Potent maturation of monocyte-derived dendritic cells after CD40L lentiviral gene delivery

Recent Advances in Good Manufacturing Practice-Grade Generation of Dendritic Cells

Dendritic cells (DCs) are pivotal regulators of immune responses, specialized in antigen presentation and bridging the gap between the innate and adaptive immune system. Due to these key features, DCs have become a pillar of the continuously growing field of cellular therapies. Here we review recent advances in good manufacturing practice strategies and their individual specificities in relation to DC production for clinical applications. These take into account both small-scale experimental approaches as well as automated systems for patient care.

Predicting combinations of immunomodulators to enhance dendritic cell-based vaccination based on a hybrid experimental and computational platform

Dendritic cell (DC)-based vaccines have been largely used in the adjuvant setting for the treatment of cancer, however, despite their proven safety, clinical outcomes still remain modest. In order to improve their efficacy, DC-based vaccines are often combined with one or multiple immunomodulatory agents. However, the selection of the most promising combinations is hampered by the plethora of agents available and the unknown interplay between these different agents. To address this point, we developed a hybrid experimental and computational platform to predict the effects and immunogenicity of dual combinations of stimuli once combined with DC vaccination, based on the experimental data of a variety of assays to monitor different aspects of the immune response after a single stimulus. To assess the stimuli behavior when used as single agents, we first developed an in vitro co-culture system of T cell priming using monocyte-derived DCs loaded with whole tumor lysate to prime autologous peripheral blood mononuclear cells in the presence of the chosen stimuli, as single adjuvants, and characterized the elicited response assessing 18 different phenotypic and functional traits important for an efficient anti-cancer response. We then developed and applied a prediction algorithm, generating a ranking for all possible dual combinations of the different single stimuli considered here. The ranking generated by the prediction tool was then validated with experimental data showing a strong correlation with the predicted scores, confirming that the top ranked conditions globally significantly outperformed the worst conditions. Thus, the method developed here constitutes an innovative tool for the selection of the best immunomodulatory agents to implement in future DC-based vaccines.

Lentiviral-Vector-Based Dendritic Cell Vaccine Synergizes with Checkpoint Blockade to Clear Chronic Viral Infection

Dendritic cell vaccines are a promising strategy for the treatment of cancer and infectious diseases but have met with mixed success. We report on a lentiviral vector-based dendritic cell vaccine strategy that generates a cluster of differentiation 8 (CD8) T cell response that is much stronger than that achieved by standard peptide-pulsing approaches. The strategy was tested in the mouse lymphocytic choriomeningitis virus (LCMV) model. Bone marrow-derived dendritic cells from SAMHD1 knockout mice were transduced with a lentiviral vector expressing the GP33 major-histocompatibility-complex (MHC)-class-I-restricted peptide epitope and CD40 ligand (CD40L) and injected into wild-type mice. The mice were highly protected against acute and chronic variant CL-13 LCMVs, resulting in a 100-fold greater decrease than that achieved with peptide epitope-pulsed dendritic cells. Inclusion of an MHC-class-II-restricted epitope in the lentiviral vector further increased the CD8 T cell response and resulted in antigen-specific CD8 T cells that exhibited a phenotype associated with functional cytotoxic T cells. The vaccination synergized with checkpoint blockade to reduce the viral load of mice chronically infected with CL-13 to an undetectable level. The strategy improves upon current dendritic cell vaccine strategies; is applicable to the treatment of disease, including AIDS and cancer; and supports the utility of Vpx-containing vectors.

Electroporation as a method of choice to generate genetically modified dendritic cell cancer vaccines

In the last few decades, immunotherapy has emerged as an alternative therapeutic approach to treat cancer. Immunotherapy offers a plethora of different treatment possibilities. Among these, dendritic cell (DC)-based cancer vaccines constitute one of the most promising and valuable therapeutic options. DC-vaccines have been introduced into the clinics more than 15 years ago, and preclinical studies showed their general safety and low toxic effects on patients. However, their treatment efficacy is still rather limited, demanding for novel avenues to improve vaccine efficacy. One way to potentially achieve this is to focus on improving the DC-T cell interaction to further increase T cell priming and downstream activity. A successful DC-T cell interaction requires three different signals (Figure 1): (1) Major Histocompatibility Complex (MHC) and antigen complex interaction with T cell receptor (TCR) (2) interaction between co-stimulatory molecules and their cognate ligands at the cell surface and (3) secretion of cytokines to polarize the immune response toward a Type 1 helper (Th1) phenotype. In recent years, many studies attempted to improve the DC-T cell interaction and overall cancer vaccine therapeutic outcomes by increasing the expression of mediators of signal 1, 2 and/or 3, through genetic modifications of DCs. Transfection of genes of interest can be achieved through many different methods such as passive pulsing, lipofection, viral transfection, or electroporation (EP). However, EP is currently emerging as the method of choice thanks to its safety, versatility, and relatively easy clinical translation. In this review we will highlight the potential benefits of EP over other transfection methods as well as giving an overview of the available studies employing EP to gene-modify DCs in cancer vaccines. Crucial aspects such as safety, feasibility, and gene(s) of choice will be also discussed, together with future perspectives and opportunities for DC genetic engineering.

Engineering dendritic cell vaccines to improve cancer immunotherapy

At the interface between the innate and adaptive immune system, dendritic cells (DCs) play key roles in tumour immunity and hold a hitherto unrealized potential for cancer immunotherapy. Here we review the role of distinct DC subsets in the tumour microenvironment, with special emphasis on conventional type 1 DCs. Integrating new knowledge of DC biology and advancements in cell engineering, we provide a blueprint for the rational design of optimized DC vaccines for personalized cancer medicine.

Dendritic cells (DCs) have been explored as a promising strategy for cancer immunotherapy. In this Perspective, the authors discuss the different types of DCs and their therapeutic potential in the context of vaccines for personalized cancer therapy.

