Immunogenicity of a contiguous T-B synthetic epitope of the A/PR/8/34 influenza virus

BepiTBR: T-B reciprocity enhances B cell epitope prediction

The ability to predict B cell epitopes is critical for biomedical research and many clinical applications. Investigators have observed the phenomenon of T-B reciprocity, in which candidate B cell epitopes with nearby CD4+ T cell epitopes have higher chances of being immunogenic. To our knowledge, existing B cell epitope prediction algorithms have not considered this interesting observation. We developed a linear B cell epitope prediction model, BepiTBR, based on T-B reciprocity. We showed that explicitly including the enrichment of putative CD4+ T cell epitopes (predicted HLA class II epitopes) in the model leads to significant enhancement in the prediction of linear B cell epitopes. Curiously, the positive impact on B cell epitope generation is specific to the enrichment of DQ allele binders. Overall, our work provides interesting mechanistic insights into the generation of B cell epitopes and points to a new avenue to improve B cell epitope prediction for the field.

T-B cell epitope peptides induce protective immunity against Mycoplasma pneumoniae respiratory tract infection in BALB/c mice

Mycoplasma pneumoniae is the most common pathogen of community-acquired pneumonia in humans. Due to its high rates of antibiotic resistance, vaccination has become the best method to control the dissemination of M. pneumoniae. The recombinant carboxyl terminus of the P1 (P1C) protein is an immunodominant antigen, but it has negative effects such as poor stability and lower purity. In the current study, T-B epitopes of the P1C protein were predicted according to bioinformatics analysis and assessed for efficacy in peptide vaccination. BALB/c mice were subcutaneously inoculated with the T-B epitope peptides four times and then infected with M. pneumoniae through the respiratory tract. The results showed that the T-B epitope peptides of the P1C protein (P1C_103-117, P1C_155-169, P1C_224-238 and P1C_244-258) induced strong antigen-specific serum antibody responses and cellular immune responses with high levels of serum IgG, IgA antibodies and Th1-biased (IFN-γ and IL-2) cytokines. Immunization with T-B epitope peptides significantly reduced the M. pneumoniae burden and the degree of inflammation in the challenged mice. Furthermore, the levels of IFN-γ and TNF-α in the supernatants of lung homogenates were observably reduced compared to those in the PBS group. Overall, our findings demonstrate that T-B epitopes (P1C_103-117, P1C_155-169, P1C_224-238 and P1C_244-258) play significant roles in the P1C protein and can be used to induce powerful humoral and cellular immune responses to provide significant protection against M. pneumoniae pulmonary infection, which provides new insight into the design of potential multiepitope vaccines to prevent host infection by M. pneumoniae.

Antibody responses to chimeric peptides derived from parasite antigens in mice and other animal species

Peptide vaccines constitute an interesting alternative to classical vaccines due to the possibility of selecting specific epitopes, easy of production and safety. However, an inadequate design may render these peptides poorly immunogenic or lead to undesirable outcomes (e.g., formation of B neoepitopes). As an approach to vaccine development, we evaluated the antibody response to chimeras composed of two or three known B epitopes from Trichinella and Fasciola, and several linkers (GSGSG, GPGPG and KK) in species as different as mice, sheep and turbot. All these species could mount an effective immune response to the short chimeric peptides. Nevertheless, this response depended on several factors including a favorable orientation of B-cell epitopes, adequateness of linkers and/or probability of formation of T neoepitopes. We also observed that, at least in mice, the inclusion of a decoy epitope may have favorable consequences on the antibody response to other epitopes in the chimera.

Generation and testing anti-influenza human monoclonal antibodies in a new humanized mouse model (DRAGA: HLA-A2. HLA-DR4. Rag1 KO. IL-2Rγc KO. NOD)

