Dendritic cells exposed to MVA-based HIV-1 vaccine induce highly functional HIV-1-specific CD8(+) T cell responses in HIV-1-infected individuals

A Zigzag but Upward Way to Develop an HIV-1 Vaccine

After decades of its epidemic, the human immunodeficiency virus type 1 (HIV-1) is still rampant worldwide. An effective vaccine is considered to be the ultimate strategy to control and prevent the spread of HIV-1. To date, hundreds of clinical trials for HIV-1 vaccines have been tested. However, there is no HIV-1 vaccine available yet, mostly because the immune correlates of protection against HIV-1 infection are not fully understood. Currently, a variety of recombinant viruses-vectored HIV-1 vaccine candidates are extensively studied as promising strategies to elicit the appropriate immune response to control HIV-1 infection. In this review, we summarize the current findings on the immunological parameters to predict the protective efficacy of HIV-1 vaccines, and highlight the latest advances on HIV-1 vaccines based on viral vectors.

Epidemiology and pathogenesis of maternal-fetal transmission of Trypanosoma cruzi and a case for vaccine development against congenital Chagas disease

Trypanos o ma cruzi (T. cruzi or Tc) is the causative agent of Chagas disease (CD). It is common for patients to suffer from non-specific symptoms or be clinically asymptomatic with acute and chronic conditions acquired through various routes of transmission. The expecting women and their fetuses are vulnerable to congenital transmission of Tc. Pregnant women face formidable health challenges because the frontline antiparasitic drugs, benznidazole and nifurtimox, are contraindicated during pregnancy. However, it is worthwhile to highlight that newborns can be cured if they are diagnosed and given treatment in a timely manner. In this review, we discuss the pathogenesis of maternal-fetal transmission of Tc and provide a justification for the investment in the development of vaccines against congenital CD.

Deletion of Vaccinia Virus A40R Gene Improves the Immunogenicity of the HIV-1 Vaccine Candidate MVA-B

Development of a safe and efficacious vaccine against the HIV/AIDS pandemic remains a major scientific goal. We previously described an HIV/AIDS vaccine based on the modified vaccinia virus Ankara (MVA) expressing HIV-1 gp120 and Gag-Pol-Nef (GPN) of clade B (termed MVA-B), which showed moderate immunogenicity in phase I prophylactic and therapeutic clinical trials. Here, to improve the immunogenicity of MVA-B, we generated a novel recombinant virus, MVA-B ΔA40R, by deleting in the MVA-B genome the vaccinia virus (VACV) A40R gene, which encodes a protein with unknown immune function. The innate immune responses triggered by MVA-B ΔA40R in infected human macrophages, in comparison to parental MVA-B, revealed an increase in the mRNA expression levels of interferon (IFN)-β, IFN-induced genes, and chemokines. Compared to priming with DNA-B (a mixture of DNA-gp120 plus DNA-GPN) and boosting with MVA-B, mice immunized with a DNA-B/MVA-B ΔA40R regimen induced higher magnitude of adaptive and memory HIV-1-specific CD4+ and CD8+ T-cell immune responses that were highly polyfunctional, mainly directed against Env. and of an effector memory phenotype, together with enhanced levels of antibodies against HIV-1 gp120. Reintroduction of the A40R gene into the MVA-B ΔA40R genome (virus termed MVA-B ΔA40R-rev) promoted in infected cells high mRNA and protein A40 levels, with A40 protein localized in the cell membrane. MVA-B ΔA40R-rev significantly reduced mRNA levels of IFN-β and of several other innate immune-related genes in infected human macrophages. In immunized mice, MVA-B ΔA40R-rev reduced the magnitude of the HIV-1-specific CD4+ and CD8+ T cell responses compared to MVA-B ΔA40R. These results revealed an immunosuppressive role of the A40 protein, findings relevant for the optimization of poxvirus vectors as vaccines.

Immunity and vaccine development efforts against Trypanosoma cruzi

Trypanosoma cruzi (T. cruzi) is the causative agent for Chagas disease (CD). There is a critical lack of methods for prevention of infection or treatment of acute infection and chronic disease. Studies in experimental models have suggested that the protective immunity against T. cruzi infection requires the elicitation of Th1 cytokines, lytic antibodies and the concerted activities of macrophages, T helper cells, and cytotoxic T lymphocytes (CTLs). In this review, we summarize the research efforts in vaccine development to date and the challenges faced in achieving an efficient prophylactic or therapeutic vaccine against human CD.

Loading dendritic cells with gold nanoparticles (GNPs) bearing HIV-peptides and mannosides enhance HIV-specific T cell responses

Gold nanoparticles (GNPs) decorated with glycans ameliorate dendritic cells (DC) uptake, antigen-presentation and T-cells cross-talk, which are important aspects in vaccine design. GNPs allow for high antigen loading, DC targeting, lack of toxicity and are straightforward prepared and easy to handle. The present study aimed to assess the capacity of DC to process and present HIV-1-peptides loaded onto GNPs bearing high-mannoside-type oligosaccharides (P1@HM) to autologous T-cells from HIV-1 patients. The results showed that P1@HM increased HIV-specific CD4⁺ and CD8⁺ T-cell proliferation and induced highly functional cytokine secretion compared with HIV-peptides alone. P1@HM elicits a highly efficient secretion of pro-T_H1 cytokines and chemokines, a moderate production of pro-T_H2 and significant higher secretion of pro-inflammatory cytokines such as TNF-α and IL-1β. Thus, co-delivery of HIV-1 antigens and HM by GNPs is an excellent vaccine delivery system inducing HIV-specific cellular immune responses in HIV+ patients, being a promising approach to improve anti-HIV-1 vaccines.

