The biochemistry and cell biology of antigen presentation by MHC class I and class II molecules. Implications for development of combination vaccines

Glycopeptides and -Mimetics to Detect, Monitor and Inhibit Bacterial and Viral Infections: Recent Advances and Perspectives

The initial contact of pathogens with host cells is usually mediated by their adhesion to glycan structures present on the cell surface in order to enable infection. Furthermore, glycans play important roles in the modulation of the host immune responses to infection. Understanding the carbohydrate-pathogen interactions are of importance for the development of novel and efficient strategies to either prevent, or interfere with pathogenic infection. Synthetic glycopeptides and mimetics thereof are capable of imitating the multivalent display of carbohydrates at the cell surface, which have become an important objective of research over the last decade. Glycopeptide based constructs may function as vaccines or anti-adhesive agents that interfere with the ability of pathogens to adhere to the host cell glycans and thus possess the potential to improve or replace treatments that suffer from resistance. Additionally, synthetic glycopeptides are used as tools for epitope mapping of antibodies directed against structures present on various pathogens and have become important to improve serodiagnostic methods and to develop novel epitope-based vaccines. This review will provide an overview of the most recent advances in the synthesis and application of glycopeptides and glycopeptide mimetics exhibiting a peptide-like backbone in glycobiology.

Identification of MHC Ligands and Establishing MHC Class I Peptide Motifs

MHC class I peptide motifs are used on a regular basis to identify and predict MHC class I ligands and CD8⁺ T cell epitopes. This approach is above all an invaluable tool for the identification of disease-associated epitopes ranging from pathogen associated epitopes, tumor associated natural and neoepitopes to autoimmune disease associated epitopes. As a matter of fact, the vast majority of T cell epitopes discovered during the past two decades was identified by means of epitope prediction and MHC ligand identification. Here we describe the steps which are necessary to identify MHC epitopes from monoallelic and multiallelic cells and establish MHC class I peptide motifs to compose a reliable scoring matrix for epitope prediction. As an example, the ligands of monoallelic C1R cells and multiallelic peripheral blood mononuclear cell tissue will be identified and a scoring matrix for the prediction of HLA-C*01:02-presented T cell epitopes will be developed.

Direct Detection of T- and B-Memory Lymphocytes by ImmunoSpot® Assays Reveals HCMV Exposure that Serum Antibodies Fail to Identify

It is essential to identify donors who have not been infected with human cytomegalovirus (HCMV) in order to avoid transmission of HCMV to recipients of blood transfusions or organ transplants. In the present study, we tested the reliability of seronegativity as an indicator for the lack of HCMV exposure in healthy human blood donors. Eighty-two HCMV seronegative individuals were identified, and their peripheral blood mononuclear cells (PBMC) were tested in ImmunoSpot® assays for the presence of HCMV-specific T- and B-memory lymphocytes. Eighty-two percent (67 of 82) of these HCMV seronegative individuals featured at least one memory cell that was lineage specific for HCMV, with the majority of these subjects possessing CD4+ and CD8+ T cells, as well as B cells, providing three independent lines of evidence for having developed immunity to HCMV. Only 15 of these 82 donors (18%) showed neither T- nor B-cell memory to HCMV, consistent with immunological naïveté to the virus. The data suggest that measurements of serum antibodies frequently fail to reveal HCMV exposure in humans, which may be better identified by direct detection of HCMV-specific memory lymphocytes.

A Positive Control for Detection of Functional CD4 T Cells in PBMC: The CPI Pool

Testing of peripheral blood mononuclear cells (PBMC) for immune monitoring purposes requires verification of their functionality. This is of particular concern when the PBMC have been shipped or stored for prolonged periods of time. While the CEF (Cytomegalo-, Epstein-Barr and Flu-virus) peptide pool has become the gold standard for testing CD8 cell functionality, a positive control for CD4 cells is so far lacking. The latter ideally consists of proteins so as to control for the functionality of the antigen processing and presentation compartments, as well. Aiming to generate a positive control for CD4 cells, we first selected 12 protein antigens from infectious/environmental organisms that are ubiquitous: Varicella, Influenza, Parainfluenza, Mumps, Cytomegalovirus, Streptococcus, Mycoplasma, Lactobacillus, Neisseria, Candida, Rubella, and Measles. Of these antigens, three were found to elicited interferon (IFN)-γ-producing CD4 cells in the majority of human test subjects: inactivated cytomegalo-, parainfluenza-, and influenza virions (CPI). While individually none of these three antigens triggered a recall response in all donors, the pool of the three (the ‘CPI pool’), did. One hundred percent of 245 human donors tested were found to be CPI positive, including Caucasians, Asians, and African-Americans. Therefore, the CPI pool appears to be suitable to serve as universal positive control for verifying the functionality of CD4 and of antigen presenting cells.

Cloning and characterization of MHC-DQA1 and MHC-DQA2 molecules from yak (<i>Bos grunniens</i>)

Abstract. The major histocompatibility complex (MHC) plays a crucial role in the processing and presentation of antigens and in discrimination between self and non-self. The aim of this investigation was to scrutinize the structural diversity and possible duplication of the MHC-DQA genes in yak (Bos grunniens). Two cDNA sequences were amplified and designated as Bogr-DQA1 (DQA*0101) and Bogr-DQA2 (DQA*2001) with GenBank accession numbers JQ864314 and JQ864315, respectively. The nucleotide and amino acid sequence alignment between Bogr-DQA1 and Bogr-DQA2 molecules showed that these two identified MHC-DQA gene sequences had more similarity to alleles of specific DQA1 and DQA2 genes from other Ruminantia species than to each other. The result from phylogenic investigation also revealed that there was a larger genetic distance between these two genes than between homologous genes from different species. The presence of different bovine DQA putative motifs and the large genetic distance between Bogr-DQA1 and Bogr-DQA2 suggest that these sequences are non-allelic. Further, these results indicate that DQA gene duplication occurs in ruminants. This study will be helpful in knowing MHC diversity in common ruminants and will deepen our understanding of the variation of immunological functions, evolutionary constraints, and selective forces that affect MHC variation within and between species.