Pandemic outbreaks of influenza type A viruses have resulted in numerous fatalities around the globe. Since the conventional influenza vaccines (CIV) provide less than 20% protection for individuals with weak immune system, it has been considered that broadly cross-neutralizing antibodies may provide a better protection. Herein, we showed that a recently generated humanized mouse (DRAGA mouse; HLA-A2. HLA-DR4. Rag1KO. IL-2Rgc KO. NOD) that lacks the murine immune system and expresses a functional human immune system can be used to generate cross-reactive, human anti-influenza monoclonal antibodies (hu-mAb). DRAGA mouse was also found to be suitable for influenza virus infection, as it can clear a sub-lethal infection and sustain a lethal infection with PR8/A/34 influenza virus. The hu-mAbs were designed for targeting a human B-cell epitope (¹⁸⁰WGIHHPPNSKEQ QNLY¹⁹⁵) of hemagglutinin (HA) envelope protein of PR8/A/34 (H1N1) virus with high homology among seven influenza type A viruses. A single administration of HA_180-195 specific hu-mAb in PR8-infected DRAGA mice significantly delayed the lethality by reducing the lung damage. The results demonstrated that DRAGA mouse is a suitable tool to (i) generate heterotype cross-reactive, anti-influenza human monoclonal antibodies, (ii) serve as a humanized mouse model for influenza infection, and (iii) assess the efficacy of anti-influenza antibody-based therapeutics for human use.

HLA-DR*0401 expression in the NOD mice prevents the development of autoimmune diabetes by multiple alterations in the T-cell compartment

Several human HLA alleles have been found associated with type 1 diabetes (T1D), but their precise role is not clearly defined. Herein, we report that a human MHC class II (HLA-DR*0401) allele transgene that has been expressed into NOD (H-2(g7)I-E(null)) mice prone to T1D rendered the mice resistant to the disease. T1D resistance occurred in the context of multi-point T-cell alterations such as: (i) skewed CD4/CD8 T-cell ratio, (ii) decreased size of CD4(+)CD44(high) T memory pool, (iii) aberrant TCR Vβ repertoire, (iv) increased neonatal number of Foxp3(+) and TR-1(+) regulatory cells, and (v) reduced IFN-γ inflammatory response vs. enhanced IL-10 suppressogenic response of T-cells upon polyclonal and antigen-specific stimulation. The T-cells from NOD/DR4 Tg mice were unable to induce or suppress diabetes in NOD/RAG deficient mice. This study describes a multifaceted regulatory function of the HLA-DR*0401 allele strongly associated with the lack of T1D development in NOD mice.

Evaluation of a non-viral vaccine in smallpox-vaccinated individuals and immunized HLA-transgenic mice

The current poxvirus vaccine is associated with rare, but serious adverse events. Therefore, we investigated a non-replicating approach to vaccine design. Peptides encoding potential HLA-binding motifs were derived from the orthopoxvirus genes, D8L, A27L, and C12L (the IL-18-binding protein [vIL18BP105]), all of which are preserved among poxviruses that infect humans, and which may be a target of host immunity. The peptides were tested with poxvirus-vaccinated human PBMC and serum for eliciting memory responses, as well as with splenocytes and serum from peptide-immunized, human HLA-DR04 transgenic (HLA tg) mice. vIL18BP105 induced 5-fold proliferation of vaccinated-donor PBMC over non-vaccinated (P<0.001), including IL-2-producing CD8+ cells. Serum IgG recognizing vIL18BP105 was detected (P<0.002 vs non-vaccinated) by ELISA. Viral peptides were conjugated to the HLA-targeting mAb, L243, for immunization of HLA tg mice. Splenocytes from vIL18BP105-L243-immunized mice proliferated upon exposure to vIL18BP105 (P<0.001). Proliferating splenocytes were interferon-γ-producing CD4(+)CD45RA(neg). vIL18BP105-L243-immunized mice generated IgG more rapidly than free-peptide-immunized mice. Peptide-specific antibody was also detected when different L243-peptide conjugates were combined. vIL18BP, by eliciting human memory responses, is a viable antigen for inclusion in a virus-free vaccine. The immunogenicity of peptides was boosted by conjugation to L243, whether administered alone or combined.