The HIV-1 integrase-LEDGF allosteric inhibitor MUT-A: resistance profile, impairment of virus maturation and infectivity but without influence on RNA packaging or virus immunoreactivity

Background

HIV-1 Integrase (IN) interacts with the cellular co-factor LEDGF/p75 and tethers the HIV preintegration complex to the host genome enabling integration. Recently a new class of IN inhibitors was described, the IN-LEDGF allosteric inhibitors (INLAIs). Designed to interfere with the IN-LEDGF interaction during integration, the major impact of these inhibitors was surprisingly found on virus maturation, causing a reverse transcription defect in target cells.

Results

Here we describe the MUT-A compound as a genuine INLAI with an original chemical structure based on a new type of scaffold, a thiophene ring. MUT-A has all characteristics of INLAI compounds such as inhibition of IN-LEDGF/p75 interaction, IN multimerization, dual antiretroviral (ARV) activities, normal packaging of genomic viral RNA and complete Gag protein maturation. MUT-A has more potent ARV activity compared to other INLAIs previously reported, but similar profile of resistance mutations and absence of ARV activity on SIV. HIV-1 virions produced in the presence of MUT-A were non-infectious with the formation of eccentric condensates outside of the core. In studying the immunoreactivity of these non-infectious virions, we found that inactivated HIV-1 particles were captured by anti-HIV-specific neutralizing and non-neutralizing antibodies (b12, 2G12, PGT121, 4D4, 10-1074, 10E8, VRC01) with efficiencies comparable to non-treated virus. Autologous CD4⁺ T lymphocyte proliferation and cytokine induction by monocyte-derived dendritic cells (MDDC) pulsed either with MUT-A-inactivated HIV or non-treated HIV were also comparable.

Conclusions

Although strongly defective in infectivity, HIV-1 virions produced in the presence of the MUT-A INLAI have a normal protein and genomic RNA content as well as B and T cell immunoreactivities comparable to non-treated HIV-1. These inactivated viruses might form an attractive new approach in vaccine research in an attempt to study if this new type of immunogen could elicit an immune response against HIV-1 in animal models.

Electronic supplementary material

The online version of this article (10.1186/s12977-017-0373-2) contains supplementary material, which is available to authorized users.

Humoral Immunity to Primary Smallpox Vaccination: Impact of Childhood versus Adult Immunization on Vaccinia Vector Vaccine Development in Military Populations

Modified Vaccinia virus has been shown to be a safe and immunogenic vector platform for delivery of HIV vaccines. Use of this vector is of particular importance to the military, with the implementation of a large scale smallpox vaccination campaign in 2002 in active duty and key civilian personnel in response to potential bioterrorist activities. Humoral immunity to smallpox vaccination was previously shown to be long lasting (up to 75 years) and protective. However, using vaccinia-vectored vaccine delivery for other diseases on a background of anti-vector antibodies (i.e. pre-existing immunity) may limit their use as a vaccine platform, especially in the military. In this pilot study, we examined the durability of vaccinia antibody responses in adult primary vaccinees in a healthy military population using a standard ELISA assay and a novel dendritic cell neutralization assay. We found binding and neutralizing antibody (NAb) responses to vaccinia waned after 5–10 years in a group of 475 active duty military, born after 1972, who were vaccinated as adults with Dryvax®. These responses decreased from a geometric mean titer (GMT) of 250 to baseline (<20) after 10–20 years post vaccination. This contrasted with a comparator group of adults, ages 35–49, who were vaccinated with Dryvax® as children. In the childhood vaccinees, titers persisted for >30 years with a GMT of 210 (range 112–3234). This data suggests limited durability of antibody responses in adult vaccinees compared to those vaccinated in childhood and further that adult vaccinia recipients may benefit similarly from receipt of a vaccinia based vaccine as those who are vaccinia naïve. Our findings may have implications for the smallpox vaccination schedule and support the ongoing development of this promising viral vector in a military vaccination program.

Clinical challenges in HIV/AIDS: Hints for advancing prevention and patient management strategies

Acquired immune deficiency syndrome has been one of the most devastating epidemics of the last century. The current estimate for people living with the HIV is 36.9 million. Today, despite availability of potent and safe drugs for effective treatment, lifelong therapy is required for preventing HIV re-emergence from a pool of latently infected cells. However, recent evidence show the importance to expand HIV testing, to offer antiretroviral treatment to all infected individuals, and to ensure retention through all the cascade of care. In addition, circumcision, pre-exposure prophylaxis, and other biomedical tools are now available for included in a comprehensive preventive package. Use of all the available tools might allow cutting the HIV transmission in 2030. In this article, we review the status of the epidemic, the latest advances in prevention and treatment, the concept of treatment as prevention and the challenges and opportunities for the HIV cure agenda.

