The induction of HIV Gag-specific CD8+ T cells in the spleen and gut-associated lymphoid tissue by parenteral or mucosal immunization with recombinant Listeria monocytogenes HIV Gag

Dendritic cell vaccine therapy for colorectal cancer

Colorectal cancer (CRC) remains a leading cause of cancer-related deaths in the United States despite an array of available treatment options. Current standard-of-care interventions for this malignancy include surgical resection, chemotherapy, and targeted therapies depending on the disease stage. Specifically, infusion of anti-vascular endothelial growth factor agents in combination with chemotherapy was an important development in improving the survival of patients with advanced colorectal cancer, while also helping give rise to other forms of anti-angiogenic therapies. Yet, one approach by which tumor angiogenesis may be further disrupted is through the administration of a dendritic cell (DC) vaccine targeting tumor-derived blood vessels, leading to cytotoxic immune responses that decrease tumor growth and synergize with other systemic therapies. Early generations of such vaccines exhibited protection against various forms of cancer in pre-clinical models, but clinical results have historically been disappointing. Sipuleucel-T (Provenge®) was the first, and to-date, only dendritic cell-based therapy to receive FDA approval after significantly increasing overall survival in prostate cancer patients. The unparalleled success of Sipuleucel-T has helped revitalize the clinical development of dendritic cell vaccines, which will be examined in this review. We also highlight the promise of these vaccines to instill anti-angiogenic immunity for individuals with advanced colorectal cancer.

Types of Recombinant Vaccines

The original scientific strategy behind vaccinology has historically been to “isolate, inactivate, and inject,” first invoked by Louis Pasteur.

Peptide-MHC multimer-based monitoring of CD8 T-cells in HIV-1 infection and AIDS vaccine development

The use of MHC multimers allows precise and direct detecting and analyzing of antigen-specific T-cell populations and provides new opportunities to characterize T-cell responses in humans and animals. MHC-multimers enable us to enumerate specific T-cells targeting to viral, tumor and vaccine antigens with exceptional sensitivity and specificity. In the field of HIV/SIV immunology, this technique provides valuable information about the frequencies of HIV- and SIV-specific CD8(+) cytotoxic T lymphocytes (CTLs) in different tissues and sites of infection, AIDS progression, and pathogenesis. Peptide-MHC multimer technology remains a very sensitive tool in detecting virus-specific T -cells for evaluation of the immunogenicity of vaccines against HIV-1 in preclinical trials. Moreover, it helps to understand how immune responses are formed following vaccination in the dynamics from priming point until T-cell memory is matured. Here we review a diversity of peptide-MHC class I multimer applications for fundamental immunological studies in different aspects of HIV/SIV infection and vaccine development.

E. coli Heat-labile Enterotoxin B Subunit as a Platform for the Delivery of HIV Gag p24 Antigen

Multiple vaccination strategies have been devised against HIV-1 including delivery of HIV moieties in attenuated or replication defective recombinant microbial agents alone or in combination with priming agents in form of soluble proteins or naked DNA. For the priming agents to be effective, adjuvants might be essential in directing the immune response to a desired outcome. E. coli enterotoxin B subunit (LTB) is an effective adjuvant and carrier for other proteins and epitopes. Here we show that conjugation of HIV gag p24 to LTB enhances the T cell response to gag p24 by increasing rate of T cell division compared to other treatments. Because HIV vaccines are likely to be multivalent, we further investigated whether gag p24 inhibits antigen presentation of an unrelated antigen, OVA. Addition of gag p24 to OVA-responsive DO.11.10 cell culture did not have adverse effects on antigen presentation. Interestingly, the presence of LTB in these cultures significantly increased proliferation of DO.11.10 cells. In all, the results suggest the use of LTB to boost immune responses against HIV gag p24 in systemic priming regimens with oral recombinant HIV vaccines.

Pre-existing immunity against vaccine vectors--friend or foe?

Over the last century, the successful attenuation of multiple bacterial and viral pathogens has led to an effective, robust and safe form of vaccination. Recently, these vaccines have been evaluated as delivery vectors for heterologous antigens, as a means of simultaneous vaccination against two pathogens. The general consensus from published studies is that these vaccine vectors have the potential to be both safe and efficacious. However, some of the commonly employed vectors, for example Salmonella and adenovirus, often have pre-existing immune responses in the host and this has the potential to modify the subsequent immune response to a vectored antigen. This review examines the literature on this topic, and concludes that for bacterial vectors there can in fact, in some cases, be an enhancement in immunogenicity, typically humoral, while for viral vectors pre-existing immunity is a hindrance for subsequent induction of cell-mediated responses.