Ex vivo dendritic cell generation-A critical comparison of current approaches

Dendritic cells (DCs) are professional antigen-presenting cells, required for the initiation of naïve and memory T cell responses and regulation of adaptive immunity. The discovery of DCs in 1973, which culminated in the Nobel Prize in Physiology or Medicine in 2011 for Ralph Steinman and colleagues, initially focused on the identification of adherent mononuclear cell fractions with uniquely stellate dendritic morphology, followed by key discoveries of their critical immunologic role in initiating and maintaining antigen-specific immunity and tolerance. The medical promise of marshaling these key capabilities of DCs for therapeutic modulation of antigen-specific immune responses has guided decades of research in hopes to achieve genuine physiologic partnership with the immune system. The potential uses of DCs in immunotherapeutic applications include cancer, infectious diseases, and autoimmune disorders; thus, methods for rapid and reliable large-scale production of DCs have been of great academic and clinical interest. However, difficulties in obtaining DCs from lymphoid and peripheral tissues, low numbers and poor survival in culture, have led to advancements in ex vivo production of DCs, both for probing molecular details of DC function as well as for experimenting with their clinical utility. Here, we review the development of a diverse array of DC production methodologies, ranging from cytokine-based strategies to genetic engineering tools devised for enhancing DC-specific immunologic functions. Further, we explore the current state of DC therapies in clinic, as well as emerging insights into physiologic production of DCs inspired by existing therapies.

Strategies to Genetically Modulate Dendritic Cells to Potentiate Anti-Tumor Responses in Hematologic Malignancies

Dendritic cell (DC) vaccination has been investigated as a potential strategy to target hematologic malignancies, while generating sustained immunological responses to control potential future relapse. Nonetheless, few clinical trials have shown robust long-term efficacy. It has been suggested that a combination of surmountable shortcomings, such as selection of utilized DC subsets, DC loading and maturation strategies, as well as tumor-induced immunosuppression may be targeted to maximize anti-tumor responses of DC vaccines. Generation of DC from CD34+ hematopoietic stem and progenitor cells (HSPCs) may provide potential in patients undergoing allogeneic HSPC transplantations for hematologic malignancies. CD34+ HSPC from the graft can be genetically modified to optimize antigen presentation and to provide sufficient T cell stimulatory signals. We here describe beneficial (gene)-modifications that can be implemented in various processes in T cell activation by DC, among which major histocompatibility complex (MHC) class I and MHC class II presentation, DC maturation and migration, cross-presentation, co-stimulation, and immunosuppression to improve anti-tumor responses.

Spontaneous Activation of Antigen-presenting Cells by Genes Encoding Truncated Homo-Oligomerizing Derivatives of CD40

The interaction between the CD40 receptor on antigen-presenting cells (APCs) and its trimeric ligand on CD4 T cells is essential for the initiation and progression of the adaptive immune response. Here we undertook to endow CD40 with the capacity to trigger spontaneous APC activation through ligand-independent oligomerization. To this end we exploited the GCN4 yeast transcriptional activator, which contains a leucine zipper DNA-binding motif that induces homophilic interactions. We incorporated GCN4 variants forming homodimers, trimers, or tetramers at the intracellular domain of human and mouse CD40 and replaced the extracellular portion with peptide-β2m or other peptide tags. In parallel we examined similarly truncated CD40 monomers lacking a GCN4 motif. The oligomeric products appeared to arrange in high-molecular-weight aggregates and were considerably superior to the monomer in their ability to trigger nuclear factor kB signaling, substantiating the anticipated constitutively active (ca) phenotype. Cumulative results in human and mouse APC lines transfected with caCD40 mRNA revealed spontaneous upregulation of CD80, IL-1β, TNFα, IL-6, and IL-12, which could be further enhanced by caTLR4 mRNA. In mouse bone-marrow-derived dendritic cells caCD40 upregulated CD80, CD86, MHC-II, and IL-12 and in human monocyte-derived dendritic cells it elevated surface CD80, CD83 CD86, CCR7, and HLA-DR. Oligomeric products carrying the peptide-β2m extracellular portion could support MHC-I presentation of the linked peptide up to 4 days post-mRNA transfection. These findings demonstrate that the expression of a single caCD40 derivative in APCs can exert multiple immunostimulatory effects, offering a new powerful tool in the design of gene-based cancer vaccines.

Reconstructing the immune system with lentiviral vectors

Lentiviral vectors (LVs) developed in the past two decades for research and pre-clinical purposes have entered clinical trials with remarkable safety and efficacy performances. Development and clinical testing of LVs for improvement of human immunity showed major advantages in comparison to other viral vector systems. Robust and persisted transduction efficiency of blood cells with LVs, resulted into a broad range of target cells for immune therapeutic approaches: from hematopoietic stem cells and precursor cells for correction of immune deficiencies, up to effector lymphoid and myeloid cells. T cells engineered for expression of chimeric antigen receptors (CARs) or epitope-specific transgenic T cell receptors (TCRs) are in several cancer immune therapy clinical trials worldwide. Development of engineered dendritic cells is primed for clinical trials for cancer and chronic infections. Technological adaptations for ex vivo cell manipulations are here discussed and presented based on properties and uses of the target cell. For future development of off-shelf immune therapies, direct in vivo administration of lentiviral vectors is warranted and intended. Approaches for lentiviral in vivo targeting to maximize immune therapeutic success are discussed.

Vpx-containing dendritic cell vaccine induces CTLs and reactivates latent HIV-1 in vitro

Eradication of human immunodeficiency virus-1 (HIV-1) from an infected individual requires a means of inducing production of virus from latently infected cells and stimulating an immune response against the infected cells. We report the development of lentiviral vectors that transduce dendritic cells (DCs) to both induce production of virus from latently infected cells and stimulate antigen-specific cytotoxic T lymphocytes (CTLs). The vectors package Vpx, a lentiviral accessory protein that counteracts the SAMHD1-mediated block to DC transduction, allowing for long-term expression of vector-encoded proteins. The vectors encode influenza or HIV-1-derived epitopes fused via a self-cleaving peptide to CD40L that releases the peptide into the endoplasmic reticulum for entry into the antigen presentation pathway. Expression of CD40L caused transduced DCs to mature and produce Th1-skewing cytokines. The DCs presented antigen to CD8 T cells, enhancing antigen-specific CTLs. Coculture of the transduced DCs with latently infected cells induced high-level virus production, an effect that was mediated by tumor necrosis factor alpha. The ability of a DC vaccine to reactivate latent HIV-1 and stimulate an adaptive immune response provide a means to reduce the size of the latent reservoir in patients. This strategy can also be applied to develop DC vaccines for other diseases.

Therapeutic cancer vaccines: past, present, and future

Therapeutic vaccines represent a viable option for active immunotherapy of cancers that aim to treat late stage disease by using a patient's own immune system. The promising results from clinical trials recently led to the approval of the first therapeutic cancer vaccine by the U.S. Food and Drug Administration. This major breakthrough not only provides a new treatment modality for cancer management but also paves the way for rationally designing and optimizing future vaccines with improved anticancer efficacy. Numerous vaccine strategies are currently being evaluated both preclinically and clinically. This review discusses therapeutic cancer vaccines from diverse platforms or targets as well as the preclinical and clinical studies employing these therapeutic vaccines. We also consider tumor-induced immune suppression that hinders the potency of therapeutic vaccines, and potential strategies to counteract these mechanisms for generating more robust and durable antitumor immune responses.