Increased expression with differential subcellular location of cytidine deaminase APOBEC3G in human CD4(+) T-cell activation and dendritic cell maturation

APOBEC3G (apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3G; A3G) is an innate defense protein showing activity against retroviruses and retrotransposons. Activated CD4(+) T cells are highly permissive for HIV-1 replication, whereas resting CD4(+) T cells are refractory. Dendritic cells (DCs), especially mature DCs, are also refractory. We investigated whether these differences could be related to a differential A3G expression and/or subcellular distribution. We found that A3G mRNA and protein expression is very low in resting CD4(+) T cells and immature DCs, but increases strongly following T-cell activation and DC maturation. The Apo-7 anti-A3G monoclonal antibody (mAb), which was specifically developed, confirmed these differences at the protein level and disclosed that A3G is mainly cytoplasmic in resting CD4(+) T cells and immature DCs. Nevertheless, A3G translocates to the nucleus in activated-proliferating CD4(+) T cells, yet remaining cytoplasmic in matured DCs, a finding confirmed by immunoblotting analysis of cytoplasmic and nuclear fractions. Apo-7 mAb was able to immunoprecipitate endogenous A3G allowing to detect complexes with numerous proteins in activated-proliferating but not in resting CD4(+) T cells. The results show for the first time the nuclear translocation of A3G in activated-proliferating CD4(+) T cells.

Current Advances in Virus-Like Particles as a Vaccination Approach against HIV Infection

HIV-1 virus-like particles (VLPs) are promising vaccine candidates against HIV-1 infection. They are capable of preserving the native conformation of HIV-1 antigens and priming CD4+ and CD8+ T cell responses efficiently via cross presentation by both major histocompatibility complex (MHC) class I and II molecules. Progress has been achieved in the preclinical research of HIV-1 VLPs as prophylactic vaccines that induce broadly neutralizing antibodies and potent T cell responses. Moreover, the progress in HIV-1 dendritic cells (DC)-based immunotherapy provides us with a new vision for HIV-1 vaccine development. In this review, we describe updates from the past 5 years on the development of HIV-1 VLPs as a vaccine candidate and on the combined use of HIV particles with HIV-1 DC-based immunotherapy as efficient prophylactic and therapeutic vaccination strategies.

Adenosine deaminase regulates Treg expression in autologous T cell-dendritic cell cocultures from patients infected with HIV-1

Regulatory T cells have an important role in immune suppression during HIV-1 infection. As regulatory T cells produce the immunomodulatory molecule adenosine, our aim here was to assess the potential of adenosine removal to revert the suppression of anti-HIV responses exerted by regulatory T cells. The experimental setup consisted of ex vivo cocultures of T and dendritic cells, to which adenosine deaminase, an enzyme that hydrolyzes adenosine, was added. In cells from healthy individuals, adenosine hydrolysis decreased CD4(+)CD25(hi) regulatory T cells. Addition of 5'-N-ethylcarboxamidoadenosine, an adenosine receptor agonist, significantly decreased CD4(+)CD25(lo) cells, confirming a modulatory role of adenosine acting via adenosine receptors. In autologous cocultures of T cells with HIV-1-pulsed dendritic cells, addition of adenosine deaminase led to a significant decrease of HIV-1-induced CD4(+)CD25(hi) forkhead box p3(+) cells and to a significant enhancement of the HIV-1-specific CD4(+) responder T cells. An increase in the effector response was confirmed by the enhanced production of CD4(+) and CD8(+) CD25(-)CD45RO(+) memory cell generation and secretion of Th1 cytokines, including IFN-γ and IL-15 and chemokines MIP-1α/CCL3, MIP-1β/CCL4, and RANTES/CCL5. These ex vivo results show, in a physiologically relevant model, that adenosine deaminase is able to enhance HIV-1 effector responses markedly. The possibility to revert regulatory T cell-mediated inhibition of immune responses by use of adenosine deaminase, an enzyme that hydrolyzes adenosine, merits attention for restoring T lymphocyte function in HIV-1 infection.

Loading dendritic cells with PLA-p24 nanoparticles or MVA expressing HIV genes induces HIV-1-specific T cell responses

Since recent data suggest that nanoparticles and modified vaccinia ankara (MVA) vectors could play a pivotal role in HIV-1 therapeutics and vaccine design, in an ex vivo model of human monocyte-derived dendritic cells (MDDCs), we compared two different loading strategies with HIV-1 vaccine vehicles, either viral or synthetic derived. We used polylactic acid (PLA) colloidal biodegradable particles, coated with HIV Gag antigens (p24), and MVA expressing Gag (rMVA-gag and rMVA-gag/trans membrane) or Tat, Nef and Rev genes (rMVA tat+rev and rMVA nef). PLA-p24 captured by MDDCs from HIV-1 individuals induced a slight degree of MDDC maturation, cytokine and chemokine secretion and migration towards a gradient of CCL19 chemokine and highly increased HIV-specific CD8(+) T-cell proliferation compared with p24 alone. After complete maturation induction of PLA-p24-pulsed MDDCs, maximal migration towards a gradient of CCL19 chemokine and induction of HIV-specific T-cell proliferation (two-fold higher for CD4(+) than CD8(+)) and cytokine secretion (IFN-γ and IL-2) in the co-culture were observed. Upon exposure to MVA-gag, MDDCs produced cytokines and chemokines and maintained their capacity to migrate to a gradient of CCL19. MDDCs infected with MVA-gag and MVA-gag trans-membrane were able to induce HIV-specific CD8(+) proliferation and secretion of IFN-γ, IL-2, IL-6 and TNF-α. We conclude that both HIV antigens loading strategies (PLA-p24 nanoparticles or MVA expressing HIV genes) induce HIV-1-specific T-cell responses, which are able to kill autologous gag-expressing cells. Thus, they are plausible candidates for the development of anti-HIV vaccines.

