Improved Immunogenicity of an Immunodominant Epitope of the Her-2/neu Protooncogene by Alterations of MHC Contact Residues

Gene Gun Her2/neu DNA Vaccination: Evaluation of Vaccine Efficacy in a Syngeneic Her2/neu Mouse Tumor Model

Genetic vaccination using naked plasmid DNA is an immunization strategy both against infectious diseases and cancer.In order to improve efficacy of DNA vaccines, particularly in large animals and humans, different strategies have been pursued. These vaccination strategies are based on different application routes, schedules and coexpression of immunomodulatory molecules as adjuvants. Our mouse tumor model offers the possibility to investigate Her2/neu DNA vaccines in different settings, that is, intramuscular or intradermal application with or without coexpression of adjuvants. The immunogenicity of predicted peptides for Her2/neu specific memory T cells were screened and confirmed after intramuscular and intradermal application. Protection from tumor growth in tumor challenge experiments and both T cell and humoral immune responses against Her2/neu peptides are used as surrogate parameters for vaccine efficacy.

Pan-Specific Prediction of Peptide-MHC Class I Complex Stability, a Correlate of T Cell Immunogenicity

Binding of peptides to MHC class I (MHC-I) molecules is the most selective event in the processing and presentation of Ags to CTL, and insights into the mechanisms that govern peptide-MHC-I binding should facilitate our understanding of CTL biology. Peptide-MHC-I interactions have traditionally been quantified by the strength of the interaction, that is, the binding affinity, yet it has been shown that the stability of the peptide-MHC-I complex is a better correlate of immunogenicity compared with binding affinity. In this study, we have experimentally analyzed peptide-MHC-I complex stability of a large panel of human MHC-I allotypes and generated a body of data sufficient to develop a neural network-based pan-specific predictor of peptide-MHC-I complex stability. Integrating the neural network predictors of peptide-MHC-I complex stability with state-of-the-art predictors of peptide-MHC-I binding is shown to significantly improve the prediction of CTL epitopes. The method is publicly available at http://www.cbs.dtu.dk/services/NetMHCstabpan.

CCL4 as an adjuvant for DNA vaccination in a Her2/neu mouse tumor model

Chemokines are key regulators of both innate and adaptive immune responses. CCL4 (macrophage inflammatory protein-1β, MIP-1β) is a CC chemokine that has a broad spectrum of target cells including immature dendritic cells, which express the cognate receptor CCR5. We asked whether a plasmid encoding CCL4 is able to improve tumor protection and immune responses in a Her2/neu+ mouse tumor model. Balb/c mice were immunized twice intramuscularly with plasmid DNA on days 1 and 15. On day 25, a tumor challenge was performed with 2 × 10(5) syngeneic Her2/neu+ D2F2/E2 tumor cells. Different groups of mice were vaccinated with pDNA(Her2/neu) plus pDNA(CCL4), pDNA(Her2/neu), pDNA(CCL4) or mock vector alone. Our results show that CCL4 is able to (i) improve tumor protection and (ii) augment a TH1-polarized immune response against Her2/neu. Although Her2/neu-specific humoral and T-cell immune responses were comparable with that induced in previous studies using CCL19 or CCL21 as adjuvants, tumor protection conferred by CCL4 was inferior. Whether this is due to a different spectrum of (innate) immune cells, remains to be clarified. However, combination of CCL19/21 with CCL4 might be a reasonable approach in the future, particularly for DNA vaccination in Her2/neu+ breast cancer in the situation of minimal residual disease.

A Therapeutic Her2/neu Vaccine Targeting Dendritic Cells Preferentially Inhibits the Growth of Low Her2/neu-Expressing Tumor in HLA-A2 Transgenic Mice

PURPOSE

E75, a peptide derived from the Her2/neu protein, is the most clinically advanced vaccine approach against breast cancer. In this study, we aimed to optimize the E75 vaccine using a delivery vector targeting dendritic cells, the B-subunit of Shiga toxin (STxB), and to assess the role of various parameters (Her2/neu expression, combination with trastuzumab) in the efficacy of this cancer vaccine in a relevant preclinical model.

