Generation of heat shock protein-based vaccines by intracellular loading of gp96 with antigenic peptides

Immunosurveillance of cancer and the heat shock protein-CD91 pathway

The intracellular functions of heat shock proteins (HSPs) as chaperones of macromolecules are well known. Current observations point to a role of these chaperones in initiating and modulating immune responses to tumors via receptor(s) on dendritic cells. In this article we provide an insight into, and a basis for, the importance of these HSP-mediated immune responses in rejecting nascent and emerging tumors.

A 14-Protein Signature for Rapid Identification of Poor Prognosis Stage III Metastatic Melanoma

PURPOSE

To validate differences in protein levels between good and poor prognosis American Joint Committee on Cancer (AJCC) stage III melanoma patients and compile a protein panel to stratify patient risk.

EXPERIMENTAL DESIGN

Protein extracts from melanoma metastases within lymph nodes in patients with stage III disease with good (n = 16, >4 years survival) and poor survival (n = 14, <2 years survival) were analyzed by selected reaction monitoring (SRM). Diagonal Linear Discriminant Analysis (DLDA) was performed to generate a protein biomarker panel.

RESULTS

SRM analysis identified ten proteins that were differentially abundant between good and poor prognosis stage III melanoma patients. The ten differential proteins were combined with 22 proteins identified in our previous work. A panel of 14 proteins was selected by DLDA that was able to accurately classify patients into prognostic groups based on levels of these proteins.

CONCLUSIONS AND CLINICAL RELEVANCE

The ten differential proteins identified by SRM have biological significance in cancer progression. The final signature of 14 proteins identified by SRM could be used to identify AJCC stage III melanoma patients likely to have poor outcomes who may benefit from adjuvant systemic therapy.

Functions of heat shock proteins in pathways of the innate and adaptive immune system

For more than 50 years, heat shock proteins (HSPs) have been studied for their role in protecting cells from elevated temperature and other forms of stress. More recently, several roles have been ascribed to HSPs in the immune system. These include intracellular roles in Ag presentation and expression of innate receptors, as well as extracellular roles in tumor immunosurveillance and autoimmunity. Exogenously administered HSPs can elicit a variety of immune responses that have been used in immunotherapy of cancer, infectious diseases, and autoimmune disease.

Heat-shock proteins as dendritic cell-targeting vaccines--getting warmer

Heat-shock proteins (hsp) provide a natural link between innate and adaptive immune responses by combining the ideal properties of antigen carriage (chaperoning), targeting and activation of antigen-presenting cells (APC), including dendritic cells (DC). Targeting is achieved through binding of hsp to distinct cell surface receptors and is followed by antigen internalization, processing and presentation. An improved understanding of the interaction of hsp with DC has driven the development of numerous hsp-containing vaccines, designed to deliver antigens directly to DC. Studies in mice have shown that for cancers, such vaccines generate impressive immune responses and protection from tumour challenge. However, translation to human use, as for many experimental immunotherapies, has been slow partly because of the need to perform trials in patients with advanced cancers, where demonstration of efficacy is challenging. Recently, the properties of hsp have been used for development of prophylactic vaccines against infectious diseases including tuberculosis and meningitis. These hsp-based vaccines, in the form of pathogen-derived hsp-antigen complexes, or recombinant hsp combined with selected antigens in vitro, offer an innovative approach against challenging diseases where broad antigen coverage is critical.

Plant heat shock protein 70 as carrier for immunization against a plant-expressed reporter antigen

Mammalian Heat Shock Proteins (HSP), have potent immune-stimulatory properties due to the natural capability to associate with polypeptides and bind receptors on antigen presenting cells. The present study was aimed to explore whether plant HSP, and in particular HSP70, share similar properties. We wanted in particular to evaluate if HSP70 extracted in association to naturally bound polypeptides from plant tissues expressing a recombinant "reporter" antigen, carry antigen-derived polypeptides and can be used to activate antigen-specific immune responses. This application of HSP70 has been very poorly investigated so far. The analysis started by structurally modeling the plant protein and defining the conditions that ensure maximal expression levels and optimal recovery from plant tissues. Afterwards, HSP70 was purified from Nicotiana benthamiana leaves transiently expressing a heterologous "reporter" protein. The purification was carried out taking care to avoid the release from HSP70 of the polypeptides chaperoned within plant cells. The evaluation of antibody titers in mice sera subsequent to the subcutaneous delivery of the purified HSP70 demonstrated that it is highly effective in priming humoral immune responses specific to the plant expressed "reporter" protein. Overall results indicated that plant-derived HSP70 shares structural and functional properties with the mammalian homologue. This study paves the way to further investigations targeted at determining the properties of HSP70 extracted from plants expressing foreign recombinant antigens as a readily available immunological carrier for the efficient delivery of polypeptides derived from these antigens.

Role of heat shock proteins in diseases and their therapeutic potential

Heat shock proteins are ubiquitously expressed intracellular proteins and act as molecular chaperones in processes like protein folding and protein trafficking between different intracellular compartments. They are induced during stress conditions like oxidative stress, nutritional deficiencies and radiation. They are released into extracellular compartment during necrosis. However, recent research findings highlights that, they are not solely present in cytoplasm, but also released into extracellular compartment during normal conditions and even in the absence of necrosis. When present in extracellular compartment, they have been shown to perform various functions like antigen presentation, intercellular signaling and induction of pro-inflammatory cytokines. Heat shock proteins represents as dominant microbial antigens during infection. The phylogenetic similarity between prokaryotic and eukaryotic heat shock proteins has led to proposition that, microbial heat shock proteins can induce self reactivity to host heat shock proteins and result in autoimmune diseases. The self-reactivity of heat shock proteins protects host against disease by controlling induction and release of pro-inflammatory cytokines. However, antibodies to self heat shock proteins haven been implicated in pathogenesis of autoimmune diseases like arthritis and atherosclerosis. Some heat shock proteins are potent inducers of innate and adaptive immunity. They activate dendritic cells and natural killer cells through toll-like receptors, CD14 and CD91. They play an important role in MHC-antigen processing and presentation. These immune effector functions of heat shock proteins are being exploited them as therapeutic agents as well as therapeutic targets for various infectious diseases and cancers.