Dendritic cell-based vaccines: barriers and opportunities

Dendritic cells (DCs) have several characteristics that make them an ideal vehicle for tumor vaccines, and with the first US FDA-approved DC-based vaccine in use for the treatment of prostate cancer, this technology has become a promising new therapeutic option. However, DC-based vaccines face several barriers that have limited their effectiveness in clinical trials. A major barrier includes the activation state of the DC. Both DC lineage and maturation signals must be selected to optimize the antitumor response and overcome immunosuppressive effects of the tumor microenvironment. Another barrier to successful vaccination is the selection of target antigens that will activate both CD8(+) and CD4(+) T cells in a potent, immune-specific manner. Finally, tumor progression and immune dysfunction limit vaccine efficacy in advanced stages, which may make DC-based vaccines more efficacious in treating early-stage disease. This review underscores the scientific basis and advances in the development of DC-based vaccines, focuses on current barriers to success and highlights new research opportunities to address these obstacles.

Enhancement of antigen presenting ability in the leukemic plasmacytoid dendritic cell line (PMDC05) by lentiviral vector-mediated transduction of CD80 gene

PMDC05, a leukemic plasmacytoid dendritic cell (pDC) line which was established in our laboratory, showed a capacity of generating antigen-specific cytotoxic T lymphocytes (CTLs). In order to enhance an antigen presenting ability of PMDC05, PMDC05 was transduced with CD80 gene by lentiviral vector, which was named as PMDC11. PMDC11 displayed a strong antigen presenting ability even without any stimulation, and by culturing with stimulators such as calcium ionophore PMDC11 gained a more potent antigen presenting ability. Our data suggested PMDC11 could be applied as antigen presenting cells more efficiently in adoptive cellular immunotherapy for tumors and severe infections in comparison with PMDC05.

Delivery of antigens by viral vectors for vaccination

Viral vectors have been developed as vaccine platforms for a number of pathogens and tumors. In particular, adenovirus (Ad)-based vectors expressing genes coding for pathogen or tumor antigens have proven efficacious to induce protective immunity. Major challenges in the use of Ad vectors are the high prevalence of anti-Ad immunity and the recent observation during an Ad-based HIV vaccine trial that led to increased HIV-1 acquisition in the presence of circulating anti-Ad5 neutralizing antibodies. In this review we summarize strategies to address these challenges and focus on modifications of the Ad capsid to enhance the adjuvant effect of anti-Ad immunogenicity and to circumvent pre-existing immunity. In addition, we summarize the current status and potential of other viral vector vaccines based on adeno-associated viruses, lentiviruses and poxviruses.

Licensing of myeloid cells promotes central nervous system autoimmunity and is controlled by peroxisome proliferator-activated receptor γ

During central nervous system autoimmunity, interactions between infiltrating immune cells and brain-resident cells are critical for disease progression and ultimately organ damage. Here, we demonstrate that local cross-talk between invading autoreactive T cells and auto-antigen-presenting myeloid cells within the central nervous system results in myeloid cell activation, which is crucial for disease progression during experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis. This T cell-mediated licensing of central nervous system myeloid cells triggered astrocytic CCL2-release and promoted recruitment of inflammatory CCR2(+)-monocytes, which are the main effectors of disease progression. By employing a cell-specific knockout model, we identify the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) in myeloid cells as key regulator of their disease-determining interactions with autoreactive T cells and brain-resident cells, respectively. LysM-PPARγ(KO) mice exhibited disease exacerbation during the effector phase of experimental autoimmune encephalomyelitis characterized by enhanced activation of central nervous system myeloid cells accompanied by pronounced local CCL2 production and inflammatory monocyte invasion, which finally resulted in increased demyelination and neuronal damage. Pharmacological PPARγ activation decreased antigen-specific T cell-mediated licensing of central nervous system myeloid cells, reduced myeloid cell-mediated neurotoxicity and hence dampened central nervous system autoimmunity. Importantly, human monocytes derived from patients with multiple sclerosis clearly responded to PPARγ-mediated control of proinflammatory activation and production of neurotoxic mediators. Furthermore, PPARγ in human monocytes restricted their capacity to activate human astrocytes leading to dampened astrocytic CCL2 production. Together, interference with the disease-promoting cross-talk between central nervous system myeloid cells, autoreactive T cells and brain-resident cells represents a novel therapeutic approach that limits disease progression and lesion development during ongoing central nervous system autoimmunity.

Construction of the HBV S-ecdCD40L fusion gene and effects of HBV S-ecdCD40L modification on function of dendritic cells

We examined the effect of dendritic cells engineered to express an HBV S antigen CD40L fusion gene (HBV S-ecdCD40L). The DNA of HBV S gene and the cDNA of the extracellular domain of human CD40 ligand were linked by cloning. Peripheral blood mononuclear cells (PBMC) from healthy adults were incubated and induced into dendritic cells (DC) in presence of granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin-4(IL-4). The DCs were transfected the novel construct, and the impact of the expressed clone assessed. We find that, compared with control groups, modification of DCs with HBV S-ecdCD40L fusion gene resulted in the activation of DCs with upregulated expression of immunologically important cell surface molecules (CD80, CD86 and HLA-DR) and proinflammatory cytokines (IL-12). The DCs modified with HBV S-ecdCD40L are able to stimulate enhanced allogeneic T-cell proliferation in vitro. Thus, the fusion gene HBV S-ecdCD40L can promote DC's activation and enhance its function and may prove to be the foundation for a new type of hepatitis B vaccine.

Immunization delivered by lentiviral vectors for cancer and infectious diseases

The increasing level of understanding of the lentivirus biology has been instrumental in shaping the design strategy of creating therapeutic lentiviral delivery vectors. As a result, lentiviral vectors have become one of the most powerful gene transfer vehicles. They are widely used for therapeutic purposes as well as in studies of basic biology, due to their unique characteristics. Lentiviral vectors have been successfully employed to mediate durable and efficient antigen expression and presentation in dendritic cells both in vitro and in vivo, leading to the activation of cellular immunity and humoral responses. This capability makes the lentiviral vector an ideal choice for immunizations that target a wide range of cancers and infectious diseases. Further advances into optimizing the vector system and understanding the relationship between the immune system and diseases pathogenesis will only augment the potential benefits and utility of lentiviral vaccines for human health.

