Multiple antigen peptide vaccines against Plasmodium falciparum malaria

Exploring malaria parasite surface proteins to devise highly immunogenic multi-epitope subunit vaccine for Plasmodium falciparum

BACKGROUND

Malaria has remained a major health concern for decades among people living in tropical and sub-tropical countries. Plasmodium falciparum is one of the critical species that cause severe malaria and is responsible for major mortality. Moreover, the parasite has generated resistance against all WHO recommended drugs and therapies. Therefore, there is an urgent need for preventive measures in the form of reliable vaccines to achieve the target of a malaria-free world. Surface proteins are the preferable choice for subunit vaccine development because they are rapidly detected and engaged by host immune cells and vaccination-induced antibodies. Additionally, abundant surface or membrane proteins may contribute to the opsonization of pathogens by vaccine-induced antibodies.

RESULTS

In our study, we have listed all those surface proteins from the literature that could be functionally important and essential for infection and immune evasion of the malaria parasite. Eight Plasmodium surface and membrane proteins from the pre-erythrocyte and erythrocyte stages were shortlisted. Thirty-seven epitopes (B-cell, CTL, and HTL epitopes) from these proteins were predicted using immune-informatic tools and joined with suitable peptide linkers to design a vaccine construct. A TLR-4 agonist peptide adjuvant was added at the N-terminus of the multi-epitope series, followed by the PADRE sequence and EAAAK linker. The TLR-4 receptor was docked with the construct's anticipated model structure. The complex of vaccine and TLR-4, with the lowest energy -1514, was found to be stable under simulated physiological settings.

CONCLUSION

This study has provided a novel multi-epitope construct that may be exploited further for the development of an efficient vaccine for malaria.

Development of a new peptide-bead coupling method for an all peptide-based Luminex multiplexing assay for detection of Plasmodium falciparum antibody responses

Using a recombinant protein antigen for antibody testing shows a sum of antibody responses to multiple different immune epitopes existing in the protein antigen. In contrast, the antibody testing to an immunogenic peptide epitope reflects a singular antibody response to the individual peptide epitope. Therefore, using a panel of peptide epitopes provides an advantage for profiling multiple singular antibody responses with potential to estimate recent malaria exposure in human infections. However, transitioning from malaria immune epitope peptide-based ELISA to an all peptide bead-based multiplex Luminex assay presents some challenges including variation in the ability of different peptides to bind beads. The aim of this study was to develop a peptide coupling method while demonstrating the utility of these peptide epitopes from multiple stage antigens of Plasmodium falciparum for measuring antibodies. Successful coupling of peptide epitopes to beads followed three steps: 1) development of a peptide tag appended to the C-terminus of each peptide epitope consisting of beta-alanine-lysine (x 4)--cysteine, 2) bead modification with a high concentration of adipic acid dihydrazide, and 3) use of the peptide epitope as a blocker in place of the traditional choice, bovine serum albumin (BSA). This new method was used to couple 12 peptide epitopes from multiple stage specific antigens of P. falciparum, 1 Anopheles mosquito salivary gland peptide, and 1 Epstein-Barr virus peptide as an assay control. The new method was applied to testing of IgG in pooled samples from 30 individuals with previously repeated malaria exposure in western Kenya and IgM and IgG in samples from 37 U.S. travelers with recent exposure to malaria. The new peptide-bead coupling method and subsequent multiplex Luminex assay showed reliable detection of IgG to all 14 peptides in Kenyan samples. Among 37 samples from U.S. travelers recently diagnosed with malaria, IgM and IgG to the peptide epitopes were detected with high sensitivity and variation. Overall, the U.S. travelers had a much lower positivity rates of IgM than IgG to different peptide epitopes, ranging from a high of 62.2% positive for one epitope to a low of only 5.4% positive for another epitope. In contrast, the travelers had IgG positive rates from 97.3% to 91.9% to various peptide epitopes. Based on the different distribution in IgM and IgG positivity to overall number of peptide epitopes and to the number of pre-erythrocytic, erythrocytic, gametocytic, and salivary stage epitopes at the individual level, four distinct patterns of IgM and IgG responses among the 37 samples from US travelers were observed. Independent peptide-bead coupling and antibody level readout between two different instruments also showed comparable results. Overall, this new coupling method resolves the peptide-bead coupling challenge, is reproducible, and can be applied to any other immunogenic peptide epitopes. The resulting all peptide bead-based multiplex Luminex assay can be expanded to include other peptide epitopes of P. falciparum, different malaria species, or other diseases for surveillance, either in US travelers or endemic areas.

A comprehensive and critical overview of schistosomiasis vaccine candidates

A digenetic platyhelminth Schistosoma is the causative agent of schistosomiasis, one of the neglected tropical diseases that affect humans and animals in numerous countries in the Middle East, sub-Saharan Africa, South America and China. Several control methods were used for prevention of infection or treatment of acute and chronic disease. Mass drug administration led to reduction in heavy-intensity infections and morbidity, but failed to decrease schistosomiasis prevalence and eliminate transmission, indicating the need to develop anti-schistosome vaccine to prevent infection and parasite transmission. This review summarizes the efficacy and protective capacity of available schistosomiasis vaccine candidates with some insights and future prospects.

Developments in Treatment Methodologies Using Dendrimers for Infectious Diseases

Dendrimers comprise a specific group of macromolecules, which combine structural properties of both single molecules and long expanded polymers. The three-dimensional form of dendrimers and the extensive possibilities for use of additional substrates for their construction creates a multivalent potential and a wide possibility for medical, diagnostic and environmental purposes. Depending on their composition and structure, dendrimers have been of interest in many fields of science, ranging from chemistry, biotechnology to biochemical applications. These compounds have found wide application from the production of catalysts for their use as antibacterial, antifungal and antiviral agents. Of particular interest are peptide dendrimers as a medium for transport of therapeutic substances: synthetic vaccines against parasites, bacteria and viruses, contrast agents used in MRI, antibodies and genetic material. This review focuses on the description of the current classes of dendrimers, the methodology for their synthesis and briefly drawbacks of their properties and their use as potential therapies against infectious diseases.

Peptide-Based Vaccines: Foot-and-Mouth Disease Virus, a Paradigm in Animal Health

Vaccines are considered one of the greatest global health achievements, improving the welfare of society by saving lives and substantially reducing the burden of infectious diseases. However, few vaccines are fully effective, for reasons ranging from intrinsic limitations to more contingent shortcomings related, e.g., to cold chain transport, handling and storage. In this context, subunit vaccines where the essential antigenic traits (but not the entire pathogen) are presented in rationally designed fashion have emerged as an attractive alternative to conventional ones. In particular, this includes the option of fully synthetic peptide vaccines able to mimic well-defined B- and T-cell epitopes from the infectious agent and to induce protection against it. Although, in general, linear peptides have been associated to low immunogenicity and partial protection, there are several strategies to address such issues. In this review, we report the progress towards the development of peptide-based vaccines against foot-and-mouth disease (FMD) a highly transmissible, economically devastating animal disease. Starting from preliminary experiments using single linear B-cell epitopes, recent research has led to more complex and successful second-generation vaccines featuring peptide dendrimers containing multiple copies of B- and T-cell epitopes against FMD virus or classical swine fever virus (CSFV). The usefulness of this strategy to prevent other animal and human diseases is discussed.