Lymphoid neoplastic P388D1 cells express membrane protein candidates that discriminate among the C-terminal phylogenetic diversity in heat shock protein 70 sequences

We previously found that mouse inducible Hsp72 bound more extensively to lymphoblast-like lymphoid neoplastic P388D1 cells than to RAW264.7 monocyte-macrophages. In the present study, we analyzed the characteristics of the binding to P388D1 cells of recombinant HSP70 derived from different species. Recombinant mouse inducible-type Hsp72 bound extensively to P388D1 cells in a saturable manner, but not to P815 mastocytoma or EL4 thymoma. Spinach Hsc70-1, highly homologous with mouse Hsp72 in the C-terminal region, also bound to P388D1 cells. In contrast, significant binding was not observed for bacterial DnaK derived from Lactobacillus acidophilus and Escherichia coli which have relatively little homology in this region. Analyses of surface antigens showed that B220, and CD19, but not CD91, LOX-1, and CD40, the HSP70 receptors reported so far, were present on P388D1 cells, suggesting a B-cell lineage for this cell line. A similar discrimination of the diversity between mouse Hsp72 and bacterial DnaK occurred for CD19(+) B cells derived from mouse spleen, Peyer's patches, and mesenteric lymph nodes. The binding of HSP70 to P388D1 cells was partially, but significantly, antagonized by fucoidan and maleylated BSA, implying a few types of scavenger receptors to be responsible for the binding of HSP70 to this cell line. Furthermore, photo-affinity labeling revealed several membrane protein candidates larger than 110kDa to be involved in the recognition of HSP70 molecules. Using a NF-κB-luciferase reporter assay, we found that exogenous HSP70 did not stimulate NF-κB-dependent signal transduction in P388D1 cells. It thus follows that lymphoid neoplastic P388D1 cells express membrane protein candidates that discriminate among the C-terminal sequences of the HSP70 family. The present results indicate that several types of cells in the innate immune system may distinguish among the phylogenetically specific signals in protein molecules.

Molecular mechanisms of IFN-gamma to up-regulate MHC class I antigen processing and presentation

IFN-gamma up-regulates MHC class I expression and antigen processing and presentation on cells, since IFN-gamma can induce multiple gene expressions that are related to MHC class I antigen processing and presentation. MHC class I antigen presentation-associated gene expression is initiated by IRF-1. IRF-1 expression is initiated by phosphorylated STAT1. IFN-gamma binds to IFN receptors, and then activates JAK1/JAK2/STAT1 signal transduction via phosphorylation of JAK and STAT1 in cells. IFN-gamma up-regulates MHC class I antigen presentation via activation of JAK/STAT1 signal transduction pathway. Mechanisms of IFN-gamma to enhance MHC class I antigen processing and presentation were summarized in this literature review.

Heat Shock Protein Vaccines: From Bench to Bedside

Heat shock proteins (HSPs) are immunogenic, with the specificity of the immune response provided by the peptides that they chaperone. Binding of cell surface receptors by HSPs is central to the elicitation of the innate and adaptive immune responses obtained after vaccination and also plays a physiologic role in cross-priming. These effects of HSPs have been exploited in prophylaxis and therapy of cancer and infectious disease. The data obtained from murine studies have been translated into ongoing clinical trials of cancer of which the most recent results are provided here.

Heat shock proteins HSP27 and HSP70 are present in the skin and are important mediators of allergic contact hypersensitivity

Proteomic analysis of murine skin has shown that a variety of heat shock proteins (HSPs) are constitutively expressed in the skin. Using murine allergic contact hypersensitivity as a model, we investigated the role of two heat shock proteins, HSP27 and HSP70, in the induction of cutaneous cell-mediated immune responses. Immunohistochemical examination of skin specimens showed that HSP27 was present in the epidermis and HSP70 was present in both the epidermis and dermis. Inhibition of HSP27 and HSP70 produced a reduction in the 1-fluoro-2,4-dinitrobenzene contact hypersensitivity response and resulted in the induction of Ag-specific unresponsiveness. Treatment of dendritic cell cultures with recombinant HSP27 caused in the up-regulation of IL-1beta, TNF-alpha, IL-6, IL-12p70, and IL-12p40 but not IL-23p19, which was inhibited when Abs to HSP27 were added. The 1-fluoro-2,4-dinitrobenzene-conjugated dendritic cells that had been treated with HSP27 had an increased capacity to initiate contact hypersensitivity responses compared with control dendritic cells. This augmented capacity required TLR4 signaling because neither cytokine production by dendritic cells nor the increased induction of contact hypersensitivity responses occurred in TLR4-deficient C3H/HeJ mice. Our findings indicate that a cascade of events occurs following initial interaction of hapten with the skin that includes increased activity of HSPs, their interaction with TLR4, and, in turn, increased production of cytokines that are known to enhance Ag presentation by T cells. The results suggest that HSPs form a link between adaptive and innate immunity during the early stages of contact hypersensitivity.

Translational research in melanoma

Current treatment of malignant melanoma exemplifies not only the need for translational research but also many of the challenges of moving from bench to bedside. Melanoma remains unique among solid tumors in that its treatment primarily is surgical. Radiation is of limited benefit, and chemotherapy has been disappointing in both the adjuvant and metastatic settings. This leaves clinicians with few options for reducing the chance of recurrence after surgery and for treating unresectable disease. With this in mind, there has been a fervent attempt to identify novel approaches to melanoma therapy and translate them into clinical use.

Heat-shock protein-based vaccines for cancer and infectious disease

Almost 60 years ago, the pioneering work of George Klein and others showed that cancers could be made targets for the immune system. Identification of the tumor targets, known as tumor antigens, became a focus in cancer biology that led to the discovery of the immunological properties of heat-shock proteins (HSPs) in 1986 by Pramod Srivastava and colleagues. Since then, the use of HSPs in the therapeutics of cancer and infectious disease in several clinical trials has been guided by our understanding of the role and effects of HSPs in adaptive and innate immune responses, investigated primarily in mice. This review will highlight the immunological properties of HSPs as we understand them today and review the clinical work on human cancers. Several Phase I and II clinical trials in different types of cancer that have been completed, as well as ongoing Phase III trials, will be summarized.

Cross-presentation of NY-ESO-1 cytotoxic T lymphocyte epitope fused to human heat shock cognate protein 70 by dendritic cells

The cancer-testis antigen NY-ESO-1 has been implicated as one of the most attractive candidates for a cancer vaccine. However, a protein vaccine generally meets inefficient antigen presentation to CD8(+) T cells, which could be overcome by combination with an appropriate adjuvant. Heat shock protein is a natural adjuvant and activates the antigen-presenting cells to channel exogenous antigens into the classical major histocompatibility complex class I antigen-processing pathway (cross-presentation). Therefore, we genetically fused a minigene encompassing the NY-ESO-1 cytotoxic T lymphocyte (CTL) epitope 157-165 (ESO p157-165) to the human heat shock cognate protein 70 (hsc70) and expressed the resulting fusion proteins in Escherichia coli. By using a human leukocyte antigen-A*0201-restricted NY-ESO-1-specific CTL clone, the cross-presentation of ESO p157-165 by monocyte-derived dendritic cells (mo-DC) pulsed with the fusion protein was evaluated. The fusion protein-pulsed mo-DC activates the CTL clone much more efficiently than the free NY-ESO-1 protein-pulsed mo-DC. Moreover, the magnitude of the CTL activity was comparable between ESO p157-165 and the fusion protein of hsc70 and ESO p157-165 (hsc70-ESO p157-165 fusion protein). In addition, the CTL activation induced by the fusion protein, but not by the epitope, was inhibited by paraformaldehyde fixation of the mo-DC and by treatment with lactacystin, a specific inhibitor for the proteasome. Finally, the hsc70-ESO p157-165 fusion protein-pulsed DC was able to induce an antigen-specific T-cell response. These results suggest that the hsc70-ESO p157-165 fusion protein is therefore considered to be a promising candidate as a cancer vaccine.