EBV LMP1, a viral mimic of CD40, activates dendritic cells and functions as a molecular adjuvant when incorporated into an HIV vaccine

HIV-1 does not significantly activate cellular immunity, which has made it difficult to use attenuated forms of HIV-1 as a vaccine. In contrast, EBV induces robust T cell responses in most infected individuals, perhaps as this virus contains LMP1, a viral mimic of CD40, which is a key activating molecule for DCs and macrophages. Consequently, studies were conducted using LMP1 and LMP1-CD40, a related construct formed by replacing the intracellular signaling domain of LMP1 with that of CD40. Upon electroporation into DCs, LMP1 and LMP1-CD40 mRNAs were sufficient to up-regulate costimulatory molecules and proinflammatory cytokines, indicating that these molecules can function in isolation as adjuvant-like molecules. As a first step toward an improved HIV vaccine, LMP1 and LMP1-CD40 were introduced into a HIV-1 construct to produce virions encoding these proteins. Transduction of DCs and macrophages with these viruses induced morphological changes and up-regulated costimulatory molecules and cytokine production by these cells. HIV-LMP1 enhanced the antigen-presenting function of DCs, as measured in an in vitro immunization assay. Taken together, these data show that LMP1 and LMP1-CD40 are portable gene cassettes with strong adjuvant properties that can be introduced into viruses such as HIV, which by themselves, are insufficient to induce protective cellular immunity.

The impact of ex vivo clinical grade activation protocols on human T-cell phenotype and function for the generation of genetically modified cells for adoptive cell transfer therapy

Optimized conditions for the ex vivo activation, genetic manipulation, and expansion of human lymphocytes for adoptive cell therapy may lead to protocols that maximize their in vivo function. We analyzed the effects of 4 clinical grade activation and expansion protocols over 3 weeks on cell proliferative rate, immunophenotype, cell metabolism, and transduction efficiency of human peripheral blood mononuclear cells (PBMCs). Peak lentiviral transduction efficiency was early (days 2 to 4), at a time when cells showed a larger size, maximal uptake of metabolic substrates, and the highest level of proximal T-cell receptor signaling engagement. Anti-CD2/3/28 activation beads induced greater proliferation rate and skewed PBMCs early on to a CD4 phenotype when compared with the cells cultured in OKT3. Multicolor surface phenotyping demonstrated that changes in T-cell surface markers that define T-cell functional phenotypes were dependent on the time spent in culture as opposed to the particular activation protocol. In conclusion, ex vivo activation of human PBMCs for adoptive cell therapy demonstrate defined immunophenotypic and functional signatures over time, with cells early on showing larger sizes, higher transduction efficiency, maximal metabolic activity, and zeta-chain-associated protein-70 activation.

Engineering dendritic cells to enhance cancer immunotherapy

Cancer immunotherapy aims to establish immune-mediated control of tumor growth by priming T-cell responses to target tumor-associated antigens. Three signals are required for T-cell activation: (i) presentation of cognate antigen in self MHC molecules; (ii) costimulation by membrane-bound receptor-ligand pairs; and (iii) soluble factors to direct polarization of the ensuing immune response. The ability of dendritic cells (DCs) to provide all three signals required for T-cell activation makes them an ideal cancer vaccine platform. Several strategies have been developed to enhance and control antigen presentation, costimulation, and cytokine production. In this review, we discuss progress toward developing DC-based cancer vaccines by genetic modification using RNA, DNA, and recombinant viruses. Furthermore, the ability of DC-based vaccines to activate natural killer (NK) and B-cells, and the impact of gene modification strategies on these populations is described. Clinical trials using gene-modified DCs have shown modest results, therefore, further considerations for DC manipulation to enhance their clinical efficacy are also discussed.

Emerging applications of lentiviral vectors in dendritic cell-based immunotherapy

Dendritic cells are professional antigen-presenting cells that initiate, regulate and shape the induction of specific immune responses. The ability to use dendritic cells in the induction of antigen-specific tolerance, antigen-specific immunity or specific differentiation of T-helper subsets holds great promise in dendritic cell-based immunotherapy of various diseases such as cancer, viral infections, allergy, as well as autoimmunity. Replication-incompetent HIV-1-based lentiviral vector is now emerging as a promising delivery system to genetically modify dendritic cells through antigen recognition, costimulatory molecules and/or polarization signals for the manipulation of antigen-specific immunity in vivo. This article discusses some of the recent advances in the uses of lentiviral vectors in dendritic cell-based immunotherapy.

Lentiviral vectors for immunization: an inflammatory field

Lentiviruses are retroviruses that are able to transduce both dividing and nondividing cells. Dendritic cells are key players in the innate and adaptive immune responses, and are natural targets for lentiviruses. Lentiviral vectors (LVs) have recently reached the clinical gene therapy arena, prompting their use as clinical vaccines. In recent years, LVs have emerged as a robust and practical experimental platform for gene delivery and rational genetic reprogramming of dendritic cells. Here, we present the status quo of the LV system for protective or therapeutic vaccine development. This vector system has been extensively evaluated for ex vivo and in vivo (immuno)gene delivery. Improvements of the LV design in order to further grant a higher biosafety profile for vaccine development are presented.

Incorporation of CD40 ligand into SHIV virus-like particles (VLP) enhances SHIV-VLP-induced dendritic cell activation and boosts immune responses against HIV

Engagement of CD40 with CD40L induces dendritic cell (DC) maturation and activation, thereby promoting immune responses. The objective of this study was to investigate whether immunization with chimeric CD40L/SHIV virus-like particles (CD40L/SHIV-VLP) could enhance immune responses to SIV Gag and HIV Env proteins by directly activating DCs. We found that CD83, CD40, and CD86 were significantly up-regulated and significantly increased cytokines production were observed after hCD40L/SHIV-VLP treatment in human CD14(+) monocyte-derived DCs as compared to SHIV-VLP treatment. Mice immunized with mCD40L/SHIV-VLP showed more than a two-fold increase in HIV Env-specific IgG antibody production, an increase in SIV Gag and HIV Env-specific IFN-gamma and IL-4 producing cells, and an increase in HIV Env-specific cytotoxic activity compared to that in SHIV-VLP immunized mice. Furthermore, multifunctional CD4(+) Th1 cells, which simultaneously produce IFN-gamma, IL-2 and TNF-alpha triple cytokines, and CD8(+) T-cells, which produce IFN-gamma were elevated in the mCD40L/SHIV-VLP immunized group. These data demonstrate that chimeric CD40L/SHIV-VLP potently induce DC activation and enhance the magnitude of both humoral and cellular immune responses to the SIV Gag and HIV Env proteins in the mouse model. Therefore, incorporation of CD40L into VLP may represent a novel strategy to develop effective HIV vaccines.

