Charge-dependent translocation of Bordetella pertussis adenylate cyclase toxin into eukaryotic cells: implication for the in vivo delivery of CD8(+) T cell epitopes into antigen-presenting cells

Bordetella pertussis secretes a calmodulin-activated adenylate cyclase toxin, CyaA, that is able to deliver its N-terminal catalytic domain (400-aa residues) into the cytosol of eukaryotic target cells, directly through the cytoplasmic membrane. We have previously shown that CyaA can be used as a vehicle to deliver T cell epitopes, inserted within the catalytic domain of the toxin, into antigen-presenting cells and can trigger specific class I-restricted CD8(+) cytotoxic T cell responses in vivo. Here, we constructed a series of recombinant toxins harboring at the same insertion site various peptide sequences of 11-25 amino acids, corresponding to defined CD8(+) T cell epitopes and differing in the charge of the inserted sequence. We show that inserted peptide sequences containing net negative charges (-1 or -2) decreased or completely blocked (charge of -4) the internalization of the toxin into target cells in vitro and abolished the induction of cytotoxic T cell responses in vivo. The blocking of translocation due to the inserted acidic sequences can be relieved by appropriate mutations in the flanking region of CyaA that counterbalance the inserted charges. Our data indicate that (i) the electrostatic charge of the peptides inserted within the catalytic domain of CyaA is critical for its translocation into eukaryotic cells and (ii) the delivery of T cell epitopes into the cytosol of antigen-presenting cells by recombinant CyaA toxins is essential for the in vivo stimulation of specific cytotoxic T cells. These findings will help to engineer improved recombinant CyaA vectors able to stimulate more efficiently cellular immunity.

Identification of candidate target genes for EVI-1, a zinc finger oncoprotein, using a novel selection strategy

We have sought to identify and isolate target genes for the zinc finger protein, EVI-1, which has been implicated in the genesis of myelogenous leukemia both in mouse and human. We have approached this with a two-step selection: we first selected for genomic fragments of mouse DNA that bind to the protein with high affinity; second, we employed cDNA hybrid selection to identify gene sequences contained within these fragments. We show that we have constructed a sublibrary of genomic fragments that contains a significant fraction of the EVI-1-binding sites in the mouse genome. Our data has allowed us to estimate that there are approximately 4300 binding sites per haploid genome in the mouse. We further demonstrate that by using cDNA hybrid selection, it is relatively straightforward to isolate cDNAs that correspond to genes embedded in the EVI-1-binding sublibrary. Several of these are novel, but are represented in databases of anonymous human or mouse cDNAs (expressed sequence tags). One selected gene is Itpr2, encoding the inositol trisphosphate type two receptor, which is transcriptionally regulated during myelopoiesis. Finally, using a chimeric EVI-1-VP16-fusion protein under the control of a tetracycline-regulated system, we have shown that this chimeric activator can directly regulate Itpr2.

[Relevance of the stress-coping paradigm in the elaboration of a stress management model for schizophrenics]

Studies having used the stress-vulnerability model of schizophrenia as a conceptual framework demonstrate from different perspectives the contribution of stress when symptoms and deteriorations associated with this illness appear. The stress-coping paradigm provides an explanation of the effects of stress on health according to a contextual approach underlining how the coping process allows to diminish the negative effects of stress and favour adaptation in difficult or conflicting situations. This article proposes the integration of these two dominant currents and presents the Stress management model for schizophrenics. This new model provides the opportunity to favour the comprehension of the process of rehabilitation for schizophrenics and the development of new methods of intervention in rehabilitation.