How frequently are predicted peptides actually recognized by CD8 cells?

Detection of antigen-specific CD8 cells frequently relies on the use of peptides that are predicted to bind to HLA Class I molecules or have been shown to induce immune responses. There is extensive knowledge on individual HLA alleles’ peptide-binding requirements, and immunogenic peptides for many antigens have been defined. The 32 individual peptides that comprise the CEF peptide pool represent such well-defined peptide determinants for Cytomegalo-, Epstein–barr-, and Influenza virus. We tested the accuracy of these peptide recognition predictions on 42 healthy human donors that have been high-resolution HLA-typed. According to the predictions, 241 recall responses should have been detected in these donors. Actual testing showed that 36 (15 %) of the predicted CD8 cell responses occurred in the high frequency range, 41 (17 %) in mid-frequencies, and 45 (19 %) were at the detection limit. In 119 instances (49 %), the predicted peptides were not targeted by CD8 cells detectably. The individual CEF peptides were recognized in an unpredicted fashion in 57 test cases. Moreover, the frequency of CD8 cells responding to a single peptide did not reflect on the number of CD8 cells targeting other determinants on the same antigen. Thus, reliance on one or a few predicted peptides provides a rather inaccurate assessment of antigen-specific CD8 cell immunity, strongly arguing for the use of peptide pools for immune monitoring.

Adding fuel to the fire: immunogenic intensification

The durable long term clinical benefits seen for certain patients treated with immunotherapy agents has suggested there is significant therapeutic potential to be derived from these agents, as shown by the increasing prominence of this treatment strategy in upcoming clinical trials. There has been a renewed interest and focus on the drivers of tumoral antigen recognition, and the pathways by which various cells of the immune system can stimulate, propagate and execute an effective anti-tumor response. Various challenges lie ahead in the further development of these treatments, including induction of an endogenous anti-tumor response, tumor microenvironment modulation, and T-cell response amplification. Novel treatment combinations may prove of significant added benefit by immunogenic intensification.

Establishing MHC class I peptide motifs

Major histocompatibility complex (MHC) class I peptide motifs are used on a regular basis to identify and predict MHC class I ligands and CD8(+) T-cell epitopes. This approach is above all an invaluable tool for the identification of disease-associated epitopes. As a matter of fact, the vast majority of T-cell epitopes discovered during the past two decades was identified by means of epitope prediction. Here we describe the steps which are necessary to establish MHC class I peptide motifs and to compose a reliable scoring matrix for epitope prediction. As an example, a scoring matrix for the prediction of HLA-B*35-presented T-cell epitopes will be developed by examining the characteristics of 76 naturally presented HLA ligands.

Chlamydia trachomatis outer membrane complex protein B (OmcB) is processed by the protease CPAF

We previously reported that the Chlamydia trachomatis outer membrane complex protein B (OmcB) was partially processed in Chlamydia-infected cells. We have now confirmed that the OmcB processing occurred inside live cells during chlamydial infection and was not due to proteolysis during sample harvesting. OmcB processing was preceded by the generation of active CPAF, a serine protease known to be able to cross the inner membrane via a Sec-dependent pathway, suggesting that active CPAF is available for processing OmcB in the periplasm. In a cell-free system, CPAF activity is both necessary and sufficient for processing OmcB. Both depletion of CPAF from Chlamydia-infected cell lysates with a CPAF-specific antibody and blocking CPAF activity with a CPAF-specific inhibitory peptide removed the OmcB processing ability of the lysates. A highly purified wild-type CPAF but not a catalytic residue-substituted mutant CPAF was sufficient for processing OmcB. Most importantly, in chlamydial culture, inhibition of CPAF with a specific inhibitory peptide blocked OmcB processing and reduced the recovery of infectious organisms. Thus, we have identified OmcB as a novel authentic target for the putative chlamydial virulence factor CPAF, which should facilitate our understanding of the roles of CPAF in chlamydial biology and pathogenesis.

How much of virus-specific CD8 T cell reactivity is detected with a peptide pool when compared to individual peptides?

Immune monitoring of T cell responses increasingly relies on the use of peptide pools. Peptides, when restricted by the same HLA allele, and presented from within the same peptide pool, can compete for HLA binding sites. What impact such competition has on functional T cell stimulation, however, is not clear. Using a model peptide pool that is comprised of 32 well-defined viral epitopes from Cytomegalovirus, Epstein-Barr virus, and Influenza viruses (CEF peptide pool), we assessed peptide competition in PBMC from 42 human subjects. The magnitude of the peptide pool-elicited CD8 T cell responses was a mean 79% and a median 77% of the sum of the CD8 T cell responses elicited by the individual peptides. Therefore, while the effect of peptide competition was evident, it was of a relatively minor magnitude. By studying the dose-response curves for individual CEF peptides, we show that several of these peptides are present in the CEF-pool at concentrations that are orders of magnitude in excess of what is needed for the activation threshold of the CD8 T cells. The presence of such T cells with very high functional avidity for the viral antigens can explain why the effect of peptide competition is relatively minor within the CEF-pool.