EXPERIMENTAL DESIGN

We compared the differential ability of the free E75 peptide or the STxB-E75 vaccine to elicit CD8(+) T cells, and the impact of the vaccine on murine HLA-A2 tumors expressing low or high levels of Her2/neu.

RESULTS

STxB-E75 synergized with granulocyte macrophage colony-stimulating factors and CpG and proved to be more efficient than the free E75 peptide in the induction of multifunctional and high-avidity E75-specific anti-CD8(+) T cells resulting in a potent tumor protection in HLA-A2 transgenic mice. High expression of HER2/neu inhibited the expression of HLA-class I molecules, leading to a poor recognition of human or murine tumors by E75-specific cytotoxic CD8(+) T cells. In line with these results, STxB-E75 preferentially inhibited the growth of HLA-A2 tumors expressing low levels of Her2/neu. Coadministration of anti-Her2/neu mAb potentiated this effect.

CONCLUSIONS

STxB-E75 vaccine is a potent candidate to be tested in patients with low Her2/neu-expressing tumors. It could also be indicated in patients expressing high levels of Her2/neu and low intratumoral T-cell infiltration to boost the recruitment of T cells-a key parameter in the efficacy of anti-Her2/neu mAb therapy. Clin Cancer Res; 22(16); 4133-44. ©2016 AACR.

Gene Gun Her2/neu DNA Vaccination: Evaluation of Vaccine Efficacy in a Syngeneic Her2/neu Mouse Tumor Model

Genetic vaccination using naked plasmid DNA is an immunization strategy both against infectious diseases and cancer. In order to improve the efficacy of DNA vaccines, particularly in large animals and humans, different strategies have been pursued. These vaccination strategies are based on different application routes, schedules, and coexpression of immunomodulatory molecules as adjuvants. Our mouse tumor model offers the possibility to investigate Her2/neu DNA vaccines in different settings, i.e., intramuscular or intradermal application with or without coexpression of adjuvants. Protection from tumor growth in tumor challenge experiments and both T cell and humoral immune responses against Her2/neu peptides are used as surrogate parameters for vaccine efficacy.

Preclinical HER-2 Vaccines: From Rodent to Human HER-2

Effective prevention of human cancer with vaccines against viruses, such as HBV and HPV, raises the question whether also non-virus related tumors could be prevented with immunological means. Studies in HER-2-transgenic mice showed that powerful anti-HER-2 vaccines, could almost completely prevent the onset of mammary carcinoma. Protective immune responses were orchestrated by T cells and their cytokines, and effected by antibodies against HER-2 gene product p185. Analogous findings were reported in a variety of other cancer immunoprevention systems, thus leading to the definition of oncoantigens, optimal target antigens that are causally involved in carcinogenesis and cancer progression. Prophylactic HER-2 vaccines were also effective in preventing metastasis outgrowth, indicating that concepts and approaches developed for cancer immunoprevention could prove fruitful in cancer immunotherapy as well. The availability of cancer-prone mice carrying a human HER-2 transgene is now fostering the design of novel vaccines against human p185. A further bridge toward human cancer was recently provided by novel immunodeficient models, like Rag2^−/−;Il2rg^−/− mice, which are permissive for metastatic spread of human HER-2+ cancer cells and can be engrafted with a functional human immune system, allowing for the first time the study of vaccines against oncoantigens to elicit human immune responses against human cancer cells in vivo.

