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

Local and systemic B cell and Th1 responses induced following ocular mucosal delivery of multiple epitopes of herpes simplex virus type 1 glycoprotein D together with cytosine-phosphate-guanine adjuvant

Vaccine strategies that stimulate the ocular mucosal immune system (OMIS), the immune barrier that protects the surface of the eye are needed. However, most vaccines fail to induce local ocular immune responses and, in the absence of adjuvant, may induce a state of immunological tolerance. In this study, we present a new vaccine strategy that consists of ocular mucosal (OM) delivery of peptide epitopes, selected from the herpes simplex virus (HSV-1) glycoprotein D (gD) mixed with synthetic immunostimulatory oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs (CpG2007). Repeated topical ocular application of gD peptide epitopes and CpG2007 induced peptide-specific and virus-neutralizing IgA/IgG in tears as well as in serum. As a second marker, generation of local and systemic peptide- and virus-specific T cells confirmed the potent immunogenicity of peptides-CpG2007 formulation when applied through the OM route. Moreover, OM delivery of peptides-CpG2007 induced local IFN-gamma and IL-2 responses and low IL-4 production, demonstrating the polarization towards a Th1 response. Immunization, using free CpG2007 ODNs or peptides alone did not produce OMIS stimulation. This novel vaccine strategy may be key for ocular infectious pathogens, such as HSV-1, that require both secretory antibody and the Th1 responses. The results suggest the clinical feasibility of developing an OM delivery system using epitope-based vaccines.

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity

The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4(+) T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4(+) Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2(d) mice with the four newly identified CD4(+) Th1 peptide epitopes but not with four CD4(+) Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

Three T-cell determinants of Cry j 1 and Cry j 2, the major Japanese cedar pollen antigens, retain their immunogenicity and tolerogenicity in a linked peptide

It has been demonstrated in detail that administration of a dominant T-cell determinant to animals induces activation or immunological tolerance of T cells. However, it has not been determined whether multiple T-cell determinants, when integrated into a single peptide, retain their potential to induce T-cell activation and tolerance. We prepared a synthetic peptide comprising three T-cell determinants of Cry j 1 and Cry j 2, the major Japanese cedar pollen antigens, and investigated the immunogenicity and tolerogenicity of each T-cell determinant in the linked peptide by means of lymph node cell proliferation assays using mice. Lymph node cells from mice immunized with each of the three T-cell determinants proliferated against the linked peptide in a dose-dependent manner, similar to that of the immunized peptide. Lymph node cells from mice immunized with the linked peptide proliferated against all of the three T-cell determinants. In addition, the degree of proliferation against the three T-cell determinants occurred according to their original immunogenicity, as observed in the native protein antigens. Oral administration of the linked peptide to mice before they were immunized with Cry j 1 and Cry j 2 inhibited lymph node cell proliferation against the three T-cell determinants, depending on the dose of the linked peptide administered. In conclusion, it was demonstrated that three T-cell determinants retain their original immunogenicity and tolerogenicity in a linked peptide comprising them.

Role of disulfide bonds in regulating antigen processing and epitope selection

Knowledge of the events governing Ag processing and epitope selection within APC is key to the development of novel immunotherapeutic strategies for infectious diseases, cancer, and autoimmunity. The influence of disulfides and Ag reduction on the hierarchy of epitope presentation via MHC class II molecules was investigated through studies of a self Ag, IgG kappa. HLA-DR4(+) B cells preferentially present an immunodominant IgG-derived epitope, kappaI, relative to a subdominant kappaII peptide. kappaI contains a cysteine masked within the native Ag via an intrachain disulfide, the latter of which is reduced during Ag processing. Mutagenesis of this cysteine as well as others within kappa minimally perturbed the abundance and overall conformation of IgG. Yet, disruptions in disulfide bonding within this Ag influenced the selective display of class II-restricted dominant and subdominant T cell epitopes. Presentation of the kappaI epitope from both native and variant IgG was dependent upon cellular expression of IFN-gamma-inducible lysosomal thiol reductase. These studies indicate that disulfide bonds regulate Ag processing both locally and at distant sites, thus influencing epitope selection within the class II pathway.

Absence of gamma-interferon-inducible lysosomal thiol reductase in melanomas disrupts T cell recognition of select immunodominant epitopes

Long-lasting tumor immunity requires functional mobilization of CD8+ and CD4+ T lymphocytes. CD4+ T cell activation is enhanced by presentation of shed tumor antigens by professional antigen-presenting cells (APCs), coupled with display of similar antigenic epitopes by major histocompatibility complex class II on malignant cells. APCs readily processed and presented several self-antigens, yet T cell responses to these proteins were absent or reduced in the context of class II+ melanomas. T cell recognition of select exogenous and endogenous epitopes was dependent on tumor cell expression of gamma-interferon-inducible lysosomal thiol reductase (GILT). The absence of GILT in melanomas altered antigen processing and the hierarchy of immunodominant epitope presentation. Mass spectral analysis also revealed GILT's ability to reduce cysteinylated epitopes. Such disparities in the profile of antigenic epitopes displayed by tumors and bystander APCs may contribute to tumor cell survival in the face of immunological defenses.

Cutting edge: introduction of an endopeptidase cleavage motif into a determinant flanking region of hen egg lysozyme results in enhanced T cell determinant display

The choice of which determinants of a whole Ag will be presented on cell surface MHC class II molecules after uptake and processing by APC is the result of the interplay between structural characteristics of the Ag and the processing machinery of the APC. In this study, we demonstrate that introduction of a dibasic motif adjacent to a subdominant determinant enhances the presentation of this determinant from the whole molecule. This is the first report showing that a single amino acid substitution in a whole Ag, designed to introduce an endopeptidase recognition site, enhances display of class II-restricted determinants, most likely by creating a peptide chain cleavage in the antigenic molecule. Our findings have important implications for the understanding of immunodominance and for vaccine design.

Role of APC in the Selection of Immunodominant T Cell Epitopes

Following antigenic challenge, MHC-restricted T cell responses are directed against a few dominant antigenic epitopes. Here, evidence is provided demonstrating the importance of APC in modulating the hierarchy of MHC class II-restricted T cell responses. Biochemical analysis of class II:peptide complexes in B cells revealed the presentation of a hierarchy of peptides derived from the Ig self Ag. Functional studies of κ peptide:class II complexes from these cells indicated that nearly 20-fold more of an immunodominant epitope derived from κ L chains was bound to class II DR4 compared with a subdominant epitope from this same Ag. In vivo, T cell responses were preferentially directed against the dominant κ epitope as shown using Ig-primed DR4 transgenic mice. The bias in κ epitope presentation was not linked to differences in class II:κ peptide-binding affinity or epitope editing by HLA-DM. Rather, changes in native Ag structure were found to disrupt presentation of the immunodominant but not the subdominant κ epitope; Ag refolding restored κ epitope presentation. Thus, Ag tertiary conformation along with processing reactions within APC contribute to the selective presentation of a hierarchy of epitopes by MHC class II molecules.