A Chlamydia trachomatis OmcB C-terminal fragment is released into the host cell cytoplasm and is immunogenic in humans

The Chlamydia trachomatis outer membrane complex protein B (OmcB) is an antigen with diagnostic and vaccine relevance. To further characterize OmcB, we generated antibodies against OmcB C-terminal (OmcBc) and N-terminal (OmcBn) fragments. Surprisingly, the anti-OmcBc antibody detected dominant signals in the host cell cytosol, while the anti-OmcBn antibody exclusively labeled intrainclusion signals in C. trachomatis-infected cells permeabilized with saponin. Western blot analyses revealed that OmcB was partially processed into OmcBc and OmcBn fragments. The processed OmcBc was released into host cell cytosol, while the OmcBn and remaining full-length OmcB were retained within the chlamydial inclusions. The organism-associated OmcB epitopes became detectable only after the C. trachomatis-infected cells were permeabilized with strong detergents such as SDS. However, the harsh permeabilization conditions also led to the leakage of the already secreted OmcBc and chlamydia-secreted protease (CPAF) out of the host cells. The OmcBc processing and release occurred in all biovars of C. trachomatis. Moreover, the released OmcBc but not the retained OmcBn was highly immunogenic in C. trachomatis-infected women, which is consistent with the concept that exposure of chlamydial proteins to host cell cytosol is accompanied by increased immunogenicity. These observations have provided important information for further exploring/optimizing OmcB as a target for the development of diagnosis methods and vaccines.

Roadmap to a Better Therapeutic Tumor Vaccine

Cell-based cancer vaccines are a highly attractive alternative to standard cancer therapies. They theoretically have the capability of inciting a multitargeted therapeutic response that functions by reshaping the host-tumor interaction, tipping the balance in favor of tumor rejection. Due to the polyclonal immune response induced, they are less likely to result in therapeutic escape than most cancer treatments in use today. Their immune-based mechanism of action offers a unique approach to management that should not be limited by traditional modes of drug resistance. Their favorable side-effect profile further identifies them as a potential treatment modality of choice. Despite these positive features, a number of hurdles must be overcome in order for cancer vaccines to take their place in the clinic as part of standard cancer therapy. Vaccine protocols must be optimized both to induce a high-quality antitumor T-cell response and to abrogate established mechanisms of immune tolerance that actively function to shut antitumor T cells down. By applying basic knowledge of the molecular features of T-cell biology and immune tolerance to the design of trials that combine tumor vaccines with targeted immunomodulatory drugs, potent strategies for inducing effective antitumor immunity can be developed. The first of these combinatorial trials have already been reported and offer a tantalizing glimpse of the future of cancer immunotherapy.

Cancer vaccines: on the threshold of success

BACKGROUND

Cancer vaccines are a unique approach to cancer therapy. They exert an antitumor effect by engaging the host immune response, and have great potential for circumventing the intrinsic drug resistance that limits standard cancer management. Additional advantages of cancer vaccines are exquisite specificity, low toxicity, and the potential for a durable treatment effect due to immunologic memory.

OBJECTIVES

This review aims to consider the promise of cancer vaccines, review the current state of cancer vaccine development, and suggest directions for future research.

METHODS

The scope of this review was defined peer-reviewed information found on Medline, and information found on the Internet about Phase III clinical trials that are ongoing and not yet published.

RESULTS/CONCLUSIONS

Multiple Phase III clinical trials have demonstrated the promise and challenges posed by therapeutic vaccines, and defined the next steps in their clinical development. Determining the optimal integration of cancer vaccines with chemotherapy, radiation, surgery, and biologically targeted therapies, defining predictive biomarkers of immunologic and clinical response, and combining tumor vaccines with new drugs that effectively modulate the antitumor immune response, will ensure that cancer vaccines become part of standard cancer therapy and prevention.

Importance of HLA-DQ and HLA-DP polymorphisms in cytokine responses to naturally processed HLA-DR-derived measles virus peptides

We studied the association between class II human leukocyte antigen (HLA)-DRB1*0301 presented measles virus (MV) peptide-specific cytokine responses and DQB1 and DPB1 alleles among 313 individuals who received two doses of measles-mumps-rubella-II vaccine. The overall median IFN-gamma secretion levels (first and third quartiles) for the 19-amino acid MV phosphoprotein (MV-P)- and 14-amino acid MV nucleoprotein (MV-N)-derived peptides were 27.7 pg/ml (1.8, 109.4) and 1.9 pg/ml (-6.2, 13.0), respectively; median IL-4 secretion levels were -0.6 pg/ml (-7.1, 6.2) and 2.4 pg/ml (-3.2, 9.3), respectively. Primary statistical analyses were adjusted for previously identified DRB1 associations. A marginally significant increase in the frequency of the DQB1*0604 (p=0.02) allele was found among subjects who demonstrated detectable IL-4 levels to the MV-P peptide. Further, DPB1*0201 (p=0.02) and DPB1*1301 (p=0.09) alleles provided suggestive evidence of an association with MV-P-induced IL-4 secretion. Examination of IFN-gamma responses to MV-P and MV-N indicated that none of the individual alleles of the DQB1 and DPB1 loci were associated with peptide-induced T cell response. An increase in the frequency of DPB1*0501 (p=0.01) was found among subjects who failed to produce MV-N peptide-specific IL-4 responses. These data further confirm that HLA-DRB1 alleles are the major restriction molecules for MV-P and MV-N measles virus antigen presentation to T cells. We speculate that MV-P and MV-N peptides derived from DRB1*0301 could potentially be recognized in association with different HLA molecules, including DQB1 and DPB1; however, statistical adjustments for the effect of HLA-DR locus could potentially alter these genetic relationships. This concept provides important information supporting the use of promiscuous peptides in a peptide-based vaccine approach.