HER2-based recombinant immunogen to target DCs through FcγRs for cancer immunotherapy

Dendritic cell (DC)-based immunotherapy is an attractive approach to induce long lasting antitumor effector cells aiming to control cancer progression. DC targeting is a critical step in the design of DC vaccines in order to optimize delivery and processing of the antigen, and several receptors have been characterized for this purpose. In this study, we employed the FcγRs to target DCs both in vitro and in vivo. We designed a recombinant molecule (HER2-Fc) composed of the immunogenic sequence of the human tumor-associated antigen HER2 (aa 364–391) and the Fc domain of a human IgG₁. In a mouse model, HER2-Fc cDNA vaccination activated significant T cell-mediated immune responses towards HER2 peptide epitopes as detected by IFN-γ ELIspot and induced longer tumor latency as compared to Ctrl-Fc-vaccinated control mice. Human in vitro studies indicated that the recombinant HER2-Fc immunogen efficiently targeted human DCs through the FcγRs resulting in protein cross-processing and in the activation of autologous HER2-specific CD8⁺ T cells from breast cancer patients.

Identification of a novel cytotoxic T lymphocyte epitope from CFP21, a secreted protein of Mycobacterium tuberculosis

CFP21 is a major secreted protein of Mycobacterium tuberculosis (Mtb) which is considered as a promising antigen for immunotherapy. To identify CFP21-derived HLA-A*0201 restricted epitopes, a series of native peptides and their analogues were predicted with prediction programs and synthesized. The native peptide, p134 (AVADHVAAV), and its analogues, p134-1Y2L and p134-1Y2L9L, showed potent binding affinity and stability to HLA-A*0201 molecule. In ELISPOT assay, the cytotoxic T lymphocytes (CTLs) induced by these peptides could release IFN-γ. In cytotoxicity assay, the CTLs induced by p134 and p134-1Y2L9L could specifically lyse peptide-loaded T2 cells. In these two assays, the native peptide, p134, showed the most potent activity. Our results indicated that p134 could be a novel epitope which could serve as a good candidate to develop peptide vaccines against M. tuberculosis.

TAA polyepitope DNA-based vaccines: a potential tool for cancer therapy

DNA-based cancer vaccines represent an attractive strategy for inducing immunity to tumor associated antigens (TAAs) in cancer patients. The demonstration that the delivery of a recombinant plasmid encoding epitopes can lead to epitope production, processing, and presentation to CD8+ T-lymphocytes, and the advantage of using a single DNA construct encoding multiple epitopes of one or more TAAs to elicit a broad spectrum of cytotoxic T-lymphocytes has encouraged the development of a variety of strategies aimed at increasing immunogenicity of TAA polyepitope DNA-based vaccines. The polyepitope DNA-based cancer vaccine approach can (a) circumvent the variability of peptide presentation by tumor cells, (b) allow the introduction in the plasmid construct of multiple immunogenic epitopes including heteroclitic epitope versions, and (c) permit to enroll patients with different major histocompatibility complex (MHC) haplotypes. This review will discuss the rationale for using the TAA polyepitope DNA-based vaccination strategy and recent results corroborating the usefulness of DNA encoding polyepitope vaccines as a potential tool for cancer therapy.

Identification and characterization of a HER-2/neu epitope as a potential target for cancer immunotherapy

Our aim is to develop peptide vaccines that stimulate tumor antigen-specific T-lymphocyte responses against frequently detected cancers. We describe herein a novel HLA-A*0201-restricted epitope, encompassing amino acids 828-836 (residues QIAKGMSYL), which is naturally presented by various HER-2/neu (+) tumor cell lines. HER-2/neu(828-836), [HER-2(9(828))], possesses two anchor residues and stabilized HLA-A*0201 on T2 cells in a concentration-dependent Class I binding assay. This peptide was stable for 3.5 h in an off-kinetic assay. HER-2(9(828)) was found to be immunogenic in HLA-A*0201 transgenic (HHD) mice inducing peptide-specific and functionally potent CTL and long-lasting anti-tumor immunity. Most important, using HLA-A*0201 pentamer analysis we could detect increased ex vivo frequencies of CD8(+) T-lymphocytes specifically recognizing HER-2(9(828)) in 8 out of 20 HLA-A*0201(+) HER-2/neu (+) breast cancer patients. Moreover, HER-2(9(828))-specific human CTL recognized the tumor cell line SKOV3.A2 as well as the primary RS.A2.1.DR1 tumor cell line both expressing HER-2/neu and HLA-A*0201. Finally, therapeutic vaccination with HER-2(9(828)) in HHD mice was proven effective against established transplantable ALC.A2.1.HER tumors, inducing complete tumor regression in 50% of mice. Our data encourage further exploitation of HER-2(9(828)) as a promising candidate for peptide-based cancer vaccines.