Lentiviral vectors in gene therapy: their current status and future potential

The concept of gene therapy originated in the mid twentieth century and was perceived as a revolutionary technology with the promise to cure almost any disease of which the molecular basis was understood. Since then, several gene vectors have been developed and the feasibility of gene therapy has been shown in many animal models of human disease. However, clinical efficacy could not be demonstrated until the beginning of the new century in a small-scale clinical trial curing an otherwise fatal immunodeficiency disorder in children. This first success, achieved after retroviral therapy, was later overshadowed by the occurrence of vector-related leukemia in a significant number of the treated children, demonstrating that the future success of gene therapy depends on our understanding of vector biology. This has led to the development of later-generation vectors with improved efficiency, specificity, and safety. Amongst these are HIV-1 lentivirus-based vectors (lentivectors), which are being increasingly used in basic and applied research. Human gene therapy clinical trials are currently underway using lentivectors in a wide range of human diseases. The intention of this review is to describe the main scientific steps leading to the engineering of HIV-1 lentiviral vectors and place them in the context of current human gene therapy.

Monocytes transduced with lentiviral vectors expressing hepatitis C virus non-structural proteins and differentiated into dendritic cells stimulate multi-antigenic CD8(+) T cell responses

Halting the spread of hepatitis C virus (HCV) and also eradicating HCV in subjects with chronic infection are major goals for global health. To this end, several years of research on HCV vaccine development have led to the conclusion that multi-antigenic and multi-functional vaccine types are necessary for effectiveness against HCV infection. In this study, we evaluated lentiviral vectors (LV) expressing clusters of HCV structural (LV-HCV-S) and non-structural (LV-HCV-NS) genes for future vaccine development. Batches of high titer LV were used to transduce differentiated dendritic cells (DC) and monocytes. We report successful delivery of HCV gene clusters, particularly into monocytes, leading to >80% LV-HCV-NS and >70% LV-HCV-S and transduced cells, respectively. Intracellular expression of HCV proteins in monocyte-derived DC resulted in immunophenotypic changes, such as downregulation of CD83 and CD86. Monocytes expressing NS proteins and differentiated into DC stimulated allogeneic and autologous CD8(+) and CD4(+) T cells in vitro and resulted in antigen-specific CD8(+) T cell responses against NS3, NS4a and NS5b. Hence, lentiviral-mediated expression of the multi-antigenic HCV-NS cluster in monocytes subsequently differentiated into DC is a novel potential anti-HCV vaccine modality.

Effects of herpes simplex virus amplicon transduction on murine dendritic cells

The herpes simplex virus (HSV)-based amplicon is a versatile vaccine platform that has been preclinically vetted as a gene-based immunotherapeutic for cancer, HIV, and neurodegenerative disorders. Although it is well known that injection of dendritic cells (DCs) transduced ex vivo with helper virus-free HSV amplicon vectors expressing disease-relevant antigens induces antigen-specific immune responses, the cellular receptor(s) by which the amplicon virion gains entry into DCs, as well as the effects that viral vector transduction impinges on the physiological status of these cells, is less understood. Herein, we examine the effects of amplicon transduction on mouse bone marrow-derived DCs. We demonstrate that HSV-1 cellular receptors HveC and HveA are expressed on the cell surface of murine DCs, and that HSV amplicons transduce DCs at high efficiency (>90%) with minimal effects on cell viability. Transduction of dendritic cells with amplicons induces a transient DC maturation phenotype as represented by self-limited upregulation of MHCII and CD11c markers. Mature DCs are less sensitive to HSV amplicon transduction than immature DCs regarding DC-related surface marker maintenance. From this and our previous work, we conclude that HSV amplicons transduce DCs efficiently, but impart differential and transient physiological effects on mature and immature DC pools, which will facilitate fine-tuning of this vaccination platform and further exploit its potential in immunotherapy.

The CD8 and CD4 T-cell response against Kaposi's sarcoma-associated herpesvirus is skewed towards early and late lytic antigens

Kaposi's sarcoma-associated herpesvirus (KSHV) is causally related to Kaposi's sarcoma (KS), the most common malignancy in untreated individuals with HIV/AIDS. The adaptive T-cell immune response against KSHV has not been fully characterized. To achieve a better understanding of the antigenic repertoire of the CD8 and CD4 T-cell responses against KSHV, we constructed a library of lentiviral expression vectors each coding for one of 31 individual KSHV open reading frames (ORFs). We used these to transduce monocyte-derived dendritic cells (moDCs) isolated from 14 KSHV-seropositive (12 HIV-positive) and 7 KSHV-seronegative (4 HIV-positive) individuals. moDCs were transduced with up to 3 KSHV ORFs simultaneously (ORFs grouped according to their expression during the viral life cycle). Transduced moDCs naturally process the KSHV genes and present the resulting antigens in the context of MHC class I and II. Transduced moDCs were cultured with purified autologous T cells and the CD8 and CD4 T-cell proliferative responses to each KSHV ORF (or group) was assessed using a CFSE dye-based assay. Two pools of early lytic KSHV genes ([ORF8/ORF49/ORF61] and [ORF59/ORF65/K4.1]) were frequently-recognized targets of both CD8 and CD4 T cells from KSHV seropositive individuals. One pool of late lytic KSHV genes ([ORF28/ORF36/ORF37]) was a frequently-recognized CD8 target and another pool of late genes ([ORF33/K1/K8.1]) was a frequently-recognized CD4 target. We report that both the CD8 and CD4 T-cell responses against KSHV are skewed towards genes expressed in the early and late phases of the viral lytic cycle, and identify some previously unknown targets of these responses. This knowledge will be important to future immunological investigations into KSHV and may eventually lead to the development of better immunotherapies for KSHV-related diseases.