Enhanced immunogenicity of heat shock protein 70 peptide complexes from dendritic cell-tumor fusion cells

We have developed a molecular chaperone-based tumor vaccine that reverses the immune tolerance of cancer cells. Heat shock protein (HSP) 70 extracted from fusions of dendritic (DC) and tumor cells (HSP70.PC-F) possess superior properties such as stimulation of DC maturation and T cell proliferation over its counterpart from tumor cells. More importantly, immunization of mice with HSP70.PC-F resulted in a T cell-mediated immune response including significant increase of CD8 T cells and induction of the effector and memory T cells that was able to break T cell unresponsiveness to a nonmutated tumor Ag and provide protection of mice against challenge with tumor cells. By contrast, the immune response to vaccination with HSP70-PC derived from tumor cells is muted against such nonmutated tumor Ag. HSP70.PC-F complexes differed from those derived from tumor cells in a number of key manners, most notably, enhanced association with immunologic peptides. In addition, the molecular chaperone HSP90 was found to be associated with HSP70.PC-F as indicated by coimmunoprecipitation, suggesting ability to carry an increased repertoire of antigenic peptides by the two chaperones. Significantly, activation of DC by HSP70.PC-F was dependent on the presence of an intact MyD88 gene, suggesting a role for TLR signaling in DC activation and T cell stimulation. These experiments indicate that HSP70-peptide complexes (PC) derived from DC-tumor fusion cells have increased their immunogenicity and therefore constitute an improved formulation of chaperone protein-based tumor vaccine.

Molecular chaperones and cancer immunotherapy

As one of the most abundant and evolutionally conserved intracellular proteins, heat shock proteins, also known as stress proteins or molecular chaperones, perform critical functions in maintaining cell homeostasis under physiological as well as stress conditions. Certain chaperones in extracellular milieu are also capable of modulating innate and adaptive immunity due to their ability to chaperone polypeptides and to interact with the host's immune system, particularly professional antigen-presenting cells. The immunomodulating properties of chaperones have been exploited for cancer immunotherapy. Clinical trials using chaperone-based vaccines to treat various malignancies are ongoing.

A novel anticancer approach: SEA-anchored tumor cells expressing heat shock protein 70 onto the surface elicit strong anticancer efficacy

Heat shock proteins (HSP) are attractive for their initiation of anticancer specific immunity via a distinct mechanism. To facilitate the induction process, we targeted HSP onto vaccine cell surface genetically. Then, SEA (a typical superantigen) was anchored on the cells by its fusion protein with transmembrane sequence, in order to produce immune-activated microsurrounding for further improvement of specific immunity. Thereby, the dual-modified vaccine, the surface-targeting-HSP70 and SEA-anchored vaccine, was developed successfully. Both in a therapeutic setting and in a pre-immune model, the mice vaccinated with the dual-modified vaccine displayed significant lymphocyte proliferation, higher NK and CTL activity, marked tumor suppression and prolonged survival when compared with those vaccinated with the vaccine modified alone with surface-targeting HSP70 or the SEA-anchored vaccine. Of all the vaccines, the dual-modified vaccine generated the best therapeutic efficacy on melanoma-bearing mice, the strongest protection against melanoma challenge. These results suggested that the dual-modified vaccine could induce more potent anticancer specific immunity while non-specific immunity was augmented.

Heat shock protein 70/MAGE-3 fusion protein vaccine can enhance cellular and humoral immune responses to MAGE-3 in vivo

MAGE-3, a member of melanoma antigen (MAGE) gene family, is recognized as an ideal candidate for tumor vaccine because it is expressed in a significant proportion of tumors of various histological types and can induce antigen-specific immune response in vivo. There is now substantial evidence that heat shock proteins HSPs isolated from cancer cells and virus-infected cells can be used as vaccines to produce cancer-specific or virus-specific immunity. In this research, we investigated whether M. tuberculosis HSP70 can be used as vehicle to elicit immune response to its accompanying MAGE-3 protein. A recombinant protein expression vector was constructed that permitted the production of fusion protein linking amino acids 195-314 of MAGE-3 to the C terminus of HSP70. We found that HSP70-MAGE-3 fusion protein can elicit stronger cellular and humoral immune responses against MAGE-3 expressing murine tumor than those elicited by MAGE-3 protein in vivo, which resulted in potent antitumor immunity against MAGE-3-expressing tumors. Covalent linkage of HSP70 to MAGE-3 was necessary to elicit immune response to MAGE-3. These results indicate that linkage of HSP70 to MAGE-3 enhanced immune responses to MAGE-3 in vivo and HSP70 can be exploited to enhance the cellular and humoral immune responses against any attached tumor-specific antigens.

Vaccines that facilitate antigen entry into dendritic cells

Although vaccines have been highly successful in preventing and treating many infectious diseases (including smallpox, polio and diphtheria) diseases prevalent in the developing world such as malaria and HIV, that suppress the host immune system, require new, multiple strategies that will be defined by our growing understanding of specific immune activation. The definition of adjuvants, previously thought of as any substance that enhanced the immunogenicity of antigen, could now include soluble mediators and antigenic carriers that interact with surface molecules present on DC (e.g. LPS, Flt3L, heat shock protein) particulate antigens which are taken up by mechanisms available to APC but not other cell types (e.g. immunostimulatory complexes, latex, polystyrene particles) and viral/bacterial vectors that infect antigen presenting cells (e.g. vaccinia, lentivirus, adenovirus). These approaches, summarized herein, have shown potential in vaccinating against disease in animal models, and in some cases in humans. Of these, particle-antigen conjugates provide rapid formulation of the vaccine, easy storage and wide application, with both carrier and adjuvant functions that activate DC. Combined vaccines of the future could use adjuvants such as virus-like particles and particles targeted towards a predominant cellular type or immune response, with target cell activation enhanced by growth factors or maturation signals prior to, or during immunization. Collectively, these new additions to adjuvant technology provide opportunities for more specific immune regulation than previously available.

Heat-shock proteins and the host-pathogen interaction during bacterial infection

Heat-shock proteins (HSPs) are expressed at high levels by bacterial pathogens during adaptation to intracellular survival. Both host and pathogen heat-shock proteins contribute to immunity by receptor-mediated activation of the innate immune response and by participation in the presentation of antigens for the adaptive immune response. Manipulation of these interactions presents a potential route to improved control of infection by vaccination or immunotherapy.