Peptide-conjugated PAMAM dendrimer as a universal DNA vaccine platform to target antigen-presenting cells

DNA-based vaccines hold promise to outperform conventional antigen-based vaccines by virtue of many unique features. However, DNA vaccines have thus far fallen short of expectations, due in part to poor targeting of professional antigen-presenting cells (APC) and low immunogenicity. In this study, we describe a new platform for effective and selective delivery of DNA to APCs in vivo that offers intrinsic immune-enhancing characteristics. This platform is based on conjugation of fifth generation polyamidoamine (G5-PAMAM) dendrimers, a DNA-loading surface, with MHC class II-targeting peptides that can selectively deliver these dendrimers to APCs under conditions that enhance their immune stimulatory potency. DNA conjugated with this platform efficiently transfected murine and human APCs in vitro. Subcutaneous administration of DNA-peptide-dendrimer complexes in vivo preferentially transfected dendritic cells (DC) in the draining lymph nodes, promoted generation of high affinity T cells, and elicited rejection of established tumors. Taken together, our findings show how PAMAM dendrimer complexes can be used for high transfection efficiency and effective targeting of APCs in vivo, conferring properties essential to generate effective DNA vaccines.

Characterization of a branched lipopeptide candidate vaccine against influenza A/Puerto Rico 8/34 which is recognized by human B and T-cell immune responses

The use of synthetic peptides as immunogens represents an exciting alternative to traditional vaccines. However, to date most of these synthetic peptides are not highly immunogenic. The lack of immunogenicity might be addressed by conjugation between T or B cell epitopes with universal or immunodominant T-helper epitopes. The construction of lipidated peptides, branched peptides, or designs combining both of these elements might enhance the immunogenicity, as they might target Toll-Like Receptors and/or mimic the 3-dimensional structure of epitopes within the native protein. Herein, a recognized peptide immunogen based on the hemagglutinin protein of A/Puerto Rico/8/34 was chosen as a backbone and modified to evaluate if the construction of branched peptides, lipidation, the addition of cysteine residues, or mutations could indeed alter epitope reactivity. Screening the different designs with various antibody binding and cellular assays revealed that combining a branched design with the addition of lipid moieties greatly enhanced the immunoreactivity.

Delivery of vaccine peptides by rapid conjugation to baculovirus particles

Baculoviruses deliver strong activation signals to dendritic cells and can promote potent immune responses. These properties can be harnessed to use baculovirus as an adjuvant and carrier particle for immunogenic peptides. In this study we use a chemical linker to couple peptides to the baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). Intranasal delivery of baculovirus coupled with immunogenic peptides to mice elicited antigen-specific IgG1 and IgG2a antibody. Furthermore, antigen-specific IgA was detected in the lung, and an IFN-gamma response was observed upon re-stimulation with antigen. We show that chemical coupling enables the rapid modification of AcMNPV, allowing multiple epitopes to be delivered simultaneously on a self-adjuvanting carrier particle.

Phospholipase C-gamma2 and Vav cooperate within signaling microclusters to propagate B cell spreading in response to membrane-bound antigen

B cell receptor (BCR) recognition of membrane-bound antigen initiates a spreading and contraction response, the extent of which is controlled through the formation of signaling-active BCR-antigen microclusters and ultimately affects the outcome of B cell activation. We followed a genetic approach to define the molecular requirements of BCR-induced spreading and microcluster formation. We identify a key role for phospholipase C-γ2 (PLCγ2), Vav, B cell linker, and Bruton's tyrosine kinase in the formation of highly coordinated “microsignalosomes,” the efficient assembly of which is absolutely dependent on Lyn and Syk. Using total internal reflection fluorescence microscopy, we examine at high resolution the recruitment of PLCγ2 and Vav to microsignalosomes, establishing a novel synergistic relationship between the two. Thus, we demonstrate the importance of cooperation between components of the microsignalosome in the amplification of signaling and propagation of B cell spreading, which is critical for appropriate B cell activation.

CD40-mediated enhancement of immune responses against three forms of influenza vaccine

There is potential for influenza A infections to cause massive morbidity and mortality. Vaccination may be the primary defence against pandemic influenza, and potential pandemic'flu vaccines may be produced conventionally, in embryonated eggs, or as recombinant protein or synthetic peptide vaccines. However the vaccines are produced, the supply may be limiting, and it will be important to enhance the immunogenicity of the vaccines as much as possible. We have shown that conjugation to CD40 binding antibody is a very efficient way of enhancing immune responses against model antigens, but were interested in assessing the effectiveness of this system using influenza vaccines. We produced conjugates of CD40 monoclonal antibody (mAb) and isotype control with three potential influenza vaccines: a peptide-based vaccine containing T- and B-cell epitopes from virus haemagglutinin; a whole, killed virus vaccine; and a commercially produced split virus vaccine. CD40 mAb conjugates in each case were more immunogenic, but the adjuvant effect of CD40 conjugation was greatest with the split vaccine, where antibody responses were enhanced by several hundred-fold after a single immunization, and lymphocyte proliferation in response to antigen in vitro was also strongly enhanced.