A VLP for validation of the Plasmodium falciparum circumsporozoite protein junctional epitope for vaccine development

Malaria continues to be a pressing global health issue, causing nearly half a million deaths per year. An effective malaria vaccine could radically improve our ability to control and eliminate this pathogen. The most advanced malaria vaccine, RTS,S, confers only 30% protective efficacy under field conditions, and hence the search continues for improved vaccines. New antigens and formulations are always first developed at a pre-clinical level. This paper describes the development of a platform to supplement existing tools of pre-clinical malaria vaccine development, by displaying linear peptides on a virus-like particle (VLP). Peptides from PfCSP, particularly from outside the normal target of neutralizing antibodies, the central NANP repeat region, are screened for evidence of protective efficacy. One peptide, recently identified as a target of potent neutralizing antibodies and lying at the junction between the N-terminal domain and the central repeat region of PfCSP, is found to confer protective efficacy against malaria sporozoite challenge in mice when presented on the Qβ VLP. The platform is also used to explore the effects of increasing numbers of NANP unit repeats, and including a universal CD4⁺ T-cell epitope from tetanus toxin, on immunogenicity and protective efficacy. The VLP-peptide platform is shown to be of use in screening malaria peptides for protective efficacy and answering basic vaccinology questions in a pre-clinical setting.

Orientation of Antigen Display on Self-Assembling Protein Nanoparticles Influences Immunogenicity

Self-assembling protein nanoparticles (SAPN) serve as a repetitive antigen delivery platform with high-density epitope display; however, antigen characteristics such as size and epitope presentation can influence the immunogenicity of the assembled particle and are aspects to consider for a rationally designed effective vaccine. Here, we characterize the folding and immunogenicity of heterogeneous antigen display by integrating (a) dual-stage antigen SAPN presenting the P. falciparum (Pf) merozoite surface protein 1 subunit, PfMSP1₁₉, and Pf cell-traversal protein for ookinetes and sporozoites, PfCelTOS, in addition to (b) a homogenous antigen SAPN displaying two copies of PfCelTOS. Mice and rabbits were utilized to evaluate antigen-specific humoral and cellular induction as well as functional antibodies via growth inhibition of the blood-stage parasite. We demonstrate that antigen orientation and folding influence the elicited immune response, and when appropriately designed, SAPN can serve as an adaptable platform for an effective multi-antigen display.

Designing a multi-epitope vaccine against blood-stage of Plasmodium falciparum by in silico approaches

Plasmodium falciparum causes the most severe form of malaria disease and is the major cause of infection-related mortalities in the world. Due to increasing in P. falciparum resistance to the first-line antimalarial drugs, an effective vaccine for the control and elimination of malaria infection is urgent. Because the pathogenesis of malaria disease results from blood-stage infection, and all of the symptoms and clinical illness of malaria occur during this stage, there is a strong rationale to develop vaccine against this stage. In the present study, different structural-vaccinology and immuno informatics tools were applied to design an effective antibody-inducing multi-epitope vaccine against the blood-stage of P. falciparum. The designed multi-epitope vaccine was composed of three main parts including B cell epitopes, T helper (Th) cell epitopes, and two adjuvant motives (HP91 and RS09), which were linked to each other via proper linkers. B cell and T cell epitopes were derived from four protective antigens expressed on the surface of merozoites, which are critical to invade the erythrocytes. HP91 and RS09 adjuvants and Th cell epitopes were used to induce, enhance and direct the best form of humoral immune-response against P. falciparum surface merozoite antigens. The vaccine construct was modeled, and after model quality evaluation and refinement by different software, the high-quality 3D-structure model of the vaccine was achieved. Analysis of immunological and physicochemical features of the vaccine showed acceptable results. We believe that this multi-epitope vaccine can be effective for preventing malaria disease caused by P. falciparum.

Designing of precise vaccine construct against visceral leishmaniasis through predicted epitope ensemble: A contemporary approach

Visceral leishmaniasis (VL) caused by Leishmania donovani is a fatal parasitic disease affecting primarily the poor population in endemic countries. Increasing number of deaths as well as resistant to existing drugs necessitates the development of an effective vaccine for successful treatment of VL. The present study employed a combinatorial approach for designing monomer vaccine construct against L. donovani by applying forecasted B- and T- cell epitopes from 4 genome derived antigenic proteins having secretory signal peptides and glycophosphatidylinositol (GPI) anchors with ≤ 1 transmembrane helix. The forecasted population coverage of chosen T cell epitope ensemble (combined HLA class I and II) cover 99.14 % of world-wide human population. The predicted 3D structure of vaccine constructs (VC1/VC2) were modeled using homology modeling approach and docked to innate immune receptors TLR-2 and TLR-4 with respective docking energies -1231.4/-910.3 and -1119.4/-1476 kcal/mol. Overall, the aforementioned designed vaccine constructs were found appropriate for including in self-assembly protein nanoparticles (SAPN) for further study in developing cutting-edge precision vaccine against VL in short duration with cost-effective manner.

Materials for Immunotherapy

Breakthroughs in materials engineering have accelerated the progress of immunotherapy in preclinical studies. The interplay of chemistry and materials has resulted in improved loading, targeting, and release of immunomodulatory agents. An overview of the materials that are used to enable or improve the success of immunotherapies in preclinical studies is presented, from immunosuppressive to proinflammatory strategies, with particular emphasis on technologies poised for clinical translation. The materials are organized based on their characteristic length scale, whereby the enabling feature of each technology is organized by the structure of that material. For example, the mechanisms by which i) nanoscale materials can improve targeting and infiltration of immunomodulatory payloads into tissues and cells, ii) microscale materials can facilitate cell-mediated transport and serve as artificial antigen-presenting cells, and iii) macroscale materials can form the basis of artificial microenvironments to promote cell infiltration and reprogramming are discussed. As a step toward establishing a set of design rules for future immunotherapies, materials that intrinsically activate or suppress the immune system are reviewed. Finally, a brief outlook on the trajectory of these systems and how they may be improved to address unsolved challenges in cancer, infectious diseases, and autoimmunity is presented.

Multi-functional antibodies are induced by the RTS,S malaria vaccine and associated with protection in a phase I/IIa trial

Background

RTS,S is the leading malaria vaccine candidate but only confers partial efficacy against malaria in children. RTS,S is based on the major Plasmodium falciparum sporozoite surface antigen, circumsporozoite protein (CSP). The induction of anti-CSP antibodies is important for protection; however, it is unclear how these protective antibodies function.

Methods

We quantified the induction of functional anti-CSP antibody responses in healthy malaria-naive adults (N = 45) vaccinated with RTS,S/AS01. This included the ability to mediate effector functions via the fragment crystallizable (Fc) region, such as interacting with human complement proteins and Fcγ-receptors (FcγRs) that are expressed on immune cells, which promote various immunological functions.

Results

Our major findings were (1) RTS,S-induced antibodies mediated Fc-dependent effector functions, (2) functional antibodies were generally highest after the second vaccine dose, (3) functional antibodies targeted multiple regions of CSP, (4) participants with higher levels of functional antibodies had a reduced probability of developing parasitemia following homologous challenge (P < .05), and (5) nonprotected subjects had higher levels of anti-CSP IgM.

Conclusions

Our data suggest a role for Fc-dependent antibody effector functions in RTS,S-induced immunity. Enhancing the induction of these functional activities may be a strategy to improve the protective efficacy of RTS,S or other malaria vaccines.