HER-2/neu (657-665) represents an immunogenic epitope of HER-2/neu oncoprotein with potent antitumor properties

The HER-2/neu oncoprotein is a promising cancer vaccine target. We describe herein a novel HLA-A2.1-restricted epitope, encompassing amino acids 657-665 (AVVGILLVV), which is naturally presented by human breast and ovarian cell lines. HER-2/neu(657-665), [HER-2(9(657))], binds with high affinity to HLA-A2.1 molecules as revealed by a prediction algorithm (SYFPEITHI) and in functional assays. This peptide was found to be immunogenic in HLA-A2.1 transgenic (HHD) mice inducing peptide-specific CTL, which responded with increased IFNgamma production, degranulation, and in vitro as well as in vivo cytotoxicity. Most important, HER-2(9(657)) functioned as a therapeutic vaccine by enabling HHD mice to reject established transplantable tumors. Cured mice resisted tumor growth when re-challenged with the same tumor, demonstrating the capacity of HER-2(9(657)) to generate tumor-specific memory immune response. Finally, this peptide was also found to be immunogenic in PBMCs from HLA-A2.1(+) patients with HER-2/neu(+) breast cancer. Our data encourage further exploitation of HER-2(9(657)) as a promising candidate for peptide-based cancer vaccines.

Towards in silico design of epitope-based vaccines

BACKGROUND

Epitope-based vaccines (EVs) make use of immunogenic peptides (epitopes) to trigger an immune response. Due to their manifold advantages, EVs have recently been attracting growing interest. The success of an EV is determined by the choice of epitopes used as a basis. However, the experimental discovery of candidate epitopes is expensive in terms of time and money. Furthermore, for the final choice of epitopes various immunological requirements have to be considered.

METHODS

Numerous in silico approaches exist that can guide the design of EVs. In particular, computational methods for MHC binding prediction have already become standard tools in immunology. Apart from binding prediction and prediction of antigen processing, methods for epitope design and selection have been suggested. We review these in silico approaches for epitope discovery and selection along with their strengths and weaknesses. Finally, we discuss some of the obvious problems in the design of EVs.

CONCLUSION

State-of-the-art in silico approaches to MHC binding prediction yield high accuracies. However, a more thorough understanding of the underlying biological processes and significant amounts of experimental data will be required for the validation and improvement of in silico approaches to the remaining aspects of EV design.

Adoptive transfer of autologous, HER2-specific, cytotoxic T lymphocytes for the treatment of HER2-overexpressing breast cancer

The human epidermal growth factor receptor 2 (HER2) has been targeted as a breast cancer-associated antigen by immunotherapeutical approaches based on HER2-directed monoclonal antibodies and cancer vaccines. We describe the adoptive transfer of autologous HER2-specific T-lymphocyte clones to a patient with metastatic HER2-overexpressing breast cancer. The HLA/multimer-based monitoring of the transferred T lymphocytes revealed that the T cells rapidly disappeared from the peripheral blood. The imaging studies indicated that the T cells accumulated in the bone marrow (BM) and migrated to the liver, but were unable to penetrate into the solid metastases. The disseminated tumor cells in the BM disappeared after the completion of adoptive T-cell therapy. This study suggests the therapeutic potential for HER2-specific T cells for eliminating disseminated HER2-positive tumor cells and proposes the combination of T cell-based therapies with strategies targeting the tumor stroma to improve T-cell infiltration into solid tumors.

