Analysis of the mechanism for extracellular processing in the presentation of human immunodeficiency virus-1 envelope protein-derived peptide to epitope-specific cytotoxic T lymphocytes

An Overview of Peptides and Peptide Pools for Antigen-Specific Stimulation in T-Cell Assays

The analysis of antigen-specific T-cell responses has become routine in many laboratories. Functional T-cell assays like enzyme-linked-immuno-spot (ELISPOT), which depend on antigen-specific stimulation, increasingly use peptides to represent the antigen of interest. Besides single peptides, mixtures of peptides (peptide pools) are very frequently applied. Such peptide pools may, for example, represent entire proteins (with overlapping peptides covering a protein sequence) or include noncontiguous peptides such as a collection of T-cell-stimulating peptides. The optimum specification of single peptides or peptide pools for T-cell stimulation assays will depend on the purpose of the test, the target T-cell population, the availability of sample, requirements regarding reproducibility, and, last but not least, the available budget, to mention only the most important factors. Because of the way peptides are produced, they will always contain certain amounts of impurities such as peptides with deletions or truncated peptides, and there may be additional by-products of peptide synthesis. Optimized synthesis protocols as well as purification help reduce impurities that might otherwise cause false-positive assay results. However, specific requirements with respect to purity will vary depending on the purpose of an assay. Finally, storage conditions significantly affect the shelf life of peptides, which is relevant especially for longitudinal studies. The present book chapter addresses all of these aspects in detail. It should provide the researcher with all necessary background knowledge for making the right decisions when it comes to choosing, using, and storing peptides for ELISPOT and other T-cell stimulation assays.

Overexpression of angiotensin-converting enzyme in myelomonocytic cells enhances the immune response

Angiotensin-converting enzyme (ACE) converts angiotensin I to the vasoconstrictor angiotensin II and thereby plays an important role in blood pressure control. However, ACE is relatively non-specific in its substrate specificity and cleaves many other peptides. Recent analysis of mice overexpressing ACE in monocytes, macrophages, and other myelomonocytic cells shows that these animals have a marked increase in resistance to experimental melanoma and to infection by Listeria monocytogenes or methicillin-resistant Staphylococcus aureus (MRSA). Several other measures of immune responsiveness, including antibody production, are enhanced in these animals. These studies complement a variety of studies indicating an important role of ACE in the immune response.

Rediscovering ACE: novel insights into the many roles of the angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is best known for the catalytic conversion of angiotensin I to angiotensin II. However, the use of gene-targeting techniques has led to mouse models highlighting many other biochemical properties and actions of this enzyme. This review discusses recent studies examining the functional significance of ACE tissue-specific expression and the presence in ACE of two independent catalytic sites with distinct substrates and biological effects. It is these features which explain why ACE makes important contributions to many different physiological processes including renal development, blood pressure control, inflammation, and immunity.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Loss of Angiotensin-converting enzyme-related (ACER) peptidase disrupts night-time sleep in adult Drosophila melanogaster

Drosophila Acer (Angiotensin-converting enzyme-related) encodes a member of the angiotensin-converting enzyme family of metallopeptidases that have important roles in the endocrine regulation of blood homeostasis in mammals. Acer is expressed in the embryonic heart of Drosophila and expression in the adult head appears to be regulated by two clock genes. To study the role of Acer in development and in circadian activity, we have generated Acer null mutants by imprecise excision of a P-element and have compared their development and circadian behaviour with that of wild-type flies with the same genetic background. We show that Acer is not required for normal development, but that night sleep, which is clock regulated, is disrupted in adult flies lacking ACER. Acer null adults have reduced night-time sleep and greater sleep fragmentation, but normal levels of daytime sleep. The quality of night sleep in flies fed inhibitors of ACER is affected in a very similar manner. We have shown, using specific antibodies, that ACER is present in the adult fat body of the head and abdomen, and is secreted into the haemolymph. ACER might therefore have a role in cleaving regulatory peptides involved in metabolism and activity behaviour. There are similarities with mammals, where ACE peptidases are also expressed in adipose tissue and are thought to be part of a signalling system linking metabolism with sleep.

Expression of angiotensin-converting enzyme changes major histocompatibility complex class I peptide presentation by modifying C termini of peptide precursors

We recently reported a mouse model called ACE 10/10 in which macrophages overexpress the carboxypeptidase angiotensin-converting enzyme (ACE). These mice have an enhanced inflammatory response to tumors that markedly inhibits tumor growth. Here, we show that ACE modifies the C termini of peptides for presentation by major histocompatibility complex (MHC) class I molecules. The peptide-processing activity of ACE applies to antigens from either the extracellular environment (cross-presentation) or antigens produced endogenously. Consistent with its role in MHC class I antigen processing, ACE localizes to the endoplasmic reticulum. ACE overexpression does not appear to change the overall supply of peptides available to MHC class I molecules. The immunization of wild type mice previously given ACE 10/10 macrophages enhances the efficiency of antigen-specific CD8+ T cell priming. These data reveal that ACE is a dynamic participant in fashioning the peptide repertoire for MHC class I molecules by modifying the C termini of peptide precursors. Manipulation of peptidase expression by antigen-presenting cells may ultimately prove a useful strategy to enhance the immune response.