Induction of BCR-ABL-specific immunity following vaccination with chaperone-rich cell lysates derived from BCR-ABL+ tumor cells

We have previously reported that chaperonerich cell lysates (CRCL) derived from the BCR-ABL+ 12B1 leukemia activate dendritic cells (DCs) and stimulate leukemia-specific immune responses. Because CRCL contain a variety of heat shock/chaperone proteins, we theorized that CRCL obtained from BCR-ABL+ leukemias are likely to chaperone BCR-ABL-derived fusion peptides and that DCs pulsed with 12B1 CRCL could cross-present BCR-ABL fusion peptides to T cells. We found that splenocytes from mice vaccinated with BCR-ABL+ leukemia-derived CRCL secreted interferon-gamma (IFN-gamma) when restimulated with a BCR-ABL peptide, GFKQSSKAL, indicating that BCR-ABL peptides are chaperoned by leukemia-derived CRCL. We next eluted peptides from 12B1 leukemia-derived CRCL and used high-pressure liquid chromatography (HPLC) fractions to restimulate splenocytes harvested from mice vaccinated with DC/GFKQSSKAL or DC/12B1 CRCL. We found that the same peptide fractions derived from 12B1 CRCL and from "refractionated" GFKQSSKAL stimulated IFN-gamma production, suggesting the presence of BCR-ABL peptides in the peptide repertoire of 12B1 CRCL. We also demonstrated that immunization with DCs loaded with leukemia-derived CRCL induced BCR-ABL-specific cytotoxic T lymphocytes (CTLs) in vivo. Moreover, mice immunized with DCs pulsed with 12B1-derived CRCL had superior survival (60%) when compared with those immunized with DCs pulsed with BCR-ABL peptide (20%), indicating that CRCL vaccines provide additional immune stimulus over and above individual peptide vaccination.

Heat shock protein 70 / MAGE-1 tumor vaccine can enhance the potency of MAGE-1-specific cellular immune responses in vivo

The cancer-testis antigen encoded by the MAGE-1 gene is an attractive antigen in tumor immunotherapy because it can be processed as a foreign antigen by the immune system and generate tumor-specific cellular immune response in vivo. However, increase of the potency of MAGE-1 DNA vaccines is still needed. The high degree of sequence homology and intrinsic immunogenicity of heat shock protein 70 (HSP70) have prompted the suggestion that HSP70 might have immunotherapeutic potential, as HSP70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen-presenting cells to elicit peptide-specific immunity. In this research, we evaluated the enhancement of linkage of Mycobacterium tuberculosis HSP70 to MAGE-1 gene of the potency of antigen-specific immunity elicited by naked DNA vaccines. We found that vaccines containing MAGE-1-HSP70 fusion genes enhanced the frequency of MAGE-1-specific cytotoxic T cells in contract to vaccines containing the MAGE-1 gene alone. More importantly, the fusion converted a less effective DNA vaccine into one with significant potency against established MAGE-1-expressing tumors. These results indicate that linkage of HSP70 to MAGE-1 gene may greatly enhance the potency of DNA vaccines, and generate specific antitumor immunity against MAGE-1-expressing tumors.

Glucose-regulated protein 94/glycoprotein 96 elicits bystander activation of CD4+ T cell Th1 cytokine production in vivo

Glucose-regulated protein 94 (GRP94/gp96), the endoplasmic reticulum heat shock protein 90 paralog, elicits both innate and adaptive immune responses. Regarding the former, GRP94/gp96 stimulates APC cytokine expression and dendritic cell maturation. The adaptive component of GRP94/gp96 function reflects a proposed peptide-binding activity and, consequently, a role for native GRP94/gp96-peptide complexes in cross-presentation. It is by this mechanism that tumor-derived GRP94/gp96 is thought to suppress tumor growth and metastasis. Recent data have demonstrated that GRP94/gp96-elicited innate immune responses can be sufficient to suppress tumor growth and metastasis. However, the immunological processes activated in response to tumor Ag-negative sources of GRP94/gp96 are currently unknown. We have examined the in vivo immunological response to nontumor sources of GRP94/gp96 and report that administration of syngeneic GRP94/gp96- or GRP94/gp96-N-terminal domain-secreting KBALB fibroblasts to BALB/c mice stimulates CD11b(+) and CD11c(+) APC function and promotes bystander activation of CD4(+) T cell Th1 cytokine production. Only modest activation of CD8(+) T cell or NK cell cytolytic function was observed. The GRP94/gp96-dependent induction of CD4(+) T cell cytokine production was markedly inhibited by carrageenan, indicating an essential role for APC in this response. These results identify the bystander activation of CD4(+) T lymphocytes as a previously unappreciated immunological consequence of GRP94/gp96 administration and demonstrate that GRP94/gp96-elicited alterations in the in vivo cytokine environment influence the development of CD4(+) T cell effector functions, independently of its proposed function as a peptide chaperone.

Heat shock proteins: to present or not, that is the question

The contribution of major histocompatibility complex (MHC) I and II to the adaptive immune response has been well documented. In 1996, Peter Doherty and Rolf Zinkernagel were awarded the Nobel Prize, for their fundamental observations concerning the genetic elements involved in specific antigen (Ag) recognition. These elements encode molecules that present self and non-self peptide fragments to both CD4+ and CD8+ cytolytic T lymphocytes (CTL). The recognition by Srivastava and coworkers that heat shock proteins (HSPs) might also present Ag in chemically induced sarcomas brought about many new questions concerning the central dogma of Ag processing and presentation. HSPs, in particular glucose-regulated peptide 94 (GRP94), HSP70 and to a lesser extent HSP90, bind peptides that are immunogenic in vitro and in vivo. There is mounting evidence that these HSP-peptide complexes provide alternative Ag-specific recognition in many systems. Whether a separate genetic program evolved in addition to MHC that increases the antigenic repertoire of the cell or if this newly observed function of HSP is predominantly a laboratory-based phenomena and/or a normal chaperone function of this family of proteins remains to be answered. Nevertheless, there are clinical therapeutic strategies that involve HSP-derived peptides isolated from various tumors that look extremely promising.

DNA vaccines expressing antigens with a stress protein-capturing domain display enhanced immunogenicity

An expression system for DNA vaccines is described, in which a fusion protein with an N-terminal, viral J-domain that captures heat-shock proteins (Hsps) is translated in-frame with C-terminal antigen-encoding sequences (of various lengths and origins). The system supports enhanced expression of chimeric antigens (of >800 residues in length) with an extended half life (>8 h). When used as a DNA vaccine, it delivers antigen together with the intrinsic adjuvant activity provided by bound Hsps. We describe the design of vectors for DNA vaccination that support the expression of different immunogenic domains of different origins as large, Hsp-capturing chimeric fusion antigens. The immunogenicity of the antigens produced by this expression system (when it is built into DNA vaccines) has been characterized in detail, with particular emphasis on priming CD8+ T-cell responses. We also discuss areas of vaccine research to which the new technology may provide useful contributions.

Induction of cytotoxic T lymphocyte activity by immunization with recombinant Semliki Forest virus: indications for cross-priming

For the rational design of vaccines capable of inducing CD8+ T cell responses knowledge of the identity of the antigen-presenting cell (APC) and the mechanism of antigen presentation is very important. Here, we address these issues for alphavirus-based immunization, in particular immunization with recombinant Semliki Forest virus (rSFV). Studies with dendritic cells (DCs) from various origins revealed that rSFV has a very limited capacity to transfect this cell type in vitro. To further investigate in vivo whether rSFV transfects professional antigen-presenting cells directly or whether the antigens reach APCs via a mechanism of cross-priming we compared the immunological effects of three different SFV-constructs encoding the influenza nucleoprotein (NP). These constructs differ in the amount of NP produced per cell or in the stability of the NP, respectively. Induction of cytotoxic T lymphocytes (CTLs) appeared to benefit from a large amount of stable antigen. In contrast, rapid antigen degradation, and thus availability of antigenic peptides in the transfected cell, was found to be disadvantageous. Based on these in vitro and in vivo results, we hypothesize that antigen presentation after SFV-based immunization proceeds via a mechanism in which APCs are not transfected directly but acquire antigen from other transfected cells and present it to CTLs in a process of cross-priming.