Clinical Trials Registration

NCT00075049

Main B-cell epitopes of PvAMA-1 and PvMSP-9 are targeted by naturally acquired antibodies and epitope-specific memory cells in acute and convalescent phases of vivax malaria

Although antibodies are considered critical for malaria protection, little is known about the mechanisms/factors that maintain humoral immunity, especially regarding the induction and maintenance of memory B cells over time. In Brazilian endemic areas, this is the first time that the profile of antibody responses and the occurrence of antigen-specific memory B cells (MBC) against P vivax were investigated during acute malaria and up to six months after parasite clearance. For this, we selected two peptides, PvAMA-1_(S290-K307) and PvMSP-9_(E795-A808) , which represent the apical membrane antigen-1 and merozoite surface protein-9 of P vivax, respectively. Both peptides were previously described as containing linear B-cell epitopes. Our findings were as follows: 1-both peptides were recognized by IgG antibodies at a high frequency (between 24% and 81%) in all study groups; 2-in the absence of infection, the IgG levels remained stable throughout 6 months of follow-up; and 3-PvAMA-1_(S290-K307) and PvMSP-9_(E795-A808) -specific MBCs were detected in all individual groups in the absence of reinfection throughout the follow-up period, suggesting long-lived MBC. However, no positive association was observed between malaria-specific antibody levels and frequency of MBCs over time. Taken together, these results suggest that peptides can be, in the future, an alternative strategy to polypeptidic vaccine formulation.

Identification of Plasmodium falciparum circumsporozoite protein-specific CD8+ T cell epitopes in a malaria exposed population

BACKGROUND

Sterile protection against malaria, most likely mediated by parasite-specific CD8+ T cells, has been achieved by attenuated sporozoite vaccination of animals as well as malaria-naïve and malaria-exposed subjects. The circumsporozoite protein (CSP)-based vaccine, RTS,S, shows low efficacy partly due to limited CD8+ T cell induction, and inclusion of such epitopes could improve RTS,S. This study assessed 8-10mer CSP peptide epitopes, present in predicted or previously positive P. falciparum 3D7 CSP 15mer overlapping peptide pools, for their ability to induce CD8+ T cell IFN-γ responses in natural malaria-exposed subjects.

METHODS

Cryopreserved PBMCs from nine HLA-typed subjects were stimulated with 23 8-10mer CSP peptides from the 3D7 parasite in IFN-ɣ ELISpot assays. The CD8+ T cell specificity of IFN-γ responses was confirmed in ELISpot assays using CD8+ T cell-enriched PBMC fractions after CD4+ cell depletion.

RESULTS

Ten of 23 peptide epitopes elicited responses in whole PBMCs from five of the nine subjects. Four peptides tested positive in CD8+ T cell-enriched PBMCs from two previously positive responders and one new subject. All four immunodominant peptides are restricted by globally common HLA supertypes (A02, A03, B07) and mapped to regions of the CSP antigen with limited or no reported polymorphism. Association of these peptide-specific responses with anti-malarial protection remains to be confirmed.

CONCLUSIONS

The relatively conserved nature of the four identified epitopes and their binding to globally common HLA supertypes makes them good candidates for inclusion in potential multi-epitope malaria vaccines.

Identification and characterization of protective CD8+ T-epitopes in a malaria vaccine candidate SLTRiP

INTRODUCTION

Efforts are required at developing an effective vaccine that can inhibit malaria prevalence and transmission. Identifying the critical immunogenic antigens and understanding their interactions with host proteins forms a major focus of subunit vaccine development. Previously, our laboratory showed that SLTRiP conferred protection to the liver stage of Plasmodium growth in rodents. In the follow-up of earlier research, we demonstrate that SLTRiP-mediated protection is majorly concentrated in specific regions of protein.

METHOD

To identify particular protective regions of protein, we synthesized multiple nonoverlapping fragments from SLTRiP protein. From this, we designed a panel of 8-20mer synthetic peptides, which were predicted using T-epitope-based prediction algorithm. We utilized the IFN-γ enzyme-linked immunosorbent spot assay to identify immunodominant peptides. The latter were used to immunize mice, and these mice were challenged to assess protection.

RESULTS

The protective polypeptide fragment SLTRiP C3 and SLTRiP C4 were identified, by expressing and testing multiple fragments of PbSLTRiP protein. The immune responses generated by these fragments were compared to identify the immunodominant fragment. The T-epitopes were predicted from SLTRiP protein using computer-based algorithms. The in vitro immune responses generated by these peptides were compared with each other to identify the immunodominant T-epitope. Immunization using these peptides showed significant reduction in parasite numbers during liver stage.

CONCLUSION

Our findings show that the protective efficacy shown by SLTRiP is localized in particular protein fragments. The peptides designed from such regions showed protective efficacy equivalent to whole protein. The sequence conservation analysis with human Plasmodium species also showed that these peptides were conserved. In conclusion, these peptides or their equivalent from other Plasmodium species could impart protection against malaria in their respective hosts too. Our studies provide a basis for the inclusion of these peptides in clinical vaccine constructs against malaria.

A Multiple Antigen Peptide Vaccine Containing CD4+ T Cell Epitopes Enhances Humoral Immunity against Trichinella spiralis Infection in Mice

Multiepitope peptide vaccine has some advantages over traditional recombinant protein vaccine due to its easy and fast production and possible inclusion of multiple protective epitopes of pathogens. However, it is usually poorly immunogenic and needs to conjugate to a large carrier protein. Peptides conjugated to a central lysine core to form multiple antigen peptides (MAPs) will increase the immunogenicity of peptide vaccine. In this study, we constructed a MAP consisting of CD4⁺ T cell and B cell epitopes of paramyosin (Pmy) of Trichinella spiralis (Ts-Pmy), which has been proved to be a good vaccine candidate in our previous work. The immunogenicity and induced protective immunity of MAP against Trichinella spiralis (T. spiralis) infection were evaluated in mice. We demonstrated that mice immunized with MAP containing CD4⁺ T cell and B cell epitopes (MAP-TB) induced significantly higher protection against the challenge of T. spiralis larvae (35.5% muscle larva reduction) compared to the MAP containing B cell epitope alone (MAP-B) with a 12.4% muscle larva reduction. The better protection induced by immunization of MAP-TB was correlated with boosted antibody titers (both IgG1 and IgG2a) and mixed Th1/Th2 cytokine production secreted by the splenocytes of immunized mice. Further flow cytometry analysis of lymphocytes in spleens and draining lymph nodes demonstrated that mice immunized with MAP-TB specifically enhanced the generation of T follicular helper (Tfh) cells and germinal center (GC) B cells, while inhibiting follicular regulatory CD4⁺ T (Tfr) cells and regulatory T (Treg) cells. Immunofluorescence staining of spleen sections also confirmed that MAP-TB vaccination enhanced the formation of GCs. Our results suggest that CD4⁺ T cell epitope of Ts-Pmy is crucial in vaccine component for inducing better protection against T. spiralis infection.

