Immunization against polyoma tumors with synthetic peptides derived from the sequences of middle-and large-T antigens

Peptides for Vaccine Development

This review discusses peptide epitopes used as antigens in the development of vaccines in clinical trials as well as future vaccine candidates. It covers peptides used in potential immunotherapies for infectious diseases including SARS-CoV-2, influenza, hepatitis B and C, HIV, malaria, and others. In addition, peptides for cancer vaccines that target examples of overexpressed proteins are summarized, including human epidermal growth factor receptor 2 (HER-2), mucin 1 (MUC1), folate receptor, and others. The uses of peptides to target cancers caused by infective agents, for example, cervical cancer caused by human papilloma virus (HPV), are also discussed. This review also provides an overview of model peptide epitopes used to stimulate non-specific immune responses, and of self-adjuvanting peptides, as well as the influence of other adjuvants on peptide formulations. As highlighted in this review, several peptide immunotherapies are in advanced clinical trials as vaccines, and there is great potential for future therapies due the specificity of the response that can be achieved using peptide epitopes.

Immunotherapy for polyomaviruses: opportunities and challenges

Polyomaviruses are small DNA viruses present in mammals and birds, and in 1953 the first one to be described was murine polyomavirus. It was not until 1971 that the first two human polyomaviruses (HPyVs), BK virus and JC virus, were discovered and found to be common in humans, but only associated with disease in severely immunosuppressed patients. Since 2007, seven new HPyVs have been identified: KI polyomavirus, WU polyomavirus, Merkel cell polyomavirus, HPyV6, HPyV7, trichodyplasia spinulosa polyomavirus and HPyV9. Notably, Merkel cell polyomavirus was detected in Merkel cell cancer, a tumor mainly found in elderly and immunocompromised individuals, while trichodyplasia spinulosa polyomavirus was found in trichodyplasia spinulosa, a skin disorder observed only in immunosuppressed individuals. Consequently, many polyomaviruses cause problems in immunosuppressed individuals. This review deals with these issues, and the potential of the capsid protein VP1 to form virus-like particles for use as vaccines against polyomavirus infections.

Mechanisms of peptide vaccination in mouse models: tolerance, immunity, and hyperreactivity

The development of synthetic peptide vaccines capable of inducing strong and protective T-cell immunity has taken more than 20 years. Peptide vaccines come in many flavors and although their design is simple, their use is more complicated as the success of a particular peptide vaccine is influenced by many parameters. In fact, peptide vaccination may lead to tolerance, immunity or even hyper-reactivity causing death of the animals. Here we systematically dissect the parameters that influence the final outcome of peptide vaccines as examined in mouse models and this will guide the rational design of new vaccines in the future.

Cancer immunotherapy

Recent scientific advances have expanded our understanding of the immune system and its response to malignant cells. The clinical goal of tumour immunotherapy is to provide either passive or active immunity against malignancies by harnessing the immune system to target tumours. Monoclonal antibodies, cytokines, cellular immunotherapy, and vaccines have increasingly become successful therapeutic agents for the treatment of solid and haematological cancers in preclinical models, clinical trials, and practice. In this article, we review recent advances in the immunotherapy of cancer, focusing on new strategies and future perspectives as well as on clinical trials attempting to enhance the efficacy of immunotherapeutic modalities and translate this knowledge into effective cancer therapies.

Immunotherapy of established (pre)malignant disease by synthetic long peptide vaccines

This Review deals with recent progress in the immunotherapy of established (pre)malignant disease of viral or non-viral origin by synthetic vaccines capable of inducing robust T-cell responses. The most attractive vaccine compounds are synthetic long peptides (SLP) corresponding to the sequence of tumour viral antigens or tumour-associated non-viral antigens. Crucial to induction of therapeutic T-cell immunity is the capacity of SLP to deliver specific cargo to professional antigen-presenting cells (dendritic cells (DC)). Proper DC activation then induces the therapeutic CD4+ and CD8+ T-cell responses that are associated with regression of established (pre)malignant lesions, including those induced by high-risk human papilloma virus.