Outbreak of trichinellosis in the Midi-Pyrenees region of France January - March 1998

Two outbreaks of trichinellosis in the Tarn et Garonne, departement, France were reported by the departmental health autorities on 2 March 1998, to the Reseau National de Sante Publique (RNSP). An epidemiological investigation began on 3 March in order to

Activation of B cells by 1 microm particulate lysozyme or peptides: a Th-dependent pathway requiring CD40-CD40 ligand interaction

Many antigens encountered by the immune system are included in complex structures such as bacteria or parasites. We previously developed an in vivo model to study the immunogenicity of particulate antigens, based on covalent linkage of proteins or peptides to 1 microm latex particles and showed that these antigens cannot be presented to MHC class II-restricted specific T cells by B cells. However, they induce strong CD4+ T cell responses when injected to mice without adjuvant. The present study demonstrates that four out of the five proteins tested did not stimulate antibody synthesis when linked to 1 microm microparticles, although a strong IgG production was induced by the same proteins administered in soluble form with adjuvant. In contrast, lysozyme and two synthetic peptides containing B and T cell viral epitopes induced strong and long-lasting specific antibody responses when linked to 1 micrometer synthetic beads. The isotypic pattern of antibodies induced by particulate lysozyme was similar to that induced by the soluble protein in alum. Studies using CD4+ T cell-depleted mice revealed that the induction of antibodies by particulate lysozyme strictly required Th cell activity. Moreover, the T-B cell cooperation involved in B cell activation by antigens linked to beads required CD40-CD40 ligand interaction. Thus, these particulate antigens provide a useful tool to study the mechanisms of induction of antibody response against complex bacterial or parasitic antigens. Moreover, they may represent attractive candidates to elaborate efficient new vaccines using short synthetic peptides.

Outbreak of trichinellosis in the Midi-Pyrénées region of France January - March 1998

Two outbreaks of trichinellosis in the Tarn et Garonne, département, France were reported by the departmental health autorities on 2 March 1998, to the Réseau National de Santé Publique (RNSP). An epidemiological investigation began on 3 March in order to

Reduced response to multiple vaccines sharing common protein epitopes that are administered simultaneously to infants

The plethora of newly discovered vaccines implies that, in the future, many vaccines will have to be administered simultaneously to infants. We examined the potential interference with the immune response of several coadministered vaccines containing the same protein component, namely, tetanus toxoid (TT). Infants simultaneously receiving a tetravalent pneumococcal vaccine conjugated to TT (PncT) and a diphtheria-tetanus-pertussis-poliovirus-Haemophilus influenzae type b-tetanus conjugate vaccine showed significantly lower anti-H. influenzae type b polysaccharide (polyribosylribitol phosphate [PRP]) antibody concentrations than those receiving either a tetravalent pneumococcal vaccine conjugated to diphtheria toxoid or placebo. A dose range study showed that anti-PRP antibody concentrations were inversely related to the TT content of the PncT vaccines administered in infancy. Postimmunization antitetanus antibody concentrations were also affected adversely as the TT content of the coadministered vaccines was increased. This phenomenon, which we believe derives from interference by a common protein carrier, should be taken into account when the introduction of an immunization program including multiple conjugate vaccines is considered.

A recombinant virus-like particle system derived from parvovirus as an efficient antigen carrier to elicit a polarized Th1 immune response without adjuvant

Hybrid virus-like particles (VLP) were prepared by self-assembly of the modified porcine parvovirus (PPV) VP2 capsid protein carrying a CD8+ or CD4+ T cell epitope. Immunization of mice with a single dose of these hybrid pseudo-particles, without adjuvant, induced strong cytotoxic T lymphocyte and T helper (Th) responses against the reporter epitope. The Th response was characterized by a Th1 phenotype. We also analyzed in vitro the uptake mechanism of these parvovirus-like particles and the processing requirements associated with presentation by MHC molecules. Although previously shown to be presented by MHC class I molecules, these particles also enter very efficiently the MHC class II endocytic pathway, and behave as conventional exogenous antigens. Indeed, the processing of chimeric PPV:VLP was performed in endosomal/lysosomal acidic vesicles and the presentation of the foreign epitope carried by these particles was sensitive to brefeldin A and cycloheximide, showing that the foreign peptide was loaded on nascent MHC class II molecules. These results give some indication of how PPV:VLP can be presented by MHC class I and class II molecules, and underscore the wide potency of such VLP system to deliver foreign antigens for vaccine design.