Gene Expression Driven by a Strong Viral Promoter in MVA Increases Vaccination Efficiency by Enhancing Antibody Responses and Unmasking CD8⁺ T Cell Epitopes

Viral vectors are promising tools for vaccination strategies and immunotherapies. However, CD8⁺ T cell responses against pathogen-derived epitopes are usually limited to dominant epitopes and antibody responses to recombinant encoded antigens (Ags) are mostly weak. We have previously demonstrated that the timing of viral Ag expression in infected professional Ag-presenting cells strongly shapes the epitope immunodominance hierarchy. T cells recognizing determinants derived from late viral proteins have a clear disadvantage to proliferate during secondary responses. In this work we evaluate the effect of overexpressing the recombinant Ag using the modified vaccinia virus early/late promoter H5 (mPH5). Although the Ag-expression from the natural promoter 7.5 (P7.5) and the mPH5 seemed similar, detailed analysis showed that mPH5 not only induces higher expression levels than P7.5 during early phase of infection, but also Ag turnover is enhanced. The strong overexpression during the early phase leads to broader CD8 T cell responses, while preserving the priming efficiency of stable Ags. Moreover, the increase in Ag-secretion favors the induction of strong antibody responses. Our findings provide the rationale to develop new strategies for fine-tuning the responses elicited by recombinant modified vaccinia virus Ankara by using selected promoters to improve the performance of this viral vector.

Deletion of the vaccinia virus N2L gene encoding an inhibitor of IRF3 improves the immunogenicity of modified vaccinia virus Ankara expressing HIV-1 antigens

A modified vaccinia virus Ankara poxvirus vector expressing the HIV-1 Env, Gag, Pol, and Nef antigens from clade B (MVA-B) is currently being tested in clinical trials. To improve its immunogenicity, we have generated and characterized the immune profile of MVA-B containing a deletion of the vaccinia viral gene N2L, which codes for an inhibitor of IRF3 (MVA-B ΔN2L). Deletion of N2L had no effect on virus growth kinetics or on the expression of HIV-1 antigens; hence, the N2 protein is not essential for MVA replication. The innate immune responses triggered by MVA-B ΔN2L revealed an increase in beta interferon, proinflammatory cytokines, and chemokines. Mouse prime-boost protocols showed that MVA-B ΔN2L improves the magnitude and polyfunctionality of HIV-1-specific CD4(+) and CD8(+) T cell adaptive and memory immune responses, with most of the HIV-1 responses mediated by CD8(+) T cells. In the memory phase, HIV-1-specific CD8(+) T cells with an effector phenotype were predominant and in a higher percentage with MVA-B ΔN2L than with MVA-B. In both immunization groups, CD4(+) and CD8(+) T cell responses were directed mainly against Env. Furthermore, MVA-B ΔN2L in the memory phase enhanced levels of antibody against Env. For the vector immune responses, MVA-B ΔN2L induced a greater magnitude and polyfunctionality of VACV-specific CD8(+) T memory cells than MVA-B, with an effector phenotype. These results revealed the immunomodulatory role of N2L, whose deletion enhanced the innate immunity and improved the magnitude and quality of HIV-1-specific T cell adaptive and memory immune responses. These findings are relevant for the optimization of poxvirus vectors as vaccines.

IMPORTANCE

On the basis of the limited efficacy of the RV144 phase III clinical trial, new optimized poxvirus vectors as vaccines against HIV/AIDS are needed. Here we have generated and characterized a new HIV/AIDS vaccine candidate on the basis of the poxvirus MVA vector expressing HIV-1 Env, Gag, Pol, and Nef antigens (MVA-B) and containing a deletion in the vaccinia virus N2L gene. Our findings revealed the immunomodulatory role of N2L and proved that its deletion from the MVA-B vector triggered an enhanced innate immune response in human macrophages and monocyte-derived dendritic cells. Furthermore, in immunized mice, MVA-B ΔN2L induced improvements in the magnitude and quality of adaptive and memory HIV-1-specific CD4(+) and CD8(+) T cell immune responses, together with an increase in the memory phase of levels of antibody against Env. Thus, the selective deletion of the N2L viral immunomodulatory gene is important for the optimization of MVA vectors as HIV-1 vaccines.

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.