Analytical challenges and strategies for the characterization of gp96-associated peptides

This paper describes the methods that were used for the preparation of gp96-associated peptides and the analysis of these peptides using mass spectrometry. A general approach for stripping, enriching, and separating peptides associated with gp96 is presented. Protocols for the demonstration of the diversity of gp96-associated peptides using mass spectrometry and the identification of these peptides using a combination of tandem mass spectrometry and protein database searching are described. Important parameters and factors that affect the outcome of the experiments are discussed.

Facets of heat shock protein 70 show immunotherapeutic potential

Amongst the families of intracellular molecules that chaperone and assist with the trafficking of other proteins, notably during conditions of cellular stress, heat shock protein (hsp) 70 is one of the most studied. Although its name suggests that expression is exclusively induced during cellular hyperthermia, members of the hsp70 family of proteins can be constitutively expressed and/or induced by a range of other cellular insults. The ubiquitous presence of hsp70 in eukaryotic and prokaryotic cells, combined with its high degree of sequence homology and intrinsic immunogenicity, have prompted the suggestion that inappropriate immune reactivity to hsp70 might lead to pro-inflammatory responses and the development of autoimmune disease. Indeed, hsp70 has been shown to be a potent activator of innate immunity and aberrant expression of hsp70 in certain organs promotes immunopathology. However, studies also suggest that hsp70 might have immunotherapeutic potential, as hsp70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen-presenting cells to elicit peptide-specific immunity and, in contrast to its reported pro-inflammatory effects, the administration of recombinant hsp70 can attenuate experimental autoimmune disease. This review focuses on the immunoregulatory capacity of hsp70 and its potential therapeutic value.

Heat shock proteins as regulators of the immune response

Until recently, heat shock proteins (also known as heat stress proteins) have mostly been regarded as intracellular molecules that mediate a range of essential housekeeping and cytoprotective functions. However, interest in their role as intercellular signalling molecules has been fuelled by the observations that these molecules can be released and are present in the extracellular environment under physiological conditions. They can elicit cytokine production by, and adhesion molecule expression of, a range of cell types, and they can deliver maturation signals and peptides to antigen presenting cells through receptor-mediated interactions. These functions suggest that heat shock proteins could be immunoregulatory agents with potent and widely-applicable therapeutic uses. Furthermore, the induction of self heat shock protein immune reactivity can attenuate autoimmunity and delay transplant rejection, and heat shock proteins derived from tumours and pathogens can elicit specific, protective immunity. This review will focus on this rapidly evolving area of heat shock protein biology.

Enhanced priming of multispecific, murine CD8+ T cell responses by DNA vaccines expressing stress protein-binding polytope peptides

A polytope DNA vaccine (pCI/pt10) was used that encodes within a 106-residue sequence 10-well characterized epitopes binding MHC class I molecules encoded by the K, D, or L locus (of H-2(d), H-2(b), and H-2(k) haplotype mice). The pCI/pt10 DNA vaccine efficiently primed all four K(b)/D(b)-restricted CD8(+) T cell responses in H-2(b) mice, but was deficient in stimulating most CD8(+) T cell responses in H-2(d) mice. Comparing CD8(+) T cell responses elicited with the pCI/pt10 DNA vaccine in L(d+) BALB/c and L(d-) BALB/c(dm2) (dm2) mice revealed that L(d)-restricted CD8(+) T cell responses down-regulated copriming of CD8(+) T cell responses to other epitopes regardless of their restriction or epitope specificity. Although the pt10 vaccine could thus efficiently co prime multispecific CD8(+) T cell responses, this priming was impaired by copriming L(d)-restricted CD8(+) T cell responses. When the pt10 sequence was fused to a 77-residue DnaJ-homologous, heat shock protein 73-binding domain (to generate a 183-residue cT(77)-pt10 fusion protein), expression and immunogenicity (for CD8(+) T cells) of the chimeric Ag were greatly enhanced. Furthermore, priming of multispecific CD8(+) T cell responses was readily elicited even under conditions in which the suppressive, L(d)-dependent immunodominance operated. The expression of polytope vaccines as chimeric peptides that endogenously capture stress proteins during in situ production thus facilitates copriming of CD8(+) T cell populations with a diverse repertoire.

Evolution of heat shock protein and immunity

Heat shock proteins (hsps) are among the most abundant intracellular proteins. Their synthesis is rapidly up-regulated by various 'stressors' including temperature, glucose deprivation, infection and cancer. Certain hsps are able to: (i). associate and chaperone a large variety of cellular peptides; (ii). be efficiently internalized by antigen presenting cells (APC) through receptor-mediated endocytosis; (iii). channel antigenic peptides they chaperone in the APC's MHC class I presentation pathway; (iv). and stimulate inflammatory cytokines, chemokines and co-stimulatory molecules through the NFkappab signaling pathway. Extracellular release of hsps upon necrotic cell death and their modulated access at the surface of some cells, can be considered as a putative 'danger' signal. Based on the ancient origins and structural conservation of hsps, it has been proposed that, the role of hsps in immunity emerged early in evolution and to be widespread in extant organisms. Data from studies with the frog Xenopus support this proposition.

Tumor cell membrane-bound heat shock protein 70 elicits antitumor immunity

A novel membrane-bound heat shock protein 70 (mbHSP70) was expressed on the surface of the mouse mastocytoma cell line P815 to enhance immunogenicity of tumor cells. The in vivo effect of mbHSP70 was evaluated by comparing the growth of mbHSP70 cells to that of mock-transfected cells in DBA/2 mice. Fifty percent mice rejected mbHSP70 cells while 100% mice developed tumors in the counterparts. We then tested whether vaccination with these cells would elicit a protective antitumor response by injecting mice with either inactivated mbHSP70 cells or mock-transfected cells and challenging them with wild-type P815 cells. MbHSP70 cells-treated mice grew small tumors that soon disappeared in all animals. In contrast, 60% of animals receiving the mock-transfected cells vaccine grew large tumors and died. Lymphocytes from mbHSP70-vaccinated mice were able to kill wild-type P815 cells, suggesting that the antitumor response involved CTL. However, the activity of NK from mbHSP70 and mock-transfected cells vaccinated mice also increased. It implied that the non-specific immunity was also involved in tumor rejection. These findings indicate that the tumor cell membrane-bound HSP70 can be used as cancer vaccine to elicit protective antitumor immunity.