Genetic fusion of proteins to the SIV Tat protein enhances their immunogenicity

The potential of genetically fusing recombinant proteins to the simian immunodeficiency virus (SIV) Tat protein has been investigated. The recombinant SIV Tat protein was initially expressed in very low amounts in E. coli, but optimization of the coding sequence for translation in the bacterial host significantly improved protein expression. Whilst fusion of SIV Tat to an experimental antigen (GST) facilitated the binding of the antigen to cell surfaces it did not appear to facilitate the transport of the protein into the cytosol. The immunogenicity of GST was significantly enhanced, in the absence of adjuvants, when fused to SIV Tat, with the induction of IgG1 and IgG2a antibodies indicative of a Th1 response being induced. However, no evidence was obtained that such an immunization scheme efficiently induced a CTL response.

Clinical link between MHC class II haplotype and interferon-beta (IFN-beta) immunogenicity

Interferon-beta (IFN-beta) is currently the first-line therapy for the treatment of multiple sclerosis (MS). However, a significant percentage of MS patients develop anti-IFN-beta antibodies, which can reduce the efficacy of the drug. We describe an association between a common MHC class II allele (DRB1*0701), present in 23% of the patients studied, and the anti-IFN-beta antibody response. We identified IFN-beta epitopes using a peptide-binding assay with B cell lines expressing this allele. Moreover, epitope-specific activation responses obtained with peripheral blood mononuclear cells (PBMCs) from IFN-beta treated patients with the DRB1*0701 allele indicated a role for T-cell activation in IFN-beta immunogenicity. These results suggest that HLA typing of MS patients may provide an accurate screen for subjects who are likely to develop anti-IFN-beta antibodies and should therefore be considered for alternative therapies. In addition, elucidation of the factors underlying the anti-IFN-beta antibody response should accelerate the engineering of less immunogenic IFN-beta therapeutics.

Recent developments in veterinary vaccinology

Advancement in technology and science and our detailed knowledge of immunology, molecular biology, microbiology, and biochemistry among other basic science disciplines have defined new directions for vaccine development strategies. The applicability of genetic engineering and proteomics along with other new technologies have played pivotal roles in introducing novel ideas in vaccinology, and resulted in developing new vaccines and improving the quality of existing ones. Subunit vaccines, recombinant vaccines, DNA vaccines and vectored vaccines are rapidly gaining scientific and public acceptance as the new generation of vaccines and are seriously considered as alternatives to current conventional vaccines. The present review focuses on recent advances in veterinary vaccinology and addresses the effects and impact of modern microbiology, immunology, and molecular biology.

Intracellular delivery of a novel multiepitope peptide vaccine by an amphipathic peptide carrier enhances cytotoxic T-cell responses in HLA-A*201 mice

Cytotoxic T lymphocytes (CTL) are key players in the neutralization of viruses and killing of tumor cells. However, for generating an optimal CTL response by vaccination, the antigen has to be delivered directly into the cytoplasm for presentation by the conventional MHC class I pathway. To mimic the presentation of multiple epitopes by a tumor or virus infected cell, we have designed a multiepitope peptide vaccine incorporating thee CTL epitopes in tandem with double arginine spacers to facilitate efficient cleavage of the individual epitopes. To deliver the multiepitope peptide vaccine into the cytoplasm of mature dendritic cells for presentation by the MHC class I pathway we made use of an amphipathic peptide carrier. Direct injection of a non-covalent complex of the multiepitope peptide vaccine and amphipathic peptide carrier in an aqueous formulation into HLA-A*0201 (HHD) transgenic mice enhanced the cytotoxic T-cell responses by two to sixfold compared with multiepitope peptide vaccination alone. This novel antigen delivery strategy may find general application in the development of more effective vaccines for the treatment of cancer and infectious disease.

Identification of HLA-DRB1-bound self-peptides following measles virus infection

We developed a B-lymphocyte cell line derived from a measles seropositive individual who was homozygous for the HLA-DRB1*0301 allele. Peptides associated with the HLA-DRB1*0301 protein were purified from this lymphoblastoid cell line after infection with the Attenuvax measles vaccine virus (Merck Research Laboratories, West Point, PA) and with "sham" infection. More than 40 peptide sequences were obtained by nano-scale reversed phase-high performance liquid chromatography coupled to tandem mass spectrometry (nano-LC/MS/MS). These peptides originated from 21 different source proteins--the majority from membrane-bound proteins. Most of the peptides (>73%) bound to HLA-DRB1*0301 appeared to be in lower abundance on measles-infected cells compared to the "sham-infected" cells. However, 26% of the identified peptides seem to have increased expression after measles infection. Measles vaccine virus infection did not change the level of HLA-DR expression. We demonstrate the power of nano-LC/MS/MS in the rapid determination of changes in the spectrum and expression of HLA-DRB1*0301-bound peptides after infection with measles virus. This provides further knowledge of the changes in peptide expression after viral infection and provides a powerful tool for identifying HLA-presented host and viral epitopes in the context of class II HLA molecules.