V3 CTL epitope density in a single recombinant molecule antigen differentially affects the number and activity of primary and memory CD8+ T cells

Previous studies have found the close correlation between epitope density and epitope-specific response, which have shown that high epitope density in a single recombinant protein molecule significantly enhances the humoral response and protective immunity. However, it has not been determined whether this kind of high epitope density could also significantly influence T cell response. Based on this, a series of recombinant DNA and proteins were designed and prepared. Each molecule consists of various copy numbers of the V3 CTL epitope on HIV-1 gp120 (one, two, four and eight copies). Our results show clearly that different V3-epitope densities in just one single DNA or protein molecules have respectively different effects on the number and activity of both primary and memory T cells. Interestingly, this effect is more complex than that on the B cells: epitope density in one plasmid or protein antigen affects the number, not the cytotoxic avidity, of primary CD8+ T cells, but affects both the number and cytotoxic avidity of memory CD8+ T cells. It indicates epitope density in the antigen is an important consideration to optimize T cell response induction and may facilitate the development of effective T cell-based anti-virus vaccines.

Mice with enhanced macrophage angiotensin-converting enzyme are resistant to melanoma

Angiotensin-converting enzyme (ACE) is a peptidase responsible for the cleavage of angiotensin I and several other peptides. Here, gene targeting was used to switch control of the ACE locus from the endogenous promoter to the macrophage-specific c-fms promoter. Challenge of these mice, called ACE 10/10, with the aggressive mouse melanoma cell line B16 showed that they are remarkably resistant to tumor growth. Tumor resistance was seen after challenge with different melanoma cell lines and in mice with different genetic backgrounds. Histological study of the tumors that did grow in ACE 10/10 mice showed an enhanced inflammatory response. ACE 10/10 mice had increased numbers of tumor epitope-specific CD8(+) T cells after challenge with melanoma or lymphoma. ACE 10/10 macrophages showed increased production of interleukin-12 and nitric oxide but reduced interleukin-10. Engraftment of wild-type mice with ACE 10/10 bone marrow transferred B16 tumor resistance. Injection of B16 tumors with ACE 10/10 macrophages also reduced tumor growth. ACE 10/10 mice may define a new means of enhancing the immune response, which may be potentially useful in several human clinical situations.

Angiotensin-converting enzyme gene insertion/deletion polymorphism is associated with risk of oral precancerous lesion in betel quid chewers

To investigate whether angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism is related to the risk of oral precancerous lesions (OPL) in Taiwanese subjects who chew betel quid, a total of 61 betel quid chewers having OPL were compared with 61 asymptomatic betel quid chewers matched for betel quid chewing duration and dosage. The frequency of homozygote for ACE D variant is significantly higher in the case subjects than that of the controls (44.3 vs 24.6%; P=0.0108). The adjusted odds ratio of the D homozygous for the risk of OPL is 8.10 (95% confidence interval (CI)=2.04–32.19, P=0.003). In the allelic base analysis, the D allele is also significantly associated with higher risk of OPL. When grouping the study subjects by smoking status, the association between ACE I/D polymorphism and risk of OPL was only observed in nonsmokers. Our results support the theory that genetic factors may contribute to the susceptibility of OPL and suggest that smoking and genetic factors may be differently involved in the development of OPL.

Analysis of antigen-specific T-cell responses with synthetic peptides--what kind of peptide for which purpose?

The analysis of T-cell responses to peptides has recently become a busy area of immunologic research. Peptides may be used as single stimulants, pools or libraries, or as part of peptide/major histocompatibility complexes (MHC) for direct T-cell receptor staining. For stimulating T cells, peptides must be bound to MHC molecules. In this study we have used 9- or 10-amino acid peptides, 15-amino acid peptides containing stimulating shorter sequences, and peptides with modified C-terminal function. On average 67% of the T cells from healthy cytomegalovirus-positive donors that bound a frequently used cytomegalovirus pp65/HLA-A*0201 tetramer were able to produce interferon-gamma on stimulation with the respective 9-amino acid peptide. Peptides of 15 amino acids length used at the same concentration (in microg/ml) stimulated CD8 T cells somewhat less efficiently (on average 77% of the frequencies induced with the respective shorter peptides). Modifications of 9-amino acid peptides such as addition of amino acids or functional groups often resulted in a decreased ability to stimulate. However, based on our own results, published data, and theoretic considerations, we conclude that sets of peptides of 15 amino acids length with 11 amino acids overlap represent a good compromise for stimulating both CD8 and CD4 T cells in a number of applications. These parameters may be modified subject to the purpose of a study.