CD8+ CTL priming by exact peptide epitopes in incomplete Freund's adjuvant induces a vanishing CTL response, whereas long peptides induce sustained CTL reactivity

Therapeutic vaccination trials, in which patients with cancer were vaccinated with minimal CTL peptide in oil-in-water formulations, have met with limited success. Many of these studies were based on the promising data of mice studies, showing that vaccination with a short synthetic peptide in IFA results in protective CD8(+) T cell immunity. By use of the highly immunogenic OVA CTL peptide in IFA as a model peptide-based vaccine, we investigated why minimal CTL peptide vaccines in IFA performed so inadequately to allow full optimization of peptide vaccination. Injection of the minimal MHC class I-binding OVA(257-264) peptide in IFA transiently activated CD8(+) effector T cells, which eventually failed to undergo secondary expansion or to kill target cells, as a result of a sustained and systemic presentation of the CTL peptides gradually leaking out of the IFA depot without systemic danger signals. Complementation of this vaccine with the MHC class II-binding Th peptide (OVA(323-339)) restored both secondary expansion and in vivo effector functions of CD8(+) T cells. Simply extending the CTL peptide to a length of 30 aa also preserved these CD8(+) T cell functions, independent of T cell help, because the longer CTL peptide was predominantly presented in the locally inflamed draining lymph node. Importantly, these functional differences were reproduced in two additional model Ag systems. Our data clearly show why priming of CTL with minimal peptide epitopes in IFA is suboptimal, and demonstrate that the use of longer versions of these CTL peptide epitopes ensures the induction of sustained effector CD8(+) T cell reactivity in vivo.

Design and development of synthetic peptide vaccines: past, present and future

Synthetic peptide vaccines aiming at the induction of a protective CD8(+) T-cell response against infectious or malignant diseases are widely used in the clinic but, despite their success in animal models, they do not yet live up to their promise in humans. This review assesses the development of synthetic peptide vaccines, weighs it against the immunological concepts that have emerged, and identifies the key issues that play a role in the failure or success of a synthetic peptide vaccine. The current state-of-the-art peptide vaccine is a complete synthetic inflammatory product that is ingested by professional antigen-presenting cells and stimulates both CD4(+) and CD8(+) T cells.

Therapeutic effect of interleukin 12 on mouse haemangiosarcomas is not associated with an increased anti-tumour cytotoxic T-lymphocyte activity

In syngeneic mice, the H5V polyoma middle-T oncogene-transformed endothelioma cell line induces Kaposi's sarcoma-like cavernous haemangiomas that regress transiently, probably because of an anti-tumour immune response, but eventually grow progressively and kill the host. To evaluate the generation of tumour-specific cytotoxic T lymphocytes (CTLs), spleen cells of tumour-bearing mice were restimulated with irradiated H5V cells in mixed leucocyte-tumour cell cultures. Tumour-specific CTLs were demonstrable only when low numbers of H5V stimulator cells were used (<1 H5V cell per 50 splenocytes). We found that H5V cells secrete immunosuppressive mediators because CTL generation was blocked when H5V cells culture supernatants were added to allogeneic mixed leucocyte cultures. As numerous tumour-derived immunosuppressive mediators may interfere with interleukin 12 (IL-12) production, we tested whether IL-12 treatment of the tumour-bearing mice would augment their immune response and thus suppress tumour growth. Indeed, IL-12 inhibited tumour growth and prevented mortality, but did not increase anti-H5V CTL generation either in vitro or in vivo. Moreover, the anti-tumour activity in IL-12-treated mice was abrogated by anti-interferon (IFN)-gamma monoclonal antibody (MAb) co-administration. These results strongly suggest that the anti-tumour effect of IL-12 is principally mediated by IFN-gamma release that in turn blocks H5V cell proliferation and induces the release of factors that suppress angiogenesis.

Minimal phenotype panels. A method for achieving maximum population coverage with a minimum of HLA antigens

Vaccination with peptides that induce a specific immune response is a potential prophylactic or therapeutic strategy against viral infections and tumors. Because of the extensive polymorphism of the HLA loci, synthetic peptide vaccines must consist of a cocktail of peptides that bind specifically to different HLA molecules. Such cocktails should be optimized for the target population as each population has its specific HLA gene frequencies. To achieve maximum population coverage with a minimum number of peptides, information is needed on the ranking of the most frequent HLA phenotypes. We introduce the minimal phenotype panel, which is the smallest combination of HLA antigens selected so that the proportion of individuals in a population that express at least one of the antigens in the panel exceeds a desired minimum value. We developed a method for assembling minimal phenotype panels based on known HLA class I gene frequencies. We give an example based on a set of 2446 well-defined HLA-typed, random, healthy, unrelated, Dutch Caucasoid individuals. In addition, we discuss the possibility of assembling minimal phenotype panels based on two-locus haplotypes, which enables the assembly of phenotype panels from the antigens of both loci.

