Expansion of HIV-specific CD4+ and CD8+ T cells by dendritic cells transfected with mRNA encoding cytoplasm- or lysosome-targeted Nef

Evolving understanding of autoimmune mechanisms and new therapeutic strategies of autoimmune disorders

Autoimmune disorders are characterized by aberrant T cell and B cell reactivity to the body's own components, resulting in tissue destruction and organ dysfunction. Autoimmune diseases affect a wide range of people in many parts of the world and have become one of the major concerns in public health. In recent years, there have been substantial progress in our understanding of the epidemiology, risk factors, pathogenesis and mechanisms of autoimmune diseases. Current approved therapeutic interventions for autoimmune diseases are mainly non-specific immunomodulators and may cause broad immunosuppression that leads to serious adverse effects. To overcome the limitations of immunosuppressive drugs in treating autoimmune diseases, precise and target-specific strategies are urgently needed. To date, significant advances have been made in our understanding of the mechanisms of immune tolerance, offering a new avenue for developing antigen-specific immunotherapies for autoimmune diseases. These antigen-specific approaches have shown great potential in various preclinical animal models and recently been evaluated in clinical trials. This review describes the common epidemiology, clinical manifestation and mechanisms of autoimmune diseases, with a focus on typical autoimmune diseases including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, and sjögren's syndrome. We discuss the current therapeutics developed in this field, highlight the recent advances in the use of nanomaterials and mRNA vaccine techniques to induce antigen-specific immune tolerance.

Made to Measure: Patient-Tailored Treatment of Multiple Sclerosis Using Cell-Based Therapies

Currently, there is still no cure for multiple sclerosis (MS), which is an autoimmune and neurodegenerative disease of the central nervous system. Treatment options predominantly consist of drugs that affect adaptive immunity and lead to a reduction of the inflammatory disease activity. A broad range of possible cell-based therapeutic options are being explored in the treatment of autoimmune diseases, including MS. This review aims to provide an overview of recent and future advances in the development of cell-based treatment options for the induction of tolerance in MS. Here, we will focus on haematopoietic stem cells, mesenchymal stromal cells, regulatory T cells and dendritic cells. We will also focus on less familiar cell types that are used in cell therapy, including B cells, natural killer cells and peripheral blood mononuclear cells. We will address key issues regarding the depicted therapies and highlight the major challenges that lie ahead to successfully reverse autoimmune diseases, such as MS, while minimising the side effects. Although cell-based therapies are well known and used in the treatment of several cancers, cell-based treatment options hold promise for the future treatment of autoimmune diseases in general, and MS in particular.

Selective inhibition of aldo-keto reductase 1C3: a novel mechanism involved in midostaurin and daunorubicin synergism

Midostaurin is an FMS-like tyrosine kinase 3 receptor (FLT3) inhibitor that provides renewed hope for treating acute myeloid leukaemia (AML). The limited efficacy of this compound as a monotherapy contrasts with that of its synergistic combination with standard cytarabine and daunorubicin (Dau), suggesting a therapeutic benefit that is not driven only by FLT3 inhibition. In an AML context, the activity of the enzyme aldo-keto reductase 1C3 (AKR1C3) is a crucial factor in chemotherapy resistance, as it mediates the intracellular transformation of anthracyclines to less active hydroxy metabolites. Here, we report that midostaurin is a potent inhibitor of Dau inactivation mediated by AKR1C3 in both its recombinant form as well as during its overexpression in a transfected cell model. Likewise, in the FLT3^- AML cell line KG1a, midostaurin was able to increase the cellular accumulation of Dau and significantly decrease its metabolism by AKR1C3 simultaneously. The combination of those mechanisms increased the nuclear localization of Dau, thus synergizing its cytotoxic effects on KG1a cells. Our results provide new in vitro evidence of how the therapeutic activity of midostaurin could operate beyond targeting the FLT3 receptor.

Recent developments of RNA-based vaccines in cancer immunotherapy

INTRODUCTION

Cancer immunotherapy is more dependent on monoclonal antibodies, proteins, and cells, as therapeutic agents, to attain prominent outcomes. However, cancer immunotherapy's clinical benefits need to be enhanced, as many patients still do not respond well to existing treatments, or their diseases may relapse after temporary control. RNA-based approaches have provided new options for advancing cancer immunotherapy. Moreover, considerable efforts have been made to utilize RNA for vaccine production. RNA vaccines, which encode tumor-associated or specific epitopes, stimulate adaptive immunity. This adaptive immune response is capable of elimination or reduction of tumor burden. It is crucial to develop effective RNA transfer technologies that penetrate the lipid bilayer to reach the cytoplasm for translation into functional proteins. Two important delivery methods include the loading of mRNA into dendritic cells ex vivo; and direct injection of naked RNA with or without a carrier.

AREAS COVERED

The latest results of pre-clinical and clinical studies with RNA vaccines in cancer immunotherapy are summarized in this review.

EXPERT OPINION

RNA vaccines are now in early clinical development with promising safety and efficacy outcomes. Also, the translation capacity and durability of these vaccines can be increased with chemical modifications and sequence engineering.

Nanomedicines to Deliver mRNA: State of the Art and Future Perspectives

The use of messenger RNA (mRNA) in gene therapy is increasing in recent years, due to its unique features compared to plasmid DNA: Transient expression, no need to enter into the nucleus and no risk of insertional mutagenesis. Nevertheless, the clinical application of mRNA as a therapeutic tool is limited by its instability and ability to activate immune responses; hence, mRNA chemical modifications together with the design of suitable vehicles result essential. This manuscript includes a revision of the strategies employed to enhance in vitro transcribed (IVT) mRNA functionality and efficacy, including the optimization of its stability and translational efficiency, as well as the regulation of its immunostimulatory properties. An overview of the nanosystems designed to protect the mRNA and to overcome the intra and extracellular barriers for successful delivery is also included. Finally, the present and future applications of mRNA nanomedicines for immunization against infectious diseases and cancer, protein replacement, gene editing, and regenerative medicine are highlighted.

Characterization of monocyte-derived dendritic cells used in immunotherapy for HIV-1-infected individuals

AIMS

A therapeutic vaccine based on monocyte-derived dendritic cells (MDDCs) has been shown to represent a promising strategy for the treatment of cancer and viral infections. Here, we characterized the MDDCs used as an immunogen in a clinical trial for an anti-HIV-1 therapeutic vaccine.

PATIENTS & METHODS

Monocytes obtained from 17 HIV-infected individuals were differentiated into MDDCs and, after loading with autologous HIV, the cells were characterized concerning surface molecule expression, migratory and phagocytosis capacity, cytokine production and the induction of an effective cell-mediated immune response.

RESULTS

The MDDCs were able to induce antigen-specific responses in autologous CD4+ and CD8+ T lymphocytes.