Fusion of interleukin-2 to subunit antigens increase their antigenicity in vitro due to an interleukin-2 receptor beta-mediated antigen uptake mechanism

Subunit vaccines, based on one or more epitopes, offer advantages over whole vaccines in terms of safety but are less antigenic. We investigated whether fusion of the cytokine interleukin-2 (IL-2) to influenza-derived subunit antigens could increase their antigenicity. The fusion of IL-2 to the subunit antigens increased their antigenicity in vitro. Encapsulation of the subunit antigen in liposomes also increased its antigenicity in vitro, yet encapsulation of the subunit IL-2 fusion did not. The use of anti-IL-2 receptor beta (IL-2Rbeta) antibody to block the receptor subunit on macrophages suggested that the adjuvancy exerted by IL-2 in our in vitro system is due to, at least in part, a previously unreported IL-2Rbeta-mediated antigen uptake mechanism.

Lipopolysaccharide-stimulated or granulocyte-macrophage colony-stimulating factor-stimulated monocytes rapidly express biologically active IL-15 on their cell surface independent of new protein synthesis

Although IL-15 shares many of the biological activities of IL-2, IL-2 expression is primarily under transcriptional regulation, while the mechanisms involved in the regulation of IL-15 are complex and not completely understood. In the current study, we found that CD14(+) monocytes constitutively exhibit both IL-15 mRNA and protein. IL-15 protein was found stored intracellularly and stimulation of CD14(+) monocytes with either LPS or GM-CSF resulted in mobilization of IL-15 stores to the plasma membrane. This rapidly induced surface expression was the result of a translocation of preformed stores, confirming that posttranslational regulatory stages limit IL-15, because it was not accompanied by an increase in IL-15 mRNA and occurred independent of de novo protein synthesis. After fixation, activated monocytes, but not resting monocytes, were found to support T cell proliferation, and this effect was abrogated by the addition of an IL-15-neutralizing Ab. The presence of preformed IL-15 stores and the ability of stimulated monocytes to mobilize these stores to their surface in an active form is a novel mechanism of regulation for IL-15.

Diepitopic construct of functionally and epitopically complementary peptides enhances immunogenicity, reactivity with glucosyltransferase, and protection from dental caries

Coimmunization with peptide constructs from catalytic (CAT) and glucan-binding (GLU) domains of glucosyltransferase (GTF) of mutans streptococci has resulted in enhanced levels of antibody to the CAT construct and to GTF. We designed and synthesized a diepitopic construct (CAT-GLU) containing two copies of both CAT (B epitope only) and GLU (B and T epitope) peptides. The immunogenicity of this diepitopic construct was compared with that of individual CAT and GLU constructs by immunizing groups of Sprague-Dawley rats subcutaneously in the salivary gland vicinity with the CAT-GLU, CAT, or GLU construct or by treating rats by sham immunization. Levels of serum immunoglobulin G (IgG) antibody to GTF or CAT in the CAT-GLU group were significantly greater than in GLU- or CAT-immunized groups. Immunization with CAT-GLU was compared to coimmunization with a mixture of CAT and GLU in a second rodent experiment under a similar protocol. CAT-GLU immunization resulted in serum IgG and salivary IgA responses to GTF and CAT which were greater than after coimmunization. Immunization with the diepitopic construct and communization with CAT and GLU constructs showed proliferation of T lymphocytes to GTF. Immunization with either the CAT or GLU construct has been shown to elicit significant protection in a rodent dental caries model. Similarly in this study, the enhanced response to GTF after immunization with the CAT-GLU construct resulted in protective effects on dental caries. Therefore, the CAT-GLU diepitopic construct can be a potentially important antigen for a caries vaccine, giving rise to greater immune response than after immunization with CAT, GLU, or a mixture of the two.

