Peptide-based vaccination: where do we stand?

A Concise Review on the Role of Natural and Synthetically Derived Peptides in Colorectal Cancer

Colorectal cancer being the second leading cause of cancer-associated deaths has become a significant health concern around the globe. Though there are various cancer treatment approaches, many of them show adverse effects and some compromise the health of cancer patients. Hence, significant efforts are being made for the evolution of a novel biological therapeutic approach with better efficacy and minimal side effects. Current research suggests that the application of peptides in colorectal cancer therapeutics holds the possibility of the emergence of an anticancer reagent. The primary beneficial factors of peptides are their comparatively rapid and easy process of synthesis and the enormous potential for chemical alterations that can be evaluated for designing novel peptides and enhancing the delivery capacity of peptides. Peptides might be utilized as agents with cytotoxic activities or as a carrier of a specific drug or as cytotoxic agents that can efficiently target the tumor cells. Further, peptides can also be used as a tool for diagnostic purposes. The recent analysis aims at developing peptides that have the potential to efficiently target the tumor moieties without harming the nearby normal cells. Additionally, decreasing the adverse effects, and unfolding the other therapeutic properties of potential peptides, are also the subject matter of in-depth analysis. This review provides a concise summary of the function of both natural and synthetically derived peptides in colorectal cancer therapeutics that are recently being evaluated and their potent applications in the clinical field.

Understanding of the Molecular Mechanisms of Allergy

The prevalence of allergic disease has dramatically increased over the past 30 years in Westernized countries. It is unlikely that the rapid increase in the prevalence of allergic disease is the result of genetic changes, which highlights the importance of environmental factors in the development of allergic disease. The "hygiene hypothesis" was put forward in 1989 and focused attention on the notion that exposure to microbes and their products in early life can modify the risk for development of allergic disease. Infections were thought to polarize the immunological response toward a Th2-mediated immune response causing allergic disease. However, it is likely that the Th1/Th2 imbalance is too simplistic to explain the increased prevalence of allergic disease. Current research is focusing on understanding the role of T-regulatory cells in inducing a state of tolerance and the resulting modified Th2 response observed in natural and induced tolerance.

Membranolytic anticancer peptides

Understanding the structure–activity relationships and mechanisms of action of membranolytic anticancer peptides could help them advance to therapeutic success.

Peptide-Based Treatment: A Promising Cancer Therapy

Many new therapies are currently being used to treat cancer. Among these new methods, chemotherapy based on peptides has been of great interest due to the unique advantages of peptides, such as a low molecular weight, the ability to specifically target tumor cells, and low toxicity in normal tissues. In treating cancer, peptide-based chemotherapy can be mainly divided into three types, peptide-alone therapy, peptide vaccines, and peptide-conjugated nanomaterials. Peptide-alone therapy may specifically enhance the immune system's response to kill tumor cells. Peptide-based vaccines have been used in advanced cancers to improve patients' overall survival. Additionally, the combination of peptides with nanomaterials expands the therapeutic ability of peptides to treat cancer by enhancing drug delivery and sensitivity. In this review, we mainly focus on the new advances in the application of peptides in treating cancer in recent years, including diagnosis, treatment, and prognosis.

Vaccines

Since vaccination was documented by Edward Jenner in 1798, it has become the most successful means of preventing infectious diseases, saving millions of lives every year. However, application of vaccines is currently not limited to the prevention of infectious diseases. Vaccines in the pipeline include anti-drug abuse vaccines (nicotine, cocaine) and vaccines against allergies, cancer, and Alzheimer’s disease.

Multiple T cell epitope peptides suppress allergic responses in an egg allergy mouse model by the elicitation of forkhead box transcription factor 3- and transforming growth factor-beta-associated mechanisms

BACKGROUND

Peptide-based immunotherapy (PIT) represents an attractive approach for targeted interventions in immunological disorders, but has not been widely explored in the context of food allergy.

OBJECTIVE

In this study, we built on the information obtained from the recent identification of three immunodominant T cell epitopes of hen ovalbumin (OVA), a major egg allergen, to assess the therapeutic potential of PIT for food allergy, using the BALB/c mouse model.