CONCLUSIONS

Despite a large interindividual variability, the results suggested that MDDCs present the potential to promote immune responses in vaccinated patients.

de la Fuente I. Weighted lambda superstrings applied to vaccine design

We generalize the notion of λ-superstrings, presented in a previous paper, to the notion of weighted λ-superstrings. This generalization entails an important improvement in the applications to vaccine designs, as it allows epitopes to be weighted by their immunogenicities. Motivated by these potential applications of constructing short weighted λ-superstrings to vaccine design, we approach this problem in two ways. First, we formalize the problem as a combinatorial optimization problem (in fact, as two polynomially equivalent problems) and develop an integer programming (IP) formulation for solving it optimally. Second, we describe a model that also takes into account good pairwise alignments of the obtained superstring with the input strings, and present a genetic algorithm that solves the problem approximately. We apply both algorithms to a set of 169 strings corresponding to the Nef protein taken from patiens infected with HIV-1. In the IP-based algorithm, we take the epitopes and the estimation of the immunogenicities from databases of experimental epitopes. In the genetic algorithm we take as candidate epitopes all 9-mers present in the 169 strings and estimate their immunogenicities using a public bioinformatics tool. Finally, we used several bioinformatic tools to evaluate the properties of the candidates generated by our method, which indicated that we can score high immunogenic λ-superstrings that at the same time present similar conformations to the Nef virus proteins.

HIV-Infected Dendritic Cells Present Endogenous MHC Class II-Restricted Antigens to HIV-Specific CD4+ T Cells

It is widely assumed that CD4(+) T cells recognize antigenic peptides (epitopes) derived solely from incoming, exogenous, viral particles or proteins. However, alternative sources of MHC class II (MHC-II)-restricted Ags have been described, in particular epitopes derived from newly synthesized proteins (so-called endogenous). In this study, we show that HIV-infected dendritic cells (DC) present MHC-II-restricted endogenous viral Ags to HIV-specific (HS) CD4(+) T cells. This endogenous pathway functions independently of the exogenous route for HIV Ag presentation and offers a distinct possibility for the immune system to activate HS CD4(+) T cells. We examined the implication of autophagy, which plays a crucial role in endogenous viral Ag presentation and thymic selection of CD4(+) T cells, in HIV endogenous presentation. We show that infected DC do not use autophagy to process MHC-II-restricted HIV Ags. This is unlikely to correspond to a viral escape from autophagic degradation, as infecting DC with Nef- or Env-deficient HIV strains did not impact HS T cell activation. However, we demonstrate that, in DC, specific targeting of HIV Ags to autophagosomes using a microtubule-associated protein L chain 3 (LC3) fusion protein effectively enhances and broadens HS CD4(+) T cell responses, thus favoring an endogenous MHC-II-restricted presentation. In summary, in DC, multiple endogenous presentation pathways lead to the activation of HS CD4(+) T cell responses. These findings will help in designing novel strategies to activate HS CD4(+) T cells that are required for CTL activation/maintenance and B cell maturation.

Immunization of HIV-1-Infected Persons With Autologous Dendritic Cells Transfected With mRNA Encoding HIV-1 Gag and Nef: Results of a Randomized, Placebo-Controlled Clinical Trial

BACKGROUND

HIV-1 eradication may require reactivation of latent virus along with stimulation of HIV-1-specific immune responses to clear infected cells. Immunization with autologous dendritic cells (DCs) transfected with viral mRNA is a promising strategy for eliciting HIV-1-specific immune responses. We performed a randomized controlled clinical trial to evaluate the immunogenicity of this approach in HIV-1-infected persons on antiretroviral therapy.

METHODS

Fifteen participants were randomized 2:1 to receive intradermal immunization with HIV-1 Gag- and Nef-transfected DCs (vaccine) or mock-transfected DCs (placebo) at weeks 0, 2, 6, and 10. All participants also received DCs pulsed with keyhole limpet hemocyanin (KLH) to assess whether responses to a neo-antigen could be induced.

RESULTS

After immunization, there were no differences in interferon-gamma enzyme-linked immunospot responses to HIV-1 Gag or Nef in the vaccine or placebo group. CD4 proliferative responses to KLH increased 2.4-fold (P = 0.026) and CD8 proliferative responses to KLH increased 2.5-fold (P = 0.053) after vaccination. There were increases in CD4 proliferative responses to HIV-1 Gag (2.5-fold vs. baseline, 3.4-fold vs. placebo, P = 0.054) and HIV-1 Nef (2.3-fold vs. baseline, 6.3-fold vs. placebo, P = 0.009) among vaccine recipients, but these responses were short-lived.

CONCLUSION

Immunization with DCs transfected with mRNA encoding HIV-1 Gag and Nef did not induce significant interferon-gamma enzyme-linked immunospot responses. There were increases in proliferative responses to HIV-1 antigens and to a neo-antigen, KLH, but the effects were transient. Dendritic cell vaccination should be optimized to elicit stronger and long-lasting immune responses for this strategy to be effective as an HIV-1 therapeutic vaccine.

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.

RNA-Based Vaccines in Cancer Immunotherapy

RNA vaccines traditionally consist of messenger RNA synthesized by in vitro transcription using a bacteriophage RNA polymerase and template DNA that encodes the antigen(s) of interest. Once administered and internalized by host cells, the mRNA transcripts are translated directly in the cytoplasm and then the resulting antigens are presented to antigen presenting cells to stimulate an immune response. Alternatively, dendritic cells can be loaded with either tumor associated antigen mRNA or total tumor RNA and delivered to the host to elicit a specific immune response. In this review, we will explain why RNA vaccines represent an attractive platform for cancer immunotherapy, discuss modifications to RNA structure that have been developed to optimize mRNA vaccine stability and translational efficiency, and describe strategies for nonviral delivery of mRNA vaccines, highlighting key preclinical and clinical data related to cancer immunotherapy.

Reprogramming to pluripotency and differentiation of cells with synthetic mRNA

Changing cell fate without altering its genome is very desirable in many experimental systems and for cell therapy. Compared to DNA plasmid or viral-based approach, mRNA has the advantage of high transfection efficiency, no danger of changing the genome or creating mutational insertions. Here, we describe a straightforward protocol to synthesize mRNA of genes of interest, and use them to induce pluripotency and direct cell differentiation.

Lipoplexes carrying mRNA encoding Gag protein modulate dendritic cells to stimulate HIV-specific immune responses

AIM

Cationic lipids (Lipofectamine™ [Invitrogen, Merelbeke, Belgium] and 1,2-dioleoyl-3-trimethylammonium-propane/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) and polymers (jetPEI™ and in vivo-jetPEI™ [Polyplus-transfection, Illkirch, France]) were evaluated for their potential to deliver mRNA to monocyte-derived dendritic cells.

MATERIALS & METHODS

Lipoplexes and polyplexes, containing mRNA encoding GFP or Gag protein, were incubated with human monocyte-derived dendritic cells and transfection efficiencies were assessed by flow cytometry.

