Use of a lentiviral vector encoding a HCMV-Chimeric IE1-pp65 protein for epitope identification in HLA-Transgenic mice and for ex vivo stimulation and expansion of CD8+ cytotoxic T cells from human peripheral blood cells

Virus-Like Particles and Nanoparticles for Vaccine Development against HCMV

Human cytomegalovirus (HCMV) infects more than 70% of the human population worldwide. HCMV is responsible for high morbidity and mortality in immunocompromised patients and remains the leading viral cause of congenital birth defects. Despite considerable efforts in vaccine and therapeutic development, HCMV infection still represents an unmet clinical need and a life-threatening disease in immunocompromised individuals and newborns. Immune repertoire interrogation of HCMV seropositive patients allowed the identification of several potential antigens for vaccine design. However, recent HCMV vaccine clinical trials did not lead to a satisfactory outcome in term of efficacy. Therefore, combining antigens with orthogonal technologies to further increase the induction of neutralizing antibodies could improve the likelihood of a vaccine to reach protective efficacy in humans. Indeed, presentation of multiple copies of an antigen in a repetitive array is known to drive a more robust humoral immune response than its soluble counterpart. Virus-like particles (VLPs) and nanoparticles (NPs) are powerful platforms for multivalent antigen presentation. Several self-assembling proteins have been successfully used as scaffolds to present complex glycoprotein antigens on their surface. In this review, we describe some key aspects of the immune response to HCMV and discuss the scaffolds that were successfully used to increase vaccine efficacy against viruses with unmet medical need.

A synthetic human cytomegalovirus pp65-IE1 fusion antigen efficiently induces and expands virus specific T cells

Infection with human cytomegalovirus (HCMV) can cause severe complications in newborns and immunocompromised patients, and a prophylactic or therapeutic vaccine against HCMV is not available. Here, we generated a HCMV vaccine candidate fulfilling the regulatory requirements for GMP-compliant production and clinical testing. A novel synthetic fusion gene consisting of the coding sequences of HCMV pp65 and IE1 having a deleted nuclear localization sequence and STAT2 binding domain was introduced into the genome of the attenuated vaccinia virus strain MVA. This recombinant MVA, MVA-syn65_IE1, allowed for the production of a stable ∼120kDa syn65_IE1 fusion protein upon tissue culture infection. MVA-syn65_IE1 infected CD40-activated B cells activated and expanded pp65- and IE1-specific T cells derived from HCMV-seropositive donors to at least equal levels as control recombinant MVA expressing single genes for pp65 or IE1. Additionally, we show that MVA-syn65_IE1 induced HCMV pp65- and IE1-epitope specific T cells in HLA-A2.1-/HLA-DR1-transgenic H-2 class I-/class II-knockout mice. Thus, MVA-syn65_IE1 represents a promising vaccine candidate against HCMV and constitutes a basis for the generation of a multivalent vaccine targeting relevant pathogens in immunocompromised patients.

Immunogenicity of a recombinant lentiviral vector carrying human telomerase tumor antigen in HLA-B*0702 transgenic mice

Over expression of telomerase represents a hallmark of cancer cells and the induction of T cell immunity against this universal tumor antigen have gained promising interest for anticancer immunotherapy. In this study we evaluated a recombinant lentiviral vector expressing the human telomerase reverse transcriptase (lv-hTERT) vaccination in the humanized HLA-B*0702 transgenic (HLA-B7 Tg) mice. A single lv-hTERT vector immunization induces potent and broad HLA-B7-restricted CTL responses against hTERT. Unlike conventional hTERT peptide or DNA immunization, the lv-hTERT vector triggers high and sustained IFN-gamma producing CD8(+) T cell responses in HLA-B7 Tg mice. The avidity and in vivo cytotoxicity of CD8(+) T cells were stronger in lv-hTERT vector-immunized mice than in hTERT peptide or DNA vaccinated groups. The study also showed that the use of prime-boost vaccination drastically improved the magnitude and strength of lentivector-primed CD8(+) T cells. Our data indicated that lentiviral delivery of hTERT is suitable for enhancing cellular immunity against hTERT and offers a promising alternative for telomerase-based cancer vaccine.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Protective antiviral immunity conferred by a nonintegrative lentiviral vector-based vaccine