Selective expression of immunogenic, virus-like particle-derived antibody-binding epitopes

The incorporation of linear and conformational antibody-binding epitopes into polyepitope, chimeric antigens with satisfactory immunogenicity is a challenge. We selectively expressed antigen fragments encoding the linear e2 epitope (C(79-149)) of hepatitis B virus (pre)core antigen (HBc/eAg) and the conformational 'a' epitope (S(80-180)) of hepatitis B surface antigen (HBsAg) in a novel system. The domains were expressed as chimeric antigens containing either heat shock protein (hsp)73-binding simian virus 40 large tumor antigen (e.g. T(77)) or non-hsp-binding (e.g. T(60)) sequences at their N-termini. We compared their type of expression with their immunogenicity for B cells (when delivered as a DNA vaccine). The type of expression investigated included their level of expression, the secretion or intracellular expression of the antigen and the stress protein (hsp)-associated versus nonassociated expression. The linear e2 epitope of HBc/eAg was efficiently expressed as an intracellular, hsp73-binding fusion protein, and efficiently primed an HBc/eAg-specific antibody response when delivered in this form. The conformational 'a' epitope of HBsAg most efficiently stimulated B cells as a secreted, non-hsp-associated fusion protein. These data demonstrate that different B cell-stimulating epitopes of vaccine-relevant viral antigens can be selectively isolated and expressed in suitable expression systems, but that the requirements that have to be fulfilled to obtain optimal immunogenicity differ strikingly between individual epitopes.

Role for heat shock proteins in the immune response to measles virus infection

Heat shock proteins (HSPs) are recognized for their support of protein metabolism. Interaction with viral proteins also enhances the development of innate and adaptive immune responses against the infecting agent. At the level of the infected cell, HSPs are uniquely expressed on the cell surface, where they represent targets of lymphokine activated killer cells. Necrosis of the infected cell releases complexes of HSP and viral protein, which, in turn, binds antigen-presenting cells (APCs). One effect of binding is to stimulate APC maturation and the release of proinflammatory cytokines, an adjuvant effect that prepares the way for adaptive immune responses. A second effect of binding is to direct the antigenic cargo of the HSP into endogenous MHC presentation pathways for priming of naive cytotoxic T cells (CTL) or activation of antigen-specific CTLs. This alternate pathway of antigen presentation is essential to CTL priming following primary brain infection. Using heat shock to elevate brain levels of HSP in a mouse model of measles virus (MV) persistent infection, we provide evidence supporting a role for HSPs in promoting cell-mediated viral clearance from brain. The findings highlight the probable relevance of HSPs to anti-MV immunity, suggesting novel routes of both therapeutic intervention and preventative measures.

Alternative processing of endogenous or exogenous antigens extends the immunogenic, H-2 class I-restricted peptide repertoire

We investigated the murine, MHC class I-restricted cytotoxic T lymphocyte (CTL) response to a viral antigen delivered by different vaccination strategies to either the endogenous, or an alternative exogenous processing pathway. The immunization techniques used primed distinct (though overlapping) repertoires of CTL epitopes. In vitro studies revealed evidence for the generation of immunogenic, L(d)- and K(b)-binding peptides from endocytosed, exogenous antigen by alternative (endolysosomal) processing. Endogenous antigens expressed by DNA vaccines as a stress protein-associated fusion proteins gains access from the cytosol to endolysosomal processing. Hence, exogenous as well as endogenous protein antigens can gain access to alternative processing pathways and can give rise to an extended repertoire of antigenic epitopes. These studies indicate novel ways for the rational design of vaccine candidates that can prime CTL responses.

Priming polyvalent immunity by DNA vaccines expressing chimeric antigens with a stress protein-capturing, viral J-domain

The N-terminal domain of large tumor antigens (T-Ag) of polyomaviruses forms a DnaJ-like structure with a conserved J domain that associates with constitutively expressed stress protein heat shock protein (hsp)73. Mutant (but not wild-type) SV40 T-Ag show stable, ATP-dependent binding to the stress protein hsp73 when expressed in cells from different vertebrate tissues. Intracellular T/hsp73 complexes accumulate to high steady-state levels. From this observation, we designed a vector system that supports stable expression of a large variety of hsp73-capturing, chimeric antigens containing an N-terminal, T-Ag-derived domain, and different C-terminal antigenic domains from unrelated antigens. Most antigenic domains tested could be stably expressed only in eukaryotic cells as fusion protein/hsp73 complexes. The N-terminal 77 residues representing the J domain of T-Ag were required for stable hsp73 binding and efficient expression of chimeric antigens. Hsp73-bound chimeric antigens expressed by DNA vaccines showed strikingly enhanced immunogenicity evident in humoral (antibody) and cellular cytolytic T lymphocytes (CTL) responses. The described system supports efficient expression of chimeric, polyvalent antigens and their codelivery with hsp73 as a "natural adjuvant" for enhanced immunogenicity for T and B cells.

Interaction of heat shock proteins with peptides and antigen presenting cells: chaperoning of the innate and adaptive immune responses

Heat shock proteins are abundant soluble intracellular proteins, present in all cells. Members of the heat shock protein family bind peptides including antigenic peptides generated within cells. Heat shock proteins also interact with antigen presenting cells through CD91 and other receptors, eliciting a cascade of events including re-presentation of heat shock protein-chaperoned peptides by MHC, translocation of NF kappa B into the nuclei and maturation of dendritic cells. These consequences point to a key role of heat shock proteins in fundamental immunological phenomena such as activation of antigen presenting cells, indirect presentation (or cross-priming), and chaperoning of peptides during antigen presentation. Heat shock proteins appear to have been involved in innate immune responses since the emergence of phagocytes in early multicellular organisms and to have been commandeered for adaptive immune responses with the advent of specificity. These properties of heat shock proteins also allow them to be used for immunotherapy of cancers and infections in novel ways.

Roles of heat-shock proteins in innate and adaptive immunity

Heat-shock proteins (HSPs) are the most abundant and ubiquitous soluble intracellular proteins. In single-cell organisms, invertebrates and vertebrates, they perform a multitude of housekeeping functions that are essential for cellular survival. In higher vertebrates, their ability to interact with a wide range of proteins and peptides--a property that is shared by major histocompatibility complex molecules--has made the HSPs uniquely suited to an important role in organismal survival by their participation in innate and adaptive immune responses. The immunological properties of HSPs enable them to be used in new immunotherapies of cancers and infections.

Heat shock protein micro-encapsulation as a double tool for the improvement of new generation vaccines

The modern vaccinology encompasses the recombinant DNA technology, protein and carbohydrate chemistry to obtain safe molecularly defined vaccines. Nevertheless most of the vaccines are poorly immunogenic because a large number of antigens are membrane proteins and consequently they are not present in their active conformation in the vaccine. Others are not as potent because they contain only B epitopes and therefore, cannot stimulate cellular memory. We have been studying the characteristics of the recombinant heat shock protein 18kDa-hsp from Mycobacterium leprae as an alternative carrier protein with a T epitope source to enhance the activity of these second generation vaccines. Here we proved that the 18kDa-hsp acted as carrier, without masking the activity of the carried antigen, with similar immune stimulatory effect when compared with ODN1668. Supramolecular aggregates of 18kDa-hsp and Mice serum albumin (MSA) were obtained using glutaraldehyde as cross linker. The Neisseria meningitides serogroup C polysaccharide (PSC, a B epitope) and the carrier protein 18kDa-hsp were co-encapsulated within Soybean phosphatidylcholine liposomes (SPC: Cho : alpha-Toc, 22 : 5 : 0.18 molar ratio, respectively). These liposomes were prepared in MPB buffer (20 mM phosphate, 295 mM mannitol pH 7.2) in the presence or absence of the ODN1668, TCCATGACGTTCCTGATGCT. When mice were injected with 18kDa-hsp-MSA no antibody against the MSA was observed. This means that the 18kDa-hsp acted as carrier, without masking the carried protein immune activity. Stable liposomes of 150 nm were obtained using mannitol as a cryoprotector. Genetically selected mice when injected with liposomes containing PSC and 18kDa-hsp displayed an antibody titer of 12. In contrast, in those mice injected with free PSC there was no response. The 18kDa-hsp adjuvant effect on the PSC liposomal formulation was comparable to that observed when ODN1668 was co-encapsulated with PSC. Confirming our expectations we observed that the formulation containing 18kDa-hsp conferred a memory response to the carried antigen--the Neisseria meningitidis serogroup C polysaccharide.