RESULTS

Lipofectamine was by far the most efficient in mRNA delivery, therefore it was used in further experiments. Incubation of monocyte-derived dendritic cells isolated from HIV-1-positive donors with mRNA encoding Gag protein complexed to Lipofectamine resulted in 50% transfection. Importantly, coculture of these Gag-transfected dendritic cells with autologous T cells induced an over tenfold expansion of IFN-γ- and IL-2-secreting CD4(+) and CD8(+) T cells.

CONCLUSION

Cationic lipid-mediated mRNA delivery may be a useful tool for therapeutic vaccination against HIV-1. This approach can be applied to develop vaccination strategies for other infectious diseases and cancer.

Optimizing dendritic cell-based immunotherapy: tackling the complexity of different arms of the immune system

Earlier investigations have revealed a surprising complexity and variety in the range of interaction between cells of the innate and adaptive immune system. Our understanding of the specialized roles of dendritic cell (DC) subsets in innate and adaptive immune responses has been significantly advanced over the years. Because of their immunoregulatory capacities and because very small numbers of activated DC are highly efficient at generating immune responses against antigens, DCs have been vigorously used in clinical trials in order to elicit or amplify immune responses against cancer and chronic infectious diseases. A better insight in DC immunobiology and function has stimulated many new ideas regarding the potential ways forward to improve DC therapy in a more fundamental way. Here, we discuss the continuous search for optimal in vitro conditions in order to generate clinical-grade DC with a potent immunogenic potential. For this, we explore the molecular and cellular mechanisms underlying adequate immune responses and focus on most favourable DC culture regimens and activation stimuli in humans. We envisage that by combining each of the features outlined in the current paper into a unified strategy, DC-based vaccines may advance to a higher level of effectiveness.

Interleukin-12p70 expression by dendritic cells of HIV-1-infected patients fails to stimulate gag-specific immune responses

A variety of immune-based therapies has been developed in order to boost or induce protective CD8⁺ T cell responses in order to control HIV replication. Since dendritic cells (DCs) are professional antigen-presenting cells (APCs) with the unique capability to stimulate naïve T cells into effector T cells, their use for the induction of HIV-specific immune responses has been studied intensively. In the present study we investigated whether modulation of the activation state of DCs electroporated with consensus codon-optimized HxB2 gag mRNA enhances their capacity to induce HIV gag-specific T cell responses. To this end, mature DCs were (i) co-electroporated with mRNA encoding interleukin (IL)-12p70 mRNA, or (ii) activated with a cytokine cocktail consisting of R848 and interferon (IFN)-γ. Our results confirm the ability of HxB2 gag-expressing DCs to expand functional HIV-specific CD8⁺ T cells. However, although most of the patients had detectable gag-specific CD8⁺ T cell responses, no significant differences in the level of expansion of functional CD8⁺ T cells could be demonstrated when comparing conventional or immune-modulated DCs expressing IL-12p70. This result which goes against expectation may lead to a re-evaluation of the need for IL-12 expression by DCs in order to improve T-cell responses in HIV-1-infected individuals.

Aminopeptidase substrate preference affects HIV epitope presentation and predicts immune escape patterns in HIV-infected individuals

Viruses evade immune detection partly through immune-associated mutations. Analyses of HIV sequences derived from infected individuals have identified numerous examples of HLA-associated mutations within or adjacent to T cell epitopes, but the potential impact of most mutations on epitope production and presentation remains unclear. The multistep breakdown of proteins into epitopes includes trimming of N-extended peptides into epitopes by aminopeptidases before loading onto MHC class I molecules. Definition of sequence signatures that modulate epitope production would lead to a better understanding of factors driving viral evolution and immune escape at the population level. In this study, we identified cytosolic aminopeptidases cleavage preferences in primary cells and its impact on HIV Ag degradation into epitopes in primary human cell extracts by mass spectrometry and on epitope presentation to CTL. We observed a hierarchy of preferred amino acid cleavage by cytosolic aminopeptidases. We demonstrated that flanking mutations producing more or less cleavable motifs can increase or decrease epitope production and presentation by up to 14-fold. We found that the efficiency of epitope production correlates with cleavability of flanking residues. These in vitro findings were supported by in vivo population-level analyses of clinically derived viral sequences from 1134 antiretroviral-naive HIV-infected individuals: HLA-associated mutations immune pressures drove the selection of residues that are less cleavable by aminopeptidases predominantly at N-flanking sites, leading to reduced epitope production and immune recognition. These results underscore an important and widespread role of Ag processing mutations in HIV immune escape and identify molecular mechanisms underlying impaired epitope presentation.

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.

In vitro and in vivo mRNA delivery using lipid-enveloped pH-responsive polymer nanoparticles

Biodegradable core--shell structured nanoparticles with a poly(β-amino ester) (PBAE) core enveloped by a phospholipid bilayer shell were developed for in vivo mRNA delivery with a view toward delivery of mRNA-based vaccines. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. Messenger RNA was efficiently adsorbed via electrostatic interactions onto the surface of these net positively charged nanoparticles. In vitro, mRNA-loaded particle uptake by dendritic cells led to mRNA delivery into the cytosol with low cytotoxicity, followed by translation of the encoded protein in these difficult-to-transfect cells at a frequency of ~30%. Particles loaded with mRNA administered intranasally (i.n.) in mice led to the expression of the reporter protein luciferase in vivo as soon as 6 h after administration, a time point when naked mRNA given i.n. showed no expression. At later time points, luciferase expression was detected in naked mRNA-treated mice, but this group showed a wide variation in levels of transfection, compared to particle-treated mice. This system may thus be promising for noninvasive delivery of mRNA-based vaccines.

Preclinical evaluation of HIV-1 therapeutic ex vivo dendritic cell vaccines expressing consensus Gag antigens and conserved Gag epitopes

BACKGROUND

Dendritic cell (DC) therapy is a promising technology for the treatment of HIV infected individuals. HIV-1 Gag- and Nef RNA-loaded DC have previously been shown to induce immune responses ex vivo following coculture with autologous lymphocytes. However, polyfunctionality and memory responses following coculture have not been evaluated. In addition, little is known regarding whether specific HIV-1 proteome components, such as highly conserved regions of the HIV-1, could enhance clinical responses following DC therapy.

METHODOLOGY AND PRINCIPAL FINDINGS

To determine the breadth of the immune responses to antigen loaded DC, we analyzed polyfunctional T cell response ex vivo to Gag RNA loaded DC. Blood samples were used to generate monocyte derived DC, which were then matured and cocultured with autologous lymphocytes. We found that cytokine-matured DC loaded with Gag RNA was able to induce Gag-specific IFN-γ and IL-2 responses after a 12-day coculture. We characterized these responses by polyfunctional intracellular cytokine staining and evaluation of T cell memory phenotypes. Central memory CD8+ T cells were induced ex vivo after DC coculture from each of 3 patients, and the effector memory pool was increased by DC coculture from 2 patients. We also observed a decrease in the terminal effector and intermediate CD8+ T cell pool and an increase in the naïve/other population. There was a reduction in terminal effector and intermediate CD4+ T cells, and a corresponding increase in naïve/other CD4+ T cells. Finally, we evaluated conserved regions of Gag as a novel DC therapy immunogen and found that a conserved element (CE) p24 Gag antigen elicited IFN-γ and IL-2 responses comparable to those induced by a full-length Gag antigen.