Immunotherapy of cancer by peptide-based vaccines for the induction of tumor-specific T cell immunity

Recent progress in defining the molecular nature of antigens and in finding ways to manipulate T cell-mediated immune responses may provide new modalities for cancer treatment. In this report, we review preclinical studies as well as the first clinical trials with vaccination strategies aiming at the induction of anti-tumor immunity. In particular, we focus on the development of a vaccine against human papillomavirus-induced cervical carcinoma.

Polyoma tumor development in neonatally polyoma-virus-infected CD4-/- and CD8-/- single knockout and CD4-/-8-/- double knockout mice

CD4-/- or CD8-/- single knockout as well as CD4-/-8-/- double knockout mice were infected with polyoma virus as newborns or 1 week after birth. The animals were followed for tumor development and virus persistence. Double knockout mice developed tumors at a higher incidence (29%) than either the CD8-/- or CD4-/- single knockout mice (11% and 2%, respectively). Persistence of polyoma virus was examined by PCR in one third of all animals included in the study. Seven of the 17 CD4-/-8-/- double knockout mice gave positive evidence of virus persistence up to 6 months p.i. where virus DNA was present in most organs. Corresponding tests in single knockout mice gave positive results of persistent viral DNA in 2 of the 19 CD8-/-and 2 of the 7 CD4-/-mice. In the single knockout mice polyoma DNA could only be detected in a more limited variety of organs compared to the double knockouts.

Peptide vaccination can lead to enhanced tumor growth through specific T-cell tolerance induction

Vaccination with synthetic peptides representing cytotoxic T lymphocyte (CTL) epitopes can lead to a protective CTL-mediated immunity against tumors or viruses. We now report that vaccination with a CTL epitope derived from the human adenovirus type 5 E1A-region (Ad5E1A234-243), which can serve as a target for tumor-eradicating CTL, enhances rather than inhibits the growth of Ad5E1A-expressing tumors. This adverse effect of peptide vaccination was rapidly evoked, required low doses of peptide (10 micrograms), and was achieved by a mode of peptide delivery that induces protective T-cell-mediated immunity in other models. Ad5E1A-specific CTL activity could no longer be isolated from mice after injection of Ad5E1A-peptide, indicating that tolerization of Ad5E1A-specific CTL activity causes the enhanced tumor outgrowth. In contrast to peptide vaccination, immunization with adenovirus, expressing Ad5E1A, induced Ad5E1A-specific immunity and prevented the outgrowth of Ad5E1A-expressing tumors. These results show that immunization with synthetic peptides can lead to the elimination of anti-tumor CTL responses. These findings are important for the design of safe peptide-based vaccines against tumors, allogeneic organ transplants, and T-cell-mediated autoimmune diseases.

A short peptide eluted from the H-2Kb molecule of a polyomavirus-positive tumor corresponds to polyomavirus large T antigen peptide at amino acids 578 to 585 and induces polyomavirus-specific immunity

A short peptide in complex with the H-2Kb molecule on PyRMA, a polyomavirus transfectant of the mouse lymphoma cell line RMA, was identified as a polyomavirus tumor-specific transplantation antigen. The peptide was obtained by affinity chromatography, acidic extraction, and reverse-phase high-pressure liquid chromatography (HPLC). In one HPLC fraction, a peptide sequence in which 5 of 8 amino acids, GKxGLxxA, corresponded to residues 578 to 585 of polyomavirus large T antigen was identified. In tumor rejection assays, we therefore tested three related synthetic peptides, corresponding to the octapeptide LT 578-585, GKTGLAAA; the nonapeptide LT 578-586, GKTGLAAAL; and the decapeptide LT 578-587, GKTGLAAALI. The octapeptide was found to give the most effective immunization against the outgrowth of the polyomavirus DNA-positive PyRMA tumor. However, none of the three peptides immunized against the original polyoma-virus-negative RMA line.