Clinical development of Listeria monocytogenes-based immunotherapies

Active immunotherapy targeting dendritic cells (DCs) has shown great promise in preclinical models and in human clinical trials for the treatment of malignant disease. Sipuleucel-T (Provenge, Dendreon, Seattle, WA), which consists of antigen-loaded dendritic cells (DCs), recently became the first targeted therapeutic cancer vaccine to be approved by the US Food and Drug Administration (FDA). However, ex vivo therapies such as Provenge have practical limitations and elicit an immune response with limited scope. By contrast, live-attenuated Listeria monocytogenes (Lm) naturally targets DCs in vivo and stimulates both innate and adaptive cellular immunity. Lm-based vaccines engineered to express cancer antigens have demonstrated striking efficacy in several animal models and have resulted in encouraging anecdotal survival benefit in early human clinical trials. Two different Lm-based vaccine platforms have advanced into phase II clinical trials in cervical and pancreatic cancer. Future Lm-based clinical vaccine candidates are expected to feature polyvalent antigen expression and to be used in combination with other immunotherapies or conventional therapies such as radiotherapy and chemotherapy to augment efficacy.

Targeting tumor vasculature with novel Listeria-based vaccines directed against CD105

The FDA approval of bevacizumab (Avastin®, Genentech/Roche), a monoclonal antibody raised against human VEGF-A, as second-line therapy for colon and lung carcinoma validated the approach of targeting human tumors with angiogenesis inhibitors. While the VEGF/VEGFR pathway is a viable target for anti-angiogenesis tumor therapy, additional targets involved in tumor neovascularization have been identified. One promising target present specifically on tumor vasculature is endoglin (CD105), a member of the TGF-β receptor complex expressed on vascular endothelium and believed to play a role in angiogenesis. Monoclonal antibody therapy and preventive vaccination against CD105 has met with some success in controlling tumor growth. This report describes the in vivo proof-of-concept studies for two novel therapeutic vaccines, Lm-LLO-CD105A and Lm-LLO-CD105B, directed against CD105 as a strategy to target neovascularization of established tumors. Listeria-based vaccines directed against CD105 lead to therapeutic responses against primary and metastatic tumors in the 4T1-Luc and NT-2 mouse models of breast cancer. In a mouse model for autochthonous Her-2/neu-driven breast cancer, Lm-LLO-CD105A vaccination prevented tumor incidence in 20% of mice by week 58 after birth while all control mice developed tumors by week 40. In comparison with previous Listeria-based vaccines targeting tumor vasculature, Lm-LLO-CD105A and Lm-LLO-CD105B demonstrated equivalent or superior efficacy against two transplantable mouse models of breast cancer. Support is provided for epitope spreading to endogenous tumor antigens and reduction in tumor vascularity after vaccination with Listeria-based CD105 vaccines. Reported here, these CD105 therapeutic vaccines are highly effective in stimulating anti-angiogenesis and anti-tumor immune responses leading to therapeutic efficacy against primary and metastatic breast cancer.

A live attenuated Listeria monocytogenes vaccine vector expressing SIV Gag is safe and immunogenic in macaques and can be administered repeatedly

Listeria monocytogenes (Lm) is known to induce strong cellular immune responses. We constructed a live-attenuated Lm vector, Lmdd-BdopSIVgag, which encodes SIVmac239 gag. Intragastric (i.g.) administration of 3 × 10(12) bacteria to rhesus macaques was safe and induced anti-Gag cellular but no humoral immune responses. Boosting of Gag-specific cellular responses was observed after i.g. administration of Lmdd-BdopSIVgag to previously vaccinated RM despite preexisting anti-Lm immunity shown by lymphoproliferative responses. Surprisingly, anti-Lm cellular responses were also detected in non-vaccinated controls, which may reflect the fact that Lm is a ubiquitous bacterium. The novel, live-attenuated Lmdd-BdopSIVgag may be an attractive platform for oral vaccine delivery.