Antigenicity and immune correlate assessment of seven Plasmodium falciparum antigens in a longitudinal infant cohort from northern Ghana

The current global malaria control and elimination agenda requires development of additional effective disease intervention tools. Discovery and characterization of relevant parasite antigens is important for the development of new diagnostics and transmission monitoring tools and for subunit vaccine development. This study assessed the natural antibody response profile of seven novel Plasmodium falciparum pre-erythrocytic antigens and their potential association with protection against clinical malaria. Antigen-specific antibody levels in plasma collected at six time points from a longitudinal cohort of one-to-five year old children resident in a seasonal malaria transmission area of northern Ghana were assessed by ELISA. Antibody levels were compared between parasite-positive and parasite-negative individuals and the association of antibody levels with malaria risk assessed using a regression model. Plasma antibody levels against five of the seven antigens were significantly higher in parasite-positive children compared to parasite-negative children, especially during low transmission periods. None of the antigen-specific antibodies showed an association with protection against clinical malaria. The study identified five of the seven antigens as markers of exposure to malaria, and these will have relevance for the development of disease diagnostic and monitoring tools. The vaccine potential of these antigens requires further assessment.

The acquisition of long-lived memory B cell responses to merozoite surface protein-8 in individuals with Plasmodium vivax infection

BACKGROUND

The ability of a malaria antigen to induce effective, long-lasting immune responses is important for the development of a protective malaria vaccine. Plasmodium vivax merozoite surface protein-8 (PvMSP8) has been shown to be immunogenic in natural P. vivax infections and produces both cell-mediated and antibody-mediated immunity. Thus, PvMSP8 has been proposed as a vaccine candidate following fusion with other merozoite antigens in blood stage vaccine design. Here, the long-term responses of antibodies and memory B cells (MBCs) specific to PvMSP8 in individuals were monitored in a longitudinal cohort study.

METHODS

Both cross-sectional surveys and cohort studies were utilized to explore the persistence of antibody and MBC responses to PvMSP8. Antibody titers were detected in individuals with acute disease and those who recovered from an infection for 4 years. The dominant peptide epitope of PvMSP8 recognized by naturally acquired antibodies was examined to observe the durability of the post-infection antibody response. PvMSP8-specific MBCs were also in subjects 4 years post-infection using an enzyme-linked immunospot assay.

RESULTS

The prevalence of antibodies to PvMSP8 was high during and after infection. The antibody levels in individual responders were monitored for up to 12 months post-infection and showed that most patients maintained their seropositive response. Interestingly, the anti-PvMSP8 antibody responses stably persisted in some patients who had recovered from an infection for 4 years. Positive PvMSP8-specific MBCs were also detected at 4 years post-infection. However, analysis in these individuals showed no correlation with the presence or titer of circulating antibody.

CONCLUSION

PvMSP8 had the ability to induce a long-term humoral immune response. The antibodies and MBCs specific for this antigen developed and persisted in subjects who acquired a natural P. vivax infection. Inclusion of the PvMSP8 antigen in blood stage vaccine design should be considered.

Inhibition of parasite invasion by monoclonal antibody against epidermal growth factor-like domain of Plasmodium vivax merozoite surface protein 1 paralog

The Plasmodium vivax merozoite surface protein 1 paralog (PvMSP1P), which has epidermal growth factor (EGF)-like domains, was identified as a novel erythrocyte adhesive molecule. This EGF-like domain (PvMSP1P-19) elicited high level of acquired immune response in patients. Antibodies against PvMSP1P significantly reduced erythrocyte adhesion activity to its unknown receptor. To determine PvMSP1P-19-specific antibody function and B-cell epitopes in vivax patients, five monoclonal antibodies (mAbs) and 18-mer peptides were generated. The mAb functions were determined by erythrocyte-binding inhibition assay and invasion inhibition assay with P. knowlesi. B-cell epitopes of PvMSP1P-19 domains were evaluated by peptide microarray. The pvmsp1p-19 sequences showed limited polymorphism in P. vivax worldwide isolates. The 1BH9-A10 showed erythrocyte binding inhibitory by interaction with the N-terminus of PvMSP1P-19, while this mAb failed to recognize PkMSP1P-19 suggesting the species-specific for P. vivax. Other mAbs showed cross-reactivity with PkMSP1P-19. Among them, the 2AF4-A2 and 2AF4-A6 mAb significantly reduced parasite invasion through C-terminal recognition. The linear B-cell epitope in naturally exposed P. vivax patient was identified at three linear epitopes. In this study, PvMSP1P-19 N-terminal-specific 1BH9-A10 and C-terminal-specific 2AF4 mAbs showed functional activity for epitope recognition suggesting that PvMSP1P may be useful for vaccine development strategy for specific single epitope to prevent P. vivax invasion.

Immunogenicity and Protective Efficacy of T-Cell Epitopes Derived From Potential Th1 Stimulatory Proteins of Leishmania (Leishmania) donovani

Development of a suitable vaccine against visceral leishmaniasis (VL), a fatal parasitic disease, is considered to be vital for maintaining the success of kala-azar control programs. The fact that Leishmania-infected individuals generate life-long immunity offers a viable proposition in this direction. Our prior studies demonstrated that T-helper1 (Th1) type of cellular response was generated by six potential recombinant proteins viz. elongation factor-2 (elF-2), enolase, aldolase, triose phosphate isomerase (TPI), protein disulfide isomerase (PDI) and p45, derived from a soluble antigenic fraction (89.9–97.1 kDa) of Leishmania (Leishmania) donovani promastigote, in treated Leishmania patients and golden hamsters and showed significant prophylactic potential against experimental VL. Moreover, since, it is well-known that our immune system, in general, triggers production of specific protective immunity in response to a small number of amino acids (peptide), this led to the identification of antigenic epitopes of the above-stated proteins utilizing immunoinformatics. Out of thirty-six, three peptides-P-10 (enolase), P-14, and P-15 (TPI) elicited common significant lymphoproliferative as well as Th1-biased cytokine responses both in golden hamsters and human subjects. Further, immunization with these peptides plus BCG offered 75% prophylactic efficacy with boosted cellular immune response in golden hamsters against Leishmania challenge which is indicative of their candidature as potential vaccine candidates.

Expression of vitamin D receptor in bronchial asthma and its bioinformatics prediction

Vitamin D receptors (VDRs) are associated with the occurrence and development of asthma. The aim of the present study was to analyze the secondary structure and B‑cell and T‑cell epitopes of VDR using online prediction software and aid in the future development of a highly efficient epitope‑based vaccine against asthma. Blood samples were collected from peripheral blood of asthmatic children. Reverse transcription quantitative‑polymerase chain reaction (RT‑qPCR) was performed to detect the expression of VDR in the peripheral blood. Mouse models of asthma were established. Hematoxylin and eosin staining was performed to observe the pathological alterations of the lungs of mice. Immunohistochemistry, western blot analysis and RT‑qPCR were performed to detect the expression of VDR in the lungs of asthmatic mice. Online prediction software immune epitope database and analysis resource, SYFPEITHI and linear epitope prediction based on propensity scale and support vector machines were used to predict the B‑cell and T‑cell epitopes and the RasMol and 3DLigandSite were used to analyze the tertiary structure of VDR. RT‑qPCR demonstrated that VDR expression in the peripheral blood of asthmatic children was decreased. Immunohistochemistry, western blotting and RT‑qPCR demonstrated that VDR expression also decreased in the lungs of mouse models of asthma. VDR B‑cell epitopes were identified at 37‑45, 88‑94, 123‑131, 231‑239, 286‑294 and 342‑350 positions of the amino acid sequence and VDR T‑cell epitopes were identified at 125‑130, 231‑239 and 265‑272 positions. A total of six B‑cell epitopes and three T‑cell epitopes for VDR were predicted by bioinformatics, which when validated, may in the future aid in immunological diagnosis and development of a targeted drug therapy for clinical asthma.

