In vitro reconstitution of heat shock protein-peptide complexes for generating peptide-specific vaccines against cancers and infectious diseases

Known commonly as molecular chaperones for proteins, heat shock proteins (HSPs) have also been found to chaperone small molecular weight cellular peptides. HSP-peptide complexes can prime T cell immunity specific against the peptides bound to HSPs, but not against HSPs per se. This immunomodulatory functions of HSPs are based on two intrinsic properties. One, HSPs are excellent adjuvants due to their ability to activate dendritic cells (DCs). Two, HSPs can bind directly to their receptors on DCs to then channel HSP-associated peptides to associate with MHC molecules. When a specific antigenic peptide is defined, this peptide can also be complexed with either tissue derived or recombinant HSPs in vitro to generate HSP-peptide complexes as peptide-specific vaccines. This article focuses on the methods commonly used to reconstitute HSP-peptide complexes, and discusses assays to verify the efficiency of complexing for immunotherapy against cancers and infectious diseases.     

Purification of recombinant and endogenous HSP70s

Heat shock proteins (HSPs) are powerful immunogens against the antigenic peptides they chaperone. The antigenic peptides are MHC I-binding peptides and their elongated precursors derived from tumor antigens, viral antigens, minor histocompatibility antigens, or model antigens. HSP-peptide complexes can immunize against tumors and pathogen-infected cells. Remarkably, HSPs do not immunize after elution of the peptides they chaperone, demonstrating that HSPs are not immunogenic per se, whereas HSP-peptide complexes are. Additionally, HSPs activate professional antigen presenting cells (APC) through specific receptor(s) to stimulate secretion of pro-inflammatory cytokines, up-regulation of co-stimulatory molecules and activation of dendritic cells. The mechanistic exploration of the role of the HSPs on the innate and adaptive component of the immune system requires their isolation in large quantity. On one hand, isolation of naturally formed HSP-peptide complexes is key to study their specific immunogenicity. On the other hand, purification of HSPs free of endotoxin contamination is an absolute requirement for the analysis of their ability to activate APC in vitro. This chapter describes a convenient and fast method of purification of endogenous and recombinant HSP of 70 kDa (HSP70) that addresses these two considerations.     

In vivo and in vitro activation of T cells after administration of Ag-negative heat shock proteins

Heat shock proteins (HSP) Hsp70 and gp96 prime class I-restricted cytotoxic T cells against Ags present in the cells from which they were isolated. The immunization capacity of HSPs is believed to rely on their ability to bind antigenic peptides. In this study, we employed the well-established OVA and beta-galactosidase (beta-gal) antigenic model systems. We show that in vitro long-term established OVA and beta-gal-specific CTL clones release TNF-alpha and IFN-gamma when incubated with Ag-negative Hsp70 and gp96. In the absence of antigenic peptides, HSP-mediated secretion of TNF-alpha and IFN-gamma requires cell contact of the APC with the T cell but is not MHC-I restricted. Moreover, Hsp70 molecules purified from Ag-negative tissue, e.g., negative for antigenic peptide, are able to activate T cells in vivo, leading to significant higher frequencies in OVA-specific CD8+ T cells. In unprimed animals, these T cells lyse OVA-transfected cell lines and produce TNF-alpha and IFN-gamma after Ag stimulus. Taken together our data show that, besides the well-established HSP/peptide-specific CTL induction and activation, a second mechanism exists by which Hsp70 and gp96 molecules activate T cells in vivo and in vitro.     

Development of cancer vaccines using autologous and recombinant high molecular weight stress proteins

High molecular weight heat shock proteins (HSPs), hsp110 and grp170, derived from cancer cells have been previously shown to elicit tumor-specific immunity. This phenomenon is attributed to the antigenic peptides associated with the HSPs. Based on the unique chaperoning properties of these HSPs, a new vaccination strategy has been recently developed to elicit antigen-specific antitumor immunity. This approach utilizes tumor-associated antigens naturally complexed to these highly efficient molecular chaperones under heat shock conditions. This chapter focuses on the methodologies of these two vaccine strategies: I. purification of hsp110 and grp170 from tumor tissue or cell lines; II. generation and characterization of in vitro HSP-antigen complexes by heat shock using recombinant HSPs derived from a baculovirus protein expression system.     

