Comparison of cytotoxic T lymphocyte responses induced by peptide or DNA immunization: implications on immunogenicity and immunodominance

Vaccination against Epstein-Barr Latent Membrane Protein 1 Protects against an Epstein-Barr Virus-Associated B Cell Model of Lymphoma

In this study, we demonstrate that expression of viral latent membrane protein 1 (LMP1) in a mouse B cell line renders the animals responsive to protection from a 38C13-LMP1 tumor challenge with a novel vaccine. The Epstein-Barr virus (EBV) preferentially infects circulating B lymphocytes, has oncogenic potential, and is associated with a wide variety of B cell lymphomas. EBV is ectotrophic to human cells, and currently there are no B cell animal models of EBV-associated lymphoma that can be used to investigate vaccine immunotherapy. Since most EBV-infected human tumor cells express latent membrane protein 1 (LMP1) on their surface, this viral antigen was tested as a potential target for an anticancer vaccine in a mouse model. Here, we describe a new mouse model of LMP1-expressing B cell lymphoma produced with plasmid transduction of 38C13 into mouse B cells. The expression of LMP-1 was confirmed with a western blot analysis and immunocytochemistry. We then designed a novel LMP1 vaccine, by fusing viral antigen LMP1 surface loop epitopes to the surface of a viral antigen carrier, the Tobacco Mosaic virus (TMV). Vaccinated mice produced high titer antibodies against the TMV-LMP1 vaccine; however, cellular responses were at the baseline, as measured with IFNγ ELISpot. Despite this, the vaccine showed significant protection from a 38C13-LMP1 tumor challenge. To provide additional immune targets, we compared TMV-LMP1 peptide immunization with DNA immunization with the full-length LMP1 gene. Anti-LMP1 antibodies were significantly higher in TMV-LMP1-vaccinated mice compared to the DNA-immunized mice, but, as predicted, DNA-vaccinated mice had improved cellular responses using IFNγ ELISpot. Surprisingly, the TMV-LMP1 vaccine provided protection from a 38C13-LMP1 tumor challenge, while the DNA vaccine did not. Thus, we demonstrated that LMP1 expression in a mouse B cell line is responsive to antibody immunotherapy that may be applied to EBV-associated disease.

Liver organoids as a primary human model to study HBV-mediated Hepatocellular carcinoma. A review

Hepatitis B Virus (HBV) is the prevailing cause of chronic liver disease, which progresses to Hepatocellular carcinoma (HCC) in 75% of cases. It represents a serious health concern being the fourth leading cause of cancer-related mortality worldwide. Treatments available to date fail to provide a complete cure with high chances of recurrence and related side effects. The lack of reliable, reproducible, and scalable in vitro modeling systems that could recapitulate the viral life cycle and represent virus-host interactions has hindered the development of effective treatments so far. The present review provides insights into the current in-vivo and in-vitro models used for studying HBV and their major limitations. We highlight the use of three-dimensional liver organoids as a novel and suitable platform for modeling HBV infection and HBV-mediated HCC. HBV organoids can be expanded, genetically altered, patient-derived, tested for drug discovery, and biobanked. This review also provides the general guidelines for culturing HBV organoids and highlights their several prospects for HBV drug discovery and screening.

A Systematic Review of T Cell Epitopes Defined from the Proteome of Hepatitis B Virus

Hepatitis B virus (HBV) infection remains a worldwide health problem and no eradicative therapy is currently available. Host T cell immune responses have crucial influences on the outcome of HBV infection, however the development of therapeutic vaccines, T cell therapies and the clinical evaluation of HBV-specific T cell responses are hampered markedly by the lack of validated T cell epitopes. This review presented a map of T cell epitopes functionally validated from HBV antigens during the past 33 years; the human leukocyte antigen (HLA) supertypes to present these epitopes, and the methods to screen and identify T cell epitopes. To the best of our knowledge, a total of 205 CD8⁺ T cell epitopes and 79 CD4⁺ T cell epitopes have been defined from HBV antigens by cellular functional experiments thus far, but most are restricted to several common HLA supertypes, such as HLA-A0201, A2402, B0702, DR04, and DR12 molecules. Therefore, the currently defined T cell epitope repertoire cannot cover the major populations with HLA diversity in an indicated geographic region. More researches are needed to dissect a more comprehensive map of T cell epitopes, which covers overall HBV proteome and global patients.

RNA-loaded dendritic cells: more than a tour de force in cancer therapeutics

A wide array of therapeutic strategies has been implemented against cancers, yet their clinical benefit is limited. The lack of clinical efficacy of the conventional treatment options might be due to the inept immune competency of the patients. Dendritic cells (DCs) have a vital role in initiating and directing immune responses and have been frequently used as delivery vehicles in clinical research. The recent clinical data suggest the potential use of DCs pulsed with nucleic acid, especially with RNA holds a great potential as an immunotherapeutic measure with compare to other cancer therapeutics. This review mainly deals with the DCs and their role in transfection with RNA in cancer immunotherapy.

2L-PCA: a two-level principal component analyzer for quantitative drug design and its applications

A two-level principal component predictor (2L-PCA) was proposed based on the principal component analysis (PCA) approach. It can be used to quantitatively analyze various compounds and peptides about their functions or potentials to become useful drugs. One level is for dealing with the physicochemical properties of drug molecules, while the other level is for dealing with their structural fragments. The predictor has the self-learning and feedback features to automatically improve its accuracy. It is anticipated that 2L-PCA will become a very useful tool for timely providing various useful clues during the process of drug development.

New insights into germ cell migration and survival/apoptosis in spermatogenesis: Lessons from CD147

CD147, also named basigin (Bsg) or extracellular matrix (ECM) metalloproteinase inducer (EMMPRIN), is a highly glycosylated protein first identified as a tumor cell surface molecule. In cancer, it is well established that CD147 promotes metastasis by stimulating the production of MMPs. Recent studies have also suggested that it may be associated with tumor growth and angiogenesis. Interestingly, CD147 is expressed in germ cells of different development stages in the testis and its knockout mice are infertile, indicating an essential role of CD147 in spermatogenesis. While the detailed involvement of CD147 in spermatogenesis remains elusive, our recent findings have revealed a dual role of CD147 in germ cell development. On the one hand, it regulates the migration of spermatogonia and spermatocytes via the induction of MMP-2 production; on the other hand, it specifically regulates the survival/apoptosis of spermatocytes but not spermatogonia through a p53-independent pathway. In this review, we aim to provide an overview on the functions of CD147, comparing its roles in cancer and the testis, thereby providing new insights into the regulatory mechanisms underlying the process of spermatogenesis.

RNA pulsed dendritic cells: an approach for cancer immunotherapy

The immunotherapy of cancer is aimed at evoking both branches of immune system to elicite specific immune responses directed against tumor antigens to deal with residual tumor cells upon interaction, and thereby decreases mortality as well as morbidity of cancer patients. As dendritic cells (DCs) are specialized for antigen presentation, and their immunogenicity leads to the induction of antigen specific immune responses, various immunotherapeutic approaches have been designed for using DCs to present tumor-associated antigens to T-lymphocytes. As a part of proposed strategy ex vivo generated DCs might be loaded with antigens and re-infused to the patients and/or they can be used for the ex vivo expansion of anti-tumor lymphocytes. The DCs loaded ex vivo with RNA can be safely administered which proves to be an asset for producing antigen specific immune responses. Furthermore, already conducted studies have prompted clinical trials to be designed to investigate immunological and clinical effects of RNA pulsed DCs administered as an engineered therapeutic vaccine in cancer patients. However, selection of the antigens of interest, methods for introducing TAAgs into MHC class I and II processing pathways, methods for isolation and activation of DCs, and route of administration are the parameters to be considered for designing and conducting clinical trials with engineered DCs. The enhanced RNA transfection efficiency would further improve antigen processing and presentation and T-cell co-stimulation, resulting in the induction of heightened anti-tumor immune responses. Therefore, RNA transfected dendritic cells continue to hold promise for cellular immunotherapy and opens new avenues to devising further strategies for cancer therapeutic interventions.