CONCLUSIONS

We showed that RNA-loaded DC therapy induced a polyfunctional T cell response ex vivo, supporting the use of such DC-therapy for HIV infection. However, the central and effector memory phenotypes of T cells did not appear to be enhanced during coculture with Gag RNA-loaded DC. Furthermore, comparable antigen-specific responses were induced in HIV infected individuals using full-length Gag or only conserved elements of the Gag p24 protein. This indicates that immune responses can be focused onto the conserved elements of Gag in the absence of other Gag components.

Evaluation of cellular immune responses in cancer vaccine recipients: lessons from NY-ESO-1

The rigorous evaluation of cancer vaccination requires evidence of benefit to patients with cancer or those at risk of relapse from the disease. Clinical trials are expensive and require considerable human and clinical resources in order to demonstrate this benefit. In the era of defined cancer antigens, it is possible to evaluate immunogenic targets, and assess the quality and magnitude of immune responses against these antigens following vaccination. Analyzing these surrogate end points complements clinical assessment and provides a depth of understanding to better inform trial evaluation and design. We have used the immunogenic cancer testis antigen NY-ESO-1 as a model antigen. This article summarizes our experience in monitoring immunity against NY-ESO-1.

Soluble HLA-G inhibits myeloid dendritic cell function in HIV-1 infection by interacting with leukocyte immunoglobulin-like receptor B2

Dendritic cells represent a specialized class of professional antigen-presenting cells that are responsible for priming and maintaining antigen-specific effector cell responses and regulating immune activation by cytokine secretion. In HIV-1 infection, myeloid dendritic cells are highly dysfunctional, but mechanisms contributing to their functional alterations are not well defined. Here, we show that soluble molecules of the nonclassical major histocompatibility complex class Ib (MHC-Ib) antigen HLA-G are highly upregulated in the plasma during progressive HIV-1 infection, while levels of membrane-bound HLA-G surface expression on dendritic cells, monocytes, and T cells only slightly differ among HIV-1 progressors, HIV-1 elite controllers, and HIV-1-negative persons. These elevated levels of soluble HLA-G in progressive HIV-1 infection likely result from increased secretion of intracellularly stored HLA-G molecules in monocytes and dendritic cells and contribute to a functional disarray of dendritic cells by inhibiting their antigen-presenting properties, while simultaneously enhancing their secretion of proinflammatory cytokines. Interestingly, we observed that these immunoregulatory effects of soluble HLA-G were mainly mediated by interactions with the myelomonocytic HLA class I receptor leukocyte immunoglobulin-like receptor B2 (LILRB2; ILT4), while binding of soluble HLA-G to its alternative high-affinity receptor, LILRB1 (ILT2), appeared to be less relevant for its immunomodulatory functions on dendritic cells. Overall, these results demonstrate a critical role for soluble HLA-G in modulating the functional characteristics of professional antigen-presenting cells in progressive HIV-1 infection and suggest that soluble HLA-G might represent a possible target for immunotherapeutic interventions in HIV-1-infected persons.

Immunotherapy of viral infections

Among the microorganisms that cause diseases of medical or veterinary importance, the only group that is entirely dependent on the host, and hence not easily amenable to therapy via pharmaceuticals, is the viruses. Since viruses are obligate intracellular pathogens, and therefore depend a great deal on cellular processes, direct therapy of viral infections is difficult. Thus, modifying or targeting nonspecific or specific immune responses is an important aspect of intervention of ongoing viral infections. However, as a result of the unavailability of effective vaccines and the extended duration of manifestation, chronic viral infections are the most suitable for immunotherapies. We present an overview of various immunological strategies that have been applied for treating viral infections after exposure to the infectious agent.

Leukocyte immunoglobulin-like receptors maintain unique antigen-presenting properties of circulating myeloid dendritic cells in HIV-1-infected elite controllers

Elite controllers maintain undetectable levels of HIV-1 replication in the absence of antiretroviral therapy, but the correlates of immune protection in this patient population are ill defined. Here, we demonstrate that in comparison to patients with progressive HIV-1 infection or healthy persons not infected with HIV-1, elite controllers have circulating myeloid dendritic cells with significantly increased antigen-presenting properties, while their ability to secrete proinflammatory cytokines is substantially diminished. This unique functional profile is associated with a distinct surface expression pattern of immunomodulatory leukocyte-immunoglobulin-like receptors (LILR) and a strong and selective upregulation of LILRB1 and LILRB3. Blockade of these two receptors by monoclonal antibodies or short interfering RNA (siRNA) abrogated the specific antigen-presenting properties of dendritic cells, implying an important regulatory role of these molecules. These data reveal previously unrecognized innate components of immune protection against HIV-1 in elite controllers and offer novel perspectives for the manipulation of host immunity for the prevention and treatment of HIV-1 infection.

Polyelectrolyte capsules-containing HIV-1 p24 and poly I:C modulate dendritic cells to stimulate HIV-1-specific immune responses

Polyelectrolyte microcapsules (MCs) are potent protein delivery vehicles which can be tailored with ligands to stimulate maturation of dendritic cells (DCs). We investigated the immune stimulatory capacity of monocyte-derived DC (Mo-DC) loaded with these MCs, containing p24 antigen from human immunodeficiency virus type 1 (HIV-1) alone [p24-containing MC (MCp24)] or with the Toll-like receptor ligand 3 (TLR3) ligand poly I:C (MCp24pIC) as a maturation factor. MO-DC, loaded with MCp24pIC, upregulated CCR7, CD80, CD83, and CD86 and produced high amounts of interleukin-12 (IL-12) cytokine, to a similar extent as MCp24 in the presence of an optimized cytokine cocktail. MO-DC from HIV-infected patients under highly active antiretroviral therapy (HAART) exposed to MCp24 together with cytokine cocktail or to MCp24pIC expanded autologous p24-specific CD4(+) and CD8(+) T-cell responses as measured by interferon-gamma (IFN-gamma) and IL-2 cytokine production and secretion. In vivo relevance was shown by immunizing C57BL/6 mice with MCp24pIC, which induced both humoral and cellular p24-specific immune responses. Together these data provide a proof of principle that both antigen and DC maturation signal can be delivered as a complex with polyelectrolyte capsules to stimulate virus-specific T cells both in vitro and in vivo. Polyelectrolyte MCs could be useful for in vivo immunization in HIV-1 and other infections.