High-affinity interactions between peptides and heat shock protein 70 augment CD8+ T lymphocyte immune responses

Exogenously delivered antigenic peptides complexed to heat shock proteins (HSPs) are able to enter the endogenous Ag-processing pathway and prime CD8+ CTL. It was determined previously that a hybrid peptide containing a MHC class I-binding epitope and HSP70-binding sequence Javelin (J0) in complex with HSP70 could induce cytotoxic T cell responses in vivo that were more robust than those induced by the minimal epitope complexed with HSP70. The present study introduces a novel, higher-affinity HSP70-binding sequence (J1) that significantly enhances binding of various antigenic peptides to HSP70. A competition binding assay revealed a dissociation constant that was 15-fold lower for the H2-K(b) OVA epitope SIINFEKL-J1 compared with SIINFEKL-J0, indicating a substantially higher affinity for HSP70. Further, modifying the orientation of the hybrid epitope and introducing a cleavable linker sequence between the Javelin and the epitope results in even greater immunogenicity, presumably by greater efficiency of epitope processing. The enhanced immunogenicity associated with Javelin J1 and the cleavable linker is consistently observed with multiple mouse and human epitopes. Thus, by creating a series of epitopes with uniform, high-affinity binding to HSP70, successful multiple epitope immunizations are possible, with equal delivery of each antigenic epitope to the immune system via HSP70. These modified epitopes have the potential for creating successful multivalent vaccines for immunotherapy of both infectious disease and cancer.     

The role of heat shock proteins and their receptors in the activation of the immune system

Heat shock proteins (HSPs) have been described as potent tumor vaccines in animal models and are currently studied in clinical trials. The underlying immune response relies on immunogenic peptides that the HSPs have acquired intracellularly by interfering with the classical antigen processing pathways. There have been numerous reports shedding light on how HSPs are able to gain this function and a number of important requirements for HSP-mediated specific immunity have been described: first, the ability of HSPs to bind immunogenic peptides. Second, the acquisition of HSPs by specialized antigen presenting cells with efficient antigen processing pathways capable of inducing cellular immune responses. Third, the existence of specific receptors on the surfaces of antigen presenting cells, allowing efficient and rapid uptake of HSP-peptide complexes from the extracellular fluid. And fourth, the ability of heat shock proteins to activate antigen presenting cells, enabling the latter to prime cytotoxic T cell responses against the peptides associated to HSPs.     

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.     

Peptide epitope mapping in vaccine development: Introduction

Protection from infectious disease by the host immune response requires specific molecular recognition of unique antigenic determinants of a given pathogen. An epitope is an antigenic determinant which: 1) specifically stimulates the immune response (either B or T cell mediated); and 2) is acted upon by the products of these protective mechanisms. In B cell immunity, antibodies produced from stimulation by specific epitopes recognize and bind to these same antigenic structures. Identification of protective epitopes is extremely valuable to successful vaccine development. In order to be protective these antibodies must, in addition to recognition and binding, interfere with some vital step in pathogenesis such as adherence or toxin action. Protein B cell epitopes are frequently composed of the side chains (R-groups) of the amino acids found at solvent-exposed surfaces. These epitopes are classified as continuous (also linear or sequential) if composed of a single antibody-recognizing element located at a single locus of the primary structure. They are discontinuous (or assembled) if more than one physically separated entity is involved. T cell epitopes are peptides on the surface of antigen-presenting cells (macrophages, dendritic cells, and B cells) that are bound to major histocompatibility proteins; the T cell recognizes this peptide-MHC complex. Received 12 August 1996/ Accepted in revised form 03 November 1996     

Cutting edge: receptor-mediated endocytosis of heat shock proteins by professional antigen-presenting cells