Noncovalent association with stress protein facilitates cross-priming of CD8+ T cells to tumor cell antigens by dendritic cells

A viral oncogene carrying well-defined K(b)/D(b)-restricted epitopes was expressed in a heat shock protein (hsp)-associated or nonassociated form in the murine tumor cells P815 and Meth-A. Wild-type SV40 large T-Ag (wtT-Ag) is expressed without stable hsp association; mutant (cytoplasmic cT-Ag) or chimeric (cT272-green fluorescent fusion protein) T-Ag is expressed in stable association with the constitutively expressed, cytosolic hsp73 (hsc70) protein. In vitro, remnants from apoptotic wtT-Ag- or cT-Ag-expressing tumor cells are taken up and processed by immature dendritic cells (DC), and the K(b)/D(b)-binding epitopes T1, T2/3, and T4 of the T-Ag are cross-presented to CTL in a TAP-independent way. DC pulsed with remnants of transfected, apoptotic tumor cells cross-presented the three T-Ag epitopes more efficiently when they processed ATP-sensitive hsp73/cT-Ag complexes than when they processed hsp-nonassociated (native) T-Ag. In vivo, more IFN-gamma-producing CD8+ T cells were elicited by a DNA vaccine that encoded hsp73-binding mutant T-Ag than by a DNA vaccine that encoded native, non-hsp-binding T-Ag. Three- to 5-fold higher numbers of T-Ag (T1-, T2/3-, or T4-) specific, D(b)/K(b)-restricted IFN-gamma-producing CD8+ T cells were primed during the growth of transfected H-2(d) Meth-A/cT tumors than during the growth of transfected Meth-A/T tumors in F(1)(b x d) hosts. Hence, the association of an oncogene with constitutively expressed, cytosolic hsp73 facilitates cross-priming in vitro and in vivo of CTL by DC that process material from apoptotic cells.

Generation of cytotoxic T lymphocytes by MHC class I ligands fused to heat shock cognate protein 70

Immunization with gp96 and heat shock cognate protein 70 (hsc70) purified with in vivo bound naturally occurring peptides or bound to synthetic peptides by in vitro reconstitution has been shown to induce peptide-specific cytotoxic T lymphocytes (CTL). In addition, mycobacterial heat shock protein 70 covalently fused to ovalbumin (OVA)-derived fragments has been shown to generate MHC class I-restricted CTL responses. Here, we genetically fused five different CTL epitopes, including peptides derived from Plasmodium yoelii circumsporozoite protein, tumor antigens, HY antigen and OVA, to either the N- or C-terminus of murine hsc70 and expressed the resulting proteins in Escherichia coli. Vaccination with all five fusion proteins induced peptide-specific CTL, indicating that no cognate flanking regions of CTL epitopes are necessary for the immune response. The point of injection was crucial for CTL induction. CD4(+) T cells were not required for the priming of CD8(+) T cells and vaccination with bone marrow-derived dendritic cells pulsed with hsc70 fusion proteins also elicited CTL responses. Furthermore, by using deletion mutants of hsc70, we identified amino acid residues 280-385 of hsc70 as the region most critical for inducing the CTL response.

gp96-peptide vaccination of mice against intracellular bacteria

This work demonstrates that gp96 preparations isolated from cells infected with intracellular bacteria induce cytotoxic T-lymphocyte responses and confer protection. Our findings extend previous reports on the immunogenicity of gp96-associated peptides to antigens derived from intracellular bacteria. Immunization with gp96 may therefore represent a promising vaccination strategy against bacterial pathogens.

Enhancement of Sindbis virus self-replicating RNA vaccine potency by linkage of Mycobacterium tuberculosis heat shock protein 70 gene to an antigen gene

Recently, self-replicating RNA vaccines (RNA replicons) have emerged as an effective strategy for nucleic acid vaccine development. Unlike naked DNA vaccines, RNA replicons eventually cause lysis of transfected cells and therefore do not raise the concern of integration into the host genome. We evaluated the effect of linking human papillomavirus type 16 E7 as a model Ag to Mycobacterium tuberculosis heat shock protein 70 (HSP70) on the potency of Ag-specific immunity generated by a Sindbis virus self-replicating RNA vector, SINrep5. Our results indicated that this RNA replicon vaccine containing an E7/HSP70 fusion gene generated significantly higher E7-specific T cell-mediated immune responses in vaccinated mice than did vaccines containing the wild-type E7 gene. Furthermore, our in vitro studies demonstrated that E7 Ag from E7/HSP70 RNA replicon-transfected cells can be processed by bone marrow-derived dendritic cells and presented more efficiently through the MHC class I pathway than can wild-type E7 RNA replicon-transfected cells. More importantly, the fusion of HSP70 to E7 converted a less effective vaccine into one with significant potency against E7-expressing tumors. This antitumor effect was dependent on NK cells and CD8(+) T cells. These results indicated that fusion of HSP70 to an Ag gene may greatly enhance the potency of self-replicating RNA vaccines.

Heat shock proteins: the 'Swiss Army Knife' vaccines against cancers and infectious agents

The ability of heat shock proteins to: (a) chaperone peptides, including antigenic peptides; (b) interact with antigen presenting cells through a receptor; (c) stimulate antigen presenting cells to secrete inflammatory cytokines; and (d) mediate maturation of dendritic cells, makes them a one-stop shop for the immune system. These properties also permit the utilization of heat shock proteins for development of a new generation of prophylactic and therapeutic vaccines against cancers and infectious diseases.

Heat shock proteins: the fountainhead of innate and adaptive immune responses

The ability of heat shock proteins to (1) chaperone peptides, including antigenic peptides; (2) interact with antigen-presenting cells through a receptor; (3) stimulate antigen-presenting cells to secrete inflammatory cytokines; and (4) mediate maturation of dendritic cells, makes them a unique starting point for generation of immune responses. These properties also permit the use of heat shock proteins for development of a new generation of prophylactic and therapeutic vaccines against cancers and infectious diseases.