Platform technology to deliver prophylactic molecules orally: an example using the Class A select agent Yersinia pestis

Consumed for centuries, lactic acid bacteria are excellent candidates for the development of safe mucosal delivery vehicles for prophylactic and therapeutic molecules. We have recently reported that the immune response to an effective OspA-expressing L. plantarum vaccine for Lyme disease is modulated by the lipid modification of the antigen. In this study, we investigated if this technology can be applied to developing vaccines for other diseases by focusing on the Class A select agent, Yersinia pestis. We used a number of biochemistry and immunology techniques to determine the localization of the immunogen in our delivery vehicle and to evaluate the mucosal as well as the systemic immune response to the immunogen. We found that only LcrV cloned downstream of the signal sequence of B. burgdorferi OspA ((ss)LcrV), but not wildtype LcrV (LcrV), is localized to the desired peptidoglycan layer of the delivery vehicle. In addition, only mice that received L. plantarum expressing (ss)LcrV produced significant titers of IgG antibody as well as IgA in distant mucosal sites such as lungs and vagina. Furthermore, only L. plantarum expressing (ss)LcrV induced significant amounts of pro-inflammatory cytokines TNFα, IL-12, IFNγ and IL-6 as well as anti-inflammatory IL-10 in human peripheral blood mononuclear cells derived dendritic cells, suggesting that the mechanism by which LcrV-expressing L. plantarum stimulates the immune response involves polarization to Th1 mediated immunity with some involvement of Th2. The study reported here proves that this system is a platform technology to develop oral vaccines for multiple diseases.

Immune response to Lactobacillus plantarum expressing Borrelia burgdorferi OspA is modulated by the lipid modification of the antigen

BACKGROUND

Over the past decade there has been increasing interest in the use of lactic acid bacteria as mucosal delivery vehicles for vaccine antigens, microbicides and therapeutics. We investigated the mechanism by which a mucosal vaccine based in recombinant lactic acid bacteria breaks the immunological tolerance of the gut in order to elicit a protective immune response.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed how the lipid modification of OspA affects the localization of the antigen in our delivery vehicle using a number of biochemistry techniques. Furthermore, we examined how OspA-expressing L. plantarum breaks the oral tolerance of the gut by stimulating human intestinal epithelial cells, peripheral blood mononuclear cells and monocyte derived dendritic cells and measuring cytokine production. We show that the leader peptide of OspA targets the protein to the cell envelope of L. plantarum, and it is responsible for protein export across the membrane. Mutation of the lipidation site in OspA redirects protein localization within the cell envelope. Further, we show that lipidated-OspA-expressing L. plantarum does not induce secretion of the pro-inflammatory cytokine IL-8 by intestinal epithelial cells. In addition, it breaks oral tolerance of the gut via Th1/Th2 cell mediated immunity, as shown by the production of pro- and anti-inflammatory cytokines by human dendritic cells, and by the production of IgG2a and IgG1 antibodies, respectively.

CONCLUSIONS/SIGNIFICANCE

Lipid modification of OspA expressed in L. plantarum modulates the immune response to this antigen through a Th1/Th2 immune response.

Alphavirus replicon-based enhancement of mucosal and systemic immunity is linked to the innate response generated by primary immunization

Venezuelan equine encephalitis virus replicon particles (VRP) function as an effective systemic, cellular and mucosal adjuvant when codelivered with antigen, and show promise for use as a component in new and existing human vaccine formulations. We show here that VRP are effective at low dose and by intramuscular delivery, two useful features for implementation of VRP as a vaccine adjuvant. In mice receiving a prime and boost with antigen, we found that VRP are required in prime only to produce a full adjuvant effect. This outcome indicates that the events triggered during prime with VRP are sufficient to establish the nature and magnitude of the immune response to a second exposure to antigen. Events induced by VRP in the draining lymph node after prime include robust secretion of many inflammatory cytokines, upregulation of CD69 on leukocytes, and increased cellularity, with a disproportionate increase of a cell population expressing CD11c, CD11b, and F4/80. We show that antigen delivered 24h after administration of VRP does not benefit from an adjuvant effect, indicating that the events which are critical to VRP-mediated adjuvant activity occur within the first 24h. Further studies of the events induced by VRP will help elucidate the mechanism of VRP adjuvant activity and will advance the safe implementation of this adjuvant in human vaccines.

Live, attenuated strains of Listeria and Salmonella as vaccine vectors in cancer treatment

Live, attenuated strains of many bacteria that synthesize and secrete foreign antigens are being developed as vaccines for a number of infectious diseases and cancer. Bacterial-based vaccines provide a number of advantages over other antigen delivery strategies including low cost of production, the absence of animal products, genetic stability and safety. In addition, bacterial vaccines delivering a tumor-associated antigen (TAA) stimulate innate immunity and also activate both arms of the adaptive immune system by which they exert efficacious anti-tumor effects. Listeria monocytogenes and several strains of Salmonella have been most extensively studied for this purpose. A number of attenuated strains have been generated and used to deliver antigens associated with infectious diseases and cancer. Although both bacteria are intracellular, the immune responses invoked by Listeria and Salmonella are different due to their sub-cellular locations. Upon entering antigen-presenting cells by phagocytosis, Listeria is capable of escaping from the phagosomal compartment and thus has direct access to the cell cytosol. Proteins delivered by this vector behave as endogenous antigens, are presented on the cell surface in the context of MHC class I molecules, and generate strong cell-mediated immune responses. In contrast, proteins delivered by Salmonella, which lacks a phagosomal escape mechanism, are treated as exogenous antigens and presented by MHC class II molecules resulting predominantly in Th2 type immune responses. This fundamental disparity between the life cycles of the two vectors accounts for their differential application as antigen delivery vehicles. The present paper includes a review of the most recent advances in the development of these two bacterial vectors for treatment of cancer. Similarities and differences between the two vectors are discussed.