Survivin-derived peptide epitopes and their role for induction of antitumor immunity in hematological malignancies

The immune system's ability to detect and destroy tumor cells offers an attractive approach to broaden the spectrum of cancer therapies. Survivin, a member of the apoptosis inhibitor protein family, is a tumor antigen, overexpressed in human cancers giving rise to peptides eliciting spontaneous CD8+ and CD4+ responses. Due to its dual function, blockade of apoptosis and regulation of cell division, survivin is directly associated with tumor survival and therefore regarded as an ideal target structure for immunotherapeutic approaches. Strong evidence that survivin acts as a T-cell activating antigen has been collected in recent years and the first clinical trials using survivin-based vaccines aim to prove its therapeutic efficacy in the clinic. We focus on the role of survivin in hematological malignancies, including a list of survivin-derived peptides eliciting potent immune responses.

Antigen recognition and T-cell biology

Despite the wealth of information that has been acquired regarding the way T cells recognize their targets, we are left with far more questions than answers regarding how to manipulate the immune response to better treat cancer patients. Clearly, most patients have a broad repertoire of T cells capable of recognizing their tumor cells. Despite the presence of these tumor reactive T cells and our ability to increase their frequency though vaccination or adoptive transfer, patients still progress. From the T cell side, defects in T cell signaling may account for much of our failure to achieve significant numbers of objective clinical responses. In spite of these negatives, the horizon does remain bright for T cell based immune therapy of cancer. The periodic objective clinical response tells us that immune therapy can work. Now that we know that cancer patients have the capacity to mount immune responses against their tumors, current and future investigations with agents which alter T cell function combined with vaccination or adoptive T cell transfer may help tip the balance towards effective immune therapies.

Identification of T-cell epitopes for cancer immunotherapy

The effectiveness of T-cell-mediated immunotherapy of cancer depends on both an optimal immunostimulatory context of the therapy and the proper selection with respect to quality and quantity of the targeted tumor-associated antigens (TAA), and, more precisely, the T-cell epitopes contained in these tumor proteins. Our progressing insight in human leukocyte antigen (HLA) class I and class II antigen processing and presentation mechanisms has improved the prediction by reverse immunology of novel cytotoxic T lymphocyte and T-helper cell epitopes within known antigens. Computer algorithms that in silico predict HLA class I and class II binding, proteasome cleavage patterns and transporter associated with antigen processing translocation are now available to expedite epitope identification. The advent of genomics allows a high-throughput screening for tumor-specific transcripts and mutations, with that identifying novel shared and unique TAA. The increasing power of mass spectrometry and proteomics will lead to the direct identification from the tumor cell surface of numerous novel tumor-specific HLA class I and class II presented ligands. Together, the expanded repertoire of tumor-specific T-cell epitopes will enable more precise immunomonitoring and the development of effective epitope-defined adoptive T-cell transfer and multi-epitope-based vaccination strategies targeting epitopes derived from a wider diversity of TAA presented in a broader array of HLA molecules.

Recognition of Carcinoembryonic Antigen Peptide and Heteroclitic Peptide by Peripheral Blood T Lymphocytes

