Mimotope vaccines for cancer immunotherapy

Advances in phage display based nano immunosensors for cholera toxin

Cholera, a persistent global public health concern, continues to cause outbreaks in approximately 30 countries and territories this year. The imperative to safeguard water sources and food from Vibrio cholerae, the causative pathogen, remains urgent. The bacterium is mainly disseminated via ingestion of contaminated water or food. Despite the plate method's gold standard status for detection, its time-consuming nature, taking several days to provide results, remains a challenge. The emergence of novel virulence serotypes raises public health concerns, potentially compromising existing detection methods. Hence, exploiting Vibrio cholerae toxin testing holds promise due to its inherent stability. Immunobiosensors, leveraging antibody specificity and sensitivity, present formidable tools for detecting diverse small molecules, encompassing drugs, hormones, toxins, and environmental pollutants. This review explores cholera toxin detection, highlighting phage display-based nano immunosensors' potential. Engineered bacteriophages exhibit exceptional cholera toxin affinity, through specific antibody fragments or mimotopes, enabling precise quantification. This innovative approach promises to reshape cholera toxin detection, offering an alternative to animal-derived methods. Harnessing engineered bacteriophages aligns with ethical detection and emphasizes sensitivity and accuracy, a pivotal stride in the evolution of detection strategies. This review primarily introduces recent advancements in phage display-based nano immunosensors for cholera toxin, encompassing technical aspects, current challenges, and future prospects.

Position-Scanning Peptide Libraries as Particle Immunogens for Improving CD8+ T-Cell Responses

Short peptides reflecting major histocompatibility complex (MHC) class I (MHC-I) epitopes frequently lack sufficient immunogenicity to induce robust antigen (Ag)-specific CD8+ T cell responses. In the current work, it is demonstrated that position-scanning peptide libraries themselves can serve as improved immunogens, inducing Ag-specific CD8+ T cells with greater frequency and function than the wild-type epitope. The approach involves displaying the entire position-scanning library onto immunogenic nanoliposomes. Each library contains the MHC-I epitope with a single randomized position. When a recently identified MHC-I epitope in the glycoprotein gp70 envelope protein of murine leukemia virus (MuLV) is assessed, only one of the eight positional libraries tested, randomized at amino acid position 5 (Pos5), shows enhanced induction of Ag-specific CD8+ T cells. A second MHC-I epitope from gp70 is assessed in the same manner and shows, in contrast, multiple positional libraries (Pos1, Pos3, Pos5, and Pos8) as well as the library mixture give rise to enhanced CD8+ T cell responses. The library mixture Pos1-3-5-8 induces a more diverse epitope-specific T-cell repertoire with superior antitumor efficacy compared to an established single mutation mimotope (AH1-A5). These data show that positional peptide libraries can serve as immunogens for improving CD8+ T-cell responses against endogenously expressed MHC-I epitopes.

Immunotherapy in prostate cancer: current state and future perspectives

Metastatic castrate resistant prostate cancer (PCa) remains an incurable entity. In the era of immunotherapy, the complex PCa microenvironment poses a unique challenge to the successful application of this class of agents. However, in the last decade, a tremendous effort has been made to explore this field of therapeutics. In this review, the physiology of the cancer immunity cycle is highlighted in the context of the prostate tumor microenvironment, and the current evidence for use of various classes of immunotherapy agents including vaccines (dendritic cell based, viral vector based and DNA/mRNA based), immune checkpoint inhibitors, Chimeric antigen receptor T cell therapy, antibody-mediated radioimmunotherapy, antibody drug conjugates, and bispecific antibodies, is consolidated. Finally, the future directions for combinatorial approaches to combat PCa are discussed.

In Silico-Guided Sequence Modification of Epitopes in Cancer Vaccine Development

Discovery of tumor antigenic epitopes is important for cancer vaccine development. Such epitopes can be designed and modified to become more antigenic and immunogenic in order to overcome immunosuppression towards the native tumor antigen. In silico-guided modification of epitope sequences allows predictive discrimination of those that may be potentially immunogenic. Therefore, only candidates predicted with high antigenicity will be selected, constructed, and tested in the lab. Here, we described the employment of in silico tools using a multiparametric approach to assess both potential T-cell epitopes (MHC class I/II binding) and B-cell epitopes (hydrophilicity, surface accessibility, antigenicity, and linear epitope). A scoring and ranking system based on these parameters was developed to shortlist potential mimotope candidates for further development as peptide cancer vaccines.