Clinical applications of attenuated MVA poxvirus strain

The highly attenuated poxvirus strain modified vaccinia virus Ankara (MVA) has reached maturity as a vector delivery system and as a vaccine candidate against a broad spectrum of diseases. This has been largely recognized from research on virus-host cell interactions and immunological studies in pre-clinical and clinical trials. This review addresses the studies of MVA vectors used in phase I/II clinical trials, with the aim to provide the main findings obtained on their behavior when tested against relevant human diseases and cancer and also highlights the strategies currently implemented to improve the MVA immunogenicity. The authors assess that MVA vectors are progressing as strong vaccine candidates either alone or when administered in combination with other vectors.

Vaccine and immunotherapeutic interventions

PURPOSE OF REVIEW

As we enter the fourth decade in HIV epidemic, advances in understanding HIV pathogenesis and development of potent and safer antiretroviral drugs have been spectacular. More than 30 antiviral drugs have been registered and the impact of combination antiviral therapy on morbidity and mortality has been dramatic. However, despite long-term virus suppression, HIV invariably rebounds after interruption of therapy. Long-term antiviral therapy does not cure HIV infection nor does it induce restoration/development of virus-specific immune responses capable of controlling HIV replication. Therefore, development of immune-based interventions is needed to restore effective defenses that can lead to HIV functional cure and ultimately eradication.

RECENT FINDINGS

Therapeutic vaccination and immune interventions that generate de-novo or that boost preexisting HIV-specific T-cell responses are being investigated as a potential means to achieve a 'functional HIV cure'. One major hurdle in the quest of an HIV cure is control and elimination of the HIV latent reservoir. Several immune interventions that target the latent reservoir have been tried in recent years. In parallel, several therapeutic vaccination strategies have been developed and tested in early clinical studies. Recent encouraging studies show for the first time that vaccination can have an impact on HIV load.

SUMMARY

This review summarizes the main immune interventions evaluated over the last years. Ways to improve them, as well as challenges in monitoring/evaluating effects of such strategies, are being discussed. In addition, clinical efficacy and potential clinical benefits of immunotherapeutic interventions are particularly difficult to measure. This review highlights current assays used and their shortcoming.

Improving Adaptive and Memory Immune Responses of an HIV/AIDS Vaccine Candidate MVA-B by Deletion of Vaccinia Virus Genes (C6L and K7R) Blocking Interferon Signaling Pathways

Poxvirus vector Modified Vaccinia Virus Ankara (MVA) expressing HIV-1 Env, Gag, Pol and Nef antigens from clade B (termed MVA-B) is a promising HIV/AIDS vaccine candidate, as confirmed from results obtained in a prophylactic phase I clinical trial in humans. To improve the immunogenicity elicited by MVA-B, we have generated and characterized the innate immune sensing and the in vivo immunogenicity profile of a vector with a double deletion in two vaccinia virus (VACV) genes (C6L and K7R) coding for inhibitors of interferon (IFN) signaling pathways. The innate immune signals elicited by MVA-B deletion mutants (MVA-B ΔC6L and MVA-B ΔC6L/K7R) in human macrophages and monocyte-derived dendritic cells (moDCs) showed an up-regulation of the expression of IFN-β, IFN-α/β-inducible genes, TNF-α, and other cytokines and chemokines. A DNA prime/MVA boost immunization protocol in mice revealed that these MVA-B deletion mutants were able to improve the magnitude and quality of HIV-1-specific CD4⁺ and CD8⁺ T cell adaptive and memory immune responses, which were mostly mediated by CD8⁺ T cells of an effector phenotype, with MVA-B ΔC6L/K7R being the most immunogenic virus recombinant. CD4⁺ T cell responses were mainly directed against Env, while GPN-specific CD8⁺ T cell responses were induced preferentially by the MVA-B deletion mutants. Furthermore, antibody levels to Env in the memory phase were slightly enhanced by the MVA-B deletion mutants compared to the parental MVA-B. These findings revealed that double deletion of VACV genes that act blocking intracellularly the IFN signaling pathway confers an immunological benefit, inducing innate immune responses and increases in the magnitude, quality and durability of the HIV-1-specific T cell immune responses. Our observations highlighted the immunomodulatory role of the VACV genes C6L and K7R, and that targeting common pathways, like IRF3/IFN-β signaling, could be a general strategy to improve the immunogenicity of poxvirus-based vaccine candidates.

Adenosine deaminase enhances the immunogenicity of human dendritic cells from healthy and HIV-infected individuals

ADA is an enzyme implicated in purine metabolism, and is critical to ensure normal immune function. Its congenital deficit leads to severe combined immunodeficiency (SCID). ADA binding to adenosine receptors on dendritic cell surface enables T-cell costimulation through CD26 crosslinking, which enhances T-cell activation and proliferation. Despite a large body of work on the actions of the ecto-enzyme ADA on T-cell activation, questions arise on whether ADA can also modulate dendritic cell maturation. To this end we investigated the effects of ADA on human monocyte derived dendritic cell biology. Our results show that both the enzymatic and non-enzymatic activities of ADA are implicated in the enhancement of CD80, CD83, CD86, CD40 and CCR7 expression on immature dendritic cells from healthy and HIV-infected individuals. These ADA-mediated increases in CD83 and costimulatory molecule expression is concomitant to an enhanced IL-12, IL-6, TNF-α, CXCL8(IL-8), CCL3(MIP1-α), CCL4(MIP-1β) and CCL5(RANTES) cytokine/chemokine secretion both in healthy and HIV-infected individuals and to an altered apoptotic death in cells from HIV-infected individuals. Consistently, ADA-mediated actions on iDCs are able to enhance allogeneic CD4 and CD8-T-cell proliferation, globally yielding increased iDC immunogenicity. Taken together, these findings suggest that ADA would promote enhanced and correctly polarized T-cell responses in strategies targeting asymptomatic HIV-infected individuals.