Salmonella pathogenicity island 2-mediated overexpression of chimeric SspH2 proteins for simultaneous induction of antigen-specific CD4 and CD8 T cells

Salmonella enterica serovar Typhimurium employs two different type III secretion systems (TTSS) encoded within Salmonella pathogenicity islands 1 and 2 (SPI1 and SPI2) for targeting of effector proteins into the cytosol of eukaryotic cells during different stages of the infection cycle. The SPI1 TTSS translocates virulence factors across the plasma membrane when the bacterium initially contacts the host cell. In contrast, the SPI2 TTSS functions to translocate proteins across the membrane of the Salmonella-containing vacuole and promotes intracellular survival and replication. The aim of the present study was to directly compare the potentials of SPI1 and SPI2 type III effector proteins to act as carrier molecules for a heterologous antigen. The p60 protein of Listeria monocytogenes was used as a model antigen to construct chimeric SopE2 (SPI1), SifA (SPI2), and SspH2 (SPI2) proteins. SPI1- and SPI2-dependent up- and down-regulation of hybrid gene expression led to sequential translocation of p60 fusion proteins into the cytosol of Salmonella-infected macrophages. Mice orally immunized with recombinant Salmonella strains expressing these hybrid proteins revealed comparable numbers of p60-specific CD8 T cells. However, only overexpression of translocated SspH2/p60 from a medium-copy-number vector induced simultaneous antigen-specific CD4 and CD8 T-cell responses, suggesting that SspH2 is an attractive carrier molecule for foreign-protein delivery.

Associations between human leukocyte antigen (HLA) alleles and very high levels of measles antibody following vaccination

Associations between human leukocyte antigen (HLA) genes and very high levels of antibodies (or hyperseroresponsiveness) to measles antigens in a genetically heterogeneous human population are poorly understood. We studied the association between antibody levels after measles vaccination and HLA class I and II alleles among 170 US schoolchildren who received one dose of measles-mumps-rubella II vaccine. Vaccine recipients were divided into two groups: 93 recipients who were seropositive and 77 recipients who were hyperseropositive (the upper 10th percentile of antibody levels of all subjects). Out of all the alleles analyzed, HLA-B(*)7 (odds ratio (OR) 1.9; P = 0.05), DQA1(*)0104 (OR 4.6; P = 0.02) and DPA1(*)0202 (OR 4.8; P = 0.04) alleles were positively associated with hyperseropositivity, whereas HLA-B(*)44 (OR 0.4; P = 0.02), DRB1(*)01 (OR 0.6; P = 0.09), DRB1(*)08 (OR 0.3; P = 0.04), DQB1(*)0301 (OR 0.5; P = 0.04), and DPB1(*)0401 (OR 0.6; P = 0.03) alleles were negatively associated with hyperseropositivity. The alleles B(*)44, DRB1(*)01, DRB1(*)08 and DQA1(*)0104 remained statistically significant after accounting for the effects of other alleles. The results suggest that HLA alleles have important associations with measles antibody hyperseropositivity. These data increase our understanding of measles vaccine-induced immune response and will be useful for future mechanistic work on measles virus antigen processing and presentation in seronegative and hyperseropositive individuals.

Co-immunization with an HIV-1 Tat transduction peptide-rotavirus enterotoxin fusion protein stimulates a Th1 mucosal immune response in mice

The cholera toxin B subunit (CTB) and a 12 aa HIV-1 Tat transduction peptide were genetically linked to a 90 aa peptide from the murine rotavirus non-structural enterotoxin protein (NSP4) for comparison of receptor directed and transduction peptide mediated antigen targeting to the gut associated lymphoid tissues for enhanced protection against rotavirus infection. Oral immunization with Tat-NSP4(90) fusion protein isolated from Escherichia coli generated detectable anti-NSP4(90) IgG titers in mice. CTB-NSP4(90) fusion protein stimulated higher serum IgG titers than CTB fused to a 22 aa immunodominant epitope NSP4(22) indicating the presence of additional immunogenic epitopes in the NSP4(90) peptide. Mice immunized with CTB-NSP4(22) stimulated high IgG2a antibody levels suggesting a dominant Th1 lymphocyte response. However, mice immunized with CTB-NSP4(90) generated similar levels of IgG1 and IgG2a suggesting equal stimulation of Th1 and Th2 responses. Mice co-immunized with CTB-NSP4(90) and Tat-NSP4(90) fusion proteins generated dominant IgG2a levels indicating that the two ligands co-operate to generate an increased Th1 response.

Inverted pathogenicity: the use of pathogen-specific molecular mechanisms for prevention or therapy of disease

The term "inverted pathogenicity" stands for the exploitation of microbial toxins, virulence factors and cellular mechanisms for preventive or therapeutic purposes. This mini-review will focus on the major pathogenicity concept of Salmonella and Yersinia and how to use its underlying molecular principle for the development of a novel vaccination strategy. Both bacterial species employ a type III secretion system which mediates secretion and direct delivery (translocation) of antihost factors into the cytosol of eukaryotic cells. One of the best studied type III effector proteins is the 25-kDa Yersinia outer protein E (YopE). During the interaction of Yersinia with professional phagocytes, YopE translocation disturbs eukaryotic cytoskeleton dynamics and inhibits phagocytosis. YopE is a GTPase-activating protein that is active towards G proteins from the Rho family. Fusion of the N-terminal 138 amino acids of YopE comprising the translocation domain of the type III molecule to listeriolysin O (LLO) or p60 of Listeria monocytogenes results in hybrid proteins that are engaged and translocated by both Yersinia and Salmonella type III secretion systems. Oral immunization of mice with attenuated Yersinia or Salmonella vaccine strains expressing translocated chimeric YopE leads to pronounced LLO- or p60-peptide-specific CD8 T-cell responses that confer protective immunity. Surprisingly, cytosolic delivery of YopE/LLO by Yersinia also results in LLO-specific CD4 T-cell priming.