T cells recognizing a 11mer influenza peptide complexed to H-2D(b) show promiscuity for peptide length

T-cell repertoire is selected according to self peptide-MHC (major histocompatibility complex) complexes in the thymus. Although most peripheral T cells recognize specific pathogen-derived peptides complexed to self-MHC exclusively, some possess cross-reactivity to other self or foreign peptides presented by self-MHC molecules; a phenomenon often termed T-cell receptor (TCR) promiscuity or degeneracy. TCR promiscuity has been attributed to various autoimmune conditions. On the other hand, it is considered a mechanism for a relatively limited TCR repertoire to deal with a potentially much larger antigenic peptide repertoire. Such property has also been utilized to bypass self-tolerance for cancer vaccine development. Although many studies explored such degeneracy for peptide of the same length, few studies reported such properties for peptides of different length. In this study, we finely characterized the CD8(+) T-cell response specific for a 11mer peptide derived from influenza A viral polymerase basic protein 2. The short-term T-cell line, despite possessing highly biased TCR, was able to react with multiple peptides of different length sharing the same core sequence. Out data clearly showed the importance of detailed and quantitative assessments for such T-cell specificity. Our data also emphasize the importance of biochemical demonstration of the naturally presented minimal peptide.

Leishmania spp. Proteome Data Sets: A Comprehensive Resource for Vaccine Development to Target Visceral Leishmaniasis

Visceral leishmaniasis is a neglected infectious disease caused primarily by Leishmania donovani and Leishmania infantum protozoan parasites. A significant number of infections take a fatal course. Drug therapy is available but still costly and parasites resistant to first line drugs are observed. Despite many years of trial no commercial vaccine is available to date. However, development of a cost effective, needle-independent vaccine remains a high priority. Reverse vaccinology has attracted much attention since the term has been coined and the approach tested by Rappuoli and colleagues. This in silico selection of antigens from genomic and proteomic data sets was also adapted to aim at developing an anti-Leishmania vaccine. Here, an analysis of the efforts is attempted and the challenges to be overcome by these endeavors are discussed. Strategies that led to successful identification of antigens will be illustrated. Furthermore, these efforts are viewed in the context of anticipated modes of action of effective anti-Leishmania immune responses to highlight possible advantages and shortcomings.

Cancer-associated CD43 glycoforms as target of immunotherapy

CD43 is a sialoglycosylated membrane protein that is involved in cell proliferation and differentiation. CD43 glycoforms that are recognized by the UN1 monoclonal antibody (mAb) were expressed in lymphoblastoid T-cell lines and solid tumors, such as breast, colon, gastric, and squamous cell lung carcinomas, while unexpressed in the normal counterparts. The cancer association of UN1/CD43 epitope suggested the possibility to use the UN1 mAb for tumor diagnosis and therapy. In this study, we show that the UN1 mAb was endowed with antitumor activity in vivo because its passive transfer inhibited the growth of UN1-positive HPB-ALL lymphoblastoid T cells in mice. Furthermore, we demonstrate that tumor inhibition was due to UN1 mAb-dependent natural killer-mediated cytotoxicity. By screening a phage-displayed random peptide library, we identified the phagotope 2/165 as a mimotope of the UN1 antigen, as it harbored a peptide sequence that was specifically recognized by the UN1 mAb and inhibited the binding of the UN1 mAb to UN1-positive tumor cells. On the basis of sequence homology with the extracellular region of CD43 (amino acids 64 to 83), the 2/165 peptide sequence was likely mimicking the protein core of the UN1/CD43 epitope. When used as vaccine in mice, the 2/165 phagotope raised antibodies against the UN1/CD43 antigen, indicating that the 2/165 phagotope mimicked the UN1 antigen structure, and could represent a novel immunogen for cancer immunotherapy. These findings support the feasibility of using monoclonal antibodies to identify cancer-associated mimotopes for immunotherapy.

Cancer vaccines inducing antibody production: more pros than cons

To date, passive immunotherapy with monoclonal antibodies is a well-established option in clinical oncology. By contrast, anticancer vaccines are less advanced, with the exception of successfully applied prophylactic vaccines against oncogenic virus infections. The creation of therapeutic vaccines is still a great challenge mostly due to the self-nature of tumor antigens. Therapeutic vaccines may be based on patient-specific material including pulsed effector cells, or tumor-associated antigens and derivatives thereof, such as peptides, mimotopes and nucleic acids. The latter represents a more universal approach, which would set an ideal economic framework resulting in broad patient access. In this article we focus on cancer vaccines for antibody production, in particular mimotope vaccines. The collected evidence suggests that they will open up new treatment options in minimal residual disease and early stage disease.