Lentiviral vectors are under intense scrutiny as unique candidate viral vector vaccines against tumor and aggressive pathogens because of their ability to initiate potent and durable specific immune responses. Strategies that alleviate safety concerns will facilitate the clinical developments involving lentiviral vectors. In this respect, the development of integration deficient lentiviral vectors circumvents the safety concerns relative to insertional mutagenesis and might pave the way for clinical applications in which gene transfer is targeted to non-dividing cells. We thus evaluated the potential use of nonintegrative lentiviral vectors as vaccination tools since the main targeted cell in vaccination procedures is the non-dividing dendritic cell (DC). In this study, we demonstrated that a single administration of nonintegrative vectors encoding a secreted form of the envelope of a virulent strain of West Nile Virus (WNV) induces a robust B cell response. Remarkably, nonintegrative lentiviral vectors fully protected mice from a challenge with a lethal dose of WNV and a single immunization was sufficient to induce early and long-lasting protective immunity. Thus, nonintegrative lentiviral vectors might represent a safe and efficacious vaccination platform for the development of prophylactic vaccines against infectious agents.

A novel approach to evaluate the immunogenicity of viral antigens of clinical importance in HLA transgenic murine models

Transgenic (Tg) mice expressing HLA class I alleles and lacking murine MHC class I represent a useful model for the pre-clinical evaluation of human vaccines, which focus on induction of CD8(+) T-cell responses. We have developed a platform to be used in Tg mice for exploring the immunogenicity of T-cell targets, whose immunologic epitopes have yet to be defined. To test the attributes of the evaluation system in the context of an important human pathogen, we have explored multiple antigens from cytomegalovirus (CMV). A panel of recombinant modified vaccinia Ankara (MVA) vectors, expressing various CMV proteins (CMV-MVA) was used to immunize HLA-A*0201, B*0702 and A*1101 Tg mice. Immune splenocytes were in vitro stimulated (IVS) either using syngeneic lipo-polysaccharide activated lymphoblasts or Tg HLA-I matched human EBV-transformed B-lymphoblastoid cells (LCL), both loaded with peptide libraries, encompassing the CMV protein under investigation. IVS performed with peptide library loaded lymphoblasts failed to provide a reliable stimulation. In contrast, the usage of LCL as antigen presenting cells (APC) of CMV peptide libraries resulted in a consistent and specific amplification of the Tg T-cell response in animals immunized with CMV-MVAs. The LCL IVS method reliably allowed defining the immunogenicity and immunodominant CD8(+) T-cell regions of uncharacterized CMV antigens. The combination of CMV-MVA vectors, unbiased pools of CMV-specific peptide libraries presented by Tg HLA-I matched LCL constitutes a valid tool for the pre-clinical evaluation of model candidate vaccines. This convenient method could find application to investigate the immunogenicity profile of cancer antigens or proteins from infectious human pathogens.

A fusion protein of HCMV IE1 exon4 and IE2 exon5 stimulates potent cellular immunity in an MVA vaccine vector

A therapeutic CMV vaccine incorporating an antigenic repertoire capable of eliciting a cellular immune response has yet to be successfully implemented for patients who already have acquired an infection. To address this problem, we have developed a vaccine candidate derived from modified vaccinia Ankara (MVA) that expresses three immunodominant antigens (pp65, IE1, IE2) from CMV. The novelty of this vaccine is the fusion of two adjacent exons from the immediate-early region of CMV, their successful expression in MVA, and robust immunogenicity in both primary and memory response models. Evaluation of the immunogenicity of the viral vaccine in mouse models shows that it can stimulate primary immunity against all three antigens in both the CD4(+) and CD8(+) T cell subsets. Evaluation of human PBMC from healthy CMV-positive donors or patients within 6 months of receiving hematopoietic cell transplant shows robust stimulation of existing CMV-specific CD4(+) and CD8(+) T cell subsets.