METHODS

Groups of mice were sensitized to OVA by repeated oral gavages, and subsequently administered with single or multiple synthetic peptides containing OVA T cell epitopes. Following the peptide administration period, all mice were orally challenged with high doses of OVA to elicit active anaphylaxis. Serum, spleen, and intestinal tissues were collected for the determination of immunoglobulin levels, cytokine secretions, and intestinal gene expression.

RESULTS

Significantly lower anaphylactic scores were exhibited by mice that received multiple epitope-containing peptides, accompanied by lower serum histamine and OVA-specific IgE levels, compared with placebo-treated mice. Mechanistically, the quantification of cytokine secretions in splenocyte cultures revealed a T helper type 1-biased response (IFN-gamma) in all peptide-treated mice to the detriment of a T helper type 2-response (IL-4). Interestingly, a similar cytokine expression profile was determined in intestinal tissues, accompanied by a pronounced mRNA expression of regulatory molecules TGF-beta and forkhead box transcription factor 3 (FOXP3). These data suggest the activation of local repressive mechanisms mediated by subsets of regulatory T cells.

CONCLUSION

We demonstrated the therapeutic potential of PIT in a mouse model of food allergy model and provided evidence that mechanistic pathways entailing regulatory molecules TGF-beta and FOXP3, stand as promising trails for the further understanding of peptide-based strategies for food allergy.

Desensitization of ovalbumin-sensitized mice by repeated co-administrations of di-(2-ethylhexyl) phthalate and ovalbumin

Background

The plasticizer di-(2-ethylhexyl) phthalate (DEHP) has been shown to stimulate a non-allergy related immune response with increased levels of IgG1 and IgG2a, but not IgE, after co-administration with the model allergen ovalbumin (OVA) in mice. In mice, decreased IgG1 and increased IgG2a have been associated with the development of mucosal tolerance towards inhaled allergens. As DEHP selectively promote formations of IgG1 and IgG2a without stimulating the IgE response, it was hypothesized that DEHP may suppress an established IgE mediated allergic response. Mice pre-sensitised to OVA were repeatedly co-exposed to DEHP and OVA and the effects were evaluated on the levels of OVA-specific antibodies, ex vivo cytokine levels and the degree of lung inflammation after challenge with an OVA aerosol.

Findings

Compared to the OVA-sensitised control mice, multiple co-exposures to DEHP+OVA reduced the IgG1 level and reduced the IgE/IgG2a ratio. This suggests that DEHP may attenuate allergic sensitisation, as the IgE/IgG2a ratio has been shown to correlate with the degree of anaphylaxis. Nevertheless, no effect of DEHP exposures was seen on inflammatory cells in bronchoalveolar lavage fluid and on cytokine levels in spleen cell culture.

Conclusion

Data from humane and murine studies suggest that DEHP may attenuate the allergic response. More studies are necessary in order to assess the size of this effect and to rule out the underlying mechanism.

Displaying Fel d1 on virus-like particles prevents reactogenicity despite greatly enhanced immunogenicity: a novel therapy for cat allergy

Allergen-specific desensitization is the only disease-modifying therapy currently available for the treatment of allergies. These therapies require application of allergen over several years and some may induce life-threatening anaphylactic reactions. An ideal vaccine for desensitization should be highly immunogenic and should alleviate allergic symptoms upon few injections while being nonreactogenic. We describe such a vaccine for the treatment of cat allergy, consisting of the major cat allergen Fel d1 coupled to bacteriophage Qβ-derived virus-like particles (Qβ–Fel d1). Qβ–Fel d1 was highly immunogenic, and a single vaccination was sufficient to induce protection against type I allergic reactions. Allergen-specific immunoglobulin G antibodies were shown to be the critical effector molecules and alleviated symptoms by two distinct mechanisms. Although allergen-induced systemic basophil degranulation was inhibited in an FcγRIIb-dependent manner, inhibition of local mast cell degranulation in tissues occurred independently of FcγRIIb. In addition, treatment with Qβ–Fel d1 abolished IgE memory responses upon antigen recall. Despite high immunogenicity, the vaccine was essentially nonreactogenic and vaccination induced neither local nor systemic anaphylactic reactions in sensitized mice. Moreover, Qβ–Fel d1 did not induce degranulation of basophils derived from human volunteers with cat allergies. These data suggest that vaccination with Qβ–Fel d1 may be a safe and effective treatment for cat allergy.