Identification of peptide mimotopes of gp96 using single-chain antibody library

Heat shock proteins such as gp96 are immunogenic and are widely used as vaccines in immunotherapy of cancers. The present study focuses on the use of peptide mimotopes as immunotherapeutic vaccines for prostate cancer. To this end, we developed a 15-mer gp96 peptide mimotope specifically reactive to MAT-LyLu gp96-peptide complex using combinatorial single-chain antibody and peptide phage display library. The immunogenicity of the synthesized gp96 mimotope was analyzed initially in normal BALB/c mice in combination with various adjuvants such as complete Freund's adjuvant (CFA), aluminum salts (ALUM), granulocyte-macrophage colony-stimulating factor (GM-CSF), and liposome, of which CFA served as a positive control. The antibody response was determined and found that the gp96 mimotope with ALUM showed a significant increase in antibody titer, followed by GM-CSF and liposomes. Further, the T cell (CD4(+) and CD8(+)) populations from splenocytes, as well as IgG isotypes, interleukin-4, and interleukin-5 of gp96 mimotope with ALUM-immunized animals, were analyzed. The results suggest that the gp96 mimotope may elicit a potent and effective antitumor antibody response. Further, the study identifies ALUM and GM-CSF as adjuvant options to drive an appropriate protective immune response as these adjuvants have prior use in humans.

Generation of robust CD8+ T-cell responses against subdominant epitopes in conserved regions of HIV-1 by repertoire mining with mimotopes

HLA-A 0201-restricted virus-specific CD8(+) CTL do not appear to control HIV effectively in vivo. To enhance the immunogenicity of a highly conserved subdominant epitope, TV9 (TLNAWVKVV, p24 Gag(19-27)), mimotopes were designed by screening a large combinatorial nonapeptide library with TV9-specific CTL primed in vitro from healthy donors. A mimic peptide with a low binding affinity to HLA-A 0201, TV9p6 (KINAWIKVV), was studied further. Parallel cultures of in vitro-primed CTL showed that TV9p6 consistently activated cross-reactive and equally functional CTL as measured by cytotoxicity, cytokine production and suppression of HIV replication in vitro. Comparison of TCRB gene usage between CTL primed from the same donors with TV9 or TV9p6 revealed a degree of clonal overlap in some cases and an example of a conserved TCRB sequence encoded distinctly at the nucleotide level between individuals (a "public" TCR); however, in the main, distinct clonotypes were recruited by each peptide antigen. These findings indicate that mimotopes can mobilize functional cross-reactive clonotypes that are less readily recruited from the naïve T-cell pool by the corresponding WT epitope. Mimotope-induced repertoire diversification could potentially override subdominance under certain circumstances and enhance vaccine-induced responses to conserved but poorly immunogenic determinants within the HIV proteome.

Antibodies designed as effective cancer vaccines

Antigen/antibody complexes can efficiently target antigen presenting cells to allow stimulation of the cellular immune response. Due to the difficulty of manufacture and their inherent instability complexes have proved inefficient cancer vaccines. However, anti-idiotypic antibodies mimicking antigens have been shown to stimulate both antibody and T cell responses. The latter are due to T cell mimotopes expressed within the complementarity-determining regions (CDRs) of antibodies that are efficiently presented to dendritic cells in vivo. Based on this observation we have designed a DNA vaccine platform called ImmunoBody, where cytotoxic T lymphocyte (CTL) and helper T cell epitopes replace CDR regions within the framework of a human IgG1 antibody. The ImmunoBody expression system has a number of design features which allow for rapid production of a wide range of vaccines. The CDR regions of the heavy and light chain have been engineered to contain unique restriction endonuclease sites, which can be easily opened, and oligonucleotides encoding the T cell epitopes inserted. The variable and constant regions of the ImmunoBody are also flanked by restriction sites, which permit easy exchange of other IgG subtypes. Here we show a range of T cell epitopes can be inserted into the ImmunoBody vector and upon immunization these T cell epitopes are efficiently processed and presented to stimulate high frequency helper and CTL responses capable of anti-tumor activity.

Induction of antigen-specific CTL and antibody responses in mice by a novel recombinant tandem repeat DNA vaccine targeting at mucin 1 of pancreatic cancer

PURPOSE

Tandem repeat (TR) is the key epitope of mucin 1 (MUC1) for inducing cytotoxic T lymphocytes (CTL) to kill the tumor cells specifically. This study aimed to construct a new recombinant DNA vaccine based on single TR and to investigate the induced immune responses in mice.