Molecular cancer vaccines: Tumor therapy using antigen-specific immunizations

Vaccination against tumors promises selective destruction of malignant cells by the host's immune system. Molecular cancer vaccines rely on recently identified tumor antigens as immunogens. Tumor antigens can be applied in many forms, as genes in recombinant vectors, as proteins or peptides representing T cell epitopes.Analysis of various aspects indicates some advantage for peptide-based vaccines over the other modalities. Further refinements and extensively monitored clinical trials are necessary to advance molecular cancer vaccines from concepts into powerful therapy.

Mamu-A01/K(b) transgenic and MHC Class I knockout mice as a tool for HIV vaccine development

We have developed a murine model expressing the rhesus macaque (RM) Mamu-A01 MHC allele to characterize immune responses and vaccines based on antigens of importance to human disease processes. Towards that goal, transgenic (Tg) mice expressing chimeric RM (alpha1 and alpha2 Mamu-A01 domains) and murine (alpha3, transmembrane, and cytoplasmic H-2K(b) domains) MHC Class I molecules were derived by transgenesis of the H-2K(b)D(b) double MHC Class I knockout strain. After immunization of Mamu-A01/K(b) Tg mice with rVV-SIVGag-Pol, the mice generated CD8(+) T-cell IFN-gamma responses to several known Mamu-A01 restricted epitopes from the SIV Gag and Pol antigen sequence. Fusion peptides of highly recognized CTL epitopes from SIV Pol and Gag and a strong T-help epitope were shown to be immunogenic and capable of limiting an rVV-SIVGag-Pol challenge. Mamu-A01/K(b) Tg mice provide a model system to study the Mamu-A01 restricted T-cell response for various infectious diseases which are applicable to a study in RM.

A novel approach to evaluate the immunogenicity of viral antigens of clinical importance in HLA transgenic murine models

Transgenic (Tg) mice expressing HLA class I alleles and lacking murine MHC class I represent a useful model for the pre-clinical evaluation of human vaccines, which focus on induction of CD8(+) T-cell responses. We have developed a platform to be used in Tg mice for exploring the immunogenicity of T-cell targets, whose immunologic epitopes have yet to be defined. To test the attributes of the evaluation system in the context of an important human pathogen, we have explored multiple antigens from cytomegalovirus (CMV). A panel of recombinant modified vaccinia Ankara (MVA) vectors, expressing various CMV proteins (CMV-MVA) was used to immunize HLA-A*0201, B*0702 and A*1101 Tg mice. Immune splenocytes were in vitro stimulated (IVS) either using syngeneic lipo-polysaccharide activated lymphoblasts or Tg HLA-I matched human EBV-transformed B-lymphoblastoid cells (LCL), both loaded with peptide libraries, encompassing the CMV protein under investigation. IVS performed with peptide library loaded lymphoblasts failed to provide a reliable stimulation. In contrast, the usage of LCL as antigen presenting cells (APC) of CMV peptide libraries resulted in a consistent and specific amplification of the Tg T-cell response in animals immunized with CMV-MVAs. The LCL IVS method reliably allowed defining the immunogenicity and immunodominant CD8(+) T-cell regions of uncharacterized CMV antigens. The combination of CMV-MVA vectors, unbiased pools of CMV-specific peptide libraries presented by Tg HLA-I matched LCL constitutes a valid tool for the pre-clinical evaluation of model candidate vaccines. This convenient method could find application to investigate the immunogenicity profile of cancer antigens or proteins from infectious human pathogens.

Vaccinia virus-specific CD4+ T cell responses target a set of antigens largely distinct from those targeted by CD8+ T cell responses

Recent studies have defined vaccinia virus (VACV)-specific CD8(+) T cell epitopes in mice and humans. However, little is known about the epitope specificities of CD4(+) T cell responses. In this study, we identified 14 I-A(b)-restricted VACV-specific CD4(+) T cell epitopes by screening a large set of 2146 different 15-mer peptides in C57BL/6 mice. These epitopes account for approximately 20% of the total anti-VACV CD4(+) T cell response and are derived from 13 different viral proteins. Surprisingly, none of the CD4(+) T cell epitopes identified was derived from VACV virulence factors. Although early Ags were recognized, late Ags predominated as CD4(+) T cell targets. These results are in contrast to what was previously found in CD8(+) T cells responses, where early Ags, including virulence factors, were prominently recognized. Taken together, these results highlight fundamental differences in immunodominance of CD4(+) and CD8(+) T cell responses to a complex pathogen.

Cytotoxic T cells generated against heteroclitic peptides kill primary tumor cells independent of the binding affinity of the native tumor antigen peptide

Heteroclitic peptide modifications increase immunogenicity, allowing generation of cytotoxic T lymphocytes (CTLs) against weakly immunogenic tumor-associated antigens (TAAs). A critical issue is whether T cells generated against heteroclitic peptides retain the ability to recognize and kill tumor cells expressing the original weak TAAs, and whether there is a lower threshold of binding affinity of the native peptides, below which such CTLs can still kill primary tumor cells. To examine this we used a model examining the ability of native and heteroclitic immunoglobulin (Ig)-derived peptides to generate CTLs that can kill chronic lymphocytic leukemia (CLL) cells. We demonstrate that CTLs generated against heteroclitic peptides have enhanced killing of CD40-activated B cells pulsed with either heteroclitic (P < .001) or native peptide (P = .04) and primary CLL cells (P = .01). The novel finding reported here is that the rate-limiting factor appears to be the ability to generate CTLs and that once generated, CTL lysis of primary tumor cells is independent of the binding affinity of the native peptide. These findings have implications for vaccination strategies in malignancies and are currently being further examined in vivo in murine models.

Role of immunoproteasome catalytic subunits in the immune response to hepatitis B virus

Inhibition of hepatitis B virus (HBV) replication and viral clearance from an infected host requires both the innate and adaptive immune responses. Expression of interferon (IFN)-inducible proteasome catalytic and regulatory subunits correlates with the IFN-alpha/beta- and IFN-gamma-mediated noncytopathic inhibition of HBV in transgenic mice and hepatocytes, as well as with clearance of the virus in acutely infected chimpanzees. The immunoproteasome catalytic subunits LMP2 and LMP7 alter proteasome specificity and influence the pool of peptides available for presentation by major histocompatibility complex class I molecules. We found that these subunits influenced both the magnitude and specificity of the CD8 T-cell response to the HBV polymerase and envelope proteins in immunized HLA-A2-transgenic mice. We also examined the role of LMP2 and LMP7 in the IFN-alpha/beta- and IFN-gamma-mediated inhibition of virus replication using HBV transgenic mice and found that they do not play a direct role in this process. These results demonstrate the ability of the IFN-induced proteasome catalytic subunits to shape the HBV-specific CD8 T-cell response and thus potentially influence the progression of infection to acute or chronic disease. In addition, these studies identify a potential key role for IFN in regulating the adaptive immune response to HBV through alterations in viral antigen processing.