Lumenal part of the DC-LAMP protein is not required for induction of antigen-specific T cell responses by means of antigen-DC-LAMP messenger RNA-electroporated dendritic cells

Previous studies showed that stimulation of T cells derived from HIV-1-infected patients with autologous dendritic cells electroporated with mRNA encoding HIV antigens can induce antigen-specific T cell responses in vitro. Linking the antigen to an MHC class II-targeting sequence, such as dendritic cell lysosome-associated membrane protein (DC-LAMP), in the mRNA construct results in presentation of antigenic peptides in both MHC class I and class II molecules and therefore enhances the induced T cell responses. To analyze whether the lumenal domain of DC-LAMP is required for optimal induction of cellular immunity against HIV antigens, we compared fusion constructs with or without the lumenal domain of the DC-LAMP protein. A human codon-optimized consensus Gag sequence and a chimeric cDNA sequence encompassing Tat, Rev, and Nef codons (TaReNef ) were cloned into a vector containing the DC-LAMP sequence with or without its lumenal domain. The Gag protein lacking the DC-LAMP-derived sequence altogether elicited only weak T cell responses. DCs electroporated with Gag or TaReNef linked to DC-LAMP were able to elicit similar levels of antigen-specific CD4(+) and CD8(+) T cell responses for both Gag and TaReNef, irrespective of the addition of the DC-LAMP lumenal domain. These data show that DC-LAMP-mediated antigen targeting is absolutely required for optimal T cell stimulation, but that in our experimental setup, the lumenal part of DC-LAMP does not improve the overall induction of antigen-specific T cell responses.

Cellular immune responses against CT7 (MAGE-C1) and humoral responses against other cancer-testis antigens in multiple myeloma patients

The type I melanoma antigen gene (MAGE) proteins CT7 (MAGE-C1) and MAGE-A3 are commonly expressed in multiple myeloma (MM), and their expression correlates with increased plasma cell proliferation and poor clinical outcome. They belong to the cancer-testis antigen (CTAg) group of tumor-associated proteins, some of which elicit spontaneous immune responses in cancer patients. CT7 and MAGE-A3 are promising antigenic targets for therapeutic tumor vaccines in myeloma; therefore, it is critical to determine if they are immunogenic in MM patients. We analyzed cellular and humoral immune responses against CTAgs in patients with plasma cell dyscrasias: MM, monoclonal gammopathy of undetermined significance (MGUS), and Waldenström's macroglobulinemia (WM). Bone marrow lymphocytes from two of four untreated MM patients exhibited CT7-specific cellular immune responses as measured by an autologous cellular immunity assay, the first such immune response to CT7 to be reported in cancer patients. Sera from 24 patients were screened by ELISA for humoral immune responses to CTAgs. Two patients with MM demonstrated positive titers, one for MAGE-A1 and the other for SSX1. These data demonstrate that CTAgs, particularly CT7, are immunogenic in MM patients and merit further exploration as targets of immunological therapy in MM.

HLA-B*35-Px-mediated acceleration of HIV-1 infection by increased inhibitory immunoregulatory impulses

A subset of HLA-B*35 alleles, B*35-Px, are strongly associated with accelerated HIV-1 disease progression for reasons that are not understood. Interestingly, the alternative set of B*35 subtypes, B*35-PY, have no detectable impact on HIV-1 disease outcomes, even though they can present identical HIV-1 epitopes as B*35-Px molecules. Thus, the differential impact of these alleles on HIV-1 disease progression may be unrelated to interactions with HIV-1-specific CD8(+) T cells. Here, we show that the B*35-Px molecule B*3503 binds with greater affinity to immunoglobulin-like transcript 4 (ILT4), an inhibitory MHC class I receptor expressed on dendritic cells, than does the B*35-PY molecule B*3501, even though these two B*35 molecules differ by only one amino acid and present identical HIV-1 epitopes. The preferential recognition of B*3503 by ILT4 was associated with significantly stronger dendritic cell dysfunction in in vitro functional assays. Moreover, HIV-1-infected carriers of B*3503 had poor dendritic cell functional properties in ex vivo assessments when compared with carriers of the B*3501 allele. Differential interactions between HLA class I allele subtypes and immunoregulatory MHC class I receptors on dendritic cells thus provide a novel perspective for the understanding of MHC class I associations with HIV-1 disease progression and for the manipulation of host immunity against HIV-1.

Dendritic cell immunotherapy for HIV infection: from theory to reality

Knowledge concerning the immunology of dendritic cells (DCs) accumulated over the last few decades and the development of methodologies to generate and manipulate these cells in vitro has made their therapeutic application a reality. Currently, clinical protocols for DC-based therapeutic vaccine in HIV-infected individuals show that it is a safe and promising approach. Concomitantly, important advances continue to be made in the development of methodologies to optimize DC acquisition, as well as the selection of safe, immunogenic HIV antigens and the evaluation of immune response in treated individuals.

A randomized therapeutic vaccine trial of canarypox-HIV-pulsed dendritic cells vs. canarypox-HIV alone in HIV-1-infected patients on antiretroviral therapy

Targeting canarypox (CP)-HIV vaccine to dendritic cells (DCs) elicits anti-HIV-1 immune responses in vitro. We conducted a phase I/II clinical trial to evaluate whether adding DC to a CP-HIV vaccine improved virologic control during analytic treatment interruption (ATI) in HIV-1-infected subjects. Twenty-nine subjects on suppressive antiretroviral therapy were randomized to vaccination with autologous DCs infected with CP-HIV+keyhole limpet hemocyanin (KLH) (arm A, n=14) or CP-HIV+KLH alone (arm B, n=15). The mean viral load (VL) setpoint during ATI did not differ between subjects in arms A and B. A higher percentage of subjects in the DC group had a VL setpoint < 5,000 c/mL during ATI (4/13 or 31% in arm A compared with 0/13 in arm B, p=0.096), but virologic control was transient. Subjects in arm A had a greater increase in KLH lymphoproliferative response than subjects in arm B; however, summed ELISPOT responses to HIV-1 antigens did not differ by treatment arm. We conclude that a DC-CP-HIV vaccine is well-tolerated in HIV-1-infected patients, but does not lower VL setpoint during ATI compared with CP-HIV alone. New methods to enhance the immunogenicity and antiviral efficacy of DC-based vaccines for HIV-1 infection are needed.