Antigenic properties of HCMV peptides displayed by filamentous bacteriophages vs. synthetic peptides

Several efforts have been invested in the identification of CTL and Th epitopes, as well as in the characterization of their immunodominance and MHC restriction, for the generation of a peptide-based HCMV vaccine. Small synthetic peptides are, however, poor antigens and carrier proteins are important for improving the efficacy of synthetic peptide vaccines. Recombinant bacteriophages appear as promising tools in the design of subunit vaccines. To investigate the antigenicity of peptides carried by recombinant bacteriophages we displayed different HCMV MHCII restricted peptides on the capsid of filamentous bacteriophage (fd) and found that hybrid bacteriophages are processed by human APC and activate HCMV-specific CD4 T-cells. Furthermore we constructed a reporter T-cell hybridoma expressing a chimeric TCR comprising murine alphabeta constant regions and human variable regions specific for the HLA-A2 restricted immunodominant NLV peptide of HCMV. Using the filamentous bacteriophage as an epitope carrier, we detected a more robust and long lasting response of the reporter T-cell hybridoma compared to peptide stimulation. Our results show a general enhancement of T-cell responses when antigenic peptides are carried by phages.

Lentiviral Vectors Encoding HIV-1 Polyepitopes Induce Broad CTL Responses In Vivo

Lentiviral vectors have been tested as vaccination vectors in anti-tumoral and anti-viral models. They efficiently transduce dendritic cells and stimulate strong T-cell responses against the encoded antigen. However, their capacity to stimulate a cytotoxic T-lymphocyte (CTL) response against several antigens has not been evaluated. Broad anti-human immunodeficiency virus 1 (HIV-1) T-cell immune responses are important for the control of HIV replication. We evaluated the potential of polyepitope-encoding lentiviral vectors to induce broad anti-HIV CTL responses. We constructed two lentiviral vectors coding for an HLA-A2- or HLA-B7-restricted polyepitope and evaluated their immunogenicity by direct injection of vector particles in HLA-A2 or HLA-B7 transgenic mice. In vitro cytotoxicity assays showed that a single immunization induces a strong, diversified, and long-lasting CTL response in both mouse models. CTL responses were directed against all 13 epitopes in the HLA-A2 system and 8 out of 12 in the HLA-B7 system. A second immunization augmented the number of responding mice in the HLA-A2 system but not in the HLA-B7 system. HLA-B7-immunized mice mounted strong interferon-gamma (IFN-gamma)-secreting T-cell responses against a majority of the epitopes and lysed peptide-loaded target cells in vivo. CTL responses in HLA-B7 mice were only partially dependent on CD4 T-cell help. This work underlines the potential of lentiviral vectors as candidates for therapeutic vaccination against acquired immunodeficiency syndrome.

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).

HLA class I transgenic mice: development, utilisation and improvement

Classical major histocompatibility complex (MHC) class I antigens are trimeric molecules found on the surface of nucleated cells in all jawed vertebrates. MHC I are recognised by two families of receptors: clonotypic T cell receptors expressed on the surface of CD8+ cytotoxic T lymphocytes (CTLs), and monomorphic receptors expressed by both natural killer cells and CTLs. The production of MHC I molecules within the cells is a sequential process performed with the help of interacting proteins: proteases, chaperones, transporters and so on. Although largely homologous in their structure, organisation and function, the human and mouse MHC I antigen processing and presentation machineries show fine differences. Transgenesis and 'knockout' or 'knock-in' technologies permit the addition of relevant human genes or the replacement of mouse genes by their human orthologues in order to produce immunologically humanised mice. Such experimental animals are especially relevant for the comparative evaluation of immunotherapies and for the characterisation of MHC I peptide epitopes. This review presents the similarities and differences between mouse and human MHC I antigen processing machinery, and describes the development and utilisation of improving mouse models of human cytotoxic T cell immunity.