Critical factors in the development of fluorescence polarization-based peptide binding assays: an equilibrium study monitoring specific peptide binding to soluble HLA-A*0201

There is currently a significant interest in the identification and validation of HLA-restricted CTL epitopes, which are thought to have important implications for the development of preventive and/or therapeutic applications in bacterial or viral infections, autoimmune diseases, and cancer. To better facilitate epitope discovery and validation, we present a cell- and radioisotope-free HLA-A*0201 assay system which relies upon fluorescence polarization. The assay has the advantage of allowing real-time measurements in solution without separation steps. In this report, we directed our efforts towards enhancing the sensitivity and reproducibility of the assay by conducting an in-depth analysis of parameters critical for standardization. Initial experiments demonstrated that the attachment of a fluorescence moiety at positions 5 and 8 for 9-mers and positions 5 and 6 for 10-mers, respectively, does not interfere with ligand binding to soluble HLA-A*0201. In addition, it was found that their binding to HLA-A*0201 was very effective showing high affinity binding with K(d)'s between 10.7 to 21.8 nM and binding capacities of up to 37%. In order to deliver maximized responses, factors such as the regulation of thermal HLA activation parameters to initiate peptide exchange as well as the specific adjustment of assay components were identified. Overall, the results obtained clearly demonstrate high accuracy, sensitivity and reproducibility of the FP-based assay approach. With the need for both increased throughput and miniaturized volumes, this fully homogenous, fluorescent-type binding assay is expected to be useful for routine analysis of peptide binding to MHC class I as well as class II molecules.

Analysis of peptide-protein binding using amino acid descriptors: prediction and experimental verification for human histocompatibility complex HLA-A0201

Amino acid descriptors are often used in quantitative structure-activity relationship (QSAR) analysis of proteins and peptides. In the present study, descriptors were used to characterize peptides binding to the human MHC allele HLA-A0201. Two sets of amino acid descriptors were chosen: 93 descriptors taken from the amino acid descriptor database AAindex and the z descriptors defined by Wold and Sandberg. Variable selection techniques (SIMCA, genetic algorithm, and GOLPE) were applied to remove redundant descriptors. Our results indicate that QSAR models generated using five z descriptors had the highest predictivity and explained variance (q2 between 0.6 and 0.7 and r2 between 0.6 and 0.9). Further to the QSAR analysis, 15 peptides were synthesized and tested using a T2 stabilization assay. All peptides bound to HLA-A0201 well, and four peptides were identified as high-affinity binders.

Development and validation of a fluorescence polarization-based competitive peptide-binding assay for HLA-A*0201--a new tool for epitope discovery

Various approaches are currently proposed to successfully develop therapies for the prevention and treatment of infectious diseases and cancer. One of the most promising approaches is the development of vaccines that elicit cytotoxic T lymphocyte (CTL) responses. Consequently, identification and exact definition of molecular parameters involved in peptide-MHC class-I interactions of putative CTL epitopes are of prime importance for the development of immunomodulating compounds. To better facilitate epitope discovery, we developed and validated a novel state-of-the-art biochemical HLA-A0201 assay, which is comprised of technologically advanced cutting edge reagents. The technique is based on competition and uses a FITC-labeled reference peptide and highly purified soluble HLA-A0201 molecules to quantitatively measure the binding capacity of nonlabeled peptide candidates. Detection by fluorescence polarization allows real-time measurement of binding ratios without separation steps. During standardization, the problem of assay parameter variation is discussed, showing the dramatic influence of HLA and reference peptide concentrations as well as the choice of the reference peptide itself on IC(50) determinations. For validation, a panel of 15 well-defined HLA-A0201 ligands from various sources covering a broad range of binding affinities was tested. Binding data were used to compare against pre-existing quantitative assay systems. The results obtained demonstrated significant correlation among assay procedures, suggesting that the application of fluorescence polarization in combination with recombinant sHLA molecules is highly advantageous for the accurate assessment of peptide binding. Furthermore, the assay also features high-throughput screening capacity, providing uniquely efficient means of identifying and evaluating immune target molecules.

Human CTL Epitopes Prostatic Acid Phosphatase-3 and Six-Transmembrane Epithelial Antigen of Prostate-3 as Candidates for Prostate Cancer Immunotherapy

Specific immunotherapy of prostate cancer may be an alternative or be complementary to other approaches for treatment of recurrent or metastasized disease. This study aims at identifying and characterizing prostate cancer-associated peptides capable of eliciting specific CTL responses in vivo. Evaluation of peptide-induced CTL activity in vitro was done following immunization of HLA-A2 transgenic (HHD) mice. An in vivo tumor rejection was tested by adoptive transfer of HHD immune lymphocytes to nude mice bearing human tumors. To confirm the existence of peptide-specific CTL precursors in human, lymphocytes from healthy and prostate cancer individuals were stimulated in vitro in the presence of these peptides and CTL activities were assayed. Two novel immunogenic peptides derived from overexpressed prostate antigens, prostatic acid phosphatase (PAP) and six-transmembrane epithelial antigen of prostate (STEAP), were identified; these peptides were designated PAP-3 and STEAP-3. Peptide-specific CTLs lysed HLA-A2.1+ LNCaP cells and inhibited tumor growth on adoptive immunotherapy. Furthermore, peptide-primed human lymphocytes derived from healthy and prostate cancer individuals lysed peptide-pulsed T2 cells and HLA-A2.1+ LNCaP cells. Based on the results presented herein, PAP-3 and STEAP-3 are naturally processed CTL epitopes possessing anti-prostate cancer reactivity in vivo and therefore may constitute vaccine candidates to be investigated in clinical trials.

Toward the quantitative prediction of T-cell epitopes: QSAR studies on peptides having affinity with the class I MHC molecular HLA-A*0201

It would be useful for vaccine development to develop a method of rapidly identifying peptide epitopes. In this paper, the empirical three-dimensional quantitative structure-affinity relationship (3D-QSAR) methods were used to study the relationship between the three dimensional structural parameters (the isotropic surface area, ISA, and the electronic charge index, ECI) of the HLA-A*0201 binding peptide and the HLA-A*0201/peptide binding affinities. A set of 102 peptides having affinity with the class I MHC HLA-A*0201 molecule was used as training set. A test set of 40 peptides was used to determine the predictive value of the models. The 3D-QSAR models yielded a q2 = 0.5724 and a high rpred2 = 0.6955. The standard regression coefficients indicated that the hydrophobic interactions played an important role in peptide-MHC molecule binding and predicted the specific amino acid residue essential at a certain position of the peptide. The approach tested in the current paper is highly complementary to many of the methods described in references and possesses good predictability. It is a rapid and convenient method to detect high affinity peptide epitopes.

DNA immunization followed by a viral vector booster in a Chlamydia pneumoniae mouse model

Vaccination against Chlamydia pneumoniae would be a beneficial strategy for either preventing or controlling infection by this human respiratory pathogen that also causes persistent infections. In the present study, we used recombinant Semliki Forest virus (rSFV) particles for delivering C. pneumoniae antigens major outer membrane protein (MOMP) or outer membrane protein 2 (Omp2) to the mice or applied the prime-boost technique, where mice were first primed with naked DNA and then boosted with the viral vector coding for the same proteins. Partial protection suggested by the reduced number of cultivable bacteria from the lungs of the challenged mice was seen in mice immunized by either method with MOMP expressing constructs. A significant protection was also achieved after DNA/rSFV immunization with Omp2. DNA priming followed by rSFV boosting induced a more prominent IFN-gamma production after challenge at the site of the infection in pulmonary and mediastinal cells.