Developing effective vaccines: Cues from natural infection

The ultimate goal of any vaccine is to generate a heterogeneous and stable pool of memory lymphocytes. Vaccine are designed with the hope to generate antigen specific long-lived T cell responses, as it may be the case in natural infection; however, inducing such response by sub-unit vaccine has been a challenge. Although significant progress has been made, there is lot of scope for designing novel vaccine strategies by taking cues from the natural infection. This review focuses upon the roadblocks and the possible ways to overcome them leading to developing effective vaccines. Here we propose that mimicking the natural course of infection as well as the inclusion of non-target antigens in vaccine formulations might generate heterogeneous pool of memory T cells to ensure long-lived protection.

Immunoprophylaxis of multi-antigen peptide (MAP) vaccine for human lymphatic filariasis

Human lymphatic filariasis, the parasitic disease caused by the filarial nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori, is ranked as the second most complex clinical condition leading to permanent and long-term disability. The multiple antigen peptide (MAP) approach is an effective method to chemically synthesize and deliver multiple T and B cell epitopes as the constituents of a single immunogen. Here, we report on the design, chemical synthesis, and immunoprophylaxis of three epitopes that have been identified from promising vaccine candidates reported in our previous studies, constructed as MAP on an inert lysine core for human lymphatic filariasis in Jird model. Two epitopes from Thioredoxin and one epitope from Transglutaminase were constructed as MAP in an inert lysine core. The immunoprophylaxis of the synthetic vaccine construct studied in Jird models showed protective antibody (1 in 64,000 titer) and cellular immune response. Thioredoxin-Transglutaminase MAP (TT MAP) conferred a significantly high protection of 63.04% compared to control (8.5%). Multi-antigen peptide vaccine is one best approach to provide immunity against multiple antigens delivered by the complex filarial parasite.

Conserved Binding Regions Provide the Clue for Peptide-Based Vaccine Development: A Chemical Perspective

Synthetic peptides have become invaluable biomedical research and medicinal chemistry tools for studying functional roles, i.e., binding or proteolytic activity, naturally-occurring regions’ immunogenicity in proteins and developing therapeutic agents and vaccines. Synthetic peptides can mimic protein sites; their structure and function can be easily modulated by specific amino acid replacement. They have major advantages, i.e., they are cheap, easily-produced and chemically stable, lack infectious and secondary adverse reactions and can induce immune responses via T- and B-cell epitopes. Our group has previously shown that using synthetic peptides and adopting a functional approach has led to identifying Plasmodium falciparumconserved regions binding to host cells. Conserved high activity binding peptides’ (cHABPs) physicochemical, structural and immunological characteristics have been taken into account for properly modifying and converting them into highly immunogenic, protection-inducing peptides (mHABPs) in the experimental Aotus monkey model. This article describes stereo–electron and topochemical characteristics regarding major histocompatibility complex (MHC)-mHABP-T-cell receptor (TCR) complex formation. Some mHABPs in this complex inducing long-lasting, protective immunity have been named immune protection-inducing protein structures (IMPIPS), forming the subunit components in chemically synthesized vaccines. This manuscript summarizes this particular field and adds our recent findings concerning intramolecular interactions (H-bonds or π-interactions) enabling proper IMPIPS structure as well as the peripheral flanking residues (PFR) to stabilize the MHCII-IMPIPS-TCR interaction, aimed at inducing long-lasting, protective immunological memory.

Protection via a ROM4 DNA vaccine and peptide against Toxoplasma gondii in BALB/c mice

Background

Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan parasite with a broad host range including most warm-blooded animals, including humans. T. gondii surface antigen 1 (SAG1) is a well-characterized T. gondii antigen. T. gondii expresses five nonmitochondrial rhomboid intramembrane proteases, TgROM1-5. TgROM4 is uniformly distributed on the surface of T. gondii and involved in regulating MIC2, MIC3, MIC6, and AMA1 during T. gondii invasion of host cells. Bioinformatics have predicted ROM4 B-cell and T-cell epitopes. Immunization strategy is also a key factor in determining the effectiveness of the immune response and has gained increasing attention in T. gondii vaccine research. In this study, we used a DNA prime-peptide boost vaccination regimen to assess the protective efficacy of various vaccination strategies using TgROM4.

Methods

We identified a polypeptide (YALLGALIPYCVEYWKSIPR) using a bioinformatics approach, and immunized mice using a DNA-prime and polypeptide-boost regimen. BALB/c mice were randomly divided into six groups, including three experimental groups (peptide, pROM4 and pROM4/peptide) and three control groups (PBS, pEGFP-C1 and pSAG1). Mice were then immunized intramuscularly four times. After immunization, IgG and cytokine productions were determined using enzyme-linked immunosorbent assays. The survival time of mice was evaluated after challenge with tachyzoites of T. gondii RH strain. Additionally, the number of cysts in the brain was determined after intragastric challenge with cysts of T. gondii PRU strain.

Results

Mice vaccinated with different immunization regimens (peptide, pROM4 and pROM4/peptide) elicited specific humoral and cellular responses, with high levels of IgG, IgG2a, and interferon (IFN)-γ. Moreover, IgG, IgG2a and IFN-γ levels were highest in the pROM4/peptide group. Immunized mice, especially those in the pROM4/peptide group, had prolonged survival times after challenge with tachyzoites and reduced numbers of brain cysts after infection compared with negative controls.

Conclusion

A DNA prime-peptide boost regimen based on ROM4 elicited the highest level of humoral and cellular immune responses among immunization regimens, and may be a promising approach to increase the efficacy of DNA immunization.

Post-Genomics and Vaccine Improvement for Leishmania

Leishmaniasis is a parasitic disease that primarily affects Asia, Africa, South America, and the Mediterranean basin. Despite extensive efforts to develop an effective prophylactic vaccine, no promising vaccine is available yet. However, recent advancements in computational vaccinology on the one hand and genome sequencing approaches on the other have generated new hopes in vaccine development. Computational genome mining for new vaccine candidates is known as reverse vaccinology and is believed to further extend the current list of Leishmania vaccine candidates. Reverse vaccinology can also reduce the intrinsic risks associated with live attenuated vaccines. Individual epitopes arranged in tandem as polytopes are also a possible outcome of reverse genome mining. Here, we will briefly compare reverse vaccinology with conventional vaccinology in respect to Leishmania vaccine, and we will discuss how it influences the aforementioned topics. We will also introduce new in vivo models that will bridge the gap between human and laboratory animal models in future studies.

Malaria vaccine based on self-assembling protein nanoparticles

Despite recent progress with GSK's RTS,S malaria vaccine, there remains a desperate need for an efficient malaria vaccine. We have used a repetitive antigen display technology to display malaria specific B cell and T cell epitopes in an effort to design a vaccine against Plasmodium falciparum malaria. Our protein sequence when assembled into a nanoparticle induces strong, long-lived and protective immune responses against infection with the parasite. We are confident that the clinical trials with our most developed vaccine candidate will show good protection in a controlled human malaria infection trial.