Enhancement of suicidal DNA vaccine potency by linking Mycobacterium tuberculosis heat shock protein 70 to an antigen

Naked DNA vaccines represent an attractive approach for generating antigen-specific immunity because of their stability and simplicity of delivery. There are particular concerns with DNA vaccines however, such as potential integration into the host genome, cell transformation, and limited potency. The usage of DNA-based alphaviral RNA replicons (suicidal DNA vectors) may alleviate the concerns of integration or transformation since suicidal DNA vectors eventually cause lysis of transfected cells. To improve further the potency of suicidal DNA vaccines, we evaluated the effect of linking Mycobacterium tuberculosis heat shock protein 70 (Hsp70) to human papillomavirus type 16 (HPV-16) E7 as a model antigen on antigen-specific immunity generated by a DNA-based Semliki Forest virus (SFV) RNA vector, pSCA1. Our results indicated that this suicidal DNA vaccine containing E7/Hsp70 fusion genes generated significantly higher E7-specific T cell-mediated immune responses than vaccines containing the wild-type E7 gene in vaccinated mice. More importantly, this fusion converted a less effective vaccine into one with significant potency against established E7-expressing metastatic tumors. The antitumor effect was predominantly CD8-dependent. These results indicate that linkage of Hsp70 to the antigen may greatly enhance the potency of suicidal DNA vaccines.

Analysis of the adjuvant effect of recombinant Leishmania infantum Hsp83 protein as a tool for vaccination

The properties of Leishmania infantum hsp83 (LiHsp83) to elicit an immune response against a fused reporter antigen, maltose binding protein (MBP), was studied. CF1 mice were immunized with different purified recombinant proteins: MBP, LiHsp83 and MBP fused to LiHsp83 (MBP-LiHsp83). Serum samples were obtained at days 0, 21, 28, 60, 90, 120 and 150 post-immunization. MBP-LiHsp83 fusion protein elicited a strong humoral response against MBP, higher than that one obtained in mice immunized with MBP alone or MBP mixed with LiHsp83, showing the secretion of both anti-MBP IgG2a and IgG1 isotypes (IgG2a/IgG1 ratio: 2:1). This response was specific for recombinant proteins and was maintained for at least 150 days, whereas the reactivity in mice immunized with MBP alone dissapeared at day 90. After in vitro stimulation with MBP, spleen cells from MBP-LiHsp83 immunized mice showed higher proliferation indices and produced higher secretion of IFN-gamma than spleen cells from either control or MBP-immunized mice. In all groups of mice IL-4 was undetectable. Thus we consider that LiHsp83 may be a promising candidate to be used as carrier of fused antigens for adjuvant-free vaccination.

Biophysical analysis of the endoplasmic reticulum-resident chaperone/heat shock protein gp96/GRP94 and its complex with peptide antigen

Animals vaccinated with heat shock protein (HSP)--peptide complexes develop specific protective immunity against cancers from which the HSPs were originally isolated. This autologous specific immunity has been demonstrated using a number of HSP--peptide antigen complexes. A prototypical HSP-based cancer vaccine is the gp96--peptide antigen complex, which is currently undergoing human clinical trials. Here, we analyzed the structure of a recombinant wild-type and a mutant gp96 protein and their peptide complexes using a number of biophysical techniques. Gel filtration chromatography, dynamic light scattering, and equilibrium analytical ultracentrifugation demonstrated that both a wild-type gp96 and a gp96 mutant lacking a dimerization domain formed higher order structures. More detailed analysis using scanning transmission electron microscopy indicated that both the wild-type and dimerization deletion mutant gp96 protein were organized, unexpectedly, into large aggregates. Size distributions ranged from dimers to octamers and higher. Circular dichroism and intrinsic Trp fluorescence suggested that the gp96 dimerization domain deletion mutant protein was more compact than the wild-type gp96. A fluorescent peptide antigen was synthesized, and the peptide-binding properties of wild-type and the dimerization domain deletion mutant gp96 were studied. Fluorescence lifetime and anisotropy decay showed that the bound antigenic peptide was located in a hydrophobic pocket, with considerable free space for the rotation of the probe. Deletion of the dimerization domain affected the peptide-binding microenvironment, although peptide-binding affinity was reduced by only a small extent. Peptide--gp96 complexes were extremely stable, persisting for many days in the cold. The extraordinary stability of peptide--gp96 complexes and the plasticity of the peptide-binding pocket support the proposed relay of diverse peptides to MHC and/or other molecules via molecular recognition.

Heat shock protein-peptide complexes elicit cytotoxic T-lymphocyte and antibody responses specific for bovine herpesvirus 1

Epitope-based vaccines offer a promising alternative to modified live vaccines against viruses such as herpesviruses which give rise to latent infections, and induce immunosuppression. The success of this approach depends on the ability to direct the CTL epitopes to the MHC class I antigen presentation pathway. The objective of this study was to evaluate the potential of the heat shock protein gp96 in this regard. A group of BALB/c mice was injected with three murine CTL epitope peptides of bovine herpesvirus 1 (BHV-1) complexed in vitro with bovine gp96 (gp96-peptides). Three other groups were injected with either the peptides alone, gp96 alone, or the peptides complexed with BSA. CTLs from mice immunized with gp96-peptides specifically lysed the peptide-pulsed syngeneic targets, as well as BHV-1-infected targets. CTLs from the other three groups did not lyse these targets. To further evaluate the utility of this approach, groups of BALB/c mice were immunized with gp96 isolated from a syngeneic cell-line transduced with BHV-1 glycoprotein D (BC-gD). Mice immunized with gp96 from BC-gD developed CTLs, as well as Abs specific for BHV-1 gD. Furthermore, in vitro stimulation of naive bovine PBMCs with gp96 from BC-gD resulted in CTLs specific for BHV-1. These results demonstrate the feasibility of using gp96-peptide complexes isolated from cells expressing BHV-1 proteins to induce CTL and Ab responses against BHV-1, without the prior knowledge of the CTL and Ab epitope sequences.

Heat shock proteins: novel therapeutic tools for HIV-infection?

Heat shock proteins (Hsps), cyclophilins (Cyps) and FK binding proteins (FKBPs) form a family of intracellular chaperone molecules that facilitate protein folding and assembly. These stress proteins are selectively expressed in cells in response to a range of stimuli, including heat, lymphokine and microbial/viral infections. This review discusses the role of stress proteins in the HIV-1 viral life cycle, with regard to the development of specific Hsp-based therapeutic strategies against HIV-1 infection. Cumulative findings are cited implicating CypA, Hsp27, Hsp70 and FKBPs in host cell and viral activation, viral entry, assembly or formation of infectious virions. Biological response modifiers that show specific high-affinity interactions with Cyp, FKBPs and Hsps, including cyclosporins, FK-506 and cyclopentenone prostaglandins respectively, may block HIV-1 replication and infection, providing novel HIV-1 therapeutic strategies. Moreover, Hsp binding to viral complexes can enhance antiviral immunity, including natural killer (NK), antibody-dependent (ADCC), gamma delta T-cell and cytotoxic T-lymphocyte (CTL) activities against HIV-1 infected cells. The ability of Hsps to interact with HIV-1 viral proteins, combined with their inherent adjuvant and immunogenic properties indicates that Hsps may also serve as vehicles for antigen delivery and the design of AIDS vaccines.