Susceptibility to tumors induced by polyoma virus is conferred by an endogenous mouse mammary tumor virus superantigen

A dominant gene carried in certain inbred mouse strains confers susceptibility to tumors induced by polyoma virus. This gene, designated Pyvs, was defined in crosses between the highly susceptible C3H/BiDa strain and the highly resistant but H-2k-identical C57BR/cdJ strain. The resistance of C57BR/cdJ mice is overcome by irradiation, indicating an immunological basis. In F1 x C57BR/cdJ backcross mice, tumor susceptibility cosegregates with Mtv-7, a mouse mammary tumor provirus carried by the C3H/BiDa strain. This suggests that Pyvs might encode the Mtv-7 superantigen (SAG) and abrogate polyoma tumor immunosurveillance through elimination of T cells bearing specific V beta domains. DNA typing of 110 backcross mice showed no evidence of recombination between Pyvs and Mtv-7. Strongly biased usage of V beta 6 by polyoma virus-specific CD8+ cytotoxic T lymphocytes in C57BR/cdJ mice implicates T cells bearing this Mtv-7 SAG-reactive V beta domain as critical anti-polyoma tumor effector cells in vivo. These results indicate identity between Pyvs and Mtv-7 sag, and demonstrate a novel mechanism of inherited susceptibility to virus-induced tumors based on effects of an endogenous superantigen on the host's T cell repertoire.

A computer program for predicting possible cytotoxic T lymphocyte epitopes based on HLA class I peptide-binding motifs

Vaccination with peptides recognized by antigen-specific CTLs can prevent lethal virus infections and tumor growth. In order to avoid the synthesis and testing of the numerous overlapping peptide of long AA sequences of proteins of interest, we developed a computer program which utilizes the rules, "motifs" which govern how peptides bind to HLA class I molecules, to derive a predicted binding score for each overlapping peptide. Correlations between the predicted and actual binding results to HLA-A*0201 for 100 peptides selected from six early and two late protein sequences of human papillomavirus type 1a revealed an acceptable level (61%) of concordance. The program is very flexible with regard to the input of protein sequences and motif definitions and is able to handle various motif and peptide lengths.

The cell-binding carboxyterminal undecapeptide of SV40 tumour antigen provides protective cell-dependent immunity

This paper describes the use of the synthetic carboxyterminal undecapeptide of large SV40 tumour antigen, lys698-thr708 (KT) to protect Balb/c mice against growth of subcutaneously transplanted tumorigenic SV40-transformed cells (VLM). The vaccine was prepared by conjugation of KT with 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide (SPDP). Addition of the SPDP-derivative of KT to syngeneic spleen cells rendered KT covalently linked to free thiol-groups of the cell membranes by the formation of -S-S-CH2-CH2-CO-epsilon-NH-lys698 bonds. Vaccination with KT-conjugated cells was intraperitoneal. Alternatively, KT-conjugated cells were generated in the peritoneum by injection of PDP-KT ((2-pyridyldithio)propionic acid-KT). As a control 60Co-irradiated VLM cells were used. In five experiments all VLM-vaccinated and the majority of the PDP-KT-(or KT-spleen cell)-vaccinated mice were protected against tumour growth. However, mice pretreated with saline, unconjugated spleen cells, free KT, KT conjugated to bovine serum albumin, or KT with incomplete Freund's adjuvant developed tumours. Treatment of PDP-KT-vaccinated mice with anti-CD4 or anti-CD8 immunoglobulin abolished tumour immunity completely. Thus, covalent binding of the carboxyterminal undecapeptide of SV40 tumour antigen to viable, untransformed cells yielded a vaccine which protects Balb/c mice against SV40 tumours.