MHC–peptide specificity and T-cell epitope mapping: where immunotherapy starts

The evaluation and characterization of epitope-specific human leukocyte antigen (HLA)-restricted memory T-cell reactivity is an important step for the development of preventive vaccines and peptide-based immunotherapies for viral and tumor diseases. The past decade has witnessed the use of HLA-restricted peptides as tools to activate strong immune responses of naïve or memory T cells specifically. This has fuelled an active search for methodological approaches focusing on HLA and peptide associations. Here, we outline new perspective on the emerging opportunity of evaluating HLA and peptide restriction by using novel approaches, such as quantitative real-time PCR, that can identify epitope specificities that are potentially useful in clinical settings.

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.

A single immunization with a minute dose of a lentiviral vector-based vaccine is highly effective at eliciting protective humoral immunity against West Nile virus

BACKGROUND

Lentiviral vectors, due to their capacity to transduce non-dividing cells, have become precious and worldwide used gene transfer systems. Their ability to efficiently and stably transduce dendritic cells (DCs) has led to their successful use as vaccination vectors for eliciting strong, specific and protective cellular immune responses mostly in anti-tumoral but also in anti-viral applications. However, the ability of lentiviral vectors to elicit an antibody-based protective immunity has, to date, not been evaluated. In the present study, we evaluated the potential of a lentiviral vector-based vaccine to elicit humoral immunity against West Nile virus (WNV). WNV is a mosquito-borne flavivirus that emerged in North America and causes encephalitis in humans, birds and horses. Neutralizing anti-WNV antibodies have been shown to be crucial for protection against WNV encephalitis.

METHODS

The ability of lentiviral vector TRIP/sE(WNV), expressing the secreted soluble form of the envelope E-glycoprotein (sE(WNV)) from the highly virulent IS-98-ST1 strain of WNV, to induce a specific humoral response and protection against WNV infection was assessed in a mouse model of WNV encephalitis.

RESULTS

Remarkably, a single immunization with a minute dose of TRIP/sE(WNV) was efficient at eliciting a long-lasting, protective and sterilizing humoral immunity, only 1 week after priming.

CONCLUSIONS

This study broadens the applicability of lentiviral vectors as efficient non-replicating vaccines against pathogens for which a neutralizing humoral response is one active arm of the protective immunity. The TRIP/sE(WNV) lentiviral vector appears to be a promising tool for veterinary vaccination against zoonotic WNV.

Immunization with a lentiviral vector stimulates both CD4 and CD8 T cell responses to an ovalbumin transgene

Lentiviral vectors encoding antigens are promising vaccine candidates because they transduce dendritic cells (DC) in vivo and prime CTL responses. Here we examine their stimulation of antigen-specific CD4(+) T cells, critical for protective immunity against tumors or infectious disease. We constructed lentiviral vectors (lentivectors) expressing ovalbumin, which was secreted (OVA), cytoplasmic (OVAcyt), or fused to either invariant chain (Ii-OVA) or transferrin receptor (TfR-OVA) sequences, targeting the MHC class II presentation pathway. Murine DC infected with the various lentivectors could stimulate OT-I (CD8(+), OVA TCR transgenic) T cells and all except OVAcyt could also stimulate OT-II (CD4(+), OVA TCR transgenic) T cells in vitro. Direct injection of the OVA-, Ii-OVA-, or TfR-OVA-expressing vectors into mice resulted in a CD4(+) T cell response, as shown by expansion of adoptively transferred OT-II T cells and upregulation of CD44 on these cells. The Ii-OVA vector was the most potent inducer of IFN-gamma-secreting CD4(+) and CD8(+) T cells and was the only vector to protect mice completely from challenge with OVA-expressing tumor cells. Therefore directly injected lentivectors can stimulate CD4(+) T cells; both CD4(+) and CD8(+) responses can be enhanced by targeting the antigen to the MHC class II pathway.