Listeria monocytogenes delivery of HPV-16 major capsid protein L1 induces systemic and mucosal cell-mediated CD4+ and CD8+ T-cell responses after oral immunization

Neutralizing antibodies are thought to be required at mucosal surfaces to prevent human papillomavirus (HPV) transmission. However, the potential for cell-mediated immunity in mediating protection against HPV infection has not been well explored. We generated recombinant Listeria monocytogenes (Lm) constructs that secrete listeriolysin O (LLO) fused with overlapping N-terminal (LLO-L1(1-258)) or C-terminal (LLO-L1(238-474)) fragments of HPV type 16 major capsid protein L1 (HPV-16-L1). Oral immunization of mice with either construct induced IFN-gamma-producing CD8+ and CD4+ T cells in the spleen and in the Peyer's patches with the C-terminal construct. Oral immunization with both constructs resulted in diminished viral titers in the cervix and uterus of mice after intravaginal challenge with vaccinia virus expressing HPV-16-L1.

Oral immunization with recombinant lactobacillus plantarum induces a protective immune response in mice with Lyme disease

Mucosal immunization is advantageous over other routes of antigen delivery because it can induce both mucosal and systemic immune responses. Our goal was to develop a mucosal delivery vehicle based on bacteria generally regarded as safe, such as Lactobacillus spp. In this study, we used the Lyme disease mouse model as a proof of concept. We demonstrate that an oral vaccine based on live recombinant Lactobacillus plantarum protects mice from tick-transmitted Borrelia burgdorferi infection. Our method of expressing vaccine antigens in L. plantarum induces both systemic and mucosal immunity after oral administration. This platform technology can be applied to design oral vaccine delivery vehicles against several microbial pathogens.

Nonmucosal alphavirus vaccination stimulates a mucosal inductive environment in the peripheral draining lymph node

The strongest mucosal immune responses are induced following mucosal Ag delivery and processing in the mucosal lymphoid tissues, and much is known regarding the immunological parameters which regulate immune induction via this pathway. Recently, experimental systems have been identified in which mucosal immune responses are induced following nonmucosal Ag delivery. One such system, footpad delivery of Venezuelan equine encephalitis virus replicon particles (VRP), led to the local production of IgA Abs directed against both expressed and codelivered Ags at multiple mucosal surfaces in mice. In contrast to the mucosal delivery pathway, little is known regarding the lymphoid structures and immunological components that are responsible for mucosal immune induction following nonmucosal delivery. In this study, we have used footpad delivery of VRP to probe the constituents of this alternative pathway for mucosal immune induction. Following nonmucosal VRP delivery, J chain-containing, polymeric IgA Abs were detected in the peripheral draining lymph node (DLN), at a time before IgA detection at mucosal surfaces. Further analysis of the VRP DLN revealed up-regulated alpha4beta7 integrin expression on DLN B cells, expression of mucosal addressin cell adhesion molecule 1 on the DLN high endothelia venules, and production of IL-6 and CC chemokines, all characteristics of mucosal lymphoid tissues. Taken together, these results implicate the peripheral DLN as an integral component of an alternative pathway for mucosal immune induction. A further understanding of the critical immunological and viral components of this pathway may significantly improve both our knowledge of viral-induced immunity and the efficacy of viral-based vaccines.