Attenuated poxviruses expressing a synthetic HIV protein stimulate HLA-A2-restricted cytotoxic T-cell responses

Efficient HIV vaccines have to trigger cell-mediated immunity directed against various viral antigens. However little is known about the breadth of the response induced by vaccines carrying multiple proteins. Here, we report on the immunogenicity of a construct harbouring a fusion of the HIV-1 IIIB gag, pol and nef genes (gpn) designed for optimal safety and equimolar expression of the HIV proteins. The attenuated poxviruses, MVA and NYVAC, harbouring the gpn construct, induced potent immune responses in conventional mice characterised by stimulation of Gpn-specific IFN-gamma-producing cells and cytotoxic T cells. In HLA-A2 transgenic mice, recombinant MVA elicited cytotoxic responses against epitopes recognised in most HLA-A2+ HIV-1-infected individuals. We also found that the MVA vaccine triggered the in vitro expansion of peripheral blood cells isolated from a HIV-1-seropositive patient and with similar specificity as found in immunised HLA-A2 transgenic mice. In conclusion, the synthetic HIV polyantigen Gpn delivered by MVA is immunogenic, efficiently processed and presented by human MHC class I molecules.

Derivation of HLA-B*0702 transgenic mice: functional CTL repertoire and recognition of human B*0702-restricted CTL epitopes

Transgenic mice expressing chimeric human leukocyte antigen (HLA)-B*0702 and murine H-2K(b) class I molecules were evaluated as a model system to study the immunogenicity of human cytotoxic T lymphocyte epitopes. Immunization of these mice with six known HLA-B*0702-restricted cytotoxic T lymphocyte epitopes emulsified in incomplete Freund's adjuvant induced significant immune responses specific for all six epitopes. A comparison of the immune responses between HLA-B*0702/K(b) and HLA-A*0201/K(b) transgenic mice demonstrated that the HLA-B*0702/K(b) mice possess a T-cell receptor repertoire capable of recognizing human B*0702 epitopes. However, the magnitude of B*0702-specific responses induced in B*0702/K(b) mice were approximately tenfold lower than A*0201-specific responses induced in HLA-A*0201/K(b) transgenic mice. A panel of 24 B*0702 motif-bearing peptides was used to examine the relationship between immunogenicity and HLA-B*0702 binding capacity. All seven peptides with high binding affinities of 50% inhibitory concentration < or =50 NM (IC(50) 50 nM or less) were immunogenic. Similarly, 75% (9 of 12) of the intermediate binders (IC(50) nM of 50-500) were also immunogenic. Finally, only two of five peptides with binding capacity > 500 nM were found to have marginal immunogenicity, whereas the other three were completely negative. HLA-B*0702/K(b) transgenic mice were found to induce B*0702-specific responses after immunization with whole DNA genes or minigenes, suggesting that, at least to some degree, B*0702 epitopes were generated as a result of natural in vivo processing and presentation.

Preclinical development of an adjuvant-free peptide vaccine with activity against CMV pp65 in HLA transgenic mice

Epitope vaccines have shown promise for inducing cellular immune responses in animal models of infectious disease. In cases where cellular immunity was augmented, peptide vaccines composed of covalently linked minimal cytotoxic T-lymphocyte (CTL) and T-helper (T(H)) epitopes generally showed the most efficacy. To address a clinical vaccine strategy for cytomegalovirus (CMV) in the context of HCT (hematopoietic cell transplantation), we observed that linking the synthetically derived pan-DR epitope peptide (PADRE) or one of several tetanus T(H) epitopes to the immunodominant human leukocyte antigen (HLA) A*0201-restricted CTL epitope from CMV-pp65 to create a fusion peptide caused robust cytotoxic cellular immune responses in HLA A*0201/K(b) transgenic mice. Significantly, the fusion peptides are immunogenic when administered in saline solution by either subcutaneous or intranasal routes. CpG-containing single-stranded DNA (ss-oligodeoxynucleotide [ODN]) added to the fusion peptides dramatically up-regulated immune recognition by either route. Notably, target cells that either expressed full-length pp65 protein from vaccinia viruses or were sensitized with the CTL epitope encoded in the vaccine were recognized by splenic effectors from immunized animals. Visualization of murine peptide-specific CTL by flow cytometry was accomplished using an HLA A*0201 tetramer complexed with the pp65(495-503) CTL epitope. T(H)-CTL epitope fusion peptides in combination with CpG ss-ODN represent a new strategy for parenteral or mucosal delivery of vaccines in a safe and effective manner that has applicability for control or prophylaxis of infectious disease, especially in situations such as vaccination of donors or recipients of HCT, where highly inflammatory adjuvants are not desired.

Physicochemical explanation of peptide binding to HLA-A*0201 major histocompatibility complex: a three-dimensional quantitative structure-activity relationship study

A three-dimensional quantitative structure-activity relationship method for the prediction of peptide binding affinities to the MHC class I molecule HLA-A*0201 was developed by applying the CoMSIA technique on a set of 266 peptides. To increase the self consistency of the initial CoMSIA model, the poorly predicted peptides were excluded from the training set in a stepwise manner and then included in the study as a test set. The final model, based on 236 peptides and considering the steric, electrostatic, hydrophobic, hydrogen bond donor, and hydrogen bond acceptor fields, had q2 = 0.683 and r2 = 0.891. The stability of this model was proven by cross-validations in two and five groups and by a bootstrap analysis of the non-cross-validated model. The residuals between the experimental pIC50 (-logIC50) values and those calculated by "leave-one-out" cross-validation were analyzed. According to the best model, 63.2% of the peptides were predicted with /residuals/ < or = 0.5 log unit; 29.3% with 1.0 < or = /residuals/ < 0.5; and 7.5% with /residuals/ > 1.0 log unit. The mean /residual/ value was 0.489. The coefficient contour maps identify the physicochemical property requirements at each position in the peptide molecule and suggest amino acid sequences for high-affinity binding to the HLA-A*0201 molecule.

Characterization of novel breast carcinoma-associated BA46-derived peptides in HLA-A2.1/D(b)-beta2m transgenic mice

The human milk fat globule membrane protein BA46 (lactadherin) is highly overexpressed in human breast tumors, making it a potential target for tumor immunotherapy. We have identified BA46-derived peptides that contain the motif recognized by the MHC class I molecule HLA-A2.1 and that are processed and presented by human breast carcinoma cells. In mice lacking normal class I molecules but expressing an HLA-A2.1/D(b)-beta2 microglobulin single chain (HHD mice), three peptides elicited specific CTL activity. Two of these peptides also stimulated cytotoxic activity in peripheral blood lymphocytes from HLA-A2.1-positive breast carcinoma patients. Adoptive transfer of HHD-derived bulk CTLs to nude mice bearing human breast carcinoma transplants reduced tumor growth. These peptides therefore represent naturally processed BA46-derived CTL epitopes that can be used in peptide-based antitumor vaccines.