Deletion of the viral anti-apoptotic gene F1L in the HIV/AIDS vaccine candidate MVA-C enhances immune responses against HIV-1 antigens

Vaccinia virus (VACV) encodes an anti-apoptotic Bcl-2-like protein F1 that acts as an inhibitor of caspase-9 and of the Bak/Bax checkpoint but the role of this gene in immune responses is not known. Because dendritic cells that have phagocytosed apoptotic infected cells cross-present viral antigens to cytotoxic T cells inducing an antigen-specific immunity, we hypothesized that deletion of the viral anti-apoptotic F1L gene might have a profound effect on the capacity of poxvirus vectors to activate specific immune responses to virus-expressed recombinant antigens. This has been tested in a mouse model with an F1L deletion mutant of the HIV/AIDS vaccine candidate MVA-C that expresses Env and Gag-Pol-Nef antigens (MVA-C-ΔF1L). The viral gene F1L is not required for virus replication in cultured cells and its deletion in MVA-C induces extensive apoptosis and expression of immunomodulatory genes in infected cells. Analysis of the immune responses induced in BALB/c mice after DNA prime/MVA boost revealed that, in comparison with parental MVA-C, the mutant MVA-C-ΔF1L improves the magnitude of the HIV-1-specific CD8 T cell adaptive immune responses and impacts on the CD8 T cell memory phase by enhancing the magnitude of the response, reducing the contraction phase and changing the memory differentiation pattern. These findings reveal the immunomodulatory role of F1L and that the loss of this gene is a valid strategy for the optimization of MVA as vaccine vector.

Can immunotherapy be useful as a "functional cure" for infection with Human Immunodeficiency Virus-1?

Immunotherapy aims to assist the natural immune system in achieving control over viral infection. Various immunotherapy formats have been evaluated in either therapy-naive or therapy-experienced HIV-infected patients over the last 20 years. These formats included non-antigen specific strategies such as cytokines that stimulate immunity or suppress the viral replication, as well as antibodies that block negative regulatory pathways. A number of HIV-specific therapeutic vaccinations have also been proposed, using in vivo injection of inactivated virus, plasmid DNA encoding HIV antigens, or recombinant viral vectors containing HIV genes. A specific format of therapeutic vaccines consists of ex vivo loading of autologous dendritic cells with one of the above mentioned antigenic formats or mRNA encoding HIV antigens.This review provides an extensive overview of the background and rationale of these different therapeutic attempts and discusses the results of trials in the SIV macaque model and in patients. To date success has been limited, which could be explained by insufficient quality or strength of the induced immune responses, incomplete coverage of HIV variability and/or inappropriate immune activation, with ensuing increased susceptibility of target cells.Future attempts at therapeutic vaccination should ideally be performed under the protection of highly active antiretroviral drugs in patients with a recovered immune system. Risks for immune escape should be limited by a better coverage of the HIV variability, using either conserved or mosaic sequences. Appropriate molecular adjuvants should be included to enhance the quality and strength of the responses, without inducing inappropriate immune activation. Finally, to achieve a long-lasting effect on viral control (i.e. a "functional cure") it is likely that these immune interventions should be combined with anti-latency drugs and/or gene therapy.

Therapeutic vaccination to treat chronic infectious diseases: current clinical developments using MVA-based vaccines

A famous milestone in the vaccine field has been the first successful vaccination against smallpox, in 1798, by Edward Jenner. Using the vaccinia cowpox virus, Jenner was able to protect vaccinees from variola or smallpox. The Modified Virus Ankara (MVA) poxvirus strain has been one of the vaccines subsequently developed to prevent smallpox infection and was selected by the US government in their Biodefense strategy. Progress in molecular biology and immunology associated with MVA infection has led to the development of MVA as vaccine platform, both in the field of preventive and therapeutic vaccines. This later class of therapeutics has witnessed growing interest that has translated into an increasing number of vaccine candidates reaching the clinics. Among those, MVA-based therapeutic vaccines have addressed four major chronic infections including viral hepatitis, AIDS, human papillomavirus-linked pathologies and tuberculosis. Clinical trials encompass phase 1 and 2 and have started to show significant results and promises.