Yersinia outer protein E, YopE. A versatile type III effector molecule for cytosolic targeting of heterologous antigens by attenuated Salmonella

Many Gram-negative pathogens evade the host's immune response by utilizing a specialized protein secretion machinery, known as type III secretion system (TTSS). Virulence factors such as the Yersinia outer protein E (YopE) are delivered directly into the cytosol of target cells in a TTSS-dependent fashion. This unique translocation mechanism can be used by attenuated Salmonella carrier vaccines for the delivery of heterologous antigens fused to YopE into the MHC class I-restricted antigen processing pathway. In orally immunized mice, this novel vaccination strategy results in the induction of pronounced peptide-specific cytotoxic CD8 T cell responses.

Naturally processed measles virus peptide eluted from class II HLA-DRB1*03 recognized by T lymphocytes from human blood

This is the first report of the direct identification of a HLA-DRB1*03 measles-derived peptide from measles virus infected EBV-transformed B cells. We purified HLA-DR3-peptide complexes from EBV-B cells infected with measles virus (Edmonston strain) and sequenced the HLA-DR3-peptides by mass spectrometry. A class II peptide, derived from a measles phosphoprotein, ASDVETAEGGEIHELLRLQ (P1, residues 179-197), exhibited the capacity to stimulate peripheral blood mononuclear cells to proliferate. Our data provides direct evidence that the antigenic peptide of measles virus was processed by antigen-presenting cells, presented in the context of HLA class II molecules, and was recognized by peripheral blood T cells from healthy individuals previously immunized with measles vaccine. The approach described herein provides a useful methodology for the future identification of HLA-presented pathogen-derived epitopes using mass spectrometry. The study of cell-mediated immune responses to the measles-derived peptide in immune persons should provide significant insight into the design and development of new vaccines.

MHC allele-specific binding of a malaria peptide makes it become promiscuous on fitting a glycine residue into pocket 6

Peptide 1585 (EVLYLKPLAGVYRSLKKQLE) has a highly conserved amino-acid sequence located in the Plasmodium falciparum main merozoite surface protein (MSP-1) C-terminal region, required for merozoite entry into human erythrocytes and therefore represents a vaccine candidate for P. falciparum malaria. Original sequence-specific binding to five HLA DRB1* alleles (0101, 0102, 0401, 0701, and 1101) revealed this peptide's specific HLA DRB1*0102 allele binding. This peptide's allele-specific binding to HLA DRB1*0102 took on broader specificity for the DRB1*0101, -0401, and -1101 alleles when lysine was replaced by glycine in position 17 (peptide 5198: EVLYLKPLAGVYRSLKG(17)QLE). Binding of the identified G(10)VYRSLKGQLE(20) C-terminal register to these alleles suggests that peptide promiscuous binding relied on fitting Y(12), L(15), and G(17) into P-1, P-4, and P-6, respectively. The implications of the findings and the future of this synthetic vaccine candidate are discussed.

Bacterial type III translocation: a unique mechanism for cytosolic display of heterologous antigens by attenuated Salmonella

Upon infection, Gram-negative animal and plant pathogens evade the host immune response by utilizing a specialized protein secretion machinery, known as type III secretion system, for the export of bacterial virulence factors delivered directly into the cytosol of target cells. This unique translocation mechanism can be used for the delivery of large protein fragments derived from immunodominant viral and bacterial heterologous antigens into the MHC class I-restricted antigen-processing pathway by attenuated Salmonella carrier vaccines. In orally immunized mice, this novel vaccination strategy results in the induction of pronounced peptide-specific cytotoxic CD8 T cell responses.

Concomitant cytosolic delivery of two immunodominant listerial antigens by Salmonella enterica serovar typhimurium confers superior protection against murine listeriosis

During its interaction with host cells, Salmonella enterica serovar Typhimurium employs a type III secretion system for cytosolic targeting of virulence factors. This protein translocation mechanism is a useful tool for heterologous antigen delivery by attenuated Salmonella vaccine carrier strains. In the present study, we used the Yersinia outer protein E (YopE) as a carrier molecule for Salmonella type III-dependent cytosolic delivery of the immunodominant CD8 T-cell antigens listeriolysin O (LLO) and p60 of Listeria monocytogenes. It is shown that concomitant translocation of hybrid YopE/LLO and YopE/p60 proteins by Salmonella led to antigen presentation and CD8 T-cell priming efficacies comparable to those of translocation of single listerial antigens. However, simultaneous translocation of LLO and p60 significantly surpassed single cytosolic antigen delivery in the ability to protect against Listeria. For the first time, this study demonstrates that concomitant expression of two independent antigens via the same recombinant plasmid leads to superior protection against a challenge with an intracellular bacterial pathogen. In conclusion, these findings emphasize the versatility of Salmonella type III-mediated heterologous antigen delivery for the induction of cytotoxic T-lymphocyte-mediated immunity.

Cytokine modified tumor vaccines

The immune system can recognize tumors, but may be actively tolerized to tumors during the tumorigenesis process. The identity of most tumor antigens remains unknown, but the number is growing due to new techniques. Most clinical trials using genetically modified tumor vaccines have shown immunological responses (DTH), but few clinical responses. Certain chemotherapeutic agents may enhance the immune effects of genetically modified tumor vaccines.