Immunodominance does not result from peptide competition for MHC class II presentation

Competition for binding to MHC class II molecules between processed peptides derived from a single protein Ag is considered an important parameter leading to the presentation of a limited set of peptides by APCs. We tested the relevance of this competition process in a model Ag, the MalE protein, by deleting T cell epitopes or by introducing a competitor T cell peptide. We identified in DBA/1 (I-Aq) mice six immunodominant T cell determinants in the MalE sequence, 89-95, 116-123, 198-205, 211-219, 274-281, and 335-341. Synthetic peptides carrying these determinants were classified in three groups as weak, intermediate, or strong I-Aq binders in competition experiments with the PreS:T peptide of hepatitis B surface Ag. In vivo, synthetic MalE peptides with weak and intermediate MHC binding capacity were inhibited in their capacity to stimulate proliferative response in the presence of the PreS:T competitor peptide, whereas the strongest MHC binder was not. Strikingly, the insertion of the potent competitor PreS:T peptide into the MalE sequence, as a single copy or as four copies, did not inhibit the proliferative response to the six immunodominant peptides of the recipient protein. Moreover, deletion in the protein sequence disrupting either the weak (198-205) or strong (335-341) MHC binding determinant of MalE did not modify the proliferative response to the remaining T cell determinants as compared with wild-type MalE protein. Altogether, these results show that peptide competition for MHC binding may not represent the most important event in processes leading to immunodominance.

In vivo treatment with recombinant IL-12 protects C57BL/6J mice against secondary alveolar echinococcosis

Using an experimental model of hepatic Echinococcus multilocularis infection in C57BL/6J mice, intraperitoneal administration of 0.8 microgram of recombinant IL-12 to mice with an established infection was shown to reduce the parasite burden as soon as two weeks after the end of treatment. At that time, in vitro Echinococcus multilocularis-induced spleen T cell proliferative responses as well as IFN-gamma and IL-5 production were higher in IL-12 treated mice than in untreated mice. Administration of 0.8 microgram of IL-12 at the time of infection was shown to be without effect on the parasite establishment. However, this treatment greatly inhibited the subsequent metacestode development. Indeed, ten weeks after infection, it induced a complete healing in 37.5% of mice. At that time, the development of metastases was inhibited in 68.75% of IL-12-treated mice. This reduction of parasite burden was mainly associated with a strong proliferation of spleen cells to E. multilocularis antigen and with a high IFN-gamma production. Altogether, our results show that IL-12 is of crucial importance in inhibiting the larval growth after the metacestode establishment in the liver and suggest that this cytokine could be of potential value in the treatment of human alveolar echinococcosis.

HgCl2-induced interleukin-4 gene expression in T cells involves a protein kinase C-dependent calcium influx through L-type calcium channels

Mercuric chloride (HgCl2) induces T helper 2 (Th2) autoreactive anti-class II T cells in Brown Norway rats. These cells produce interleukin (IL)-4 and induce a B cell polyclonal activation that is responsible for autoimmune disease. In Brown Norway rats, HgCl2 triggers early IL-4 mRNA expression both in vivo and in vitro by T cells, which may explain why autoreactive anti-class II T cells acquire a Th2 phenotype. The aim of this study was to explore the transduction pathways by which this chemical operates. By using two murine T cell hybridomas that express IL-4 mRNA upon stimulation with HgCl2, we demonstrate that: 1) HgCl2 acts at the transcriptional level without requiring de novo protein synthesis; 2) HgCl2 induces a protein kinase C-dependent Ca2+ influx through L-type calcium channels; 3) calcium/calcineurin-dependent pathway and protein kinase C activation are both implicated in HgCl2-induced IL-4 gene expression; and 4) HgCl2 can activate directly protein kinase C, which might be one of the main intracellular target for HgCl2. These data are in agreement with an effect of HgCl2 which is independent of antigen-specific recognition. It may explain the T cell polyclonal activation in the mercury model and the expansion of pathogenic autoreactive anti-class II Th2 cells in this context.