Vaccination with human papillomavirus type 16-derived peptides using a tattoo device

Tattooing has been shown to be very efficient at inducing immunity by vaccination with DNA vaccines. In this study, we examined the usability of tattooing for delivery of peptide vaccines. We compared tattooing with subcutaneous (s.c.) needle injection using peptides derived from human papillomavirus type 16 (HPV16) proteins. We observed that higher peptide-specific immune responses were elicited after vaccination with the simple peptides (E7(44-62) and E7(49-57)) and keyhole limpet hemocyanin-(KLH)-conjugated peptides (E7(49-57), L2(18-38) and L2(108-120)) with a tattoo device compared to s.c. inoculation. The administration of the synthetic oligonucleotide containing immunostimulatory CpG motifs (ODN1826) enhanced the immune responses developed after s.c. injection of some peptides (E7(44-62), KLH-conjugated L2(18-38) and L2(108-120)) to levels close to or even comparable to those after tattoo delivery of identical peptides with ODN1826. The highest efficacy of tattooing was observed in combination with ODN1826 for the vaccination with the less immunogenic E6(48-57) peptide and KLH-conjugated and non-conjugated E7(49-57) peptides which form the visible aggregates that could negatively influence the development of immune responses after s.c. injection but probably not after tattooing. In summary, we first evidenced that tattoo administration of peptide vaccines that might be useful in some cases efficiently induced both humoral and cell-mediated immune responses.

Effect of house dust mite immunotherapy on transforming growth factor beta1-producing T cells in asthmatic children

BACKGROUND

Recent evidence suggests that regulatory T cells (Treg cells) and immunosuppressive cytokines, such as transforming growth factor BETA1 (TGF-BETA1) and interleukin 10 (IL-10), may have a role in clinically effective allergen specific immunotherapy (SIT).

OBJECTIVE

To evaluate the effect of SIT on the induction of Treg cells in house dust mite-allergic children and on the expression of specific Treg cell markers (cytotoxic T-lymphocyte-associated protein 4 [CTLA-4], IL-10, and TGF-BETA1).

METHODS

In this uncontrolled open-label study, the percentage of peripheral blood CD4+ Treg cells (CD69 CD45RO+CTLA-4+ and CD3+CD4+CD25+FOXP3+) and the expression of molecules associated with their functions (CTLA-4, TGF-BETA1, and IL-10) were analyzed using flow cytometry in 16 children allergic to house dust mites before and at 3 and 12 months of subcutaneous SIT. Clinical variables, such as symptom score, medication requirements, forced expiratory volume in 1 second, peak expiratory flow rate, and serum IgE levels, were also determined. Ten healthy children were included as controls.

RESULTS

All the clinical variables improved during immunotherapy. The percentage of CD4+CD25+CD69-CD45RO+ Treg cells remained unchanged. The percentage of CTLA-4+ -expressing Treg cells transiently increased after 3 months of immunotherapy, whereas the percentage of FOXP3+ Treg cells did not change after 1 year of immunotherapy. Levels of IL-10+ cells transiently decreased after 3 months of immunotherapy. Four children who required inhaled fluticasone propionate administration for significant symptom worsening had no statistically significant increase in TGF-BETA1-secreting T cells at 12 months of SIT, in contrast to 12 children without inhaled corticosteroid treatment.

CONCLUSIONS

The increase in TGF-BETA1-positive T cells only in children without significant symptom worsening requiring inhaled corticosteroid treatment limits the usefulness of TGF-BETA1 in monitoring response to allergen immunotherapy.