The carcinoembryonic antigen (CEA)-derived peptide CAP1 and heteroclitic peptide CAP1-6D are stimulators of HLA-A*A0201 restricted CEA-specific T cells in vivo and in vitro. The goal of this study was to evaluate differences in T cell responses to peptide and modified peptide antigens from CEA. The heterogeneity of responses among individuals is potentially important for the design of future CEA-directed immunotherapy trials. Peripheral blood mononuclear cells from blood donors were stimulated with peptide, IL-2, and IL-7. Weekly, microcultures were restimulated with irradiated, autologous peptide-loaded peripheral blood mononuclear cells and expanded in IL-2. Established T cell lines were tested by cytokine release assays using peptide-loaded T2 targets. T cell avidity was measured by cytokine release using targets expressing diminishing concentrations of peptide. Fine specificities were measured using targets loaded with alanine-substituted CAP1 peptide. Tumor recognition was measured using HLA-A*A0201/CAP1-transduced COS tumor targets. Varied responses to CAP1 and CAP1-6D were seen among individuals. The immunogenicity of CAP1 or CAP1-6D was donor dependent. Many T cells recognized one peptide but did not cross-recognize the altered peptide. The avidities of T cell lines were moderate to low, and fine specificities were consistent with a narrow antigen-specific repertoire. CAP1-6D-based immune therapy may not be optimal in some patients with CAP1-specific precursors. The T cell repertoire may be a central contributor to the limited responses seen with CEA-directed immunotherapy to date. Treatment strategies designed to alter or expand the T cell repertoire against CEA should be considered for trials.

An altered peptide ligand for naïve cytotoxic T lymphocyte epitope of TRP-2(180-188) enhanced immunogenicity

Tyrosinase-related protein-2 (TRP-2) is a non-mutated melanocyte differentiation antigen. The TRP-2-recognizing CD8(+) T cells can evoke immune responses to melanoma in both humans and mice. Developing epitopes with amino acid replacements in their sequences might improve the low immunogenicity against this 'self' tumor antigen. We designed altered peptide ligands (APLs) of TRP-2((180-188)) (SVYDFFVWL) with preferred primary and auxiliary HLA-A*0201 molecule anchor residue replacement. These APLs were screened for MHC-affinity by affinity prediction plots and molecular dynamics simulation, and analyzed in vitro for stability and binding-affinity to molecular HLA-A*0201. We also investigated the CTLs activities induced by TRP-2 wild-type epitope and the APLs both in vitro in human PBMCs and HLA-A2.1/K(b) transgenic mice. The results indicate that TRP-2 2M analog simultaneously had stronger binding-affinity and a lower dissociation rate to HLA-A*0201, than wild-type peptide. In addition, the analog 2M was superior to other APLs and wild-type epitope in terms of immunological efficacy ex vivo as measured by the ELISPOT assays of IFN-gamma and granzyme B. These results demonstrate that TRP-2 2M is an agonist epitope that can induce anti-tumor immunity superior to its wild-type epitope, and has potential application in peptide-mediated immunotherapy.

Manufacturing and Quality Control of Cell-based Tumor Vaccines: A Scientific and a Regulatory Perspective

Tumor vaccines play an increasingly important role in the therapy of various malignant diseases. The efficacy of these new products is currently being explored in many clinical trials all over the world. Cell-based tumor vaccines can be classified as somatic cell therapy, or, depending on whether genetic modifications have been applied, as gene-transfer medicinal products. Few specific guidance documents are available to standardize the development and production of cell-based tumor vaccines. Here, we review the different types of cell-based cancer vaccines that are currently being used in clinical trials. Furthermore, we discuss regulatory guidance documents available in the European Union and describe methods that have been applied so far to ensure that the cell-based vaccines meet acceptable standards, including potency assays.

Vaccination with Human HER-2/neu (435-443) CTL Peptide Induces Effective Antitumor Immunity against HER-2/neu-Expressing Tumor Cells In vivo