Restricted specificity of anti-V3 antibodies induced in humans by HIV candidate vaccines

We analyzed the fine specificity of anti-V3 antibodies elicited in three different species (human, guinea pig, and macaque) by various HIV candidate vaccines. Following immunization with recombinant canarypox virus expressing gp160MN or with recombinant gp160MN/LAI, this antibody response was shown to be directed against the NH2-terminal region of the V3 loop. Although this response was increased by a prime-boost regimen using immunization with canarypox expressing gp160 followed by an rgp160 boost, its specificity remained restricted mainly to the recognition of this region of the V3 loop. Pepscan analysis of sera confirmed the results obtained by ELISA and allowed the definition of an immunodominant common binding site for these sera located within the sequence NKRKRIHIGPGR. In contrast to these results, a boost with the V3 peptide was shown to broaden the antibody response and pepscan analysis showed that sera from individuals boosted with the V3 synthetic peptide recognize determinants all along the V3 loop. Similar fine specificity of anti-V3 antibodies was obtained in human, guinea pig, and macaque following immunization by a prime-boost regimen using canarypox recombinants expressing gp160 or gp120 and purified rgp160. In contrast, a V3 synthetic peptide boost stimulated the production of antibodies that recognize multiple epitopes within the V3 loop. Because the induction of antibodies that recognize multiple sites in the V3 loop could be of major importance to neutralize different HIV isolates, these results may have implications for the design and selection of HIV candidate vaccines.

Lack of H-2 gene influence on mouse susceptibility to secondary alveolar echinococcosis

To determine whether the development of hepatic Echinococcus multilocularis infection is influenced by major histocompatibility-linked genes, metacestode growth and host immune responses were compared in 4 C57BL/10 congenic murine strains of H-2b, H-2d, H-2k and H-2q haplotypes. Although the H-2q strain appeared slightly more resistant than the other strains, the 4 strains of mice developed comparable spleen cell proliferative response and Th1/Th2 cytokine production at 13 weeks p.i. A kinetic analysis, performed in 2 of these congenic strains, showed a similar pattern of parasite growth in these mice and failed to detect any significant difference in the production of parasite-specific IgM, IgG1 and IgG2, antibodies. Consequently, this study indicates that the control of secondary alveolar echinococcosis is not H-2 gene-linked.

Intracytoplasmic delivery of listeriolysin O by a vaccinal strain of Bacillus anthracis induces CD8-mediated protection against Listeria monocytogenes

The facultative intracellular pathogen Listeria monocytogenes secretes a 58-kDa hemolysin, listeriolysin O (LLO), that allows bacteria to access the cytoplasm and to multiply inside infected cells. LLO is also a protective Ag required for the development of specific immunity. We studied the capacity of a new bacterial vector, derived from an attenuated strain of Bacillus anthracis, to deliver in vivo LLO and to induce protection against L. monocytogenes infection. The hly gene encoding LLO was fused to a B. anthracis regulatory region induced in vivo and was integrated into a resident plasmid of this bacterium. This recombinant strain secreted a functional LLO in vitro and inside phagosomes of bone marrow macrophages. This LLO production enabled the conversion of the extracellular replicating B. anthracis into an intracytoplasmic bacterium. LLO+ B. anthracis thus mimicked the intracellular behavior of L. monocytogenes in macrophages. Specific protection of mice against lethal doses of L. monocytogenes was induced by immunization with LLO+ B. anthracis. The immunity was mediated by CD8+ T lymphocytes and was associated with the activation of LLO-specific MHC class I-restricted CD8+ CTL, able to recognize the immunodominant H-2d-restricted epitope 91-99 of LLO. This study, therefore, suggests that intracytoplasmic delivery of LLO by B. anthracis is sufficient to induce a MHC class I-restricted CD8-mediated protection against L. monocytogenes. The LLO+ B. anthracis recombinant strain represents a potential vector for delivering foreign Ags involved in CD8-mediated protective responses.