Carbohydrate-based particles reduce allergic inflammation in a mouse model for cat allergy

BACKGROUND

Allergen-specific immunotherapy (ASIT) is the only treatment of allergic disease that gives long-lasting relief of symptoms. However, concerns for safety and efficiency have highlighted the need for improvement of the therapy. We have previously suggested carbohydrate-based particles (CBPs) as a novel adjuvant and allergen carrier for ASIT. Our aim of this study was to evaluate the therapeutic potential of CBPs in ASIT, employing a mouse model for cat allergy.

METHODS

BALB/c mice were subcutaneously immunized with the recombinant (r) cat allergen Fel d 1 followed by intranasal challenge with cat dander extract (CDE). The sensitized mice were therapeutically treated with rFel d 1 covalently coupled to CBPs (CBP-rFel d 1). Airway hyper-reactivity (AHR), infiltration of leucocytes in bronchoalveolar lavage (BAL) fluid, allergen-specific serum immunoglobulin levels and in vitro splenocyte responses were evaluated.

RESULTS

Mice treated with CBP-rFel d 1 showed reduced features of allergic inflammation. They responded with (i) significantly decreased AHR and infiltration of eosinophils in BAL fluid after CDE challenge, (ii) the serum level of rFel d 1-specific IgE was reduced and the level of IgG(2)a was more pronounced after CBP-rFel d 1 treatment, and (iii) there was also a tendency of decreased allergen-specific cellular response.

CONCLUSIONS

Carbohydrate-based particles are effective tools as adjuvant and allergen carriers for use in ASIT and constitutes a promising strategy to improve allergy treatment.

Biotechnology-based allergy diagnosis and vaccination

The diagnosis and immunotherapy currently applied to allergic diseases involve the use of crude extracts of the allergen source without defining the allergy-eliciting molecule(s). Advances in recombinant DNA technology have made identification, cloning, expression and epitope mapping of clinically significant allergens possible. Recombinant allergens that retain the immunological features of natural allergens form the basis of accurate protein-chip-based methods for diagnosing allergic conditions. The ability to produce rationally designed hypoallergenic forms of allergens is leading to the development of novel and safe forms of allergy vaccines with improved efficacy. The initial clinical tests on recombinant-allergen-based vaccine preparations have provided positive results, and ongoing developments in areas such as alternative routes of vaccine delivery will enhance patient compliance.

Phosphatidylinositol Mannoside Ether Analogues: Syntheses and Interleukin-12-Inducing Properties

Phosphatidylinositol mannosides (PIMs) isolated from mycobacteria have been identified as an important class of glycolipids with significant immune modulating properties. We present here the syntheses of phosphatidylinositol dimannoside ether analogues 2 and 3 and evaluate their interleukin-12 (IL-12)-inducing properties along with dipalmitoyl PIM2 (1) in an in vitro bovine dendritic cell assay. Both synthetic PIM analogues and synthetic dipalmitoyl PIM2 (1) were effective at enhancing IL-12 production by immature bovine dendritic cells. Unexpectedly, ether analogue 2 was significantly more active than dipalmitoyl PIM2 (1) which indicates that modified PIM compounds can be strongly immunoactive and may have significant adjuvant activities.

The adjuvant effect of di-(2-ethylhexyl) phthalate is mediated through a PPARα-independent mechanism

Previous studies in BALB/c mice revealed an adjuvant effect of di-(2-ethylhexyl) phthalate (DEHP) to simultaneously administered ovalbumin. DEHP is the most commonly used phthalate plasticizer. In vivo formed metabolites of DEHP are peroxisome-proliferator-activated receptor (PPAR) ligands, a group of chemicals that may have immunomodulatory properties. To study whether the PPARalpha receptor was involved in the adjuvant effect of DEHP, PPARalpha-deficient 129/Sv mice were exposed intraperitoneally to a mixture of OVA and DEHP, and the OVA-specific IgE, IgG1 and IgG2a responses were compared to the corresponding responses in the wild-type strain. The study showed that the adjuvant mechanism of DEHP is mediated through a PPARalpha-independent mechanism. Compared to mice only given OVA, DEHP induced highly increased levels of OVA-specific IgG1 and IgG2a, both in the wild-type and in the PPARalpha knock-out strains, indicating that DEHP is a mixed Th1/Th2 adjuvant.