Identification of Chlamydia pneumoniae-derived mouse CD8 epitopes

Chlamydia pneumoniae is a common intracellular human pathogen that has been associated with several severe pathological conditions, including coronary heart disease and atherosclerosis. There is no vaccine against C. pneumoniae infection, but CD8(+) T cells have been shown to be crucial for protection during experimental infection. However, the effector functions and epitope specificity of the protective CD8(+) T cell remain unknown. The aim of this study was to identify C. pneumoniae-derived mouse CD8 epitopes by using a recent epitope prediction method. Of four C. pneumoniae proteins (the major outer membrane protein, outer membrane protein 2, polymorphic outer membrane protein 5, and heat shock protein 60), 53 potential CD8(+) T-cell epitopes were predicted by H-2 class I binding algorithms. Nineteen of the 53 peptides were identified as CD8 epitopes by testing for induction of a cytotoxic response after immunization. To test whether the predicted epitopes are naturally processed and presented by C. pneumoniae-infected cells, we generated a panel of seven peptide-specific cytotoxic T lymphocyte lines that were subsequently tested for recognition of C. pneumoniae-infected target cells. By using this strategy, we were able to identify three C. pneumoniae CD8 epitopes that were, indeed, processed and presented on infected cells. Identification of these natural CD8 epitopes provides tools for characterization of CD8(+) T-cell function in vivo and generation of epitope-specific prevention strategies.

B and C hepatitis viruses, HLA-DQ1 and -DR3 alleles and autoimmunity in patients with hepatocellular carcinoma

BACKGROUND/AIMS

Hepatitis B and C involvement in hepatocellular carcinoma has been well established, but as yet not that of the human lymphocyte antigen (HLA) complex. To study viral, HLA and tumour interrelationships, 105 patients were evaluated for prevalence of viral markers and 161 patients, including 99 of the previous ones, for HLA allele frequency; the other 52 patients served as controls.

METHODS

Immunoassays, molecular assays, microlymphocytotoxicity.

RESULTS

Positivity for hepatitis B surface antigen and/or hepatitis C antibodies in 89% cirrhotic, 44% non-cirrhotic vs. 92% control patients (cirrhotic; all hepatitis C antibody positives were viraemic). Recurrent HLA alleles: HLA-Cw7 and -DQ1 in cirrhotic and control patients, HLA-Cw7, -B8 and -DR3 in non-cirrhotic patients compared with healthy controls (Pc=0.0000074, 0.000025, 0.0025, 0.00027 and 0.043, respectively).

CONCLUSIONS

Viral data suggest a high chronic infection rate for cirrhotic patients. Recurrent HLA-Cw7 is compatible with natural killer cell activity inhibition to virus-infected and tumour cells by HLA C molecules. Recurrent HLA-DQ1 and -DR3 suggest the existence of an autoimmune condition with cell destruction in cirrhotic and without cell destruction in non-cirrhotic patients as a consequence of autoreactive DQ-restricted T-helper (Th)1 and DR-restricted Th2 cells response, respectively. HLA-B8-DR3 linkage disequilibrium was possible. Thus, autoimmunity may have contributed to hepatocellular carcinoma development in these patients.

Peptide vaccines against hepatitis B virus: from animal model to human studies

An estimated 400 million people are chronically infected with the hepatitis B virus (HBV). Chronic viral hepatitis infection incurs serious sequelae such as liver cirrhosis and hepatocellular carcinoma. Prevention and treatment, thus, represent an important target for public health. Preventive vaccines using HBsAg alone or combined with other antigens allow for the generation of neutralizing antibodies which effectively prevent infection in immunocompetent individuals. Cell-mediated immunological mechanisms are thought to be crucial in determining viral persistence or viral elimination. Therapeutic approaches aiming to shift cellular immunity towards viral elimination have been on the research agenda for many years. This paper summarizes pre-clinical and clinical results obtained with the use of immunogenic peptides formulated as vaccines to selectively boost cellular immune responses. Such vaccines are capable of generating cellular immune responses in animal models as well as in humans and represent an important step towards the development of a therapeutic vaccine against chronic hepatitis.

Toward the quantitative prediction of T-cell epitopes: coMFA and coMSIA studies of peptides with affinity for the class I MHC molecule HLA-A*0201

A set of 102 peptides with affinity for the class I MHC HLA-A0201 molecule was subjected to three-dimensional quantitative structure-affinity relationship (3D QSAR) studies using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). A test set of 50 peptides was used to determine the predictive value of the models. The CoMFA models gave q(2) and r(2)pred below 0.5. The best CoMSIA model has q(2) = 0.542 and r(2)pred = 0.679, and includes hydrophobic, steric, and H-bond donor fields. The hydrophobic interactions play a dominant role in peptide-MHC molecule binding. CoMSIA coefficient contour maps were used to analyze the structural features of the peptides accounting for the affinity in terms of the three positively contributing physicochemical properties: local hydrophobicity, steric bulk and hydrogen-bond-donor ability.

The immunization of A2/K(b) transgenic mice with the KMP11-HSP70 fusion protein induces CTL response against human cells expressing the T. cruzi KMP11 antigen: identification of A2-restricted epitopes

Cytotoxic T lymphocyte response against Jurkat-A2/K(b) cells expressing the T. cruzi KMP11 protein has been evaluated after immunization of C57BL/6-A2/K(b) transgenic mice with the KMP11 and KMP11-HSP70 recombinant proteins. The results show that mice immunized with KMP11 covalently fused to the T. cruzi HSP70 protein, but not mice immunized with KMP11 alone, elicit a CTL response against the Jurkat-A2/K(b) cells expressing the KMP11 protein. The data also show that spleen cells from mice immunized with the fusion protein and stimulated with the K1 peptide induce lysis of both the Jurkat-A2/K(b) cells transfected with the KMP11 coding gene and the Jurkat-A2-K(b) cells pulsed with the K1 peptide. Splenocytes stimulated with the K3 peptide induce lysis of the Jurkat-A2/K(b) cells loaded with the K3 peptide but they do not recognize the target cells expressing the KMP11 protein. Similar results were obtained using lymph node from mice immunized with the peptides. Thus, we believe there are two cytotoxic T cell epitopes restricted to the A2 molecule (K1(KMP11) (4-12) and K3(KMP11) (41-50)) in the KMP11 protein, and suggest that the K1 peptide could be considered an immunodominant antigen whilst the K3 peptide may be regarded as a cryptic epitope. The fact that the CTL lines induced in B6-A2/K(b) mice recognize human cells expressing KMP11 protein, indicates that the KMP11 antigen fused to HSP70 could be a good candidate for the induction of immunoprotective cytotoxic responses against T. cruzi natural infection.

Contrasting Epstein-Barr virus-specific cytotoxic T cell responses to HLA A2-restricted epitopes in humans and HLA transgenic mice: implications for vaccine design

This study investigates the hierarchy of cytotoxic T cell (CTL) responses to twelve HLA A2-restricted epitopes from the latent, lytic and structural proteins of Epstein-Barr virus (EBV) in acute infectious mononucleosis and in healthy seropositive donors and the relative immunogenecity of these epitopes in transgenic mice. Responses to the lytic epitope were uniformly strong in all healthy seropositive individuals and acute infectious mononucleosis donors while moderate or low responses were observed to the latent and structural epitopes, respectively in both groups studied. In contrast, when HLA A2/Kb transgenic mice were immunised with these peptide epitopes, CTL responses were observed to all epitopes with a maximal response to the epitopes within the structural proteins and low to moderate responses to the latent epitopes. This hierarchy of CTL responses in mice was also reflected in an MHC stabilisation analysis. These contrasting CTL responses in humans following natural infection compared to the immunogenicity of these epitopes and their ability to stabilise MHC may need to be considered when designing an EBV vaccine.