Modified tumour antigen-encoding mRNA facilitates the analysis of naturally occurring and vaccine-induced CD4 and CD8 T cells in cancer patients

The development of effective anti-cancer vaccines requires precise assessment of vaccine-induced immunity. This is often hampered by low ex vivo frequencies of antigen-specific T cells and limited defined epitopes. This study investigates the applicability of modified, in vitro-transcribed mRNA encoding a therapeutically relevant tumour antigen to analyse T cell responses in cancer patients. In this study transfection of antigen presenting cells, by mRNA encoding the tumour antigen NY-ESO-1, was optimised and applied to address spontaneous and vaccine-induced T cell responses in cancer patients. Memory CD8+ T cells from lung cancer patients having detectable humoral immune responses directed towards NY-ESO-1 could be efficiently detected in peripheral blood. Specific T cells utilised a range of different T cell receptors, indicating a polyclonal response. Specific killing of a panel of NY-ESO-1 expressing tumour cell lines indicates recognition restricted to several HLA allelic variants, including a novel HLA-B49 epitope. Using a modified mRNA construct targeting the translated antigen to the secretory pathway, detection of NY-ESO-1-specific CD4+ T cells in patients could be enhanced, which allowed the in-depth characterisation of established T cell clones. Moreover, broad CD8+ and CD4+ T cell responses covering multiple epitopes were detected following mRNA stimulation of patients treated with a recombinant vaccinia/fowlpox NY-ESO-1 vaccine. This approach allows for a precise monitoring of responses to tumour antigens in a setting that addresses the breadth and magnitude of antigen-specific T cell responses, and that is not limited to a particular combination of known epitopes and HLA-restrictions.

Dendritic cell-based human immunodeficiency virus vaccine

Dendritic cells (DC) have profound abilities to induce and coordinate T-cell immunity. This makes them ideal biological agents for use in immunotherapeutic strategies to augment T-cell immunity to HIV infection. Current clinical trials are administering DC-HIV antigen preparations carried out ex vivo as proof of principle that DC immunotherapy is safe and efficacious in HIV-infected patients. These trials are largely dependent on preclinical studies that will provide knowledge and guidance about the types of DC, form of HIV antigen, method of DC maturation, route of DC administration, measures of anti-HIV immune function and ultimately control of HIV replication. Additionally, promising immunotherapy approaches are being developed based on targeting of DC with HIV antigens in vivo. The objective is to define a safe and effective strategy for enhancing control of HIV infection in patients undergoing antiretroviral therapy.

Type 2 Bias of T cells expanded from the blood of melanoma patients switched to type 1 by IL-12p70 mRNA-transfected dendritic cells

Melanoma patients may exhibit a T(H)2-skewed cytokine profile within blood and tumor-infiltrating lymphocytes. Therapies that induce beneficial T(H)1-type tumor-specific immune responses, therefore, are highly desirable. Dendritic cells (DC) are widely used as immune adjuvants for cancer. Before their administration, DC are generally induced to mature with a cocktail of recombinant cytokines [interleukin (IL)-1beta, tumor necrosis factor alpha, and IL-6] and prostaglandin E(2) (PGE(2)), which is added to preserve the ability of DC to migrate to draining lymph nodes. However, PGE(2) suppresses the production of IL-12p70, a cytokine essential for differentiation of T(H)1 responses. In this study, human DC were transfected with IL-12p70 mRNA and tested for their ability to alter the T(H)2 type bias manifested by blood T cells of patients with melanoma. Transfected DC secreted high levels of bioactive IL-12p70, as indicated by their capacity to enhance natural killer cell activity, skew T(H)1 responses in allogeneic mixed lymphocyte reactions through reduction of IL-4 and IL-5, and prime CD8(+) T cells to the melanoma-associated antigen Melan A/MART-1. Furthermore, T-cell lines primed in vitro from the blood of melanoma patients showed strong type 2 skewing that was dramatically reversed by IL-12p70 transfection of autologous DC. Thus, IL-12p70 transfection of clinical DC preparations may enhance type 1 antitumor responses and may thereby contribute to effective immune-based therapy.

High-level antigen expression and sustained antigen presentation in dendritic cells nucleofected with wild-type viral mRNA but not DNA

Dendritic cells (DC) are potent antigen-presenting cells that hold promise as cell-based therapeutic vaccines for infectious diseases and cancer. Ideally, DC would be engineered to express autologous viral or tumor antigens to ensure the presentation of relevant antigens to host T cells in vivo; however, expression of wild-type viral genes in primary cell lines can be problematic. Nucleofection is an effective means of delivering transgenes to primary cell lines, but its use in transfecting DNA or mRNA into DC has not been widely investigated. We show that nucleofection is a superior means of transfecting human and monkey monocyte-derived DC with DNA and mRNA compared to lipofection and conventional electroporation. However, the delivery of DNA and mRNA had significantly different outcomes in transfected DC. DC nucleofected with DNA encoding green fluorescent protein (GFP) had poor antigen expression and viability and were refractory to maturation with CD40 ligand. In contrast, >90% of DC expressed uniform and high levels of GFP from 3 h to 96 h postnucleofection with mRNA while maintaining a normal maturation response to CD40 ligation. Monkey DC nucleofected with wild-type, non-codon-optimized mRNA encoding simian immunodeficiency virus Gag stimulated robust antigen-specific effector T-cell responses at 24 h and 48 h postnucleofection, reflecting sustained antigen presentation in transfected DC, whereas no detectable T-cell response was noted when DC were nucleofected with DNA encoding the same Gag sequence. These data indicate that mRNA nucleofection may be an optimal means of transfecting DC with autologous tumor or viral antigen for DC-based immunotherapy.

Functional T-cell responses generated by dendritic cells expressing the early HIV-1 proteins Tat, Rev and Nef

The limitations of highly active anti-retroviral therapy (HAART) have necessitated the development of alternative therapeutic strategies. One of the approaches that has gained prominence in recent years is therapeutic vaccination. We decided to assess the capacity of mature dendritic cells, derived from blood monocytes of HIV-1 infected patients, to generate functional T-cell responses. For this purpose, we constructed a chimeric mRNA encoding the proteins Tat, Rev and Nef. The TaReNef encoding information was linked to the HLA class II-targeting sequence of DC-LAMP. Broadly directed HIV-specific CD4(+) and CD8(+) cytotoxic T cells exhibiting a poly-functional cytokine secretion pattern were generated by co-culturing with autologous chimeric mRNA electroporated dendritic cells. Thus, administration of ex vivo generated dendritic cells expressing the early proteins Tat, Rev and Nef might offer a promising approach for therapeutic vaccination in HIV-1 infection.

Quantitative effect of suboptimal codon usage on translational efficiency of mRNA encoding HIV-1 gag in intact T cells

Background

The sequences of wild-isolate strains of Human Immunodeficiency Virus-1 (HIV-1) are characterized by low GC content and suboptimal codon usage. Codon optimization of DNA vectors can enhance protein expression both by enhancing translational efficiency, and by altering RNA stability and export. Although gag codon optimization is widely used in DNA vectors and experimental vaccines, the actual effect of altered codon usage on gag translational efficiency has not been quantified.

Methodology and Principal Findings

To quantify translational efficiency of gag mRNA in live T cells, we transfected Jurkat cells with increasing doses of capped, polyadenylated synthetic mRNA corresponding to wildtype or codon-optimized gag sequences, measured Gag production by quantitative ELISA and flow cytometry, and estimated the translational efficiency of each transcript as pg of Gag antigen produced per µg of input mRNA. We found that codon optimization yielded a small increase in gag translational efficiency (approximately 1.6 fold). In contrast when cells were transfected with DNA vectors requiring nuclear transcription and processing of gag mRNA, codon optimization resulted in a very large enhancement of Gag production.