A Multiple Antigenic Peptide Mimicking Peptidoglycan Induced T Cell Responses to Protect Mice from Systemic Infection with Staphylococcus aureus

Due to the enormous capacity of Staphylococcus aureus to acquire antibiotic resistance, it becomes imperative to develop vaccines for decreasing the risk of its life-threatening infections. Peptidoglycan (PGN) is a conserved and major component of S. aureus cell wall. However, it has not been used as a vaccine candidate since it is a thymus-independent antigen. In this study, we synthesized a multiple antigenic peptide, named MAP27, which comprised four copies of a peptide that mimics the epitope of PGN. After immunization with MAP27 five times and boosting with heat-inactivated bacterium one time, anti-MAP27 serum bound directly to S. aureus or PGN. Immunization with MAP27 decreased the bacterial burden in organs of BALB/c mice and significantly prolonged their survival time after S. aureus lethal-challenge. The percentage of IFN-γ⁺CD3⁺ T cells and IL-17⁺CD4⁺ T cells in spleen, as well as the levels of IFN-γ, IL-17A/F and CCL3 in spleen and lung, significantly increased in the MAP27-immunized mice after infection. Moreover, in vitro incubation of heat-inactivated S. aureus with splenocytes isolated from MAP27-immunized mice stimulated the production of IFN-γ and IL-17A/F. Our findings demonstrated that MAP27, as a thymus-dependent antigen, is efficient at eliciting T cell-mediated responses to protect mice from S. aureus infection. This study sheds light on a possible strategy to design vaccines against S. aureus.

Analysis of a Multi-component Multi-stage Malaria Vaccine Candidate--Tackling the Cocktail Challenge

Combining key antigens from the different stages of the P. falciparum life cycle in the context of a multi-stage-specific cocktail offers a promising approach towards the development of a malaria vaccine ideally capable of preventing initial infection, the clinical manifestation as well as the transmission of the disease. To investigate the potential of such an approach we combined proteins and domains (11 in total) from the pre-erythrocytic, blood and sexual stages of P. falciparum into a cocktail of four different components recombinantly produced in plants. After immunization of rabbits we determined the domain-specific antibody titers as well as component-specific antibody concentrations and correlated them with stage specific in vitro efficacy. Using purified rabbit immune IgG we observed strong inhibition in functional in vitro assays addressing the pre-erythrocytic (up to 80%), blood (up to 90%) and sexual parasite stages (100%). Based on the component-specific antibody concentrations we calculated the IC₅₀ values for the pre-erythrocytic stage (17–25 μg/ml), the blood stage (40–60 μg/ml) and the sexual stage (1.75 μg/ml). While the results underline the feasibility of a multi-stage vaccine cocktail, the analysis of component-specific efficacy indicates significant differences in IC₅₀ requirements for stage-specific antibody concentrations providing valuable insights into this complex scenario and will thereby improve future approaches towards malaria vaccine cocktail development regarding the selection of suitable antigens and the ratios of components, to fine tune overall and stage-specific efficacy.

Characterization of Plasmodium falciparum Proteome at Asexual Blood Stages for Screening of Effective Vaccine Candidates: An Immunoinformatics Approach

Malaria is a complex parasitic disease that is currently causing great concerns globally owing to the resistance to antimalarial drugs and lack of an effective vaccine. The present study involves the characterization of extracellular secretory proteins as vaccine candidates derived from proteome analysis of Plasmodium falciparum at asexual blood stages of malaria. Among the screened 32 proteins, 31 were predicted as antigens by the VaxiJen program, and 26 proteins had less than two transmembrane spanning regions predicted using the THMMM program. Moreover, 10 and 5 proteins were predicted to contain secretory signals by SignalP and TargetP, respectively. T-cell epitope prediction using MULTIPRED2 and NetCTL programs revealed that most of the predicted antigens are immunogenic and contain more than 10% supertype and 5% promiscuous epitopes of HLA-A, -B, or -DR. We anticipate that T-cell immune responses against asexual blood stages of Plasmodium are dispersed on a relatively large number of parasite antigens. This is the first report, to the best of our knowledge, offering new insights, at the proteome level, for the putative screening of effective vaccine candidates against the malaria pathogen. The findings also suggest new ways forward for the modern omics-guided vaccine target discovery using reverse vaccinology.

Guiding principles in the design of molecular bioconjugates for vaccine applications

Antigen- and adjuvant-based bioconjugates that can stimulate the immune system play an important role in vaccine applications. Bioconjugates have demonstrated unique physicochemical and biological properties, enabling vaccines to be delivered to key immune cells, to target specific intracellular pathways, or to mimic immunogenic properties of natural pathogens. In this Review we highlight recent advances in such molecular immunomodulators, with an emphasis on the structure-function relationships that provide the foundation for rational design of safe and effective vaccines and immunotherapies.

Malaria vaccine candidate antigen targeting the pre-erythrocytic stage of Plasmodium falciparum produced at high level in plants

Plants have emerged as low-cost production platforms suitable for vaccines targeting poverty-related diseases. Besides functional efficacy, the stability, yield, and purification process determine the production costs of a vaccine and thereby the feasibility of plant-based production. We describe high-level plant production and functional characterization of a malaria vaccine candidate targeting the pre-erythrocytic stage of Plasmodium falciparum. CCT, a fusion protein composed of three sporozoite antigens (P. falciparum cell traversal protein for ookinetes and sporozoites [PfCelTOS], P. falciparum circumsporozoite protein [PfCSP], and P. falciparum thrombospondin-related adhesive protein [PfTRAP]), was transiently expressed by agroinfiltration in Nicotiana benthamiana leaves, accumulated to levels up to 2 mg/g fresh leaf weight (FLW), was thermostable up to 80°C and could be purified to >95% using a simple two-step procedure. Reactivity of sera from malaria semi-immune donors indicated the immunogenic conformation of the purified fusion protein consisting of PfCelTOS, PfCSP_TSR, PfTRAP_TSR domains (CCT) protein. Total IgG from the CCT-specific mouse immune sera specifically recognized P. falciparum sporozoites in immunofluorescence assays and induced up to 35% inhibition in hepatocyte invasion assays. Featuring domains from three promising sporozoite antigens with different roles (attachment and cell traversal) in the hepatocyte invasion process, CCT has the potential to elicit broader immune responses against the pre-erythrocytic stage of P. falciparum and represents an interesting new candidate, also as a component of multi-stage, multi-subunit malaria vaccine cocktails.

Titrating T-cell epitopes within self-assembled vaccines optimizes CD4+ helper T cell and antibody outputs

Epitope content plays a critical role in determining T-cell and antibody responses to vaccines, biomaterials, and protein therapeutics, but its effects are nonlinear and difficult to isolate. Here, molecular self-assembly is used to build a vaccine with precise control over epitope content, in order to finely tune the magnitude and phenotype of T helper and antibody responses. Self-adjuvanting peptide nanofibers are formed by co-assembling a high-affinity universal CD4+ T-cell epitope (PADRE) and a B-cell epitope from Staphylococcus aureus at specifiable concentrations. Increasing the PADRE concentration from micromolar to millimolar elicited bell-shaped dose-responses that are unique to different T-cell populations. Notably, the epitope ratios that maximize T follicular helper and antibody responses differed by an order of magnitude from those that maximized Th1 or Th2 responses. Thus, modular materials assembly provides a means of controlling epitope content and efficiently skewing the adaptive immune response in the absence of exogenous adjuvant; this approach may contribute to the development of improved vaccines and immunotherapies.