Immunization with heat shock proteins (HSPs) induces Ag-specific CTL responses. The specificity of the immune response is based on peptides associated with HSPs. To investigate how exogenous HSP/peptide complexes gain access to the MHC class I-restricted Ag presentation pathway, we incubated the monocytic cell line P388D1 and the dendritic cell line D2SC/1 with gold-labeled HSPs gp96 and HSC70. We show that HSPs bind specifically to the surface of these APCs and are internalized spontaneously by receptor-mediated endocytosis, demonstrating the existence of specific receptors for HSPs on these cells. In addition, we observe colocalization of internalized HSPs and surface MHC class I molecules in early and late endosomal structures. These findings provide possible explanations for the immunogenicity of HSP/peptide complexes and for the transfer of HSP-associated peptides onto MHC class I molecules.     

Structure and function: heat shock proteins and adaptive immunity

Heat shock proteins (HSPs) have been implicated in the stimulation and generation of both innate and adaptive immunity. The ability of HSPs to bind antigenic peptides and deliver them to APCs is the basis of the generation of peptide-specific T lymphocyte responses both in vitro and in vivo. The different HSP families are genetically and biochemically unrelated, and the structural basis of peptide binding and the dynamic models of ligand interaction are known only for some of the HSPs. We examine the contribution of HSP structure to its immunological functions and the potential "immunological repertoire" of HSPs as well as the use of biophysical techniques to quantify HSP-peptide interactions and optimize vaccine design. Although biochemical evidence for HSP-mediated endogenous processing of Ag has now emerged, the issue of whether HSP-peptide complexes act as physiological sources of Ag in cross-presentation is controversial. We assess the contribution of biochemical studies in this field.     

热激蛋白gp96免疫学功能及在主动免疫治疗肿瘤和传染病中的应用

热激蛋白gp96可特异性结合来源于肿瘤和病毒的抗原肽,与抗原呈递细胞表面CD91等受体作用进入胞内,并在内质网中将结合的抗原通过抗原呈递链呈递给MHCI类分子,激活特异性T细胞。同时,与细胞表面Toll样受体(TLR)TLR2、TLR4等相互作用,激活天然免疫。近期研究发现调节性T细胞(Treg)对gp96免疫功能有显著抑制作用,随着对影响gp96免疫功能的免疫抑制机制的深入了解,以及利用汉逊酵母表达有免疫活性的全长gp96蛋白体系的建立,gp96将在治疗肿瘤及传染性疾病中发挥更大的作用。     

Unbiased identification of target antigens of CD8+ T cells with combinatorial libraries coding for short peptides

Cytotoxic CD8(+) T cells recognize the antigenic peptides presented by class I major histocompatibility complex (MHC) molecules. These T cells have key roles in infectious diseases, autoimmunity and tumor immunology, but there is currently no unbiased method for the reliable identification of their target antigens. This is because of the low affinities of antigen-specific T cell receptors (TCR) to their target MHC-peptide complexes, the polyspecificity of these TCRs and the requirement that these TCRs recognize protein antigens that have been processed by antigen-presenting cells (APCs). Here we describe a technology for the unbiased identification of the antigenic peptides presented by MHC class I molecules. The technology uses plasmid-encoded combinatorial peptide libraries and a single-cell detection system. We validated this approach using a well-characterized influenza-virus–specific TCR, MHC and peptide combination. Single APCs carrying antigenic peptides can be detected among several million APCs that carry irrelevant peptides. The identified peptide sequences showed a converging pattern of mimotopes that revealed the parent influenza antigen. This technique should be generally applicable to the identification of disease-relevant T cell antigens.     