Lentiviral vector-mediated genetic programming of mouse and human dendritic cells

Dendritic cells (DCs) play a key role in the orchestration of immune reactions. Manipulation of DC function through genetic manipulation for vaccine development provides a multitude of applications for active immunotherapy of cancer and chronic infections. Several laboratories have shown that lentiviral vectors (LVs) are efficient and consistent tools for ex vivo gene manipulation of DCs and their precursors. LVs integrate in the genome of target cells resulting in persistent and stable transgene expression, and gene delivery does not result in cytostatic or nonspecific adverse immunomodulatory reactions. Mouse, macaque, and human DCs are efficiently transduced with LVs, allowing preclinical vaccination studies to be gradually implemented into clinical trials. This chapter describes HIV-1-derived LV transduction used for ex vivo gene delivery of marking genes, antigens, and immunomodulatory molecules into mouse and human hematopoietic precursors and DCs. With the perspective of bioengineering DCs from the inside-out, we also describe a one-hit LV transduction method for constitutive expression of GM-CSF and IL-4 genes, which allows self-differentiation of mouse and human hematopoietic precursor cells into highly viable and potent DCs.

Ectopic expression of a truncated CD40L protein from synthetic post-transcriptionally capped RNA in dendritic cells induces high levels of IL-12 secretion

BACKGROUND

RNA transfection into dendritic cells (DCs) is widely used to achieve antigen expression as well as to modify DC properties. CD40L is expressed by activated T cells and interacts with CD40 receptors expressed on the surface of the DCs leading to Th1 polarization. Previous studies demonstrated that ectopic CD40L expression via DNA transfection into DCs can activate the CD40 receptor signal transduction cascade. In contrast to previous reports, this study demonstrates that the same effect can be achieved when RNA encoding CD40L is electroporated into DCs as evidenced by secretion of IL-12. To achieve higher levels of IL-12 secretion, a systematic approach involving modification of coding and noncoding regions was implemented to optimize protein expression in the DCs for the purpose of increasing IL-12 secretion.

RESULTS

Site-directed mutagenesis of each of the first five in-frame methionine codons in the CD40L coding sequence demonstrated that DCs expressing a truncated CD40L protein initiated from the second methionine codon secreted the highest levels of IL-12. In addition, a post-transcriptional method of capping was utilized for final modification of the CD40L RNA. This method enzymatically creates a type I cap structure identical to that found in most eukaryotic mRNAs, in contrast to the type 0 cap incorporated using the conventional co-transcriptional capping reaction.

CONCLUSION

The combination of knocking out the first initiation methionine and post-transcriptional capping of the CD40L RNA allowed for approximately a one log increase in IL-12 levels by the transfected DCs. We believe this is a first report describing improved protein expression of post-transcriptionally capped RNA in DCs. The post-transcriptional capping which allows generation of a type I cap may have broad utility for optimization of protein expression from RNA in DCs and other cell types.

Enhancing the T-cell stimulatory capacity of human dendritic cells by co-electroporation with CD40L, CD70 and constitutively active TLR4 encoding mRNA

The effectiveness of the dendritic cell (DC) vaccination protocols that are currently in use could be improved by providing the DCs with a more potent maturation signal. We therefore investigated whether the T-cell stimulatory capacity of human monocyte-derived DCs could be increased by co-electroporation with different combinations of CD40L, CD70, and constitutively active toll-like receptor 4 (caTLR4) encoding mRNA. We show that immature DCs electroporated with CD40L and/or caTLR4 mRNA, but not those electroporated with CD70 mRNA, acquire a mature phenotype along with an enhanced secretion of several cytokines/chemokines. Moreover, these DCs are very potent in inducing naive CD4(+) T cells to differentiate into interferon-gamma (IFN-gamma)-secreting type 1 T helper (Th1) cells. Further, we assessed the capacity of the electroporated DCs to activate naive HLA-A2-restricted MelanA-specific CD8(+) T cells without the addition of any exogenous cytokines. When all three molecules were combined, a >500-fold increase in MelanA-specific CD8(+) T cells was observed when compared with immature DCs, and a >200-fold increase when compared with cytokine cocktail-matured DCs. In correlation, we found a marked increase in cytolytic and IFN-gamma/tumor necrosis factor-alpha (TNF-alpha) secreting CD8(+) T cells. Our data indicate that immature DCs genetically modified to express stimulating molecules can induce tumor antigen-specific T cells in vitro and could prove to be a significant improvement over DCs matured with the methods currently in use.

Lentiviral Vectors with CMV or MHCII Promoters Administered In Vivo: Immune Reactivity Versus Persistence of Expression

Lentiviral vectors (LVs) are potential tools for genetic vaccination. To improve the safety of LV vaccines, we evaluated the selectivity, bio-distribution, persistence of expression, and immune potency of vesicular stomatitis virus G (VSV-G)-pseudotyped vectors transcriptionally targeted to antigen presenting cells (APCs) through a major histocompatibility complex class II (MHCII) promoter. Control vectors contained the ubiquitous cytomegalovirus (CMV) promoter. Bio-distribution studies after intravenous injections of LVs expressing green fluorescent protein (GFP) or luciferase were conducted by a combination of flow cytometry, immunofluorescence, real-time quantitative polymerase chain reaction (RT-Q-PCR) and whole-body bioluminescence analyses. GFP-expressing vectors showed selective expression in MHCII(+) cells of spleen and LV-CMV-GFP administration produced noticeable spleen inflammation, whereas LV-MHCII-GFP did not. Long-term optical imaging analyses of C57BL/6 mice injected with LV-CMV-LUC showed diminishing luciferase expression in the liver and spleen over time. Vaccination/boost with LV-CMV expressing the melanoma antigen tyrosinase-related protein 2 (TRP2) yielded dose-dependent antigen-specific CD8(+) T-cell reactivity and high protection against B16 melanoma challenge. Unexpectedly, administration of LVs containing the MHCII promoter resulted in persistence of luciferase expression and viral integration in MHCII(+) splenocytes and virtually no CD8(+) T-cell responses against TRP2. These studies reveal that APC transduction by LVs could lead to immune reactivity (LV-CMV) or persistence of transgene expression (LV-MHCII), providing a relevant paradigm for vaccination and gene replacement approaches.

Recent Advances and Current Challenges in Tumor Immunology and Immunotherapy

Despite advances in animal studies, where the cure of the majority of mice with pre-established (albeit early-stage) tumors has become almost standard, human clinical trials have been much less successful. Here we describe some of the most recent advances in the specialist field of tumor immunology and immunotherapy, highlighting salient work to identify key problem areas and potential solutions. We make particular note of recent developments in adoptive therapy; whole-cell, DNA, and peptide vaccines; and antibody therapy. We also describe the revival of interest in regulatory T cells and conclude by detailing the need for clinical trial read-out autonomy and methods to predict which patients will respond to a particular treatment.