Conclusions

We conclude that suboptimal codon usage by HIV-1 results in only a slight loss of gag translational efficiency per se, with the vast majority of enhancement in protein expression from DNA vectors due to altered processing and export of nuclear RNA.

Efficient in vitro expansion of human immunodeficiency virus (HIV)-specific T-cell responses by gag mRNA-electroporated dendritic cells from treated and untreated HIV type 1-infected individuals

Developing an immunotherapy to keep human immunodeficiency virus type 1 (HIV-1) replication suppressed while discontinuing highly active antiretroviral therapy (HAART) is an important challenge. In the present work, we evaluated in vitro whether dendritic cells (DC) electroporated with gag mRNA can induce HIV-specific responses in T cells from chronically infected subjects. Monocyte-derived DC, from therapy-naïve and HAART-treated HIV-1-seropositive subjects, that were electroporated with consensus codon-optimized HxB2 gag mRNA efficiently expanded T cells, secreting gamma interferon (IFN-gamma) and interleukin 2 (IL-2), as well as other cytokines and perforin, upon restimulation with a pool of overlapping Gag peptides. The functional expansion levels after 1 week of stimulation were comparable in T cells from HAART-treated and treatment-naïve patients and involved both CD4(+) and CD8(+) T cells, with evidence of bifunctionality in T cells. Epitope mapping of p24 showed that stimulated T cells had a broadened response toward previously nondescribed epitopes. DC, from HAART-treated subjects, that were electroporated with autologous proviral gag mRNA equally efficiently expanded HIV-specific T cells. Regulatory T cells did not prevent the induction of effector T cells in this system, whereas the blocking of PD-L1 slightly increased the induction of T-cell responses. This paper shows that DC, loaded with consensus or autologous gag mRNA, expand HIV-specific T-cell responses in vitro.

A viral CTL escape mutation leading to immunoglobulin-like transcript 4-mediated functional inhibition of myelomonocytic cells

Viral mutational escape can reduce or abrogate recognition by the T cell receptor (TCR) of virus-specific CD8⁺ T cells. However, very little is known about the impact of cytotoxic T lymphocyte (CTL) epitope mutations on interactions between peptide–major histocompatibility complex (MHC) class I complexes and MHC class I receptors expressed on other cell types. Here, we analyzed a variant of the immunodominant human leukocyte antigen (HLA)-B2705–restricted HIV-1 Gag KK10 epitope (KRWIILGLNK) with an L to M amino acid substitution at position 6 (L6M), which arises as a CTL escape variant after primary infection but is sufficiently immunogenic to elicit a secondary, de novo HIV-1–specific CD8⁺ T cell response with an alternative TCR repertoire in chronic infection. In addition to altering recognition by HIV-1–specific CD8⁺ T cells, the HLA-B2705–KK10 L6M complex also exhibits substantially increased binding to the immunoglobulin-like transcript (ILT) receptor 4, an inhibitory MHC class I–specific receptor expressed on myelomonocytic cells. Binding of the B2705–KK10 L6M complex to ILT4 leads to a tolerogenic phenotype of myelomonocytic cells with lower surface expression of dendritic cell (DC) maturation markers and co-stimulatory molecules. These data suggest a link between CTL-driven mutational escape, altered recognition by innate MHC class I receptors on myelomonocytic cells, and functional impairment of DCs, and thus provide important new insight into biological consequences of viral sequence diversification.

Extensive HLA class I allele promiscuity among viral CTL epitopes

Promiscuous binding of T helper epitopes to MHC class II molecules has been well established, but few examples of promiscuous class I-restricted epitopes exist. To address the extent of promiscuity of HLA class I peptides, responses to 242 well-defined viral epitopes were tested in 100 subjects regardless of the individuals' HLA type. Surprisingly, half of all detected responses were seen in the absence of the originally reported restricting HLA class I allele, and only 3% of epitopes were recognized exclusively in the presence of their original allele. Functional assays confirmed the frequent recognition of HLA class I-restricted T cell epitopes on several alternative alleles across HLA class I supertypes and encoded on different class I loci. These data have significant implications for the understanding of MHC class I-restricted antigen presentation and vaccine development.

Simultaneous ex vivo quantification of antigen-specific CD4+ and CD8+ T cell responses using in vitro transcribed RNA

Assessment of antigen-specific T-cell responses has been greatly facilitated by development of ELISPOT and intracellular cytokine flow cytometry (CFC) assays. The use of autologous antigen presenting cells transfected with in vitro transcribed RNA as stimulators allows in principle quantification of antigen-specific T-cells independent of the knowledge of the epitopes. We describe here a cytokine secretion assay that enables simultaneous assessment of both antigen-specific CD4+ as well as CD8+ T-cells directly from clinical samples without the need for generation of dendritic cells. To this aim, bulk PBMCs were electroporated with RNA encoding the antigen fused to trafficking signal sequences derived from a MHC class I molecule and used as stimulators. With human cytomegalovirus (HCMV) phosphoprotein 65 (pp65) as antigen we show that for measuring ex vivo T-cell responses in ELISPOT and CFC such stimulators are superior or at least equivalent to a pool of overlapping peptides representing the entire pp65 sequence as well as to untagged pp65 encoding RNA. This approach avoids the time consuming generation of dendritic cells as immune stimulators and, in particular when used in the context of the CFC, is robust, broadly applicable and fast.

Robust CD4+ and CD8+ T cell responses to SIV using mRNA-transfected DC expressing autologous viral Ag

A potentially powerful strategy for therapeutic HIV vaccination is the use of DC transfected with mRNA encoding autologous viral Ag, as epitopes presented by transfected DC would exactly reflect those expressed by infected cells in the individual. Using human and rhesus macaque monocyte-derived DC, we show that nucleofection is a superior method for mRNA transfection, resulting in high-level protein expression and DC maturation. DC transfected with SIV gag isolated from an infected monkey stimulated robust Ag-specific recall T cell responses of similar magnitude to those induced by peptide-pulsed PBMC that were predominantly CD8+ T cell mediated. Enhanced CD4+ T cell responses were stimulated when Gag was redirected into the lysosomal pathway via the targeting signal derived from lysosome-associated membrane protein-1 (LAMP-1). Rhesus DC transfected with lysosome-targeted gag encoding an escape mutation in an immunodominant CTL epitope stimulated CD4+ and CD8+ T cell responses of almost equivalent magnitude directed towards undefined epitopes outside of the mutated region. Finally, gag-transfected DC from SIV-infected monkeys stimulated significant Ag-specific recall T cell responses in an entirely autologous system. These findings demonstrate that mRNA-transfected DC expressing SIV Ag derived from infected monkeys stimulate broad and relevant T cell responses, supporting this approach for therapeutic HIV vaccine development.