Immunotherapy of Tumors with α2-Macroglobulin-Antigen Complexes Pre-Formed In Vivo

The cell surface receptor CD91/LRP-1 binds to immunogenic heat shock proteins (HSP) and α₂M ligands to elicit T cell immune responses. In order to generate specific immune responses, the peptides chaperoned by HSPs or α₂M are cross-presented on MHC molecules to T cells. While the immunogenic HSPs naturally chaperone peptides within cells and can be purified as an intact HSP-peptide complex, the peptides have had to be complexed artificially to α₂M in previous studies. Here, we show that immunogenic α₂M-peptide complexes can be isolated from the blood of tumor-bearing mice without further experimental manipulation in vitro demonstrating the natural association of tumor antigens with α₂M. The naturally formed immunogenic α₂M-peptide complexes are effective in prophylaxis and therapy of cancer in mouse models. We investigate the mechanisms of cross-presentation of associated peptides and co-stimulation by APCs that interact with α₂M. These data have implications for vaccine design in immunotherapy of cancer and infectious disease.     

Combining proteomics and bioinformatics to explore novel tegumental antigens as vaccine candidates against Echinococcus granulosus infection

Echinococcus granulosus is the parasite responsible for cystic echinococcosis (CE), an important worldwide-distributed zoonosis. New effective vaccines against CE could potentially have great economic and health benefits. Here, we describe an innovative vaccine design scheme starting from an antigenic fraction enriched in tegumental antigens from the protoscolex stage (termed PSEx) already known to induce protection against CE. We first used mass spectrometry to characterize the protein composition of PSEx followed by Gene Ontology analysis to study the potential Biological Processes, Molecular Functions, and Cellular Localizations of the identified proteins. Following, antigenicity predictions and determination of conservancy degree against other organisms were determined. Thus, nine novel proteins were identified as potential vaccine candidates. Furthermore, linear B cell epitopes free of posttranslational modifications were predicted in the whole PSEx proteome through colocalization of in silico predicted epitopes within peptide fragments identified by matrix-assisted laser desorption/ionization-TOF/TOF. Resulting peptides were termed “clean linear B cell epitopes,” and through BLASTp scanning against all nonhelminth proteins, those with 100% identity against any other protein were discarded. Then, the secondary structure was predicted for peptides and their corresponding proteins. Peptides with highly similar secondary structure respect to their parental protein were selected, and those potentially toxic and/or allergenic were discarded. Finally, the selected clean linear B cell epitopes were mapped within their corresponding 3D-modeled protein to analyze their possible antibody accessibilities, resulting in 14 putative peptide vaccine candidates. We propose nine novel proteins and 14 peptides to be further tested as vaccine candidates against CE.     

热休克蛋白-多肽复合物在肿瘤和传染性疾病免疫中的作用

热休克蛋白家族中的许多成员如gp96\,HSP90\,HSP70等具有排斥和治疗肿瘤及传染性疾病的免疫原性,进一步研究发现热休克蛋白作为分子伴侣可结合细胞中的肽库,它本身没有抗原性,抗原性由结合的短肽所决定。热休克蛋白将结合的短肽呈递给I类MHC分子,进而激活特异性CTL和记忆性T细胞,引发机体细胞免疫反应。据最新发现gp96还可能有与MHC一样的功能,可直接将结合的多肽抗原呈递给T细胞。近年来对哺乳动物的二种主要热休克蛋白gp96和HSP70的免疫机制和作为治疗性疫苗的优越性进行了详细研究,这为乙型肝炎和乙肝继发性肝癌的免疫治疗提供了新思路。     

A large-scale evaluation of peptide vaccines against foot-and-mouth disease: lack of solid protection in cattle and isolation of escape mutants.

A large-scale vaccination experiment involving a total of 138 cattle was carried out to evaluate the potential of synthetic peptides as vaccines against foot-and-mouth disease. Four types of peptides representing sequences of foot-and-mouth disease virus (FMDV) C3 Argentina 85 were tested: A, which includes the G-H loop of capsid protein VP1 (site A); AT, in which a T-cell epitope has been added to site A; AC, composed of site A and the carboxy-terminal region of VP1 (site C); and ACT, in which the three previous capsid motifs are colinearly represented. Induction of neutralizing antibodies, lymphoproliferation in response to viral antigens, and protection against challenge with homologous infectious virus were examined. None of the tested peptides, at several doses and vaccination schedules, afforded protection above 40%. Protection showed limited correlation with serum neutralization activity and lymphoproliferation in response to whole virus. In 12 of 29 lesions from vaccinated cattle that were challenged with homologous virus, mutant FMDVs with amino acid substitutions at antigenic site A were identified. This finding suggests the rapid generation and selection of FMDV antigenic variants in vivo. In contrast with previous studies, this large-scale vaccination experiment with an important FMDV host reveals considerable difficulties for vaccines based on synthetic peptides to achieve the required levels of efficacy. Possible modifications of the vaccine formulations to increase protective activity are discussed.     