Induction of HIV-specific T and B cell responses with a replicating and conditionally infectious lentiviral vaccine

The development of an HIV vaccine that induces broad and potent immunity is critically needed. Viruses, including lentiviruses, have been used as vectors for ex vivo transduction of antigens into dendritic cells (DC). We hypothesized that DC transduced with a vector that allows selective infection of DC could induce potent immunity by continually priming DC. A lentiviral vector encoding HIV gag-pol without env would form viral cores in transduced DC, but would release non-infectious particles by budding into endosomes and releasing apoptotic bodies or exosomes containing viral cores. DC function by endocytosing DC-derived apoptotic bodies, and they are specialized in their ability to move endocytic contents into the cytoplasm. We postulated that endocytosis of vector cores could lead to transduction of a second round of DC. In this report, we demonstrate accumulation of viral cores inside transduced DC and show second-round transduction of immature DC that endocytose transduced DC in vitro. The effectiveness of immunization of mice with transduced DC to induce specific lymphocyte activation was assessed. Mice developed antigen-specific T cell responses and specific antibodies after immunization. Transduction of DC with a replication-competent but conditionally infectious lentivirus could be a novel vaccine strategy for HIV.

Constitutive Activation of the PrfA regulon enhances the potency of vaccines based on live-attenuated and killed but metabolically active Listeria monocytogenes strains

Recombinant vaccines derived from the facultative intracellular bacterium Listeria monocytogenes are presently undergoing early-stage clinical evaluation in oncology treatment settings. This effort has been stimulated in part due to preclinical results that illustrate potent activation of innate and adaptive immune effectors by L. monocytogenes vaccines, combined with efficacy in rigorous animal models of malignant and infectious disease. Here, we evaluated the immunologic potency of a panel of isogenic vaccine strains that varied only in prfA. PrfA is an intracellularly activated transcription factor that induces expression of virulence genes and encoded heterologous antigens (Ags) in appropriately engineered vaccine strains. Mutant strains with PrfA locked into a constitutively active state are known as PrfA* mutants. We assessed the impacts of three PrfA* mutants, G145S, G155S, and Y63C, on the immunologic potencies of live-attenuated and photochemically inactivated nucleotide excision repair mutant (killed but metabolically active [KBMA]) vaccines. While PrfA* substantially increased Ag expression in strains grown in broth culture, Ag expression levels were equivalent in infected macrophage and dendritic cell lines, conditions that more closely parallel those in the immunized host. However, only the prfA(G155S) allele conferred significantly enhanced vaccine potency to KBMA vaccines. In the KBMA vaccine background, we show that PrfA*(G155S) enhanced functional cellular immunity following an intravenous or intramuscular prime-boost immunization regimen. These results form the basis of a rationale for including the prfA(G155S) allele in future live-attenuated or KBMA L. monocytogenes vaccines advanced to the clinical setting.

Intragastric immunization with recombinant Lactobacillus casei expressing flagellar antigen confers antibody-independent protective immunity against Salmonella enterica serovar Enteritidis

A recombinant Lactobacillus casei expressing a flagellar antigen from Salmonella enterica serovar Enteritidis was constructed and evaluated as a mucosal vaccine. Intragastric immunization of the recombinant strain conferred protective immunity against Salmonella infection in mice. This immunization did not result in antigen-specific antibody in either feces or sera but induced the release of IFN-γ on restimulation of primed lymphocytes ex vivo. The results suggested that the protective efficacy provided by flagellin-expressing L. casei is mainly attributable to cell-mediated immune responses. In addition, an adjuvant-type effect of the antigen delivery system with L. casei was also observed.

Engineering bacterial vectors for delivery of genes and proteins to antigen-presenting cells

Bacterial vectors offer a biological route to gene and protein delivery with this article featuring delivery to antigen-presenting cells (APCs). Primarily in the context of immune stimulation against infectious disease or cancer, the goal of bacterially mediated delivery is to overcome the hurdles to effective macromolecule delivery. This review will present several bacterial vectors as macromolecule (protein or gene) delivery devices with both innate and acquirable (or engineered) biological features to facilitate delivery to APCs. The review will also present topics related to large-scale manufacture, storage, and distribution that must be considered if the bacterial delivery devices are ever to be used in a global market.

Listeria monocytogenes mutants carrying Newcastle disease virus F gene fused to its actA and plcB: in vitro expression and immunogenicity in chickens

Recombinant Listeria monocytogenes mutants carrying Newcastle disease virus (NDV) fusion protein gene F were constructed by homologous recombination. NDV F or its truncated fragment Fa was used as the model heterologous gene to be integrated into actA or plcB downstream of their signal sequences. Correct orientation of the inserted genes was verified by polymerase chain reaction amplification of F or Fa. The inserted F and Fa were expressed in the two recombinants Lm-DeltaactA-F and Lm-DeltaplcB-Fa as shown by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. Both recombinants exhibited reduced virulence to embryonated eggs and mice by about 1.5-2.5 logs as compared with the parent wild strain 10403S. They were also less invasive than strain 10403S (P<0.05). Chickens receiving the recombinant strains orally or intraperitoneally were partially protected from virulent NDV challenge possibly due to enhancement of non-specific immunity because the antibody titers against the homologous virus strain or the recombinant truncated fusion protein were marginal. Further research is needed in other animal models to see if the low antibody response results from insufficient expression of the heterologous genes as a result of failure of L. monocytogenes or its recombinants to persist or replicate in chickens.