Identification of H-2Kb-, Db- and Dd-binding peptides derived from amino acid sequences of polyoma virus T antigens

Viral and tumor antigens are presented to cytotoxic T cells (CTL) in the form of short peptides. The peptide antigen is transported to the cell surface in conjunction with molecules encoded by the major histocompatibility complex (MHC). Different methods have recently been described for the analysis of the MHC-class-I binding ability of synthetic peptides. Here, we describe a protocol, based on intact RMA-S cells cultured at 26 degrees C in the presence of synthetic peptides, which gives an allele-specific peptide binding pattern with high resolution. This allowed an analysis of the H-2Kb-, Db- and Dd-binding capacity of a panel of synthetic peptides with amino acid (aa) sequences derived from polyoma (py) virus large-, middle- and small-T (LT, MT and ST) antigens, previously used in immunization experiments against py-virus-induced tumors. Eight single aa mutants and a deletion mutant of one peptide with an ability to bind both to H-2Kb and to Db were also analyzed. We foresee that the present protocol, or variants thereof, may serve as a simple and rapid assay for the systematic screening of the class-I binding ability of large sets of synthetic peptides in vitro. Such analysis may facilitate the search for viral or tumor peptide epitopes that are recognized by CTL.

Identification of peptide sequences that potentially trigger HLA-A2.1-restricted cytotoxic T lymphocytes

We used the human processing defective cell line 174CEM.T2 (T2) to identify potential cytotoxic T lymphocyte (CTL) epitopes of human proteins. Exogenously added peptides can increase the number of properly folded HLA-A2.1 molecules on the cell surface of T2 cells, as shown by immunofluorescence measurements using the mouse monoclonal antibody BB7.2 (anti-HLA-A2.1) and fluorescein isothiocyanate-labeled goat anti-mouse F(ab')2 antibody. The peptides were selected on the basis of a computer score derived from the recently described HLA-A2.1 specific motif. Analysis of the influenza matrix protein showed that 15 out of 35 high-scoring peptides up-regulate the expression of HLA-A2.1 molecules on the T2 cell surface. The combination of the computer scoring program and an immunofluorescence-based peptide binding assay allows rapid detection of potential CTL target peptides.

Strict peptide length is not required for the induction of cytotoxic T lymphocyte-mediated antiviral protection by peptide vaccination

Sendai virus nuclear protein peptides of different lengths were titrated in peptide vaccination experiments. We observed that peptide length was not important in inducing cytotoxic T lymphocyte-mediated protective immunity in vivo against a challenge with a lethal dose of virus. These results suggest that long peptides are trimmed in vivo to peptides that fit into the groove of major histocompatibility complex class I molecules. In addition several adjuvants were screened for their effectiveness in peptide vaccination protocols. Incomplete Freund's adjuvant and Titermax turned out to be useful, whereas alum was much less effective.

Modifications of an immunodominant peptide antigen induce different anti-polyoma tumor responses in two separate mouse strains

An immunodominant polyoma peptide antigen MT162-176 was modified with regard to amino acid (aa) composition in an attempt to analyze its immunogenicity in detail. Twelve modifications of peptide MT162-176, 3 overlapping peptides and 9 peptides with point mutations, were synthesized and used for immunizations of (A.CA x C57BL/6)F1 and CBA mice against the syngeneic polyoma tumors SECA and SEBA. All 3 overlapping peptides MT162-176, MT165-174 and MT170-176, were immunogenic in (A.CA x C57BL/6)F1 mice against SECA, indicating that possibly more than one immunogenic epitope may be recognized within the MT162-176 sequence. In CBA mice, the 2 peptides covering the C-terminal half were immunogenic against SEBA, while the N-terminal peptide was possibly somewhat less efficient. The peptides with aa point mutations induced different anti-tumor responses in the 2 mouse strains. In CBA mice, only one mutant, MT162-176.28, was immunogenic. For (A.CA x C57BI)F1 3 different mutants, MT162-176.29, MT162-176.35 and MT162-176.36 were immunogenic against SECA, while the remaining 6 had lost their activity. These results suggest that a different emphasis of recognition of peptide MT162-176 exists with regard to the 2 mouse strains examined. Furthermore, different immunization procedures were tested. We found that repeated immunizations with peptide without Freund's adjuvant was the most efficient.

One explanation for F1 antiparent responses

The phenomenon of hybrid resistance, in which F1 offspring reject parental grafts, remains a perplexing problem. Here, Tina Dalianis and Lars Ahrlund-Richter propose that one component of the F1 antiparent response results from competition between the two sets of parentally derived major histocompatibility complex (MHC) molecules for 'promiscuous' peptides. Lack of tolerance in the F1 animal results from insufficient presentation of these peptides on the MHC molecule that has lower affinity for the peptides.