Lentiviral vectors for cancer immunotherapy: transforming infectious particles into therapeutics

Lentiviral vectors have emerged as promising tools for both gene therapy and immunotherapy purposes. They exhibit several advantages over other viral systems in that they are less immunogenic and are capable of transducing a wide range of different cell types, including dendritic cells (DC). DC transduced ex vivo with a whole range of different (tumor) antigens were capable of inducing strong antigen-specific T-cell responses, both in vitro and in vivo. Recently, the administration of lentiviral vectors in vivo has gained substantial interest as an alternative method for antigen-specific immunization. This method offers a number of advantages over DC vaccines as the same lentivirus can in principle be used for all patients resulting in a significantly reduced cost and requirement for considerably less expertise for the generation and administration of lentiviral vaccines. By selectively targeting lentiviral vectors to, or restricting transgene expression in certain cell types, selectivity, safety and efficacy can be further improved. This review will focus on the use of direct administration of lentiviral vectors encoding tumor-associated antigens (TAA) for the induction of tumor-specific immune responses in vivo, with a special focus on problems related to the generation of large amounts of highly purified virus and specific targeting of antigen-presenting cells (APC).

Lentiviral vector expression of tumour antigens in dendritic cells as an immunotherapeutic strategy

Therapeutic cancer vaccines need to stimulate a refractory immune system to make an effective anti-tumour response. We have explored the use of lentiviral vectors to deliver tumour antigen genes to dendritic cells (DC) as a possible mechanism of immune stimulation. Direct injection of a lentiviral vector encoding the melanoma antigen NY-ESO-1 in HLA-A2 transgenic mice primed NY-ESO-1-specific CD8+ cells that could be expanded by boosting with an NY-ESO-1 vaccinia virus. The expanded cells could kill NY-ESO-1(157-165) peptide-pulsed targets in vivo. In order to examine the priming step directly, we constructed another lentiviral vector expressing the melanoma antigen Melan-A (MART-1). Here we show that Melan-A protein is also efficiently expressed after transduction of human DC cultured from peripheral blood mononuclear cells. When these transduced DC are co-cultured with autologous naïve T cells, they cause the expansion of cells that recognise the HLA-A2 restricted Melan-A(27-35) epitope. The expanded cells are functional in that they release IFN-gamma upon antigen stimulation. Melan-A lentiviral vector transduced DC caused a similar level of naïve T-cell expansion to Melan-A(27-35) peptide-pulsed DC in four experiments using different HLA-A2 positive donors. These data suggest that a vaccine based either on DC transduced with a lentiviral vector ex vivo, or on direct lentiviral vector injection, should be assessed in a phase I clinical trial.

A single administration of lentiviral vectors expressing either full-length human immunodeficiency virus 1 (HIV-1)HXB2 Rev/Env or codon-optimized HIV-1JR-FL gp120 generates durable immune responses in mice

Genetic immunization using viral vectors provides an effective means to elicit antigen-specific cellular immune responses. Several viral vectors have proven efficacious in inducing immune responses after direct injection in vivo. Among them, recombinant, self-inactivating lentiviral vectors are very attractive delivery systems, as they are able to efficiently transduce into and express foreign genes in a wide variety of mammalian cells. A self-inactivating lentiviral vector was evaluated for the delivery of human immunodeficiency virus 1 (HIV-1) envelope sequences in mice in order to elicit specific immune responses. With this aim, BALB/c mice were immunized with a single injection of self-inactivating lentiviral vectors carrying either the full-length HIV-1HXB2 Rev/Env (TY2-IIIBEnv) or the codon-optimized HIV-1JR-FL gp120 (TY2-JREnv) coding sequence. Both vectors were able to elicit specific cellular responses efficiently, as measured by gamma interferon ELISPOT and chromium-release assays, upon in vitro stimulation of splenocytes from BALB/c immunized mice. However, only the TY2-JREnv-immunized mice were able to elicit specific humoral responses, measured as anti-gp120 antibody production. These data provide the first evidence that a single, direct, in vivo administration of a lentiviral vector encoding a viral gene might represent a useful strategy for vaccine development.

From pathogen to medicine: HIV-1-derived lentiviral vectors as vehicles for dendritic cell based cancer immunotherapy

Over the years, the unique capacity of dendritic cells (DC) for efficient activation of naive T cells has led to their extensive use in cancer immunotherapy protocols. In order to be able to fulfil their role as antigen-presenting cells, the antigen of interest needs to be efficiently introduced and subsequently correctly processed and presented by the DC. For this purpose, a variety of both viral and non-viral antigen-delivery systems have been evaluated. Amongst those, HIV-1-derived lentiviral vectors have been used successfully to transduce DC. This review considers the use of HIV-1-derived lentiviral vectors to transduce human and murine DC for cancer immunotherapy. Lentivirally transduced DC have been shown to present antigenic peptides, prime transgene-specific T cells in vitro and elicit a protective cytotoxic T-lymphocyte (CTL) response in animal models. Different parameters determining the efficacy of transduction are considered. The influence of lentiviral transduction on the DC phenotype and function is described and the induction of immune responses by lentivirally transduced DC in vitro and in vivo is discussed in detail. In addition, direct in vivo administration of lentiviral vectors aiming at the induction of antigen-specific immunity is reviewed. This strategy might overcome the need for ex vivo generation and antigen loading of DC. Finally, future perspectives towards the use of lentiviral vectors in cancer immunotherapy are presented.

Efficient Induction of Tumor Antigen–Specific CD8+ Memory T Cells by Recombinant Lentivectors

The success of active cancer immunotherapy entails a robust induction of tumor-reactive effector and memory CD8+ T cells. We compared the in vivo immunogenicity of the melanoma-associated antigen Melan-A(26-35) encoded by third-generation recombinant lentivector (rec. lv) or as peptide admixed with a strong adjuvant. Ex vivo analyses of immunized HLA-A2/H-2K(b) mice showed that rec. lv triggered a stronger anti-Melan-A CD8+ T -cell response than peptide vaccine. Importantly, the majority of anti-Melan-A T cells elicited by rec. lv expressed the memory marker CD127 at the peak of the primary response. In those mice, memory T cells were detectable several months after priming and could be activated by recall peptide vaccination. These results show that immunization with rec. lv induces not only a strong antigen-specific CD8+ T -cell response but also a long-lasting T-cell memory against a bona fide tumor-associated antigen.