Listeria monocytogenes as a vector for tumor-associated antigens for cancer immunotherapy

As a facultative intracellular bacterium, Listeria monocytogenes has adapted to live within the cytosol of the host cell. It is actively taken up by antigen-presenting cells through phagocytosis, and as Listeria survive within these cells, it is an ideal vector for the delivery of antigens to be processed and presented through both the class I and II antigen-processing pathways. Once phagocytosed, Listeria produces virulence factors within the phagolysosome of the host cell, which allows it to break out of this organelle and live in the host cytosol. It is possible that these virulence factors can enhance the immunogenicity of tumor-associated antigens, which are poorly immunogenic. Recent progress in the development of this bacterium as a vaccine vector for tumor-associated antigens is discussed in the context of bacterial vectors in general. In several mouse models, Listeria-based vaccines have been demonstrated to be an effective method of influencing tumor growth and eliciting potent antitumor immune responses. Safety issues and the transition of Listeria into human clinical trials will also be discussed in this review.

Vaginal protection and immunity after oral immunization of mice with a novel vaccine strain of Listeria monocytogenes expressing human immunodeficiency virus type 1 gag

Natural transmission of human immunodeficiency virus (HIV) occurs at mucosal surfaces. During acute infection, intestinal and other mucosae are preferential sites of virus replication and rapidly become depleted of CD4(+) T cells. Therefore, mucosal immunity may be critical to control both initial infection and the massive early spread of virus. An attenuated D-alanine-requiring strain of the oral intracellular microorganism Listeria monocytogenes expressing HIV type 1 gag was shown to induce protective cell-mediated immunity in mice against viruses that express HIV gag when immunization occurs in the presence of a transient supply of D-alanine. In this study, we examined the efficacy of new attenuated strains that are able to synthesize d-alanine from a heterologous dal gene tightly regulated by an actA-promoted resolvase recombination system. In the absence of d-alanine, Gag-specific cytotoxic T lymphocytes (CTLs) were induced systemically after intravenous immunization, and one strain, Lmdd-gag/pARS, induced strong dose-dependent Gag-specific CTLs after oral immunization. A significant level of Gag-specific CD8(+) T cells was induced in the mucosal-associated lymphoid tissues (MALTs). Upon intravaginal challenge of these orally immunized mice with recombinant vaccinia virus (rVV) expressing HIV gag, gamma interferon- and tumor necrosis factor alpha-secreting Gag-specific CD8(+) T cells were dramatically increased in the spleen and MALTs. Oral immunization with Lmdd-gag/pARS led to complete protection against vaginal challenge by a homologous clade B gag-expressing rVV. In addition, strong cross-clade protection was seen against clades A and C and partial protection against clade G gag-expressing rVV. These results suggest that Lmdd-gag/pARS may be considered as a novel vaccine candidate for use against HIV/AIDS.

Evaluation of fowlpox–vaccinia virus prime-boost vaccine strategies for high-level mucosal and systemic immunity against HIV-1

We have tested the efficacy of recombinant fowl pox (rFPV) and recombinant vaccinia virus (rVV) encoding antigens of AE clade HIV-1 in a prime-boost strategy, using both systemic and mucosal delivery routes. Of the various vaccine routes tested, intranasal/intramuscular (i.n./i.m.) AE FPV/AE VV prime-boosting generated the highest mucosal and systemic T cell responses. Peak mucosal T cell responses occurred as early as 3 days post-boost vaccination. In contrast only low systemic responses were observed at this time with the peak response occurring at day 7. Current data also revealed that, due to better uptake of the rFPV, intranasal viral priming was much more effective than intranasal rDNA priming tested previously. The i.m./i.m. prime-boost delivery also generated strong systemic but poor mucosal responses to Gag peptides. Interestingly, the oral administration of AE FPV followed by i.m. AE VV delivery elicited strong systemic responses to sub-dominant Pol 1 peptides that were absent in mice that received vaccine by other routes. Moreover, priming with AE FPV co-expressing cytokine IL-12 significantly enhanced the T cell responses to target antigens, whilst co-expression of IFNgamma decreased these responses. The results also indicated that the route of inoculation and the vaccine vector combination could radically influence not only the magnitude but also the antigen specificity of the immune response generated. Further, in contrast to the generally protracted HIV rDNA/rFPV multiple delivery prime-boosting, this single rFPV prime and rVV boost approach was more flexible and generated excellent mucosal and systemic immune responses to HIV vaccine antigens.