DNA prime and peptide boost immunization protocol encoding the Toxoplasma gondii GRA4 induces strong protective immunity in BALB/c mice

Background

Toxoplasma gondii is a widespread intracellular parasite, which infects most vertebrate animal hosts and causes zoonotic infection in humans. Vaccine strategy remains a promising method for the prevention and control of toxoplasmosis. T. gondii GRA4 protein has been identified as a potential candidate for vaccine development. In our study, we evaluated the immune response induced by four different immunization vaccination strategies encoding TgGRA4.

Methods

BALB/c mice were intramuscularly (i.m.) immunized four times according to specific immunization schedules. Generally, mice in experimental groups were immunized with polypeptide, pGRA4, peptide/DNA, or DNA/peptide, and mice in the control groups were injected with PBS or pEGFP. After immunization, the levels of IgG antibodies and cytokine productions were determined by enzyme-linked immunosorbent assays (ELISA). The survival time of mice was also evaluated after challenge infection with the highly virulent T. gondii RH strain.

Results

The results showed that mice vaccinated with different immunization regimens (polypeptide, pGRA4, peptide/DNA, or DNA/peptide) elicited specific humoral and cellular responses, with high levels of total IgG, IgG2a isotype and gamma interferon (IFN-γ), which suggested a specific Th1 immunity was activated. After lethal challenge, an increased survival time was observed in immunized mice (11.8 ± 4.8 days) compared to the control groups injected with PBS or pEGFP (P < 0.05). Mice injected with PBS or pEGFP died within 8 days, and there was no significant difference in the protection level in two groups (P > 0.05).

Conclusions

These results demonstrated that this DNA prime and peptide boost immunization protocol encoding the TgGRA4 can elicit the highest level of humoral and cellular immune responses compared to other immunized groups, which is a promising approach to increase the efficacy of DNA immunization.

Advances in the study of HLA-restricted epitope vaccines

Vaccination is a proven strategy for protection from disease. An ideal vaccine would include antigens that elicit a safe and effective protective immune response. HLA-restricted epitope vaccines, which include T-lymphocyte epitopes restricted by HLA alleles, represent a new and promising immunization approach. In recent years, research in HLA-restricted epitope vaccines for the treatment of tumors and for the prevention of viral, bacterial, and parasite-induced infectious diseases have achieved substantial progress. Approaches for the improvement of the immunogenicity of epitope vaccines include (1) improving the accuracy of the methods used for the prediction of epitopes, (2) making use of additional HLA-restricted CD8(+) T-cell epitopes, (3) the inclusion of specific CD4(+) T-cell epitopes, (4) adding B-cell epitopes to the vaccine construction, (5) finding more effective adjuvants and delivery systems, (6) using immunogenic carrier proteins, and (7) using multiple proteins as epitopes sources. In this manuscript, we review recent research into HLA-restricted epitope vaccines.

The immune effects of multiple antigen peptides containing the mimic epitopes of the adhesion protein of Mycoplasma genitalium

The purpose of this study was to investigate the humoral and cellular immune responses stimulated by multiple antigen peptides (MAPs) containing the mimic epitopes of Mycoplasma genitalium adhesion protein (MgPa). Three MAPs containing the mimic epitopes of MgPa were synthesized on a branched polylysine matrix. After purification and characterization, these MAPs were used to immunize BALB/c mice. The immunoglobulin G (IgG) antibody and the subtype of IgG antibody in the serum of the immunized mice were detected by indirect ELISA (enzyme-linked immunosorbent assay). The proliferation of the spleen lymphocyte was detected using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay. The gamma interferon (IFN-γ) and interleukin-4 (IL-4) levels in the cultured supernatant of spleen lymphocytes were measured by ELISA. The 3 different MAPs were prepared with high purity. Levels of IgG, IgG1, and IgG2a antibodies were elevated in the mice serum immunized by all 3 MAPs. The major antibody isotype was IgG2a. Importantly, mice immunized with a mixture of the 3 MAPs produced significantly more antibodies than those immunized with a single MAP (p < 0.05). Moreover, these MAPs could stimulate the proliferation of spleen lymphocytes of immunized mice and induce the production of IFN-γ and IL-4. The IFN-γ and IL-4 levels stimulated by the mixed MAPs were significantly higher than those stimulated by a single MAP (p < 0.01). The 3 different MAPs could induce strong cellular and humoral immune responses. The immunoreactivity of the mixed MAPs was stronger than that of the single MAP.

Diepitope multiple antigen peptide of hTERT trigger stronger anti-tumor immune responses in vitro

Rapid advances in immune system knowledge have led to the exploration of immunologic approaches for eliminating tumor cells. Human telomerase reverse transcriptase (hTERT) is considered to be an ideal universal target for novel immunotherapies against cancers. Thus far, studies of effective antitumor immunotherapies have focused on the quantity and quality of the effector function of the CD8 compartment. However, increasing evidence has demonstrated that CD4+ T cells play important roles in generating and maintaining antitumor immune responses in animal models. The aim of this work was to verify whether diepitope multiple antigen peptides (MAPs) that were composed of the cytotoxic T lymphocyte (CTL) epitope of hTERT and the T-helper epitope of hTERT could improve upon the immunogenicity of a monoepitope MAP of hTERT. Dendritic cells (DCs) pulsed with diepitope MAPs composed of the CTL epitope hTERT-540 and the T-helper epitope hTERT-766 were used to evaluate immune responses against various tumor cells. A standard in vitro 4-h ⁵¹Cr-release assay was employed in this study. The results demonstrated that CTLs activated by the diepitope MAP that consisted of hTERT-540 and hTERT-766 could cause 8.56% more lysis than CTLs activated by the monoepitope MAP containing hTERT-540. Moreover, the activated CTLs could kill neither hTERT-negative tumor cells, such as U2OS cells, nor HLA-A2 negative cells, such as HepG2 cells. Our results indicate that diepitope MAPs that are generated from hTERT can be exploited for cancer immunotherapy.

Production of polyclonal antibodies directed to recombinant methionyl bovine somatotropin

The administration of recombinant methionyl bovine somatotropin (rMbST) to dairy cows to increase milk yield remains a common practice in many countries including the USA, Brazil, Mexico, South Africa and Korea, whereas it has been forbidden within the European Union (EU) since 1999. A rapid screening immunoanalytical method capable of the unequivocal determination of rMbST in milk would be highly desirable in order to effectively monitor compliance with the EU-wide ban for home-made or imported dairy products. For decades, the production of specific antibodies for this recombinant isoform of bovine somatotropin (bST) has remained elusive, due to the high degree of sequence homology between both counterparts (e.g. methionine for rMbST in substitution of alanine in bST at the N-terminus). In this study, we compared several immunizing strategies for the production of specific polyclonal antibodies (pAbs), based on the use of the full-length recombinant protein, an rMbST N-terminus peptide fragment and a multiple antigen peptide (MAP) which consists of an oligomeric branching lysine core attached to the first two N-terminus amino acids of rMbST, methionine and phenylalanine (MF-MAP). The immunization with KLH-conjugated MF-MAP led to the production of the pAb with the highest rMbST/bST recognition ratio amongst the generated battery of antibodies. The pAb exhibited a specific binding ability to rMbST in a competitive antigen-coated ELISA format, which avidity was further improved after purification by rMbST N-terminus peptide-based affinity chromatography. These results suggest that immunodiscrimination between structurally related proteins can be achieved using immuno-enhanced immunogens such as MAPs.