Identification of an association between HLA class II alleles and low antibody levels after measles immunization

This is the first large cohort study to report a genetic association between humoral antibody level after measles vaccine and the HLA class II genes. The WHO goal to eradicate measles world-wide magnifies the importance of data relating to the influence of immunogenetics on measles vaccine-induced antibody responses. We present here the analysis of 242 individuals who received one dose of measles-mumps-rubella-II (MMR-II) vaccine at the age of 15 months and were genotyped for HLA class II alleles. These subjects fit into one of three categories; 72 were classified as seronegative, 93 were seropositive and 77 were serohyperpositive. HLA-DRB1*03 (odds ratio (OR), 2.22) and HLA-DPA1*0201 (OR, 1.71) were significantly associated with measles vaccine seronegativity, while additional alleles provided suggestive evidence of association with seronegativity: DQA1*0201, DQB1*0201, and DQA1*0501. The alleles DRB1*03 and DQA1*0201 remained statistically significant after accounting for the effects of other alleles. These findings are crucial in designing both measles eradication by the use of vaccine, and future vaccines to be used in genetically heterozygous populations.

Protection against murine listeriosis by oral vaccination with recombinant Salmonella expressing hybrid Yersinia type III proteins

In the present study, we have investigated the possibility to engage the Yersinia outer protein E (YopE) as a carrier molecule for heterologous Ag delivery by the type III secretion system of Salmonella typhimurium. Defined secretion and translocation domains of YopE were fused to the immunodominant T cell Ags listeriolysin O and p60 of Listeria monocytogenes. In vitro experiments showed that S. typhimurium allows secretion and translocation of large hybrid YopE proteins in a type III-dependent fashion. Translocation and cytosolic delivery of these chimeric proteins into host cells, but not secretion into endosomal compartments, led to efficient MHC class I-restricted Ag presentation of listerial nonamer peptides. Mice orally vaccinated with a single dose of attenuated S. typhimurium expressing translocated hybrid YopE proteins revealed high numbers of IFN-gamma-producing cells reactive with listeriolysin O 91-99 or p60 217-225, respectively. This CD8 T cell response protected mice against a challenge with L. monocytogenes. In conclusion, these findings suggest that YopE is a versatile carrier molecule for type III-mediated foreign Ag delivery by Salmonella vaccine strains.

Isolation and rapid identification of an abundant self-peptide from class II HLA-DRB1*0401 alleles induced by measles vaccine virus infection

Class II HLA-DR genes play an important role in the immune response to viral antigens. The effect of measles vaccine virus (MVV) infection on the induction of self-peptides presented by HLA-DR molecules during the immune response to viral infection is poorly known. Here, we describe a strategy for isolation and rapid sequence determination of an MVV-inducible class II bound peptide from a membrane protein (Leu-13). Peptides bound to HLA-DR4 (DRB1*0401 peptide complex) were eluted from immunoaffinity-purified HLA-DR4, peptides were differentially screened by MALDI-TOF-MS and subsequently sequenced by post source decay (PSD)-MALDI-TOF-MS. Human B-cells infected with MVV demonstrated an enhanced pattern of self-peptide production after MVV infection. This relatively simple analytical protocol provides a sensitive method for the direct identification of peptides associated with MHC class II DR molecules. More broadly, this same approach can be used to identify sequences of specific MVV processed peptides presented by any class II MHC DR molecule.

Enhanced major histocompatibility complex class I-dependent presentation of antigens modified with cationic and fusogenic peptides

Soluble extracellular protein antigens are notoriously poor stimulators of CD8+ cytotoxic T-lymphocyte (CTL) responses, largely because these antigens have inefficient access to an endogenous cytosolic pathway of the major histocompatibility complex (MHC) class I-dependent antigen presentation. Here, we present a strategy that facilitates antigen penetration into the cytosol of antigen-presenting cells (APC) by addition to the antigen of charge-modifying peptide sequences. As a result of this intervention, the charge modification enhances antigen uptake into APC by counteracting the repulsive cell surface charge, and then endosomal membranes are disrupted with a subsequent release of antigen into the cytosol. This technology significantly improves MHC class I-dependent antigen presentation to CTL, enabling a more efficient generation of specific CTL immunity in vivo. The strategy described here has potential for use in developing efficient vaccines for antigen-specific immunotherapy of human malignancies.

Dendritic cells: development, function and potential use for cancer immunotherapy

Dendritic cells (DC) are potent antigen presenting cells that are essential for the initiation of primary immune responses. They richly express MHC, costimulatory and adhesion molecules necessary for the stimulation of naive T cell populations. Dendritic cells are located at sites of antigen capture where they demonstrate phagocytic capacity and subsequently migrate to lymphatic areas for antigen presentation. Their phenotypic and functional characteristics are intimately linked to their stage of maturation. The hematopoietic development of dendritic cells is distinct and may follow several precursor pathways some closely linked to monocytes. Generation of large numbers of cells for potential clinical use has recently been accomplished through the in vitro culturing of progenitors with cytokines. The use of dendritic cell vaccines for cancer immunotherapy has emerged as an exciting new focus of investigation. Various strategies have been adopted to introduce tumor antigens into dendritic cells so that they may be more effectively presented to T cells in the context of costimulation. Animal models demonstrate that dendritic cell tumor vaccines reverse T-cell anergy and result in subsequent tumor rejection. Incorporating the expanding knowledge of dendritic cell biology into vaccine design is essential for the generation of effective immunotherapy for cancer patients.

Cancer vaccines: novel approaches and new promise

Cancer vaccines are a promising tool in the hands of the clinical oncologist. We have summarized the most recent findings and achievements in this exciting field. Tumor-associated antigens, as a basis for the new cancer vaccines, are reviewed. We emphasize novel approaches for the design of safe and more effective vaccines for cancer. We also discuss the possible clinical applications and the future prospects for vaccine development.