Multimeric soluble CD40 ligand and GITR ligand as adjuvants for human immunodeficiency virus DNA vaccines

For use in humans, human immunodeficiency virus (HIV) DNA vaccines may need to include immunostimulatory adjuvant molecules. CD40 ligand (CD40L), a member of the tumor necrosis factor (TNF) superfamily (TNFSF), is one candidate adjuvant, but it has been difficult to use because it is normally expressed as a trimeric membrane molecule. Soluble trimeric forms of CD40L have been produced, but in vitro data indicate that multimeric, many-trimer forms of soluble CD40L are more active. This multimerization requirement was evaluated in mice using plasmids that encoded either 1-trimer, 2-trimer, or 4-trimer soluble forms of CD40L. Fusion with the body of Acrp30 was used to produce the 2-trimer form, and fusion with the body of surfactant protein D was used to produce the 4-trimer form. Using plasmids for secreted HIV-1 antigens Gag and Env, soluble CD40L was active as an adjuvant in direct proportion to the valence of the trimers (1 < 2 < 4). These CD40L-augmented DNA vaccines elicited strong CD8(+) T-cell responses but did not elicit significant CD4(+) T-cell or antibody responses. To test the applicability of the multimeric fusion protein approach to other TNFSFs, a 4-trimer construct for the ligand of glucocorticoid-induced TNF family-related receptor (GITR) was also prepared. Multimeric soluble GITR ligand (GITRL) augmented the CD8(+) T-cell, CD4(+) T-cell, and antibody responses to DNA vaccination. In summary, multimeric CD40L and GITRL are new adjuvants for DNA vaccines. Plasmids for expressing multimeric TNFSF fusion proteins permit the rapid testing of TNFSF molecules in vivo.

Killed but metabolically active microbes: a new vaccine paradigm for eliciting effector T-cell responses and protective immunity

We developed a new class of vaccines, based on killed but metabolically active (KBMA) bacteria, that simultaneously takes advantage of the potency of live vaccines and the safety of killed vaccines. We removed genes required for nucleotide excision repair (uvrAB), rendering microbial-based vaccines exquisitely sensitive to photochemical inactivation with psoralen and long-wavelength ultraviolet light. Colony formation of the nucleotide excision repair mutants was blocked by infrequent, randomly distributed psoralen crosslinks, but the bacterial population was able to express its genes, synthesize and secrete proteins. Using the intracellular pathogen Listeria monocytogenes as a model platform, recombinant psoralen-inactivated Lm DeltauvrAB vaccines induced potent CD4(+) and CD8(+) T-cell responses and protected mice against virus challenge in an infectious disease model and provided therapeutic benefit in a mouse cancer model. Microbial KBMA vaccines used either as a recombinant vaccine platform or as a modified form of the pathogen itself may have broad use for the treatment of infectious disease and cancer.

The challenges of HIV vaccine development and testing

A vaccine against HIV remains the best hope for bringing the epidemic under control. An intensive global effort is underway to develop such a vaccine; however, the challenges are considerable. Several new vaccine technologies that have been developed and shown promise in animal models are now being tested in early phase safety trials in humans. Because there is no laboratory assay that will predict whether an HIV vaccine can protect humans from infection, clinical trials involving thousands of volunteers will need to be conducted to determine the efficacy of HIV vaccines. These trials need to take place in the developing countries that bear the burden of the epidemic, requiring a substantial amount of infrastructure development and capacity building.

Pseudovirion particle production by live poxvirus human immunodeficiency virus vaccine vector enhances humoral and cellular immune responses

Live-vector-based human immunodeficiency virus (HIV) vaccines are an integral part of a number of HIV vaccine regimens currently under evaluation. Live vectors that carry an intact gag gene are capable of eliciting HIV pseudovirion particle formation from infected host cells. The impact of pseudovirion particle formation on the immune response generated by live HIV vaccine vectors has not been established. In this study, a canarypox HIV vaccine candidate vector expressing HIV gag and env genes, vCP205, was modified by the introduction of a glycine-to-alanine coding change in the N-terminal myristylation site of gag to create Myr- vCP205. This substitution effectively eliminated particle formation without altering the level of protein production. vCP205 and Myr- vCP205 were then directly compared for the ability to induce HIV-specific immune responses in mice. The particle-competent vector vCP205 elicited higher levels of CD8+ T-cell responses, as indicated by gamma interferon enzyme-linked immunospot (ELISPOT) assay and intracellular cytokine staining. Humoral responses to Gag and Env were also markedly higher from animals immunized with the particle-competent vector. Furthermore, HIV-specific CD4+ T-cell responses were greater among animals immunized with the particle-competent vector. Using a human dendritic cell model of antigen presentation in vitro, vCP205 generated greater ELISPOT responses than Myr- vCP205. These results demonstrate that pseudovirion particle production by live-vector HIV vaccines enhances HIV-specific cellular and humoral immune responses.