Functional mapping of protective domains and epitopes in the rotavirus VP6 protein

The purpose of this study was to determine which regions of the VP6 protein of the murine rotavirus strain EDIM are able to elicit protection against rotavirus shedding in the adult mouse model following intranasal (i.n.) immunization with fragments of VP6 and a subsequent oral EDIM challenge. In the initial experiment, the first (fragment AB), middle (BC), or last (CD) part of VP6 that was genetically fused to maltose-binding protein (MBP) and expressed in Escherichia coli was examined. Mice (BALB/c) immunized with two 9-microg doses of each of the chimeras and 10 microg of the mucosal adjuvant LT(R192G) were found to be protected against EDIM shedding (80, 92, and nearly 100% reduction, respectively; P </= 0.01) following challenge. Because CD produced almost complete protection, we prepared four E. coli-expressed, MBP-fused chimeras containing overlapping fragments of the CD region (i.e., CD1, CD2, CD3, and CD4) whose lengths ranged from 61 to 67 amino acid residues. Following i.n. immunization, CD1, CD2, and CD4 induced significant (P </= 0.004) protection (88, 84, and 92% reduction, respectively). In addition, 11 peptides (18 to 30 residues) of the CD region with between 0 and 13 overlapping amino acids were synthesized. Two 50-microg doses of each peptide with LT(R192G) were administered i.n. to BALB/c mice. Five peptides were found to elicit significant (P </= 0.02) protection. Moreover, a 14-amino-acid region within peptide 6 containing a putative CD4(+) T-cell epitope was found to confer nearly complete protection, suggesting a protective role for CD4(+) T cells. Mice that were protected by fragments BC and CD1 and four of the five protective synthetic peptides did not develop measurable rotavirus antibodies in serum or stool, implying that protection induced by these domains was not dependent on antibody. Together, these observations suggest that multiple regions of VP6 can stimulate protection, a region of VP6 as small as 14 amino acids containing a CD4(+) T-cell epitope can stimulate nearly complete protection, and protection mediated by a subset of epitopes in the VP6 protein does not require antibodies in BALB/c mice.

Induction of cytotoxic T lymphocytes of heterogeneous specificities by immunization with a single peptide derived from influenza A virus

We examined whether immunization with a single peptide induces cytotoxic T lymphocytes (CTLs) of heterogeneous specificities in vivo. Immunization of BALB/c mice with the peptide H2:529-537, which corresponded to amino acid residues 529-537 on the HA2 subunit transmembrane region of influenza A/Jap virus (H2N2) and possessed an H-2Kd-binding motif, induced CD8+CD4- CTLs. These CTLs lysed influenza A/Jap virus-infected target cells as well as those pulsed with the H2:529-537 peptide. H2:529-537 peptide-induced CTLs also lysed to lower but significant levels the target cells pulsed with the H1:533-541 peptide, which corresponded to amino acid residues 533-541 on the HA2 subunit transmembrane region of influenza A/PR/8 virus (H1N1) and were compatible to H2:529-537. Immunization with the H1:533-541 peptide, which also possessed an H-2Kd-binding motif, induced CTLs in vivo. H1:533-541-induced CTLs lysed influenza A/PR/8 virus-infected target cells and those pulsed with the peptide H1:533-541. Subtype cross-reactive CTLs to the H2:529-537 peptide were not induced by immunization with the H1:533-541 peptide. Two peptides, H2:3S and H2:7S, which had one amino acid substitution, serine at the third and seventh positions, respectively, induced CTLs that lysed target cells pulsed with the respective peptides to the highest levels. These results indicate that immunization with a single peptide induces CTLs of heterogeneous specificities in vivo.

Targeting early events in T cell activation to construct improved vaccines

Live, attenuated vaccines currently offer the best protection against virulent pathogens. Recent advances in Immunology and Molecular Biology provide an opportunity to design vaccines that will be more effective and safer than existing ones. Immunologists are rapidly developing the capacity to identify and construct the minimal immunogenic units from pathogens. The molecular signals required to fully activate antigen presenting cells (APCs) and responder T cells are becoming apparent. Improved vaccine delivery systems are being designed which will mimic the actions of pathogens in vivo. These vaccines will incorporate protective epitopes fused to immunoregulatory cytokines in chimeric proteins. They will be encapsulated in formulations which allow for the slow release of these chimeric proteins thereby inducing the memory T cells required for long-lived immunity. These vaccine formulations will target receptors present on the most active APCs. Here we discuss how these advances will allow us to rationally construct "virtual pathogens" which will provide improved protection against new and old microbial foes.