Nonreplicating recombinant vaccinia virus expressing CD40 ligand enhances APC capacity to stimulate specific CD4+ and CD8+ T cell responses

Recombinant poxviruses expressing immunomodulatory molecules together with specific antigens represent powerful vaccines for cancer immunotherapy. Recently, we and others have demonstrated, in vitro and in vivo, that coexpression of CD80 and CD86 costimulatory molecules enhances the immunogenic capacity of a recombinant vaccinia virus (rVV) encoding different tumor-associated antigens. To further investigate the capacity of these vectors to provide ligands for different costimulatory pathways relevant in the generation of T cell responses, we constructed a recombinant virus (rVV) expressing CD40 ligand or CD154 (CD154rVV). Upon binding the CD40 receptor expressed on antigen presenting cells (APC), this molecule, physiologically expressed on activated CD4+ T cells, increases their antigen presentation and immunostimulatory capacities. Therefore, we evaluated the effects of CD154rVV infection on APC activation and its consequences on T cell stimulation. CD154rVV infection of autologous fibroblasts, monocytes, or iDC promoted the expression of a number of cytokines, including GM-CSF, TNF-alpha, and IL-15 in iDC. Most importantly, IL-12 p40 gene expression and protein secretion were induced by CD154rVV but not by wild-type VV (WT VV) in either CD14+ cells or iDC, and these effects could be blocked by anti-CD40 monoclonal antibodies. Furthermore, phenotypic characterization of CD154rVV infected iDC revealed enhanced expression of CD83 and CD86 surface markers as compared with wild-type vaccinia virus infection. As expected, VV infection triggered cytokines gene expression in cultures including APC and T cells from VV immune donors. However, cytokine genes typically expressed by T cell receptor triggered T cells such as those encoding IL-2 and IFN-gamma, or T cell proliferation, were detectable to a significantly higher extent in CD154rVV infected cultures, as compared with WT VV. Activation of specific CD8+ T cells was then investigated using MART-1/Melan-A(27-35) epitope as the model of tumor-associated antigen (TAA). In the presence of CD154rVV activated APCs, significantly higher numbers of specific cytotoxic CD8+ T cells were detected, as compared with cultures performed in the presence of WT VV or in the absence of virus. Taken together, these data indicate that functional CD154 expression from rVV infected cells promotes APC activation, thereby enhancing antigen-specific T cell generation. Such a recombinant vector might help bypass the requirement for activated helper cells during CTL priming, thus qualifying as a potentially relevant vector in the generation of CD8+ T cell responses in cancer immunotherapy.

Making dendritic cells from the inside out: lentiviral vector-mediated gene delivery of granulocyte-macrophage colony-stimulating factor and interleukin 4 into CD14+ monocytes generates dendritic cells in vitro

We have evaluated a one-hit lentiviral transduction approach to genetically modifying monocytes in order to promote autocrine and paracrine production of factors required for their differentiation into immature dendritic cells (DCs). High-titer third-generation self-inactivating lentiviral vectors expressing granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) efficiently achieved simultaneous and persistent codelivery of the transgenes into purified human CD14+ monocytes. Coexpression of GM-CSF and IL-4 in CD14+ cells was sufficient to induce their differentiation into a DC-like phenotype, as evidenced by their morphology, immature immunophenotypic profile (CD14-, CD1a+, CD80+, CD86+, MHC-I+, MHC-II+), and their ability to further develop into a mature phenotype (CD83+) on further treatment with soluble CD40 ligand. Mixed lymphocyte reactions showed that the T cell-stimulating activity of lentivirus-modified DCs was superior to that of DCs grown by conventional methods. Lentivirus-modified DCs displayed efficient antigen-specific, MHC class I-restricted stimulation of autologous CD8+ T cells, as shown by IFN-gamma production and CTL assays. DCs coexpressing GM-CSF and IL-4 could be kept metabolically active and viable in culture for 14 days in the absence of exogenously added growth factors, unlike conventionally produced DCs. Coexpression of FLT3 ligand did not improve the viability, expansion, or immunologic performance of lentivirus-modified DCs. This article demonstrates the proof-of-concept to genetically convert monocytes to DC-type antigen-presenting cells with lentiviral vectors.

Alefacept reduces infiltrating T cells, activated dendritic cells, and inflammatory genes in psoriasis vulgaris

Psoriasis vulgaris, a skin disease that is considered to be the result of a type 1 autoimmune response, provides an opportunity for studying the changes that occur in a target-diseased tissue during innovative immunotherapies. To gain a more comprehensive picture of the response to an approved biological therapy, we studied alfacept, which is a CD2 binding fusion protein. We examined T cells, dendritic cells (DCs), and expression of a number of inflammatory genes. In 22 patients, 55% demonstrated a clear histological remission of the disease, with a 73% reduction in lesional lymphocytes and a 79% decrease in infiltrating CD8+ cells. Only histological responders showed marked reductions in the tissue expression of inflammatory genes IFN-gamma, signal transducer and activator of transcription 1, monokine induced by IFN-gamma, inducible NO synthase, IL-8, and IL-23 subunits. Parallel decreases in CD83+ and CD11c+ DCs also were measured by immunohistochemistry. Because we observed that alefacept binds primarily to T cells and not DCs, we suggest that T cells are the primary target for therapy, but that DCs and a spectrum of type 1 inflammatory genes are coordinately suppressed.

Ex vivo generation of genetically modified dendritic cells for immunotherapy: implications of lymphocyte contamination

Genetically modified dendritic cell (DC) vaccines expressing tumor-associated antigens are currently used for cancer immunotherapy. Peripheral blood (PB) monocyte precursors are a relatively convenient source of DCs for use in clinical studies, but are often contaminated by lymphocytes. The current study was conducted to examine the impact of T-lymphocyte contamination on genetically modified DC product. PB monocyte-derived DCs were efficiently transduced (75-95%) with an HIV-1-based self-inactivating lentiviral vector encoding a model antigen, the enhanced green fluorescent protein (eGFP). The lymphocyte-free DC culture transduced with Lenti-eGFP showed stable expression of eGFP without measurable decline in viability. In contrast, the eGFP-positive DCs disappeared rapidly in transduced DC cultures containing lymphocyte contaminants, concurrent with detectable activation and expansion of T-lymphocytes. Upon antigen recall, these T cells elicited major histocompatability complex-restricted antigen-specific cytotoxicity against eGFP-positive autologous DCs and mitogen-stimulated T lymphoblasts, mainly through the perforin-mediated pathway. In summary, this study demonstrate that the relative purity of DC cultures could determine the persistence of gene-modified DC, which may affect the induction of effective immune responses by DC vaccination strategies.