DNA prime Listeria boost induces a cellular immune response to SIV antigens in the rhesus macaque model that is capable of limited suppression of SIV239 viral replication

DNA vaccines and recombinant Listeria monocytogenes that express and secrete SIV Gag and Env antigens were combined in a nonhuman primate prime-boost immunogenicity study followed by a challenge with SIV239. We report that recombinant DNA vaccine delivered intramuscularly, and recombinant L. monocytogenes delivered orally each individually have the ability to induce CD8+ and CD4+ T cell immune responses in a nonhuman primate. Four rhesus monkeys were immunized at weeks 0, 4, 8, and 12 with the pCSIVgag and pCSIVenv DNA plasmids and boosted with SIV expressing L. monocytogenes vaccines at weeks 16, 20, and 28. Four rhesus monkeys received only the L. monocytogenes vaccines at weeks 16, 20, and 28. A final group of monkeys served as a control group. Blood samples were taken before vaccination and 2 weeks post each injection and analyzed by ELISPOT for CD4+ and CD8+ T cell responses. Moderate vaccine induced SIV-specific cellular immune responses were observed following immunization with either DNA or L. monocytogenes vectors. However, the SIV antigen-specific immune responses were significantly increased when Rhesus macaques were primed with SIV DNA vaccines and boosted with the SIV expressing L. monocytogenes vectors. In addition, the combined vaccine was able to impact SIV239 viral replication following an intrarectal challenge. This study demonstrates for the first time that oral L. monocytogenes can induce a cellular immune response in a nonhuman primate and is able to enhance the efficacy of a DNA vaccine as well as provide modest protection against SIV239 challenge.

SIVmac Gag p27 capsid protein gene expression in potato

A cDNA encoding the Simian immunodeficiency virus type (SIV(mac)) Gag capsid protein was introduced into Solanum tuberosum cells by Agrobacterium tumefaciens-mediated transformation methods. The gag gene was detected in the genomic DNA of transformed leaf tissues by PCR DNA amplification. Immunoblot analysis of transformed potato plant extracts with anti-Gag monoclonal antibody showed that biologically active Gag protein was synthesized in transformed tuber tissues. Based on ELISA results, recombinant Gag protein made up 0.006-0.014% of total soluble tuber protein. The synthesis of SIV Gag in transformed potato tubers opens the way for development of Gag-based edible plant vaccines for protection against SIV and potentially HIV-1 infection.

Oral immunization with recombinant listeria monocytogenes controls virus load after vaginal challenge with feline immunodeficiency virus

Recombinant Listeria monocytogenes has many attractive characteristics as a vaccine vector against human immunodeficiency virus (HIV). Wild-type and attenuated Listeria strains expressing HIV Gag have been shown to induce long-lived mucosal and systemic T-cell responses in mice. Using the feline immunodeficiency virus (FIV) model of HIV we evaluated recombinant L. monocytogenes in a challenge system. Five cats were immunized with recombinant L. monocytogenes that expresses the FIV Gag and delivers an FIV Env-expressing DNA vaccine (LMgag/pND14-Lc-env). Control cats were either sham immunized or immunized with wild-type L. monocytogenes (LM-wt). At 1 year after vaginal challenge, provirus could not be detected in any of the nine tissues evaluated from cats immunized with the recombinant bacteria but was detected in at least one tissue in 8 of 10 control animals. Virus was isolated from bone marrow of four of five LMgag/pND14-Lc-env-immunized cats by use of a stringent coculture system but required CD8(+) T-cell depletion, indicating CD8(+) T-cell suppression of virus replication. Control animals had an inverted CD4:CD8 ratio in mesenteric lymph node and were depleted of both CD4(+) and CD8(+) intestinal epithelial T cells, while LMgag/pND14-Lc-env-immunized animals showed no such abnormalities. Vaginal FIV-specific immunoglobulin A was present at high titer in three LMgag/pND14-Lc-env-immunized cats before challenge and in all five at 1 year postchallenge. This study demonstrates that recombinant L. monocytogenes conferred some control of viral load after vaginal challenge with FIV.