Vector replication and expression of HIV-1 antigens by the HIV/AIDS vaccine candidate MVA-B is not affected by HIV-1 protease inhibitors

MVA-B is an attenuated poxvirus vector expressing human immunodeficiency virus type 1 Env, Gag, Pol, and Nef antigens from clade B, and is considered a promising HIV/AIDS vaccine candidate. Recently, a phase I clinical trial in human healthy volunteers has shown that MVA-B is safe and highly immunogenic, inducing broad, polyfunctional, and long-lasting CD4(+) and CD8(+) T cell responses to HIV-1 antigens, with preference for effector memory T cells; and it also triggers the induction of specific antibodies to Env in most of the vaccines. While MVA recombinants expressing HIV-1 antigens are being used or plan to use in therapeutic clinical trials, little is known on the effect of HIV-1 highly active antiretroviral therapy in MVA life cycle. To define this role, here we have evaluated in established cell cultures and human dendritic cells to what extent different HIV-1 protease inhibitors affect virus replication and expression of HIV-1 antigens during MVA-B infection. The results obtained revealed that the most commonly used HIV-1 protease inhibitors (atazanavir, ritonavir, and lopinavir) had no effect on MVA-B virus growth kinetics, even at higher concentrations than those normally used on HAART. Furthermore, expression of gp120 and the fused Gag-Pol-Nef polyprotein in permissive and non-permissive cells infected with MVA-B were also not affected. These findings are relevant information for the therapeutic use of MVA-B as an HIV-1/AIDS vaccine.

Systems analysis of MVA-C induced immune response reveals its significance as a vaccine candidate against HIV/AIDS of clade C

Based on the partial efficacy of the HIV/AIDS Thai trial (RV144) with a canarypox vector prime and protein boost, attenuated poxvirus recombinants expressing HIV-1 antigens are increasingly sought as vaccine candidates against HIV/AIDS. Here we describe using systems analysis the biological and immunological characteristics of the attenuated vaccinia virus Ankara strain expressing the HIV-1 antigens Env/Gag-Pol-Nef of HIV-1 of clade C (referred as MVA-C). MVA-C infection of human monocyte derived dendritic cells (moDCs) induced the expression of HIV-1 antigens at high levels from 2 to 8 hpi and triggered moDCs maturation as revealed by enhanced expression of HLA-DR, CD86, CD40, HLA-A2, and CD80 molecules. Infection ex vivo of purified mDC and pDC with MVA-C induced the expression of immunoregulatory pathways associated with antiviral responses, antigen presentation, T cell and B cell responses. Similarly, human whole blood or primary macrophages infected with MVA-C express high levels of proinflammatory cytokines and chemokines involved with T cell activation. The vector MVA-C has the ability to cross-present antigens to HIV-specific CD8 T cells in vitro and to increase CD8 T cell proliferation in a dose-dependent manner. The immunogenic profiling in mice after DNA-C prime/MVA-C boost combination revealed activation of HIV-1-specific CD4 and CD8 T cell memory responses that are polyfunctional and with effector memory phenotype. Env-specific IgG binding antibodies were also produced in animals receiving DNA-C prime/MVA-C boost. Our systems analysis of profiling immune response to MVA-C infection highlights the potential benefit of MVA-C as vaccine candidate against HIV/AIDS for clade C, the prevalent subtype virus in the most affected areas of the world.

Microparticles as immune regulators in infectious disease - an opinion

Despite their clear relationship to immunology, few existing studies have examined the potential role of microparticles (MP) in infectious disease. MP have a different size range from exosomes and apoptotic bodies, with which they are often grouped and arise by different mechanisms in association with inflammatory cytokine action or stress on the source cell. Infection with pathogens usually leads to the expression of a range of inflammatory cytokines and chemokines, as well as significant stress in both infected and uninfected cells. It is thus reasonable to infer that infection-associated inflammation also leads to MP production. MP are produced by most of the major cell types in the immune system, and appear to be involved at both innate and adaptive levels, potentially serving different functions in each. Thus, they do not appear to have a universal function; instead their functions are source- or stimulus-dependent, although likely to be primarily either pro- or anti-inflammatory. We argue that in infectious diseases, MP may be able to deliver antigen, derived from the biological cargo acquired from their cells of origin, to antigen-presenting cells. Another potential benefit of MP would be to transfer and/or disseminate phenotype and function to target cells. However, MP may also potentially be manipulated, particularly by intracellular pathogens, for survival advantage.

An old enzyme for current needs: adenosine deaminase and a dendritic cell vaccine for HIV

After nearly three decades of searching for a vaccine against HIV, a cure for this pandemic disease still remains elusive. The low immunogenicity of the surface proteins and the huge variability of the virus, together with the immunocompromised status of the host, have made developing an HIV vaccine an uphill battle. Over the past few years, both immunogen design and immunization strategies have improved, providing hope for future, although the anti-HIV responses achieved still remain modest. As developing a prophylactic vaccine seems unlikely nowadays, efforts have focused on alternative therapeutic immunization approaches, although these still need to be further optimized. Using an immunomodulator capable of restoring immune function in the context of infection, thereby boosting cell-mediated and humoral responses, could be critical in effectively improving current therapeutic approaches. Adenosine deaminase, a protein with a pivotal role in T-cell co-stimulation, has been shown to robustly enhance specific T-cell responses against HIV in vitro. Although its role in humoral responses has not yet been assessed, genetic defects in this enzyme are associated with impaired cellular and humoral responses. Importantly, this molecule is already commercially available pharmaceutically and, therefore, it fulfils all the requirements to be assayed as an anti-HIV vaccine adjuvant.