Intracytoplasmic delivery of listeriolysin O by a vaccinal strain of Bacillus anthracis induces CD8-mediated protection against Listeria monocytogenes

The facultative intracellular pathogen Listeria monocytogenes secretes a 58-kDa hemolysin, listeriolysin O (LLO), that allows bacteria to access the cytoplasm and to multiply inside infected cells. LLO is also a protective Ag required for the development of specific immunity. We studied the capacity of a new bacterial vector, derived from an attenuated strain of Bacillus anthracis, to deliver in vivo LLO and to induce protection against L. monocytogenes infection. The hly gene encoding LLO was fused to a B. anthracis regulatory region induced in vivo and was integrated into a resident plasmid of this bacterium. This recombinant strain secreted a functional LLO in vitro and inside phagosomes of bone marrow macrophages. This LLO production enabled the conversion of the extracellular replicating B. anthracis into an intracytoplasmic bacterium. LLO+ B. anthracis thus mimicked the intracellular behavior of L. monocytogenes in macrophages. Specific protection of mice against lethal doses of L. monocytogenes was induced by immunization with LLO+ B. anthracis. The immunity was mediated by CD8+ T lymphocytes and was associated with the activation of LLO-specific MHC class I-restricted CD8+ CTL, able to recognize the immunodominant H-2d-restricted epitope 91-99 of LLO. This study, therefore, suggests that intracytoplasmic delivery of LLO by B. anthracis is sufficient to induce a MHC class I-restricted CD8-mediated protection against L. monocytogenes. The LLO+ B. anthracis recombinant strain represents a potential vector for delivering foreign Ags involved in CD8-mediated protective responses.

Secondary Echinococcus multilocularis infection in A/J mice: delayed metacestode development is associated with Th1 cytokine production

The course of Echinococcus multilocularis infection was studied in four different strains of mice after intrahepatic inoculation of a metacestode homogenate. Among these strains of mice, A/J and BALB/c mice were characterized, respectively, as the most resistant and susceptible strains. Although there was no significant difference between the mean surface of hepatic metacestodes of these two strains of mice at any examination time, 13 weeks after infection, the mean metastatic burden of A/J mice was significantly lower than that of BALB/c mice. Moreover, at this time, some BALB/c mice spontaneously died from their infection whereas all A/J mice remained in good health. The relative resistance of A/J mice to parasite development was associated with a strong and sustained in vitro spleen cell proliferative response to a crude E. multilocularis extract as well as with a high parasite-induced production of IFN-gamma and IL-2. The susceptibility of BALB/c mice was on the contrary associated with a high IL-4 production. Interestingly, the parasite extract also stimulated a significant IL-4 production by spleen cells of uninfected susceptible BALB/c mice, but not by control A/J mouse spleen cells. Altogether, these results suggest that the relative resistance of A/J mice to E. multilocularis growth is associated with the development of T cell responses characterized by the production of high levels of Th1 cytokines.