T-cell responses to allergens

The allergic response in human beings is engineered by CD4(+) T lymphocytes, which secrete T(H)2 cytokines in response to activation by allergen-derived peptides. Although T(H)2 cells have been well characterized, defining the properties of allergen-specific T cells has proved challenging in human beings because of their low frequency within the T-cell repertoire. However, recent studies have provided insight into the molecular signature of long-lived human memory T(H)2 cells, which are allergen-specific. T-cell responses directed against allergens develop in early life and are heavily influenced by the type and dose of allergen, and possibly coexposure to microbial products. These responses are susceptible to suppression by regulatory T cells. This article highlights recent advances in the characterization of allergen-specific memory T(H)2 cells and discusses the heterogeneous nature of regulatory T cells and possible mechanisms of action. The relevance of T-cell epitope mapping studies to understanding the unique nature of T-cell responses to different allergens, as well as to peptide vaccine development, is reviewed. Experimental techniques and approaches for analyzing allergen-specific T cells and identifying novel T-cell epitopes are described that may lead to new T-cell-based therapies.

Cryptic B-cell epitope identification through informational analysis of protein sequenses

A comparison of the location of B-cell epitopes and information structure (IS) of protein sequences was attempted. Analysis of 62 known B-cell epitopes located in five different proteins showed that they concentrated in IS sites with increased degree of information coordination. Based on the analysis of IS six peptides from two proteins were selected and produced in a recombinant form as yeast virus-like particles (VLPs). Immunization of mice with recombinant VLP-peptides has induced the production of IgG capable of recognizing full-length antigens. This result suggests that the analysis of IS of proteins can be useful in the selection of peptides possessing cryptic B-cell epitope activity.

Inactivation and purification of cowpea mosaic virus-like particles displaying peptide antigens from Bacillus anthracis

Chimeric cowpea mosaic virus (CPMV) particles displaying foreign peptide antigens on the particle surface are suitable for development of peptide-based vaccines. However, commonly used PEG precipitation-based purification methods are not sufficient for production of high quality vaccine candidates because they do not allow for separation of chimeric particles from cleaved contaminating species. Moreover, the purified particles remain infectious to plants. To advance the CPMV technology further, it is necessary to develop efficient and scalable purification strategies and preferably eliminate the infectivity of chimeric viruses. CPMV was engineered to display a 25 amino acid peptide derived from the Bacillus anthracis protective antigen on the surface loop of the large coat protein subunit. The engineered virus was propagated in cowpea plants and assembled into chimeric virus particles displaying 60 copies of the peptide on the surface. An effective inactivation method was developed to produce non-infectious chimeric CPMV virus-like particles (VLPs). Uncleaved VLPs were separated from the contaminating cleaved forms by anion exchange chromatography. The yield of purified chimeric VLPs was 0.3 g kg(-1) of leaf tissue. The results demonstrate the ability to generate multi-gram quantities of non-infectious, chimeric CPMV VLPs in plants for use in the development of peptide-based vaccines.

Epitope characterization of ovalbumin in BALB/c mice using different entry routes

Ovalbumin (OVA) is known as a major allergen in egg white. A number of studies have reported the partial T and B cell epitope mapping of OVA using murine models and allergic patients' sera. Recently, we have reported the IgE-binding regions of the entire OVA molecule using egg allergic patients' sera. However, the entire epitope mapping of OVA in a murine model has not been completed yet. In the present study, BALB/c mice were administered a solution of OVA using three different entry routes (oral, intraperitoneal and subcutaneous) with their respective adjuvant (cholera toxin, aluminum hydroxide and Freund's adjuvant). Two nitrocellulose membranes containing 188 overlapping synthetic peptides (with a length of 12 amino acids and an offset of two amino acids) covering the primary sequence of OVA, were probed with the three different BALB/c mice antisera. Antisera obtained from orally challenged mice identified eight IgE epitope regions, i.e. I53D60; V77R84; S103E108; G127T136; E275V280; G301F306; I323A332 and A375S384, while sera raised by intraperitoneal and subcutaneous injections exhibited two (K55D60 and K277L282) and five (K55R58; G127T136; K279L282; T303S308 and I323A332) IgE binding sequences, respectively. The residues critical for the epitope-paratope interactions were finely characterized using the oral immunization serum. Analysis of IgE binding epitopes in mice provides us with potential strategies for design of specific immunotherapy.