[mRNA-transfected dendritic cells: a promising strategy in immunotherapy]

Dendritic cells play a central role in the initiation of the immune response as they are the only antigen-presenting cells able to prime naive T cells. This makes the dendritic cells the vector of choice to use as a cell-based vaccine in immunotherapy. Although there are several strategies to deliver antigen to dendritic cells, the ones transfected with mRNA coding for tumor or viral antigens are able to induce potent antigen specific T-cell responses directed against multiple epitopes. In this review, we report several advances made in the field of anti-tumoral and anti-HIV immunotherapy using mRNA-transfected dendritic cells-based approaches.

Generation of specific Th1 and CD8+ T-cell responses by immunization with mouse CD8+ dendritic cells loaded with HIV-1 viral lysate or envelope glycoproteins

Immunization with antigen-pulsed dendritic cells (DCs) can be used to elicit optimal immune responses. We developed the SRDC cell line, with a morphology, phenotype and activity similar to mouse splenic CD4(-)CD8alpha(+)CD205(+)CD11b(-) dendritic cells, which induce a polarized Th1 immune response. We evaluated the ability of SRDCs pulsed with HIV-1 viral lysate, oligomeric soluble gp140 or capsid p24 to induce specific antibody and T-cell responses in CBA/J mice. Immunization with all loaded SRDCs elicited antibody responses against the antigens tested. However, only HIV-1 viral lysate and gp140-pulsed SRDCs elicited specific CD4(+) and CD8(+) T-cell responses. These findings demonstrate the value of well characterized DC lines for optimizing the antigen-loading mixture, according to the DC population targeted. Our data suggest that splenic DCs pulsed with complex antigens, such as HIV-1 viral lysate or oligomeric soluble gp140, could be used as vaccines, eliciting strong primary Th1-polarized and humoral immune responses against HIV proteins in vivo.

Synthetic messenger RNA as a tool for gene therapy

Transfection of human cells with DNA in biomedical applications carries the risk of insertional mutagenesis. Transfection with mRNA avoids this problem; however, in vitro production of mRNA, based on preliminary DNA template cloning in special vectors, is a laborious and time-consuming procedure. We report an efficient vectorfree method of mRNA production from polymerase chain reaction-generated DNA templates. For all cell types tested mRNA was transfected more readily than DNA, and its expression was highly uniform in cell populations. Even cell types relatively resistant to transfection with DNA could express transfected mRNA well. The level of mRNA expression could be controlled over a wide range by changing the amount of input RNA. Cells could be efficiently and simultaneously loaded with several different transcripts. To test a potential clinical application of this method, we transfected human T lymphocytes with mRNA encoding a chimeric immune receptor directed against CD19, a surface antigen widely expressed in leukemia and lymphoma. The transfected mRNA conferred powerful cytotoxicity to T cells against CD19+ targets from the same donor. These results demonstrate that this method can be applied to generate autologous T lymphocytes directed toward malignant cells.

DNA encoding an HIV-1 Gag/human lysosome-associated membrane protein-1 chimera elicits a broad cellular and humoral immune response in Rhesus macaques

Previous studies of HIV-1 p55Gag immunization of mice have demonstrated the usefulness of targeting antigens to the cellular compartment containing the major histocompatibility complex type II (MHC II) complex molecules by use of a DNA antigen formulation encoding Gag as a chimera with the mouse lysosome-associated membrane protein (mLAMP/gag). In the present study, we have analyzed the magnitude and breadth of Gag-specific T-lymphocyte and antibody responses elicited in Rhesus macaques after immunization with DNA encoding a human LAMP/gag (hLAMP/gag) chimera. ELISPOT analyses indicated that the average Gag-specific IFN-gamma response elicited by the hLAMP/gag chimera was detectable after only two or three naked DNA immunizations in all five immunized macaques and reached an average of 1000 spot-forming cells (SFC)/10(6) PBMCs. High IFN-gamma ELISPOT responses were detected in CD8(+)-depleted cells, indicating that CD4(+) T-cells play a major role in these responses. The T-cell responses of four of the macaques were also tested by use of ELISPOT to 12 overlapping 15-amino acids (aa) peptide pools containing ten peptides each, encompassing the complete Gag protein sequence. The two Mamu 08 immunized macaques responded to eight and twelve of the pools, the Mamu B01 to six, and the other macaque to five pools indicating that the hLAMP/gag DNA antigen formulation elicits a broad T-cell response against Gag. Additionally, there was a strong HIV-1-specific IgG response. The IgG antibody titers increased after each DNA injection, indicating a strong amnestic B-cell response, and were highly elevated in all the macaques after three immunizations. Moreover, the serum of each macaque recognized 13 of the 49 peptides of a 20-aa peptide library covering the complete Gag amino acid sequence. In addition, HIV-1-specific IgA antibodies were present in the plasma and external secretions, including nasal washes. These data support the findings of increased immunogenicity of genetic vaccines encoded as LAMP chimeras, including the response to DNA vaccines by non-human primates.

Dendritic cell-lysosomal-associated membrane protein (LAMP) and LAMP-1-HIV-1 gag chimeras have distinct cellular trafficking pathways and prime T and B cell responses to a diverse repertoire of epitopes

Ag processing is a critical step in defining the repertoire of epitope-specific immune responses. In the present study, HIV-1 p55Gag Ag was synthesized as a DNA plasmid with either lysosomal-associated membrane protein-1 (LAMP/gag) or human dendritic cell-LAMP (DC-LAMP/gag) and used to immunize mice. Analysis of the cellular trafficking of these two chimeras demonstrated that both molecules colocalized with MHC class II molecules but differed in their overall trafficking to endosomal/lysosomal compartments. Following DNA immunization, both chimeras elicited potent Gag-specific T and B cell immune responses in mice but differ markedly in their IL-4 and IgG1/IgG2a responses. The DC-LAMP chimera induced a stronger Th type 1 response. ELISPOT analysis of T cell responses to 122 individual peptides encompassing the entire p55gag sequence (15-aa peptides overlapping by 11 residues) showed that DNA immunization with native gag, LAMP/gag, or DC-LAMP/gag induced responses to identical immunodominant CD4+ and CD8+ peptides. However, LAMP/gag and DC-LAMP/gag plasmids also elicited significant responses to 23 additional cryptic epitopes that were not recognized after immunization with native gag DNA. The three plasmids induced T cell responses to a total of 39 distinct peptide sequences, 13 of which were induced by all three DNA constructs. Individually, DC-LAMP/gag elicited the most diverse response, with a specific T cell response against 35 peptides. In addition, immunization with LAMP/gag and DC-LAMP/gag chimeras also promoted Ab secretion to an increased number of epitopes. These data indicate that LAMP-1 and DC-LAMP Ag chimeras follow different trafficking pathways, induce distinct modulatory immune responses, and are able to present cryptic epitopes.