In vivo T helper cell response to retro-inverso peptidomimetics

Peptide analogues containing reversed peptide bonds between each residue along the peptide sequence (retro-inverso modification) have been analyzed for their antigenic and in vivo immunogenic properties in the MHC II and Th cell response context. Two antigenic peptides were selected for this study, namely peptide 103-115 of poliovirus VP1, which is involved in the production of Abs that neutralize the infectivity of the virus, and peptide 435-446 from the third constant region of mouse heavy chain IgG2a allopeptide gamma 2ab, which mimics a corneal Ag implicated in autoimmune keratitis. In a competition assay performed in vitro using reference hybridomas of known MHC class II restriction, both retro-inverso analogues bound (although more weakly in our test) to I-Ad and/or I-Ed class II molecules. However, in both cases, this lower affinity was apparently largely compensated in vivo, as a T cell response (with IL-2 secretion), equivalent to that obtained with the wild-type peptides, was observed following immunization of BALB/c mice with the retro-inverso analogues. Moreover, these T cells proliferated and produced IL-2 in response to the cognate peptides. It is concluded that the T cell receptors of T cells primed in vivo with the retro-inverso analogues readily cross-react with parent and retro-inverso analogue-MHC complexes. The approach of using pseudopeptides containing changes involving the backbone, and not the orientation of side chains, may thus be promising to design potent immunogens for class II-restricted T cells.

In vivo T helper cell response to retro-inverso peptidomimetics

Peptide analogues containing reversed peptide bonds between each residue along the peptide sequence (retro-inverso modification) have been analyzed for their antigenic and in vivo immunogenic properties in the MHC II and Th cell response context. Two antigenic peptides were selected for this study, namely peptide 103-115 of poliovirus VP1, which is involved in the production of Abs that neutralize the infectivity of the virus, and peptide 435-446 from the third constant region of mouse heavy chain IgG2a allopeptide gamma 2ab, which mimics a corneal Ag implicated in autoimmune keratitis. In a competition assay performed in vitro using reference hybridomas of known MHC class II restriction, both retro-inverso analogues bound (although more weakly in our test) to I-Ad and/or I-Ed class II molecules. However, in both cases, this lower affinity was apparently largely compensated in vivo, as a T cell response (with IL-2 secretion), equivalent to that obtained with the wild-type peptides, was observed following immunization of BALB/c mice with the retro-inverso analogues. Moreover, these T cells proliferated and produced IL-2 in response to the cognate peptides. It is concluded that the T cell receptors of T cells primed in vivo with the retro-inverso analogues readily cross-react with parent and retro-inverso analogue-MHC complexes. The approach of using pseudopeptides containing changes involving the backbone, and not the orientation of side chains, may thus be promising to design potent immunogens for class II-restricted T cells.

The preferential induction of a Th1 immune response by DNA-based immunization is mediated by the immunostimulatory effect of plasmid DNA

In the present study, we have investigated the T cell response to the HBsAg, normally secreted as multivalent particles, and to beta-galactosidase, a cytoplasmic antigen, delivered as plasmid DNAs. We found that cytokines characteristic of a Th1 phenotype are produced in mice immunized by these plasmid DNAs. Using repeated injections of low doses of purified antigen, we demonstrated that neither prolonged presence of the antigen nor site of immunization resulted in an immune response with characteristics resembling those obtained with DNA-mediated immunization. Analysis of immune responses induced in mice by coinjection of plasmid DNA and beta-galactosidase or HBsAg demonstrated that the coinjected DNA stimulated a Th1 response against the injected antigen. These data therefore strongly suggest that the strong immune response obtained after intramuscular DNA immunization was due to the adjuvant effect of the plasmid DNA which is also responsible for the selective activation of CD4(+) T cells with a Th1 phenotype.

Genetic control of antibody responses induced by recombinant Mycobacterium bovis BCG expressing a foreign antigen

Recombinant Mycobacterium bovis BCG expressing foreign antigens represents a promising candidate for the development of future vaccines and was shown in several experimental models to induce protective immunity against bacterial or parasitic infections. Innate resistance to BCG infection is under genetic control and could modify the immune responses induced against an antigen delivered by such engineered microorganisms. To investigate this question, we analyzed the immune responses of various inbred strains of mice to recombinant BCG expressing beta-galactosidase. These experiments demonstrated that BALB/c mice developed strong antibody responses against BCG expressing beta-galactosidase under the control of two different promoters. In contrast, C57BL/6, C3H, and CBA mice produced high anti-beta-galactosidase antibody titers only when immunized with recombinant BCG expressing beta-galactosidase under the control of the pblaF* promoter, which induced the production of high levels of this antigen. This difference in mouse responsiveness to recombinant BCG was not due to innate resistance to BCG infection, since similar immune responses were induced in Ity(r) and Ity(s) congenic strains of mice. In contrast, the analysis of anti-beta-galactosidase antibody responses of H-2 congenic mice in two different genetic backgrounds demonstrated that H-2 genes are involved in the immune responsiveness to beta-galactosidase delivered by recombinant BCG. Together, these results demonstrate that immune responses to an antigen delivered by recombinant BCG are under complex genetic influences which could play a crucial role in the efficiency of future recombinant BCG vaccines.