Specific immunogenicity of heat shock protein gp96 derives from chaperoned antigenic peptides and not from contaminating proteins

The peptide-binding property of MHC is central to adaptive immunological functions. A similar property of heat shock proteins (HSPs) hsp70 and hsp90 has been implicated in Ag presentation by MHC and in cross-priming. The peptide-binding pocket of hsp70 has been characterized structurally and functionally and a peptide-binding site in gp96 (of hsp90 family) has been defined. Nonetheless, questions persist whether the specific immunogenicity of HSP preparations derives from the peptides chaperoned by the HSPs or by proteins contaminating the HSP preparations. Because absolute purity of a protein preparation is a metaphysical concept, other approaches are necessary to address the question. In this study, we demonstrate that the specific immunogenicity of gp96 preparations isolated from cells expressing beta-galactosidase derives from the MHC I epitope precursors associated with the gp96 and not from contaminating beta-galactosidase protein nor unassociated fragments derived from it. Although the observations here are limited to a single HSP and antigenic peptides chaperoned by it, they can be extended broadly.     

Screening of random peptide library of hemagglutinin from pandemic 2009 A(H1N1) influenza virus reveals unexpected antigenically important regions

The antigenic structure of the membrane protein hemagglutinin (HA) from the 2009 A(H1N1) influenza virus was dissected with a high-throughput screening method using complex antisera. The approach involves generating yeast cell libraries displaying a pool of random peptides of controllable lengths on the cell surface, followed by one round of fluorescence-activated cell sorting (FACS) against antisera from mouse, goat and human, respectively. The amino acid residue frequency appearing in the antigenic peptides at both the primary sequence and structural level was determined and used to identify "hot spots" or antigenically important regions. Unexpectedly, different antigenic structures were seen for different antisera. Moreover, five antigenic regions were identified, of which all but one are located in the conserved HA stem region that is responsible for membrane fusion. Our findings are corroborated by several recent studies on cross-neutralizing H1 subtype antibodies that recognize the HA stem region. The antigenic peptides identified may provide clues for creating peptide vaccines with better accessibility to memory B cells and better induction of cross-neutralizing antibodies than the whole HA protein. The scheme used in this study enables a direct mapping of the antigenic regions of viral proteins recognized by antisera, and may be useful for dissecting the antigenic structures of other viral proteins.     

UreB蛋白B细胞抗原表位快速筛选与鉴定

以幽门螺旋杆菌(Helicobacterpylori,Hp)主要抗原蛋白尿素酶B(ureaseB,UreB)为靶蛋白,建立一种新的B细胞抗原表位筛选与鉴定方法.运用Fmoc固相肽合成法合成11条HpUreB蛋白的单表位抗原肽片段,在其氨基端标记FITC荧光素,应用荧光偏振方法(fluorescencepolarization,FP)快速鉴定这些肽片段的抗原性,并通过FP法在大规模样品中快速筛选相应抗体滴度高、分布人群广的优势抗原表位肽.结果表明,合成的11条UreB蛋白线性抗原肽中,10条具有较强的抗原性,其中No.2、No.5和No.11抗原肽相应的特异性抗体在感染Hp的人群中分布较广,抗体滴度较高,为UreB的优势抗原表位肽.对抗原表位进行多参数综合分析与设计,通过FP技术快速鉴定抗原肽,并筛选优势抗原表位肽,对于疾病的抗原表位谱研究具有重要的意义,同时在疾病的诊断、分型及治疗中具有重要的应用前景.