A concise methodology for the stereoselective synthesis of O-glycosylated amino acid building blocks: complete 1H NMR assignments and their application in solid-phase glycopeptide synthesis

A facile strategy for the stereoselective synthesis of suitably protected O-glycosylated amino acid building blocks, namely, Nalpha-Fmoc-Ser-[Ac4-beta-D-Gal-(1-3)-Ac2-alpha or beta-D-GalN3]-OPfp and Nalpha-Fmoc-Thr-[Ac4-beta-D-Gal-(1-3)-Ac2-alpha or beta-D-GalN3]-OPfp is described. What is new and novel in this report is that Koenigs-Knorr type glycosylation of an aglycon serine/threonine derivative (i.e. Nalpha-Fmoc-Ser-OPfp or Nalpha-Fmoc-Thr-OPfp) with protected beta-D-Gal(1-3)-D-GalN3 synthon mediated by silver salts resulted in only alpha- and/or beta-isomers in excellent yields under two different reaction conditions. The subtle differences in stereoselectivity were demonstrated clearly when glycosylation was carried out using only AgClO4 at -40 degrees C which afforded a-isomer in a quantitative yield (alpha:beta = 5:1). On the other hand, the beta-isomer was formed exclusively when the reaction was performed in the presence of Ag2CO3/AgClO4 at room temperature. A complete assignment of 1H resonances to individual sugar ring protons and the characteristic anomeric alpha-1 H and beta-1 H in Ac4Galbeta(1-3)Ac2GalN3 alpha and/or beta linked to Ser/Thr building blocks was accomplished unequivocally by two-dimensional double-quantum filtered correlated spectroscopy and nuclear Overhauser enhancement and exchange spectroscopy NMR experiments. An unambiguous structural characterization and documentation of chemical shifts, including the coupling constants for all the protons of the aforementioned alpha- and beta-isomers of the O-glycosylated amino acid building blocks carrying protected beta-D-Gal(1-3)-D-GalN3, could serve as a template in elucidating the three-dimensional structure of glycoproteins. The synthetic utility of the building blocks and versatility of the strategy was exemplified in the construction of human salivary mucin (MUC7)-derived, O-linked glycopeptides with varied degrees of glycosylation by solid-phase Fmoc chemistry. Fmoc/tert-butyl-based protecting groups were used for the peptidic moieties in conjunction with acetyl sugar protection. The transformation of the 2-azido group into the acetamido derivative was carried out with thioacetic acid on the polymer-bound glycopeptides before the cleavage step. After cleaving the glycopeptide from the resin, the acetyl groups used for sugar OH-protection were removed with sodium methoxide in methanol. Finally, the glycopeptides were purified by reversed-phase high-performance liquid chromatography and their integrity was confirmed by proton NMR as well as by mass spectral analysis. Secondary structure analysis by circular dichroism of both the glycosylated and nonglycosylated peptides revealed that carbohydrates did not exert any profound structural effect on the peptide backbone conformation.

Protein sorting within the MHC class II antigen-processing pathway

Major histocompatibility complex (MHC) class II molecules are required for the presentation of antigenic peptides that are derived predominantly from internalized proteins. The assembly of MHC class II/peptide complexes occurs within endosomal compartments of antigen-presenting cells (APCs). Therefore, for assembly to occur, MHC class II molecules, foreign proteins, and accessory molecules must be sorted to appropriate intracellular sites. My laboratory is trying to understand how proteins are sorted to various antigen-processing compartments as well as to conventional endosomal organelles. Using chimeric marker proteins and a variety of biochemical and genetic approaches, we are addressing the specificity of protein sorting and the mechanisms by which sorting signals are deciphered. By using a similar chimeric protein approach to target endogenous proteins to distinct compartments, we hope to address the role of processing events in each compartment in the generation of MHC class II ligands.

Human T-cell recognition of synthetic peptides representing conserved and variant sequences from the merozoite surface protein 2 of Plasmodium falciparum

Merozoite surface protein 2 (MSP2) is a malaria vaccine candidate currently undergoing clinical trials. We analyzed the peripheral blood mononuclear cell (PBMC) response to synthetic peptides corresponding to conserved and variant regions of the FCQ-27 allelic form of MSP2 in Ghanaian individuals from an area of hyperendemic malaria transmission and in Danes without exposure to malaria. PBMC from 20-39% of Ghanaians responded to each of the peptides by proliferation and 29-36% had PBMC which produced interferon-gamma (IFN-gamma) in response to peptide stimulation. In Danes, there was no proliferation to two of the peptides and only PBMC from 5% of the individuals proliferated to the other three peptides. IFN-gamma production was not detected to any peptide. In both Danes and Ghanaians in only a few instances was IL-4 detected in the PBMC cultures. Overall PBMC from 79% of the Ghanaians responded by proliferation and/or cytokine secretion to at least one of three peptides tested, whereas responses were only observed in 14% of Danes (P = 0.002). These data suggest that the Ghanaians had expanded peripheral blood T-cell populations recognizing the peptides as a result of natural infection. The findings are encouraging for the development of a vaccine based on these T-epitope containing regions of MSP2, as the peptides were broadly recognized suggesting that they can bind to diverse HLA alleles and also because they include conserved MSP2 sequences. Immunisation with a vaccine construct incorporating the sequences present in these peptides could thus be expected to be immunogenic in a high percentage of individuals and lead to the establishment of memory T-cells, which can be boosted through natural infection.