Adjuvant effects of inhaled mono-2-ethylhexyl phthalate in BALB/cJ mice

Phthalates, including di(2-ethylhexyl) phthalate (DEHP), are widely used and have been linked with the development of wheezing and asthma. The main metabolite of DEHP, mono-2-ethylhexyl phthalate (MEHP), was investigated for adjuvant effects in a mouse inhalation model. BALB/cJ mice were exposed to aerosols of 0.03 or 0.4 mg/m(3) MEHP 5 days/week for 2 weeks and thereafter weekly for 12 weeks together with a low dose of ovalbumin (OVA) as a model allergen. Mice exposed to OVA alone or OVA+Al(OH)(3) served as negative and positive controls, respectively. Finally, all groups were exposed to a nebulized 1% OVA solution on 3 consecutive days to investigate the development of an inflammatory response. Serum, bronchoalveolar lavage (BAL) fluid, and draining lymph nodes were collected 24h later. In the OVA+Al(OH)(3) group, significantly increased levels of OVA-specific IgE and IgG1 in serum as well as of eosinophils in BAL fluid were observed. OVA-specific IgG1 production in both MEHP groups was significantly increased. OVA-specific IgE and IgG2a were not increased significantly. A dose-dependent increase in inflammatory cells was observed in BAL fluid, leading to significantly higher lymphocyte and eosinophil numbers in the OVA+0.4 mg/m(3) MEHP group. Ex vivo cytokine secretion by cultures of draining lymph nodes suggested a T(H)2 profile of MEHP. In conclusion, MEHP acted as a T(H)2 adjuvant after inhalation. However, it is suggested that the inflammation in the MEHP groups was primarily mediated by an IgG1-dependent mechanism. To address implications for humans, a margin-of-exposure was estimated based on the lack of significant effects on IgE production and inflammation after exposures to 0.03 mg/m(3) MEHP observed in the present study and estimated human exposure levels.

A linear peptide containing minimal T- and B-cell epitopes of Plasmodium falciparum circumsporozoite protein elicits protection against transgenic sporozoite challenge

An effective malaria vaccine is needed to address the public health tragedy resulting from the high levels of morbidity and mortality caused by Plasmodium parasites. The first protective immune mechanism identified in the irradiated sporozoite vaccine, the "gold standard" for malaria preerythrocytic vaccines, was sporozoite-neutralizing antibody specific for the repeat region of the surface circumsporozoite (CS) protein. Previous phase I studies demonstrated that a branched peptide containing minimal T- and B-cell epitopes of Plasmodium falciparum CS protein elicited antirepeat antibody and CD4(+)-T-cell responses comparable to those observed in volunteers immunized with irradiated P. falciparum sporozoites. The current study compares the immunogenicity of linear versus tetrabranched peptides containing the same minimal T- and B-cell epitopes, T1BT*, comprised of a CS-derived universal Th epitope (T*) synthesized in tandem with the T1 and B repeats of P. falciparum CS protein. A simple 48-mer linear synthetic peptide was found to elicit antisporozoite antibody and gamma interferon-secreting T-cell responses comparable to the more complex tetrabranched peptides in inbred strains of mice. The linear peptide was also immunogenic in outbred nonhuman primates (Aotus nancymaae), eliciting antibody titers equivalent to those induced by tetrabranched peptides. Importantly, the 48-mer linear peptide administered in adjuvants suitable for human use elicited antibody-mediated protection against challenge with rodent malaria transgenic sporozoites expressing P. falciparum CS repeats. These findings support further evaluation of linear peptides as economical, safe, and readily produced malaria vaccines for the one-third of the world's population at risk of malaria infection.