Recombinant parvovirus-like particles as an antigen carrier: a novel nonreplicative exogenous antigen to elicit protective antiviral cytotoxic T cells

To develop a strategy that promotes efficient antiviral immunity, hybrid virus-like particles (VLP) were prepared by self-assembly of the modified porcine parvovirus VP2 capsid protein carrying a CD8(+) T cell epitope from the lymphocytic choriomeningitis virus nucleoprotein. Immunization of mice with these hybrid pseudoparticles, without adjuvant, induced strong cytotoxic T lymphocyte (CTL) responses against both peptide-coated- or virus-infected-target cells. This CD8(+) class I-restricted cytotoxic activity persisted in vivo for at least 9 months. Furthermore, the hybrid parvovirus-like particles were able to induce a complete protection of mice against a lethal lymphocytic choriomeningitis virus infection. To our knowledge, this study represents the first demonstration that hybrid nonreplicative VLP carrying a single viral CTL epitope can induce protection against a viral lethal challenge, in the absence of any adjuvant. These recombinant particles containing a single type of protein are easily produced by the baculovirus expression system and, therefore, represent a promising and safe strategy to induce strong CTL responses for the elimination of virus-infected cells.

L-type calcium channel activation controls the in vivo transduction of the neuralizing signal in the amphibian embryos

We have analyzed the transduction pathways involved in the triggering of neural induction, in amphibian embryos, in vivo. Using a plasmid construction, we have targetted the bioluminescent calcium probe aequorin to the plasma membrane of ectoderm cells of the amphibian Pleurodeles waltl before gastrulation. We have demonstrated that the in vivo triggering of neural induction depends on the activation of calcium-dependent pathways and involves L-type calcium channels. Furthermore, on excised ectoderm taken at the gastrula stage, we show that noggin, a protein currently considered as one of the natural inducers, also activates L-type calcium channels. This activation represents the first necessary event to determine cells of the dorsal ectoderm toward the neural pathway.

Preparation of a multiple antigen glycopeptide (MAG) carrying the Tn antigen. A possible approach to a synthetic carbohydrate vaccine

The glycosidic tumor-associated Tn antigen was conjugated to a lysine backbone containing a helper T-cell epitope in order to activate immune responses specific for some types of carcinomas. As opposed to traditional protein conjugates, this multiple antigen glycopeptide (MAG) offers the advantages of the lack of immunogenicity of the polylysine core and of accurate chemical definition. The MAG construction was assembled by conventional solid-phase peptide synthesis. The analysis of its antigenicity demonstrated that the Tn antigen on the MAG is recognized by Tn-specific monoclonal antibodies.

Parameters affecting the immunogenicity of recombinant T cell epitopes inserted into hybrid proteins

In the past few years a considerable number of studies have focused on the mechanisms of antigen presentation by classical major histocompatibility complex (MHC) class I and class II encoded molecules. Among different approaches, the engineering of recombinant chimeric genes and proteins has provided new tools to analyze the parameters influencing the intracellular processing of antigenic determinants. This review will summarize and discuss the different models of recombinant genes and molecules that have been used to analyze the influence of the molecular environment of a T cell determinant on its efficient processing and MHC presentation. This approach may also represent an interesting tool for developing new vaccine strategies for inducing T cell responses against pathogens.