Multiepitopic HLA-A*0201-restricted immune response against hepatitis B surface antigen after DNA-based immunization

CTL together with anti-envelope Abs represent major effectors for viral clearance during hepatitis B virus (HBV) infection. The induction of strong cytotoxic and Ab responses against the envelope proteins after DNA-based immunization has been proposed as a promising therapeutic approach to mediate viral clearance in chronically infected patients. Here, we studied the CTL responses against previously described hepatitis B surface Ag (HBsAg)-HLA-A*0201-restricted epitopes after DNA-based immunization in HLA-A*0201 transgenic mice. The animal model used was Human Human D(b) (HHD) mice, which are deficient for mouse MHC class I molecules (beta(2)-microglobulin(-/-) D(b-/-)) and transgenic for a chimeric HLA-A*0201/D(b) molecule covalently bound to the human beta(2)-microglobulin (HHD(+/+)). Immunization of these mice with a DNA vector encoding the small and the middle HBV envelope proteins carrying HBsAg induced CTL responses against several epitopes in each animal. This study performed on a large number of animals described dominant epitopes with specific CTL induced in all animals and others with a weaker frequency of recognition. These results confirmed the relevance of the HHD transgenic mouse model in the assessment of vaccine constructs for human use. Moreover, genetic immunization of HLA-A2 transgenic mice generates IFN-gamma-secreting CD8(+) T lymphocytes specific for endogenously processed peptides and with recognition specificities similar to those described during self-limited infection in humans. This suggests that responses induced by DNA immunization could have the same immune potential as those developing during natural HBV infection in human patients.

Transgenic mice expressing human HLA and CD8 molecules generate HLA-restricted measles virus cytotoxic T lymphocytes of the same specificity as humans with natural measles virus infection

Control of primary measles virus (MV) infection in humans and continued maintenance of immune memory that protects against reinfection are mediated primarily through the anti-MV T cell response, as judged by observations of children with defects in antibody formation but competency in making T cells. Further, the failure of T cell responses in those infected with MV most often leads to overwhelming infection. To better define and manipulate the elements involved in human T cell responses to MV, we analyzed the generation of HLA-restricted cytotoxic T lymphocytes (CTL) in a small animal model. Transgenic mice expressing the human class I MHC antigen HLA-B27 in conjunction with human CD8 molecules produced vigorous HLA-restricted CTL responses to MV antigens, paralleling those in MV infection of humans. In addition, such humanized mice generated human CD8 coreceptor-dependent HLA-B27-restricted CTL with the same specificity for recognition of MV fusion (F) peptide RRYPDAVYL as reported for humans during natural MV infection. Neither murine beta(2)-microglobulin nor murine CD8 substituted adequately as coreceptors for the HLA-B27 heavy chain. By contrast, HLA-A2.1-restricted responses to measles could be generated in the absence of expression of human beta(2)-microglobulin or CD8(+) molecules in HLA-A2.1/K(b) transgenic mice. Thus a small animal model is now available for studying strategies for optimizing human CD8(+) T cell responses and for testing vaccines. This model offers the potential, when combined with the newly reported CD46 transgenic mouse model in which MV replicates in cells of the immune system, for uncoding the molecular mechanism of MV-induced immunosuppression.

HLA-A2.1/K(b) transgenic murine dendritic cells transduced with an adenovirus encoding human gp100 process the same A2.1-restricted peptide epitopes as human antigen-presenting cells and elicit A2.1-restricted peptide-specific CTL

HLA-A2.1/K(b) transgenic mice (A2.1/K(b) mice) were used to investigate the processing of human gp100 melanoma antigen by murine antigen presenting cells (APC). Bone marrow-derived dendritic cells (DC) from A2.1/K(b) mice were transduced with adenovirus encoding human gp100 (Ad2/hugp100v2). The Ad2/hugp100v2-transduced DC express human gp100, as documented by immunoperoxidase staining. Flow cytometric analysis demonstrates that Ad vector transduction does not downregulate expression of several markers, including MHC class I. We show that Ad2/hugp100v2-transduced DC are recognized by peptide-specific, A2.1-restricted CTL, suggesting correct processing and presentation of the hugp100 antigen by murine DC. To assess dominance among the various A2.1-restricted epitopes encoded by hugp100, A2.1/K(b) transgenic mice were immunized with Ad2/hugp100v2-transduced DC. Resulting effector cytotoxic T lymphocytes (CTL) were assayed for peptide specificity using a panel of six synthetic peptides known to encode A2.1-restricted epitopes of human gp100 (denoted G154, G177, G209, G280, G457, G476). CTL obtained from Ad2/hugp100v2-transduced DC immunized A2.1/K(b) mouse lysed target cells presenting five of the six epitopes, supporting the observation that murine cells correctly process the hugp100 antigen. The immunogenicity of individual gp100 epitopes correlates with their binding affinity to A2.1. CTL generated from A2.1/K(b) mice immunized with Ad2/hugp100v2-transduced DC also specifically recognize A2.1(+)/gp100(+) human melanoma cells. These data suggest that murine APC process and present the same set of HLA-restricted peptides, similar to human APC. HLA transgenic mice serve as a useful model system to study class I-restricted epitopes of human tumor-associated antigens.

A subdominant CD8(+) cytotoxic T lymphocyte (CTL) epitope from the Plasmodium yoelii circumsporozoite protein induces CTLs that eliminate infected hepatocytes from culture

Previous studies indicated that the Plasmodium yoelii circumsporozoite protein (PyCSP) 57-70 region elicits T cells capable of eliminating infected hepatocytes in vitro. Herein, we report that the PyCSP58-67 sequence contains an H-2(d) binding motif, which binds purified K(d) molecules in vitro with low affinity (3, 267 nM) and encodes an H-2(d)-restricted cytotoxic T lymphocyte (CTL) epitope. Immunization of BALB/c mice with three doses of a multiple antigen peptide (MAP) construct containing four branches of amino acids 57 to 70 linked to a lysine-glycine core [MAP4(PyCSP57-70)] and Lipofectin as the adjuvant induced both T-cell proliferation and a peptide-specific CTL response that was PyCSP59-67 specific, H-2(d) restricted, and CD8(+) T cell dependent. Immunization with either DNA encoding the PyCSP or irradiated sporozoites demonstrated that this CTL epitope is subdominant since it is not recognized in the context of whole CSP immunization. The biological relevance of this CTL response was underlined by the demonstration that it could mediate genetically restricted, CD8(+)- and nitric-oxide-dependent elimination of infected hepatocytes in vitro, as well as partial protection of BALB/c mice against sporozoite challenge. These findings indicate that subdominant epitopes with low major histocompatibility complex affinity can be used to engineer epitope-based vaccines and have implications for the selection of epitopes for subunit-based vaccines.

Impaired immunoproteasome assembly and immune responses in PA28-/- mice

In vitro PA28 binds and activates proteasomes. It is shown here that mice with a disrupted PA28b gene lack PA28a and PA28b polypeptides, demonstrating that PA28 functions as a hetero-oligomer in vivo. Processing of antigenic epitopes derived from exogenous or endogenous antigens is altered in PA28-/- mice. Cytotoxic T lymphocyte responses are impaired, and assembly of immunoproteasomes is greatly inhibited in mice lacking PA28. These results show that PA28 is necessary for immunoproteasome assembly and is required for efficient antigen processing, thus demonstrating the importance of PA28-mediated proteasome function in immune responses.