Short synthetic glycopeptides successfully induce antibody responses to carcinoma-associated Tn antigen

Glycopeptides containing a tumor-associated carbohydrate antigen (mono-, tri- or hexa-Tn antigen) as a B-cell epitope and a CD4+ T-cell epitope (PV: poliovirus or TT: tetanus toxin) were prepared for immunological studies. Several Tn antigen residues [FmocSer/Thr (alpha-GalNAc)-OH] were successively incorporated into the peptide sequence with unprotected carbohydrate groups. The tri- and hexa-Tn glycopeptides were recognized by MLS128, a Tn-specific monoclonal antibody. The position of the tri-Tn motif in the peptide sequence and the peptide backbone itself do not alter its antigenicity. As demonstrated by both ELISA and FACS analysis, the glycopeptides induced high titers of anti-Tn antibodies in mice, in the absence of a carrier molecule. In addition, the generated antibodies recognized the native Tn antigen on cancer cells. The antibody response obtained with a D-(Tn3)-PV glycopeptide containing three alpha-GalNAc-D-serine residues is similar that obtained with the Tn6-PV glycopeptide. These results demonstrate that short synthetic glycopeptides are able to induce anticancer antibody responses.

Differential reactivity of maleimide and bromoacetyl functions with thiols: application to the preparation of liposomal diepitope constructs

The comparative reactivity of maleimide and bromoacetyl groups with thiols (2-mercaptoethanol, free cysteine, and cysteine residues present at the N-terminus of peptides) was investigated in aqueous media. These studies were performed (i) with water-soluble functionalized model molecules, i.e., polyoxyethylene-based spacer arms that could also be coupled to lipophilic anchors destined to be incorporated into liposomes, and (ii) with small unilamellar liposomes carrying at their surface these thiol-reactive functions. Our results indicate that an important kinetic discrimination (2-3 orders of magnitude in terms of rate constants) can be achieved between the maleimide and bromoacetyl functions when the reactions with thiols are performed at pH 6.5. The bromoacetyl function which reacts at higher pH values (e.g., pH 9.0) retained a high chemoselectivity; i.e., under conditions where it reacted appreciably with the thiols of, e.g., HS-peptides, it did react with other nucleophilic functions such as alpha- and epsilon-amino groups or imidazole, which could also be present in peptides. This differential reactivity was applied to design chemically defined and highly immunogenic liposomal diepitope constructs as synthetic vaccines, i.e., vesicles carrying at their surface two different peptides conjugated each to a specific amphiphilic anchor. This was realized by coupling sequentially at pH 6.5 and 9.0 two HS-peptides to preformed vesicles containing lipophilic anchors functionalized with maleimide and bromoacetyl groups [Boeckler, C., et al. (1999) Eur. J. Immunol. 29, 2297-2308].

Design of highly immunogenic liposomal constructs combining structurally independent B cell and T helper cell peptide epitopes

We have designed liposomal diepitope constructs that allow the physical combination, within the same vesicle, of B and Th epitopes as structurally separate entities. The immune response against such constructs was explored using TPEDPTDPTDPQDPSS (TPE), a B cell epitope originating from a Streptococcus mutans surface adhesin and QYIKANSKFIGITEL (QYI), a "universal" Th epitope from tetanus toxin. The two peptides were linked to the outer surface of small (diameter approximately 100 nm) unilamellar liposomes by covalent conjugation to two different anchors. To that end we have developed a strategy that allows the controlled chemical coupling of TPE and QYI, functionalized at their N terminus with a thiol, to preformed liposomes containing thiol-reactive derivatives of phosphatidylethanolamine and the lipopeptide S-[2,3-bis (palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-gly cine (Pam3CAG), respectively. This synthetic construct (administered i.p. to BALB/c mice) induced highly intense (titers > 20,000), anamnestic and long-lasting (over 2 years) immune responses, indicating that this strategy is successful. Two parameters were of prime importance to elicit this response with our liposomal diepitope constructs: (1) the simultaneous expression of B and Th epitopes on the same vesicle, and (2) the lipopeptide Pam3CAG anchor of the Th epitope QYI could not be replaced by a phosphatidylethanolamine anchor (a lesser immune response was observed). Analysis of the antibody response revealed a complex pattern; thus, besides the humoral response (production of IgG1, IgG2a, IgG2b) a superposition of a T-independent (TI-2 type) response was also found (IgM and IgG3). These results indicate that liposomal diepitope constructs could be attractive in the development of synthetic peptide-based vaccines.