Random screening of proteins for HLA-A*0201-binding nine-amino acid peptides is not sufficient for identifying CD8 T cell epitopes recognized in the context of HLA-A*0201

HLA-A2 is the most frequent HLA molecule in Caucasians with HLA-A*0201 representing the most frequent allele; it was also the first human HLA allele for which peptide binding prediction was developed. The Bioinformatics and Molecular Analysis Section of the National Institutes of Health (BIMAS) and the University of Tübingen (Syfpeithi) provide the most popular prediction algorithms of peptide/MHC interaction on the World Wide Web. To test these predictions, HLA-A*0201-binding nine-amino acid peptides were searched by both algorithms in 19 structural CMV proteins. According to Syfpeithi, the top 2% of predicted peptides should contain the naturally presented epitopes in 80% of predictions (www.syfpeithi.de). Because of the high number of predicted peptides, the analysis was limited to 10 randomly chosen proteins. The top 2% of peptides predicted by both algorithms were synthesized corresponding to 261 peptides in total. PBMC from 10 HLA-A*0201-positive and CMV-seropositive healthy blood donors were tested by ex vivo stimulation with all 261 peptides using crossover peptide pools. IFN-gamma production in T cells measured by CFC was used as readout. However, only one peptide was found to be stimulating in one single donor. As a result of this work, we report a potential new T cell target protein, one previously unknown CD8-T cell-stimulating peptide, and an extensive list of CMV-derived potentially strong HLA-A*0201-binding peptides that are not recognized by T cells of HLA-A*0201-positive CMV-seropositive donors. We conclude that MHC/peptide binding predictions are helpful for locating epitopes in known target proteins but not necessarily for screening epitopes in proteins not known to be T cell targets.

Antigen presentation in vaccine development

A variety of microorganisms, nutrients or toxins are generally intrude our body through mucosal tissues or skin, where equipment for both preventing their invasions and catching their information to activate internal immune systems for adapting surroundings is arranged. Among the equipment, cells in charge of innate immunity, particularly dendritic cells (DCs), having an excellent capacity for prompt recognition of invaded pathogens via toll-like receptors (TLRs) to alert B and T cells for establishing aquired/adaptive immunity by presenting their processed antigenic fragments, have been paid great attention. These TLR-activated, antigen captured DCs are divided into two groups; one is pathogen-retaining unit and the other is pathogen-controlling unit. The latter DCs present processed antigenic molecules from the pathogens to competent alphabeta T cells together with special containers, such as class I, class II MHC and CD1 to generate specific cellular immunity. The former two MHC molecules can present processed peptide antigens, whereas the last CD1 molecule can present glycolipid/lipid antigens. In contrast, B lymphocytes that captured antigens via their specific immunoglobulin (Ig) receptors present digested peptide fragments with their class II MHC to stimulate suitable CD4(+) helper T cells which in turn secrete various cytokines to efficiently expand and maintain antibody production from that partner B cells to establish humoral immunity. These alphabeta T cells and antibodies, recognize either processed antigenic peptide or glycolipid fragments, and thus, identification of these epitopes enables us to generate artificial pathogen-specific vaccines. Based on the recent findings about precise mechanisms of antigen processing and presentation orchestrated at the surface compartment, future development of vaccines against various pathogens are discussed.

Induction of hepatic injury by hepatitis C virus-specific CD8+ murine cytotoxic T lymphocytes in transgenic mice expressing the viral structural genes

In the present study, we generated killer cells specific for hepatitis C virus (HCV) structural protein by re-stimulation of immune spleen cells from H-2(d) haplotype transgenic (Tg) mice, expressing the core, E1, E2, and NS2 genes of HCV regulated by the Cre/loxP switching system. The generated killer cells were conventional CD8(+)L(d) class-I MHC molecule-restricted cytotoxic T lymphocytes (CTLs) and specific for the HCV E1 structural protein. Because the CTLs could also kill hepatocytes from the Tg mice expressing HCV structural proteins in vitro, we attempted to transfer those CTLs intravenously into interferon regulatory factor-1 (IRF-1) negative, CD8-deficient Tg mice representing the HCV structural genes on hepatocytes to examine whether the inoculated CD8(+) CTLs can eliminate hepatocytes expressing the HCV genes in vivo. We observed an elevation of serum ALT level as well as damage of the liver tissue histologically. To our knowledge, this is the first demonstration to show that HCV-specific CD8(+) CTLs specifically attack hepatocytes expressing the HCV structural proteins both in vitro and in vivo.