Alternative pathways for processing exogenous and endogenous antigens that can generate peptides for MHC class I-restricted presentation

The concept of distinct endogenous and exogenous pathways for generating peptides for MHC-I and MHC-II-restricted presentation to CD4+ or CD8+ T cells fits well with the bulk of experimental data. Nevertheless, evidence is emerging for alternative processing pathways that generate peptides for MHC-I-restricted presentation. Using a well characterized, particulate viral antigen of prominent medical importance (the hepatitis B surface antigen), we summarize our evidence that the efficient, endolysosomal processing of exogenous antigens can lead to peptide-loaded MHC-I molecules. In addition, we describe evidence for endolysosomal processing of mutant, stress protein-bound, endogenous antigens that liberate peptides binding to (and presented by) MHC-I molecules. The putative biological role of alternative processing of antigens generating cytotoxic T-lymphocyte-stimulating epitopes is discussed.

An HLA-A2 Polyepitope Vaccine for Melanoma Immunotherapy

Epitope-based vaccination strategies designed to induce tumor-specific CD8 CTL are being widely considered for cancer immunotherapy. Here we describe a recombinant poxvirus vaccine that codes for ten HLA-A2-restricted epitopes derived from five melanoma Ags conjoined in an artificial polyepitope or polytope construct. Target cells infected with the melanoma polytope vaccinia were recognized by three different epitope-specific CTL lines derived from HLA-A2 melanoma patients, and CTL responses to seven of the epitopes were generated in at least one of six HLA-A2-transgenic mice immunized with the construct. CTL lines derived from vaccinated transgenic mice were also able to kill melanoma cells in vitro. Multiple epitopes within the polytope construct were therefore shown to be individually immunogenic, illustrating the feasibility of the polytope approach for melanoma immunotherapy. Tumor escape from CTL surveillance, through down regulation of individual tumor Ags and MHC alleles, might be overcome by polytope vaccines, which simultaneously target multiple cancer Ags.

Immunogenicity of a human immunodeficiency virus (HIV) polytope vaccine containing multiple HLA A2 HIV CD8(+) cytotoxic T-cell epitopes

Compelling evidence now suggests that alphabeta CD8 cytotoxic T lymphocytes (CTL) have an important role in preventing human immunodeficiency virus (HIV) infection and/or slowing progression to AIDS. Here, we describe an HIV type 1 CTL polyepitope, or polytope, vaccine comprising seven contiguous minimal HLA A2-restricted CD8 CTL epitopes conjoined in a single artificial construct. Epitope-specific CTL lines derived from HIV-infected individuals were able to recognize every epitope within the construct, and HLA A2-transgenic mice immunized with a recombinant virus vaccine coding for the HIV polytope also generated CTL specific for different epitopes. Each epitope in the polytope construct was therefore processed and presented, illustrating the feasibility of the polytope approach for HIV vaccine design. By simultaneously inducing CTL specific for different epitopes, an HIV polytope vaccine might generate activity against multiple challenge isolates and/or preempt the formation of CTL escape mutants.

HIV-1-Specific CTL Responses Primed In Vitro by Blood-Derived Dendritic Cells and Th1-Biasing Cytokines

Vaccine strategies designed to elicit strong cell-mediated immune responses to HIV Ags are likely to lead to protective immunity against HIV infection. Dendritic cells (DC) are the most potent APCs capable of priming both MHC class I- and II-restricted, Ag-specific T cell responses. Utilizing a system in which cultured DC from HIV-seronegative donors were used as APC to present HIV-1 Ags to autologous T cells in vitro, the strength and specificity of primary HIV-specific CTL responses generated to exogenous HIV-1 Nef protein as well as intracellularly expressed nef transgene product were investigated. DC expressing the nef gene were able to stimulate Nef-specific CTL, with T cells from several donors recognizing more than one epitope restricted by a single HLA molecule. Primary Nef-specific CTL responses were also generated in vitro using DC pulsed with Nef protein. T cells primed with Nef-expressing DC (via protein or transgene) were able to lyse MHC class I-matched target cells pulsed with defined Nef epitope peptides as well as newly identified peptide epitopes. The addition of Th1-biasing cytokines IL-12 or IFN-α, during priming with Nef-expressing DC, enhanced the Nef-specific CTL responses generated using either Ag-loading approach. These results suggest that this in vitro vaccine model may be useful in identifying immunogenic epitopes as vaccine targets and in evaluating the effects of cytokines and other adjuvants on Ag-specific T cell induction. Successful approaches may provide information important to the development of prophylactic HIV vaccines and are envisioned to be readily translated into clinical DC-based therapeutic vaccines for HIV-1.

EBV Structural Antigens, gp350 and gp85, as Targets for Ex Vivo Virus-Specific CTL During Acute Infectious Mononucleosis: Potential Use of gp350/gp85 CTL Epitopes for Vaccine Design

For many years, EBV vaccine development efforts have concentrated on the use of structural Ag, gp350, and have been directed toward Ab-mediated blocking virus attachment to the target cell. There is increasing evidence to suggest that the development of neutralizing Abs in vaccinated animals does not always correlate with protection; nevertheless, it has been postulated that gp350-specific T cell-mediated immune responses may have an effector role in protection. This hypothesis has largely remained untested. In the present study, we demonstrate that CTL from acute infectious mononucleosis patients display strong ex vivo reactivity against the EBV structural Ags, gp85 and gp350. Moreover, long-term follow up studies on infectious mononucleosis-recovered individuals showed that these individuals maintain gp350- and gp85-specific memory CTL, albeit at low levels, in the peripheral blood. These results strongly suggest that CTL specific for EBV structural proteins may play an important role in the control of EBV infection during acute infection. More importantly, we also show that prior immunization of HLA A2/Kb transgenic mice with gp350 and gp85 CTL epitopes induced a strong epitope-specific CTL response and afforded protection against gp85- or gp350-expressing vaccinia virus challenge. These results have important implications for future EBV vaccine design and provides evidence, for the first time, that CTL epitopes from EBV structural proteins may be used for establishing strong antiviral immunity against EBV infection.

Attempt to modify the immune response developed against FIV gp120 protein by preliminary FIV DNA injection

Following inactivated virus vaccination trials, the surface glycoprotein gp120 (SU) of the feline immunodeficiency virus (FIV) was considered as one of the determinants for protection. However, several vaccination trials using recombinant Env protein or some Env-derived peptides failed to induce protection. To study the influence of the environment in which the surface protein (SU) is injected. we analyzed the impact of a nucleocapsid (NC) DNA immunization on the presentation of the recSU protein to the immune system. Cats were vaccinated either with the recSU protein alone or with NC DNA followed by the recSU protein. Two routes of nucleocapsid DNA vaccination were tested: intramuscular and mucosal injections. Cats immunized with the recSU protein showed a facilitation of infection, since they presented the earliest and the highest humoral response correlating with the highest proviral load. They also showed an acceleration of the appearance of IL4 mRNA signal. Preliminary injection of the DNA coding for NC protein, regardless the route of inoculation, seemed to inhibit the facilitation induced by vaccination with the recSU protein alone. The previously nucleocapsid DNA immunized cats had infectious status similar to those of the control cats, but with lower proviral load and less developed anti-FIV humoral response. Cat No. 2, belonging to the group vaccinated with NC protein by the mucosal route, had a protected-like status which did not correlate with the humoral response. This cat was the only one to have a persisting IFN mRNA signal after challenge specific for the p10 nucleocapsid and recSU proteins. However, no NC specific cytotoxic cells were observed throughout the experiment in this cat. The role of nucleocapsid DNA vaccination is still unknown nevertheless we did demonstrate that the facilitation observed in vaccination trial with recombinant proteins could be modified and that recombinant proteins could be a component of an effective vaccine.