HER-2/neu is a self-antigen expressed by tumors and nonmalignant epithelial tissues. The possibility of self-tolerance to HER-2/neu-derived epitopes has raised questions concerning their utility in antitumor immunotherapy. Altered HER-2/neu peptide ligands capable of eliciting enhanced immunity to tumor-associated HER-2/neu epitopes may circumvent this problem. The human CTL peptide HER-2/neu (435-443) [hHER-2(9(435))] represents a xenogeneic altered peptide ligand of its mouse homologue, differing by one amino acid residue at position 4. In contrast to mHER-2(9(435)), vaccination of HLA-A*0201 transgenic (HHD) mice with hHER-2(9(435)) significantly increased the frequency of mHER-2(9(435))-specific CTL and also induced strong protective and therapeutic immunity against the transplantable ALC tumor cell line transfected to coexpress HLA-A*0201 and hHER-2/neu or rHER-2/neu. Similar results were also obtained with wild-type C57BL/6 mice inoculated with HER-2/neu transfectants of ALC. Adoptive transfer of CD8(+) CTL from mice immunized with hHER-2(9(435)) efficiently protected naive syngeneic mice inoculated with ALC tumors. In conclusion, our results show that HER-2(9(435)) serves as a tumor rejection molecule. They also propose a novel approach for generating enhanced immunity against a self-HER-2/neu CTL epitope by vaccinating with xenogeneic altered peptide ligands and provide useful insights for the design of improved peptide-based vaccines for the treatment of patients with HER-2/neu-overexpressing tumors.

Identification of Cross-Reactive Peptides Using Combinatorial Libraries Circumvents Tolerance against Her-2/neu-Immunodominant Epitope

The majority of the currently defined tumor-associated Ags are often overexpressed products of normal cellular genes. Therefore, tolerance deletes high-affinity T cells directed against the TAAs, leaving only a low-affinity repertoire. We have demonstrated previously that the T cell repertoire against the immunodominant p773-782 A2.1-Her-2/neu-restricted peptide has low affinity in A2xneu mice (Her-2/neu mice crossed with A2.1/Kb mice), compared with A2xFVB mice (A2.1/Kb crossed with FVB-wild-type mice). Immunizations with this peptide have a minor impact in preventing tumor growth in A2xneu mice. Therefore, attempts to expand these responses may be of little clinical value. We hypothesized that if not all possible cross-reactive peptides (CPs) are naturally processed and presented, the possibility exists that T cells against these CPs persist in the repertoire and can be used to induce antitumor responses with higher avidity against native epitopes present on the tumor cells. We have used the positional scanning synthetic peptide combinatorial library methodology to screen the p773-782 T cell clone. The screening data identified potential amino acids that can be substituted in the primary sequences of the p773-782 peptide. The designed CPs induce CTL responses of higher affinity in A2xneu mice compared with the native p773-783 peptide. These CTLs recognize A2+-Her-2/neu(+) tumors with high efficiency. Moreover, multiple immunizations with CPs significantly prolonged the survival of tumor-bearing A2xneu mice. These results have demonstrated that it was possible to circumvent tolerance with the identification of CPs and that these peptides could be of significant clinical value.

Immunogenic HER-2/neu peptides as tumor vaccines

During the last decade, a large number of tumor-associated antigens (TAA) have been identified, which can be recognized by T cells. This has led to renewed interest in the use of active immunization as a modality for the treatment of cancer. HER-2/neu is a 185-KDa receptor-like glycoprotein that is overexpressed by a variety of tumors including breast, ovarian, lung, prostate and colorectal carcinomata. Several immunogenic HER-2/neu peptides recognized by cytotoxic T lymphocytes (CTL) or helper T lymphocytes (TH) have been identified thus far. Patients with HER-2/neu over-expressing cancers exhibit increased frequencies of peripheral blood T cells recognizing immunogenic HER-2/neu peptides. Various protocols for generating T cell-mediated immune responses specific for HER-2/neu peptides have been examined in pre-clinical models or in clinical trials. Vaccination studies in animals utilizing HER-2/neu peptides have been successful in eliminating tumor growth. In humans, however, although immunological responses have been detected against the peptides used for vaccination, no clinical responses have been described. Because HER-2/neu is a self-antigen, functional immune responses against it may be limited through tolerance mechanisms. Therefore, it would be interesting to determine whether abrogation of tolerance to HER-2/neu using appropriate adjuvants and/or peptide analogs may lead to the development of immune responses to HER-2/neu epitopes that can be of relevance to cancer immunotherapy. Vaccine preparations containing mixtures of HER-2/neu peptides and peptide from other tumor-related antigens might also enhance efficacy of therapeutic vaccination.