Peptides and polypeptides as modulators of the immune response: thymopentin--an example with unknown mode of action

Peptides and polypeptides play a critical role in the immune system and are therefore predestined as a source for new approaches in immunotherapy. For example, antigenic peptides which can trigger a specific immunological response have been successfully used for vaccination. In contrast, cytokines have to be considered as rather non-specific immunomodulators. In addition, certain peptides with unknown mode of action have shown promising immunomodulating properties. An example is the pentapeptide thymopentin (TP5), which represents the active sequence of the originally described thymopoietin (TP). TP was recently identified as a fragment of the thymopoietins (TMPOs), a family of nuclear proteins. In vitro assays showed that TP5 affects the function of T cells and monocytes measured by enhanced cGMP level and the triggering of cellular signalling, respectively. In vivo studies demonstrated the capability of TP5 to improve an imbalanced immune system. TP5 exhibited important clinical features and further investigations on its mode of action are necessary to rationally create TP5 peptide analogs or peptidomimetics.

Cellular Mechanisms Involved in Protection Against Influenza Virus Infection in Transgenic Mice Expressing a TCR Receptor Specific for Class II Hemagglutinin Peptide in CD4+ and CD8+ T Cells

Mice transgenic for a TCR that recognizes peptide110–120 of hemagglutinin of PR8 influenza virus in the context of MHC class II I-Ed molecules express the transgenes in both CD4+ and CD8+ T cells. We have found that these TCR-hemagglutinin (TCR-HA) transgenic mice display a significantly increased resistance to the primary infection with PR8 virus compared with the wild-type mice. The TCR-HA transgenic mice mounted significant MHC type II and enhanced MHC type I-restricted cytotoxicity as well as increased cytokine responses in both spleen and lungs after infection with PR8 virus. In contrast, the primary humoral response against PR8 virus was not significantly different from that of the wild-type mice. In vivo depletion and adoptive cell transfer experiments demonstrated that both CD4+ and CD8+ TCR-HA+ T cell subsets were required for the complete clearance of pulmonary virus following infection with a dose that is 100% lethal in wild-type mice. Whereas CD4+ TCR-HA+ T cells were necessary for effective activation and local recruitment of CD8+ T cells, CD8+ TCR-HA+ T cells showed a Th1-biased pattern and MHC type II-restricted cytotoxicity. However, in the absence of in vivo expression of MHC type I molecules on the infected cells, the protection conferred by the TCR-HA+ T cells was impaired, indicating that the enhanced MHC class I-restricted cytotoxicity due to TCR-HA+ CD4+ Th cells was a critical element for clearance of the pulmonary virus by the transgenic mice.

Protective immunity elicited by vaccination with DNA encoding for a B cell and a T cell epitope of the A/PR/8/34 influenza virus

Numerous reports have demonstrated that immunization with plasmids bearing influenza virus hemagglutinin (HA) or nucleoprotein (NP) genes elicits humoral and cellular protective responses. Herein we describe the generation of a plasmid (pVH-TB) encoding for a VH region of a self-Ig in which both the major B cell epitope HA150-159 and the immunodominant CD4 T cell epitope HA110-120 of HA of the A/PR/8/34 influenza virus were genetically inserted in the CDR2 and CDR3 loops, respectively. Our results demonstrate unequivocally that i.m. injection of pVH-TB plasmid in BALB/c mice elicited specific cellular and humoral immune responses able to protect against infection with lethal doses of A/PR/8/34 influenza virus.