MATERIALS AND METHODS

After the synthesis of a recombinant human TR(rhTR)and the construction of the recombinant plasmid pcDNA3.1-TR/Myc-his (+) A (pTR plasmid), C57BL/6 (H-2(b)) mice were immunized with it (TR group, n = 15). Mice inoculated with the empty vector (EV group, n = 15) and normal saline (NS group, n = 15) were used as vector and blank control, respectively. Cytotoxic assay was carried out to measure the CTL activity. And indirect enzyme-linked immunosorbent assay (ELISA) was used to detect anti-TR-specific antibodies.

RESULTS

TR group resulted in more efficient induction of CTL-specific cytolysis against TR polypeptide than both EV and NS groups (both P < 0.01). Vaccine-immunized mice had a higher equivalent concentration of anti-TR-specific antibodies (2,324 ± 238 μg/ml) than either of EV group (1,896 ± 533 μg/ml, P < 0.01) or NS group (1,736 ± 142 μg/ml, P < 0.01).

CONCLUSION

The novel recombinant TR DNA vaccine targeting at MUC1 of pancreatic cancer was constructed successfully, effectively expressing TR polypeptide in the transfected mammalian cells and inducing TR-specific CTL and antibody response.

Molecular basis of allergen cross-reactivity: non-specific lipid transfer proteins from wheat flour and peach fruit as models

Peach non-specific lipid transfer protein (Pru p 3; nsLTP) has been characterized as the major food allergen in the adult Mediterranean population. Its wheat homologous protein, Tri a 14 has a relevant inhalant allergen in occupational baker's asthma. Different sensitization patterns to these allergens have been found in patients with this latter disorder. The objective of the present study was to characterize IgE epitopes of Tri a 14 and to compare them with those of Pru p 3 using three complementary strategies: the analysis of IgE-binding capacity of decapeptides bound to membrane, the identification of mimotopes using a phage display random peptide library, and the analysis of the surface electrostatic potential of both allergens. Thus, synthetic overlapping decapeptides, covering the Pru p 3 and Tri a 14 amino acid sequences, were used to identify sequential regions involved in recognition of IgE from baker's asthma patients sensitized to both nsLTPs. A phage display library was screened with total IgE from the same patients, and positive clones sequentially selected using the purified allergens, allowed to identify mimotopes (conformational epitopes) of Tri a 14 and Pru p 3. Both sequential regions and mimotopes were localized in the corresponding 3D molecular surface and their electrostatic properties were analyzed. Common sequential regions with strong IgE-binding capacity (residues 31-40 and 71-80) were identified in Tri a 14 and Pru p 3, whereas regions Tri a 14(51-60) and Pru p 3(11-20) were found specific of each allergen. A major conformational epitope (mimotope), L34H35N36R39S40S42D43G74V75L77P78Y79T80, which comprised the two common sequential epitopes, was located in Tri a 14, and a very similar one in Pru p 3. However, differences were detected on the surface electrostatic potential of both mimotopes: a first part (around residues 31-45) showed similar positive features in both allergens, whereas a second part (around residues 74-80) was markedly negative in Tri a 14 but neutral-positive in Pru p 3. Tri a 14 and Pru p 3 have a similar conformational region involved in IgE-binding, although their electrostatic features are different. Additionally, common and specific sequential IgE-binding regions were mapped in both allergens. These findings could be instrumental in understanding the cross-reactivity and specificity of sensitization to both homologous allergens.

Overview of mimotopes and related strategies in tumor vaccine development

Tumor vaccine has been studied extensively as an alternative or adjuvant therapy in the treatment of malignant tumors in the hope of prolonging the overall survival rates of cancer patients. The efficacy largely relies on the specificity of the target. In the last decade, many antibody epitopes, called mimotopes, have been revealed as candidates through phage-display technology. These mimotopes do not necessarily consist of amino acid sequences that are identical to the native antigen but they do mimic their structure. Tumor vaccines based on these mimotopes have been proposed as an important developing strategy. Some peptide mimotopes have produced encouraging clinical outcomes. Although most studies are still in the preclinical phase, these findings will possibly pave the way for the development of novel mimotope-based tumor vaccines.

Peptide-based vaccines for cancer: realizing their potential

Advances in the engineering of peptides, adjuvants and delivery systems have renewed the enthusiasm for peptide-based vaccination regimens in the setting of cancer, and there are a variety of clinical trials being conducted by pharmaceutical companies based on the use of peptides. The challenges to successful cancer immunotherapy are common to all immunotherapeutic strategies and not unique to peptide-based vaccination regimens. This review will describe the advances in the identification, design and delivery of peptides, the challenges to successful immunotherapy and will discuss potential options for the future.