HIV mucosal vaccine: nasal immunization with gp160-encapsulated hemagglutinating virus of Japan-liposome induces antigen-specific CTLs and neutralizing antibody responses

Nasal immunization of normal mice with HIVgp160-encapsulated hemagglutinating virus of Japan (HVJ)-liposome induced high titers of gp160-specific neutralizing IgG in serum and IgA in nasal wash, saliva, fecal extract, and vaginal wash, along with both Th1- and Th2-type responses. HIVgp160-specific IgG- and IgA-producing cells were also detected in mononuclear cells isolated from spleen, nasal cavity, salivary gland, intestinal lamina propria, and vaginal tissue of nasally immunized mice. In addition, CD8(+) CTLs were induced in mice nasally immunized with gp160-HVJ-liposome. These findings suggest that two layers of effective HIV-specific humoral and cellular immunity, in mucosal and systemic sites, were induced by this nasal vaccine. In immunodeficient mice, nasal immunization with gp160-HVJ-liposome induced Ag-specific immune responses for the systemic and mucosal compartments of both Th1 (IFN-gamma(-/-)) and Th2 (IL-4(-/-)). In vitro Ag-specific serum IgG Ab and vaginal wash samples possessing IgA and IgG Abs that had been induced by nasal immunization with gp160-HVJ-liposome were able to neutralize a clinically isolated strain of HIV-MN strain isolated from Japanese hemophiliac patients. Taken together, these results suggest that, for the prevention and control of AIDS, nasally administered gp160-HVJ-liposome is a powerful immunization tool that induces necessary Ag-specific immune responses at different stages of HIV infection.

Expression of human immunodeficiency virus type 1 gp120 from herpes simplex virus type 1-derived amplicons results in potent, specific, and durable cellular and humoral immune responses

Herpes simplex virus type 1 (HSV-1) infects a wide range of cells, including dendritic cells. Consequently, HSV-1 vectors may be capable of eliciting strong immune responses to vectored antigens. To test this hypothesis, an HSV-1 amplicon plasmid encoding human immunodeficiency virus type 1 gp120 was constructed, and murine immune responses to helper virus-free amplicon preparations derived from this construct were evaluated. Initial studies revealed that a single intramuscular (i.m.) injection of 10(6) infectious units (i.u.) of HSV:gp120 amplicon particles (HSV:gp120) elicited Env-specific cellular and humoral immune responses. A potent, CD8(+)-T-cell-mediated response to an H-2D(d)-restricted peptide from gp120 (RGPGRAFVTI) was measured by a gamma interferon ELISPOT and was confirmed by standard cytotoxic-T-lymphocyte assays. Immunoglobulin G enzyme-linked immunosorbent assay analysis showed the induction of a strong, Env-specific antibody response. An i.m. or an intradermal administration of HSV:gp120 at the tail base elicited a more potent cellular immune response than did an intraperitoneal (i.p.) inoculation, although an i.p. introduction generated a stronger humoral response. The immune response to HSV:gp120 was durable, with robust cellular and humoral responses persisting at 171 days after a single 10(6)-i.u. inoculation. The immune response to HSV:gp120 was also found to be dose dependent: as few as 10(4) i.u. elicited a strong T-cell response. Finally, HSV:gp120 elicited significant Env-specific cellular immune responses even in animals that had been previously infected with wild-type HSV-1. Taken together, these data strongly support the use of helper-free HSV-1 amplicon particles as vaccine delivery vectors.

Stimulation of HIV gp120-specific cytolytic T lymphocyte responses in vitro and in vivo using a detoxified pertussis toxin vector

CD8+ cytolytic T lymphocytes (CTL) are almost certainly an important component of a potentially protective immune response to HIV. To test the ability of pertussis toxin (PT) to deliver an HIV-derived major histocompatibility complex (MHC) class I peptide for CTL stimulation, we constructed a fusion of the gp120 P18-I10 CTL epitope with a genetically detoxified derivative of PT (PT9K/129G) and assayed this fusion for its ability to stimulate a gp120-specific CTL response in vitro and in vivo. Antigen-presenting cells incubated with this fusion protein were lysed by P18-I10-specific CTL in vitro and this activity was shown to be MHC class I restricted. The activity was inhibited by brefeldin A but was not inhibited by proteasome inhibitors, possibly because PT undergoes retrograde intracellular transport through the Golgi apparatus to the endoplasmic reticulum and delivers epitopes directly to nascent class I molecules. Mice immunized intraperitoneally with a single dose of the fusion protein without adjuvant raised a strong gp120-specific CTL response in the spleen. This CTL response was dependent on (1) the dose of fusion administered, (2) the fusion of the epitope with the toxin (since coadministration of peptide and toxin gave no response), and (3) the activity of CD8+ cells. These data demonstrate that this detoxified derivative to PT, which is already a component of a licensed vaccine for humans, could represent a useful vaccine vector molecule for stimulation of HIV-specific CTL responses.