A candidate HIV/AIDS vaccine (MVA-B) lacking vaccinia virus gene C6L enhances memory HIV-1-specific T-cell responses

The vaccinia virus (VACV) C6 protein has sequence similarities with the poxvirus family Pox_A46, involved in regulation of host immune responses, but its role is unknown. Here, we have characterized the C6 protein and its effects in virus replication, innate immune sensing and immunogenicity in vivo. C6 is a 18.2 kDa protein, which is expressed early during virus infection and localizes to the cytoplasm of infected cells. Deletion of the C6L gene from the poxvirus vector MVA-B expressing HIV-1 Env, Gag, Pol and Nef antigens from clade B (MVA-B ΔC6L) had no effect on virus growth kinetics; therefore C6 protein is not essential for virus replication. The innate immune signals elicited by MVA-B ΔC6L in human macrophages and monocyte-derived dendritic cells (moDCs) are characterized by the up-regulation of the expression of IFN-β and IFN-α/β-inducible genes. In a DNA prime/MVA boost immunization protocol in mice, flow cytometry analysis revealed that MVA-B ΔC6L enhanced the magnitude and polyfunctionality of the HIV-1-specific CD4+ and CD8+ T-cell memory immune responses, with most of the HIV-1 responses mediated by the CD8+ T-cell compartment with an effector phenotype. Significantly, while MVA-B induced preferentially Env- and Gag-specific CD8+ T-cell responses, MVA-B ΔC6L induced more Gag-Pol-Nef-specific CD8+ T-cell responses. Furthermore, MVA-B ΔC6L enhanced the levels of antibodies against Env in comparison with MVA-B. These findings revealed that C6 can be considered as an immunomodulator and that deleting C6L gene in MVA-B confers an immunological benefit by enhancing IFN-β-dependent responses and increasing the magnitude and quality of the T-cell memory immune responses to HIV-1 antigens. Our observations are relevant for the improvement of MVA vectors as HIV-1 vaccines.

The HIV/AIDS vaccine candidate MVA-B administered as a single immunogen in humans triggers robust, polyfunctional, and selective effector memory T cell responses to HIV-1 antigens

Attenuated poxvirus vectors expressing human immunodeficiency virus type 1 (HIV-1) antigens are considered promising HIV/AIDS vaccine candidates. Here, we describe the nature of T cell immune responses induced in healthy volunteers participating in a phase I clinical trial in Spain after intramuscular administration of three doses of the recombinant MVA-B-expressing monomeric gp120 and the fused Gag-Pol-Nef (GPN) polyprotein of clade B. The majority (92.3%) of the volunteers immunized had a positive specific T cell response at any time postvaccination as detected by gamma interferon (IFN-γ) intracellular cytokine staining (ICS) assay. The CD4(+) T cell responses were predominantly Env directed, whereas the CD8(+) T cell responses were similarly distributed against Env, Gag, and GPN. The proportion of responders after two doses of MVA-B was similar to that obtained after the third dose of MVA-B vaccination, and the responses were sustained (84.6% at week 48). Vaccine-induced CD8(+) T cells to HIV-1 antigens after 1 year were polyfunctional and distributed mainly within the effector memory (TEM) and terminally differentiated effector memory (TEMRA) T cell populations. Antivector T cell responses were mostly induced by CD8(+) T cells, highly polyfunctional, and of TEMRA phenotype. These findings demonstrate that the poxvirus MVA-B vaccine candidate given alone is highly immunogenic, inducing broad, polyfunctional, and long-lasting CD4 and CD8 T cell responses to HIV-1 antigens, with preference for TEM. Thus, on the basis of the immune profile of MVA-B in humans, this immunogen can be considered a promising HIV/AIDS vaccine candidate.

Challenges in dendritic cells-based therapeutic vaccination in HIV-1 infection Workshop in dendritic cell-based vaccine clinical trials in HIV-1

Therapeutic immunization has been proposed as an approach that might help limit the need for lifelong combined antiretroviral therapy (cART). One approach for therapeutic vaccination which has been explored during the last few years is the administration of autologous monocyte-derived DCs (MD-DCs) loaded ex vivo with a variety of antigens. It has been shown in experimental murine models as well as in cancer patients and in patients with chronic infections that this approach can induce and potentiate antigen-specific T-cell response (and to induce a potent protective immunity). Contrary to the wide experience with this strategy in cancer, in HIV-1 infection the experience is limited and the design of the clinical trials varies greatly between groups. This variability affects all the steps of the process, from preparation of immunogen and DCs to clinical trial design and immune monitoring. Although both the study designs and the DC preparation (the maturation stimuli and the identity and source of HIV-1 antigens used to pulse DCs) varied in most of the studies that were published so far, overall the results indicate that DC immunotherapy elicits some degree of immunological response. To address this situation and to allow comparison between trials a panel of experts working in DC-based clinical trials in HIV-1 infection met in Barcelona at the end of 2010. During this meeting, the participants shared the data of their current research activities in this field in order to unify criteria for the future. This report summarizes the present situation of the field and the discussions and conclusions of this meeting.