T-cells below 350 cell/mm3, lower increase of plasma viral load and no initiation of treatment over time. Plasma alpha-defensins1-3 levels lacked any relationship with immunologic and virologic parameters. Conclusions/Significance High production of α-defensins1-3 by immature DCs appears as a host protective factor against progression of HIV-1infection, suggesting potential diagnostic, therapeutic and preventive implications. This protective effect may arise from the activity of α-defensins1-3 to damage the virions prior and/or after their internalization by immature DC, and hence favoring a more efficient viral processing and presentation to HIV-specific CD4+ T cells, without or with a minor rate of transmission of infectious HIV-1 virions.

Dendritic cell based vaccines for HIV infection: The way ahead

Dendritic cells have a central role in HIV infection. On one hand, they are essential to induce strong HIV-specific CD4+ helper T-cell responses that are crucial to achieve a sustained and effective HIV-specific CD8+ cytotoxic T-lymphocyte able to control HIV replication. On the other hand, DCs contribute to virus dissemination and HIV itself could avoid a correct antigen presentation. As the efficacy of immune therapy and therapeutic vaccines against HIV infection has been modest in the best of cases, it has been hypothesized that ex vivo generated DC therapeutic vaccines aimed to induce effective specific HIV immune responses might overcome some of these problems. In fact, DC-based vaccine clinical trials have yielded the best results in this field. However, despite these encouraging results, functional cure has not been reached with this strategy in any patient. In this Commentary, we discuss new approaches to improve the efficacy and feasibility of this type of therapeutic vaccine.

Dendritic Cells Exposed to MVA-Based HIV-1 Vaccine Induce Highly Functional HIV-1-Specific CD8+ T Cell Responses in HIV-1-Infected Individuals

Currently, MVA virus vectors carrying HIV-1 genes are being developed as HIV-1/AIDS prophylactic/therapeutic vaccines. Nevertheless, little is known about the impact of these vectors on human dendritic cells (DC) and their capacity to present HIV-1 antigens to human HIV-specific T cells. This study aimed to characterize the interaction of MVA and MVA expressing the HIV-1 genes Env-Gag-Pol-Nef of clade B (referred to as MVA-B) in human monocyte-derived dendritic cells (MDDC) and the subsequent processes of HIV-1 antigen presentation and activation of memory HIV-1-specific T lymphocytes. For these purposes, we performed ex vivo assays with MDDC and autologous lymphocytes from asymptomatic HIV-infected patients. Infection of MDDC with MVA-B or MVA, at the optimal dose of 0.3 PFU/MDDC, induced by itself a moderate degree of maturation of MDDC, involving secretion of cytokines and chemokines (IL1-ra, IL-7, TNF-α, IL-6, IL-12, IL-15, IL-8, MCP-1, MIP-1α, MIP-1β, RANTES, IP-10, MIG, and IFN-α). MDDC infected with MVA or MVA-B and following a period of 48 h or 72 h of maturation were able to migrate toward CCL19 or CCL21 chemokine gradients. MVA-B infection induced apoptosis of the infected cells and the resulting apoptotic bodies were engulfed by the uninfected MDDC, which cross-presented HIV-1 antigens to autologous CD8+ T lymphocytes. MVA-B-infected MDDC co-cultured with autologous T lymphocytes induced a highly functional HIV-specific CD8+ T cell response including proliferation, secretion of IFN-γ, IL-2, TNF-α, MIP-1β, MIP-1α, RANTES and IL-6, and strong cytotoxic activity against autologous HIV-1-infected CD4+ T lymphocytes. These results evidence the adjuvant role of the vector itself (MVA) and support the clinical development of prophylactic and therapeutic anti-HIV vaccines based on MVA-B.

Adenosine deaminase potentiates the generation of effector, memory, and regulatory CD4 T cells

By interacting with CD26 on the CD4+ T cell surface and with the AdoR A2B on the DC surface, ADA triggers a costimulatory signal for human T cells. The aim of this study was to know whether ADA‐mediated costimulation plays a role in the differentiation of T cells. The results show that irrespective of its enzymatic activity and dependent on TNF‐α, IFN‐γ, and IL‐6 action, ADA enhanced the differentiation of CD4+CD45RA+CD45RO– naïve T cells toward CD4+CD25+CD45RO+ Teffs and CD4+CD45RA–CD45RO+ memory T cells. Furthermore, ADA potentiated generation of CD4+CD25highFoxp3+ Tregs by a mechanism that seems to be mainly dependent on the enzymatic activity of ADA. Interestingly, an ADA‐mediated increase on Teff, memory T cell, and Treg generation occurred, not only in cocultures from healthy individuals but also from HIV‐infected patients. These data suggest that ADA is a relevant modulator of CD4+ T cell differentiation, even in cells from immunologically compromised individuals.

Expression and function of the IL‐2 receptor in activated human plasmacytoid dendritic cells

Human and mouse plasmacytoid dendritic cells (PDC) express IL‐2 mRNA specifically upon TLR stimulation, but not under CD40L stimulation. Even though the expression of the IL‐2R by PDC has been described, the functional implications of this expression remain unknown. Here, we investigated the expression and function of the IL‐2R in activated human PDC. The IL‐2Rα chain, CD25, is expressed in both CpG‐ and CD40L‐activated PDC. CD25 expression is a relatively rapid event, as the receptor was detected 6 h after the initial activation signal. Exogenous IL‐2 added to CD40L‐activated PDC increased the expression of CD25, enhanced the secretion of pro‐inflammatory cytokines and promotes PDC survival. CpG‐activated PDC cultured in the presence of IL‐2R‐blocking monoclonal antibodies showed a reduced expression of pro‐inflammatory cytokines, especially TNF‐α. This reduction was dose and time dependent, suggesting a regulatory role of IL‐2 in TNF secretion that might occur at the post‐transcriptional level. These results indicate that the expression of the IL‐2R is relevant to human PDC activation, and that IL‐2 may be an important auto‐ and/or paracrine factor modulating the activation and survival of PDC. Finally, CD25 expression may be considered as a useful early activation marker for human PDC.