Structural prediction of peptides bound to MHC class I

An ab initio structure prediction approach adapted to the peptide-major histocompatibility complex (MHC) class I system is presented. Based on structure comparisons of a large set of peptide-MHC class I complexes, a molecular dynamics protocol is proposed using simulated annealing (SA) cycles to sample the conformational space of the peptide in its fixed MHC environment. A set of 14 peptide-human leukocyte antigen (HLA) A0201 and 27 peptide-non-HLA A0201 complexes for which X-ray structures are available is used to test the accuracy of the prediction method. For each complex, 1000 peptide conformers are obtained from the SA sampling. A graph theory clustering algorithm based on heavy atom root-mean-square deviation (RMSD) values is applied to the sampled conformers. The clusters are ranked using cluster size, mean effective or conformational free energies, with solvation free energies computed using Generalized Born MV 2 (GB-MV2) and Poisson-Boltzmann (PB) continuum models. The final conformation is chosen as the center of the best-ranked cluster. With conformational free energies, the overall prediction success is 83% using a 1.00 Angstroms crystal RMSD criterion for main-chain atoms, and 76% using a 1.50 Angstroms RMSD criterion for heavy atoms. The prediction success is even higher for the set of 14 peptide-HLA A0201 complexes: 100% of the peptides have main-chain RMSD values < or =1.00 Angstroms and 93% of the peptides have heavy atom RMSD values < or =1.50 Angstroms. This structure prediction method can be applied to complexes of natural or modified antigenic peptides in their MHC environment with the aim to perform rational structure-based optimizations of tumor vaccines.

T cell avidity and tumor recognition: implications and therapeutic strategies

In the last two decades, great advances have been made studying the immune response to human tumors. The identification of protein antigens from cancer cells and better techniques for eliciting antigen specific T cell responses in vitro and in vivo have led to improved understanding of tumor recognition by T cells. Yet, much remains to be learned about the intricate details of T cell – tumor cell interactions. Though the strength of interaction between T cell and target is thought to be a key factor influencing the T cell response, investigations of T cell avidity, T cell receptor (TCR) affinity for peptide-MHC complex, and the recognition of peptide on antigen presenting targets or tumor cells reveal complex relationships. Coincident with these investigations, therapeutic strategies have been developed to enhance tumor recognition using antigens with altered peptide structures and T cells modified by the introduction of new antigen binding receptor molecules. The profound effects of these strategies on T cell – tumor interactions and the clinical implications of these effects are of interest to both scientists and clinicians. In recent years, the focus of much of our work has been the avidity and effector characteristics of tumor reactive T cells. Here we review concepts and current results in the field, and the implications of therapeutic strategies using altered antigens and altered effector T cells.

Synopsis of the 6th Walker's Cay Colloquium on Cancer Vaccines and Immunotherapy

The 6th annual Cancer Vaccines and Immunotherapy Colloquium at Walker's Cay was held under the auspices of the Albert B. Sabin Vaccine Institute on March 10-13, 2004. The Colloquium consisted of a select group of 34 scientists representing academia, biotechnology and pharmaceutical industry. The main goal of this gathering was to promote in a peaceful and comfortable environment exchanges between basic and clinical science. The secondary benefit was to inspire novel bench to bedside ventures and at the same time provide feed back about promising and/or disappointing clinical results that could help re-frame some scientific question or guide the design of future trials. Several topics were covered that included tumor antigen discovery and validation, platforms for vaccine development, tolerance, immune suppression and tumor escape mechanisms, adoptive T cell therapy and dendritic cell-based therapies, clinical trials and assessment of response. Here we report salient points raised by speakers or by the audience during animated discussion that followed each individual presentation.