The use of human leucocyte antigen class I transgenic mice to investigate human immune function

HLA class I transgenic mice are a powerful research tool which have been used as models for human immune responses. This review describes the generation of the different HLA class I transgenic mice, the techniques used to improve expression of the transgene and use of the transgene product in immune responses. It also illustrates how HLA class I transgenic mice have provided insights into the nature of the allogeneic and xenogeneic response, the generation of CTL responses, the development of autoimmune diseases, and their use for the generation of anti-HLA class I antibodies. Despite these advances, the use of available HLA class I transgenic mice as models for human disease and immune responses has been limited. The development of new transgenic strains incorporating multiple human transgenes may allow the potential of HLA class I transgenic mice to be realised.

Human infection with Trypanosoma cruzi induces parasite antigen-specific cytotoxic T lymphocyte responses

Experimental models of Chagas' disease, an infection caused by the intracellular protozoan Trypanosoma cruzi, have demonstrated the crucial immunoprotective role played by CD8(+) T lymphocytes. These cells dominate inflammatory foci in parasitized tissues and their elimination from mice leads to uncontrolled parasite replication and subsequent death of the infected host. A trypomastigote surface antigen, TSA-1, and two amastigote surface molecules, ASP-1 and ASP-2, were recently identified as targets of CD8(+) cytotoxic T lymphocytes (CTL) in T. cruzi-infected mice. Until now, however, there was no evidence for the development of parasite-specific CTL in T. cruzi-infected humans. In this study, human CTL specific for TSA-1-, ASP-1-, and ASP-2-derived peptides were detected in the peripheral blood mononuclear cells from 21 of 24 HLA-A2(+) T. cruzi-infected patients. CTL recognition was antigen specific, A2-restricted, and CD8(+) T cell-dependent. Demonstration of human CTL against T. cruzi and against target molecules identified using the murine model provides important information for the optimal design and evaluation of vaccines to prevent or ameliorate Chagas' disease.

Identification of HLA class II-restricted determinants of Mycobacterium tuberculosis-derived proteins by using HLA-transgenic, class II-deficient mice

T helper 1 cells play a major role in protective immunity against mycobacterial pathogens. Since the antigen (Ag) specificity of CD4(+) human T cells is strongly controlled by HLA class II polymorphism, the immunogenic potential of candidate Ags needs to be defined in the context of HLA polymorphism. We have taken advantage of class II-deficient (Ab0) mice, transgenic for either HLA-DRA/B1*0301 (DR3) or HLA-DQB1*0302/DQA*0301 (DQ8) alleles. In these animals, all CD4(+) T cells are restricted by the HLA molecule. We reported previously that human DR3-restricted T cells frequently recognize heat shock protein (hsp)65 of Mycobacterium tuberculosis, and only a single hsp65 epitope, p1-20. DR3.Ab0 mice, immunized with bacillus Calmette-Guérin or hsp65, developed T cell responses to M. tuberculosis, and recognized the same hsp65 epitope, p1-20. Hsp65-immunized DQ8.Ab0 mice mounted a strong response to bacillus Calmette-Guérin but not to p1-20. Instead, we identified three new DQ8-restricted T cell epitopes in the regions 171-200, 311-340, and 411-440. DR3.Ab0 mice immunized with a second major M. tuberculosis protein, Ag85 (composed of 85A, 85B, and 85C), also developed T cell responses against only one determinant, 85B p51-70, that was identified in this study. Importantly, subsequent analysis of human T cell responses revealed that HLA-DR3+, Ag85-reactive individuals recognize exactly the same peptide epitope as DR3.Ab0 mice. Strikingly, both DR3-restricted T cell epitopes represent the best DR3-binding sequences in hsp65 and 85B, revealing a strong association between peptide-immunodominance and HLA binding affinity. Immunization of DR3.Ab0 with the immunodominant peptides p1-20 and p51-70 induced T cell reactivity to M. tuberculosis. Thus, for two different Ags, T cells from DR3.Ab0 mice and HLA-DR3+ humans recognize the same immunodominant determinants. Our data support the use of HLA-transgenic mice in identifying human T cell determinants for the design of new vaccines.

Pools of lipidated HTL-CTL constructs prime for multiple HBV and HCV CTL epitope responses

Various peptide-based approaches to simultaneous induction of multiple cytotoxic T lymphocyte (CTL) responses were evaluated as part of ongoing efforts to develop immunotherapeutic vaccines for use in humans. To this end, HLA (human histocompatibility leukocyte antigen)-A2-restricted epitopes from several specific viral proteins were tested in an HLA-A2 transgenic mouse model system, which mimics human CTL responses to these viral proteins. Multiple CTL responses were elicited by immunization with either peptides emulsified in incomplete Freund's adjuvant (IFA), or lipidated peptides administered in phosphate buffered saline (PBS). In the case of lipidated peptides, induction of CTL responses was crucially dependent on the presence of helper T lymphocyte (HTL) epitopes, and most efficient in the case of lipidated covalently linked HTL-CTL epitope constructs. CTL could also be induced by immunization with lipidated HTL epitopes simply mixed with CTL epitopes and formulated in PBS. However, this approach was highly dependent on the particular lipidated HTL/CTL combination utilized, and was marginally effective for simultaneous priming of multiple CTL responses. By contrast, all HTL/CTL combinations were potent immunogens when delivered as lipidated, covalently linked molecules. This was the most effective of the approaches analysed in terms of multi-epitope priming, as demonstrated by the induction of simultaneous CTL responses to a pool of five different epitopes.

A structure-based algorithm to predict potential binding peptides to MHC molecules with hydrophobic binding pockets

Binding of peptides to MHC class I molecules is a prerequisite for their recognition by cytotoxic T cells. Consequently, identification of peptides that will bind to a given MHC molecule must constitute a central part of any algorithm for prediction of T-cell antigenic peptides based on the amino acid sequence of the protein. Binding motifs, defined by anchor positions only, have proven to be insufficient to ensure binding, suggesting that other positions along the peptide sequence also affect peptide-MHC interaction. The second phase of prediction schemes therefore take into account the effect of all positions along the peptide sequence, and are based on position-dependent-coefficients that are used in the calculation of a peptide score. These coefficients can be extracted from a large ensemble of binding sequences that were tested experimentally, or derived from structural considerations, as in the algorithm developed by us recently. This algorithm uses the coordinates of solved complexes to evaluate the interactions of peptide amino acids with MHC contact residues, and results in a peptide score that reflects its binding energy. Here we present our analysis for peptide binding to four MHC alleles (HLA-A2, HLA-A68, HLA-B27 and H-2Kb), and compare the predictions of the algorithm to experimental binding data. The algorithm performs successfully in predicting peptide binding to MHC molecules with hydrophobic binding pockets but not when MHC molecules with hydrophilic, charged pockets are considered. For MHC molecules with hydrophobic pockets it is demonstrated how the algorithm succeeds in distinguishing binding from non-binding peptides, and in high ranking of immunogenic peptides within all overlapping same-length peptides spanning their respective protein sequences. The latter property of the algorithm makes it a useful tool in the rational design of peptide vaccines aimed at T-cell immunity.