Cell-mediated immune response to epitopic MAP (multiple antigen peptide) construct of LcrV antigen of Yersinia pestis in murine model

Yersinia pestis is the causative agent of plague. Cellular immunity seems to play an important role in defense against this disease. The subunit vaccine based on V (Lcr V) antigen has been proved to be immunogenic in animals and in humans. The multiple antigen peptide (MAP), incorporating all the relevant B and T cell epitopes is highly immunogenic in mice through intranasal route of immunization in PLGA particles containing CpG-ODN as an immunoadjuvant inducing humoral and mucosal immune response. In the present study, cell-mediated immune response using same MAP was studied in murine model. Primary and memory T cell responses were studied in outbred and inbred mice immunized intranasally with MAP in the presence of two immunoadjuvants (Murabutide and CpG-ODN). All the three compartments (Spleen, Lamina propria and Peyer's patches) of the lymphoid system showed increased lymphoproliferative response. Highest lymphoproliferative response was observed especially with CpG-ODN. Cytokine profile in the culture supernatant showed highest Th(1) and Th(17) levels. FACS analysis showed expansion of both CD4(+) and CD8(+) T cells producing gamma-interferon, perforin and granzyme-B with major contribution from CD4(+) T cells.

Synthesized OVA323-339MAP octamers mitigate OVA-induced airway inflammation by regulating Foxp3 T regulatory cells

Background

Antigen-specific immunotherapy (SIT) has been widely practiced in treating allergic diseases such as asthma. However, this therapy may induce a series of allergic adverse events during treatment. Peptide immunotherapy (PIT) was explored to overcome these disadvantages. We confirmed that multiple antigen peptides (MAPs) do not cause autoimmune responses, which led to the presumption that MAPs intervention could alleviate allergic airway inflammation without inducing adverse effects.

Results

In this study, synthesized OVA_323-339MAP octamers were subcutaneously injected into ovalbumin (OVA)-sensitized and -challenged Balb/c mice to observe its effect on allergic airway inflammation, Th2 immune response, and immune regulating function. It was confirmed that OVA sensitization and challenge led to significant peritracheal inflammatory, cell infiltration, and intensive Th2 response. Treatment of OVA_323-339MAP octomers in the airway inflammation mice model increased CD4⁺CD25⁺Foxp3⁺ T regulatory (Treg) cells and their regulatory function in peripheral blood, mediastinal draining lymph nodes, and the spleen. Furthermore, OVA_323-339MAP increased IL-10 levels in bronchial alveolar lavage fluid (BALF); up-regulated the expression of IL-10, membrane-bound TGF-β1, as well as Foxp3 in lung tissues; and up-regulated programmed death-1 (PD-1) and cytotoxic T lymphocyte associated antigen 4 (CTLA-4) on the surface of Treg cells. These results were further correlated with the decreased OVA specific immunoglobulin E (sIgE) level and the infiltration of inflammatory cells such as eosinophils and lymphocytes in BALF. However, OVA_323-339 peptide monomers did not show any of the mentioned effects in the same animal model.

Conclusions

Our study indicates that OVA_323-339MAP had significant therapeutic effects on mice allergic airway inflammation by regulating the balance of Th1/Th2 response through Treg cells in vivo.

Plasmodium yoelii blood-stage antigens newly identified by immunoaffinity using purified IgG antibodies from malaria-resistant mice

As the search for an effective human malaria vaccine continues, understanding immune responses to Plasmodium in rodent models is perhaps the key to unlocking new vaccine strategies. The recruitment of parasite-specific antibodies is an important component of natural immunity against infection in blood-stage malaria. Here, we describe the use of sera from naturally surviving ICR mice after infection with lethal doses of Plasmodium yoelii yoelii 17XL to identify highly immunogenic blood-stage antigens. Immobilized protein A/G was used for the affinity-chromatography purification of the IgGs present in pooled sera from surviving mice. These protective IgGs, covalently immobilized on agarose columns, were then used to isolate reactive antigens from whole P. yoelii yoelii 17XL protein extracts obtained from the blood-stage malaria infection. Through proteomics analysis of the recovered parasite antigens, we were able to identify two endoplasmic reticulum lumen proteins: protein disulfide isomerase and a member of the heat shock protein 70 family. Also identified were the digestive protease plasmepsin and the 39 kDa-subunit of eukaryotic translation initiation factor 3, a ribosome associated protein. Of these four proteins, three have not been previously identified as antigenic during blood-stage malaria infection. This procedure of isolating and identifying parasite antigens using serum IgGs from malaria-protected individuals could be a novel strategy for the development of multi-antigen-based vaccine therapies.

Cardiac troponin I: a case study in rational antibody design for human diagnostics

In vitro diagnostic (IVD) platforms provide rapid and accurate determination of disease status. The clinical performance of antibody-based diagnostic platforms is paramount as the information provided often informs the medical intervention taken and, ultimately, the patient's outcome. Breaking down such an immuno-IVD device into its component elements, the biorecognition entity is key to the analytical specificity of the test. Furthermore, tailored optimisation of the antibody is often necessary to impart the desired biophysical properties for the specific application. This tailoring is now widely facilitated by advances in combinatorial approaches to antibody generation, molecular evolution strategies and the availability of truly high-throughput (HT), refined surface plasmon resonance-based screening tools. In this paper, we demonstrate a rational, knowledge-driven approach to the generation of epitope-specific antibodies for the early detection of cardiovascular disease, discuss the merits of the approaches taken and offer a perspective on HT strategies to mining large antibody libraries. These results highlight the expedience of such methodologies for the development of truly superior cardiovascular disease biorecognition elements.

Protection from experimental cerebral malaria with a single dose of radiation-attenuated, blood-stage Plasmodium berghei parasites

Background

Whole malaria parasites are highly effective in inducing immunity against malaria. Due to the limited success of subunit based vaccines in clinical studies, there has been a renewed interest in whole parasite-based malaria vaccines. Apart from attenuated sporozoites, there have also been efforts to use live asexual stage parasites as vaccine immunogens.

Methodology and Results

We used radiation exposure to attenuate the highly virulent asexual blood stages of the murine malaria parasite P. berghei to a non-replicable, avirulent form. We tested the ability of the attenuated blood stage parasites to induce immunity to parasitemia and the symptoms of severe malaria disease. Depending on the mouse genetic background, a single high dose immunization without adjuvant protected mice from parasitemia and severe disease (CD1 mice) or from experimental cerebral malaria (ECM) (C57BL/6 mice). A low dose immunization did not protect against parasitemia or severe disease in either model after one or two immunizations. The protection from ECM was associated with a parasite specific antibody response and also with a lower level of splenic parasite-specific IFN-γ production, which is a mediator of ECM pathology in C57BL/6 mice. Surprisingly, there was no difference in the sequestration of CD8+ T cells and CD45+ CD11b+ macrophages in the brains of immunized, ECM-protected mice.

Conclusions

This report further demonstrates the effectiveness of a whole parasite blood-stage vaccine in inducing immunity to malaria and explicitly demonstrates its effectiveness against ECM, the most pathogenic consequence of malaria infection. This experimental model will be important to explore the formulation of whole parasite blood-stage vaccines against malaria and to investigate the immune mechanisms that mediate protection against parasitemia and cerebral malaria.

A new malaria antigen produces partial protection against Plasmodium yoelii challenge

Of all the parasitic diseases, malaria is the number one killer. Despite tremendous efforts in disease control and research, nearly a million people, primarily children, still die from the disease each year, partly due to drug resistance and the lack of an effective vaccine. Many parasite antigens have been identified and evaluated for vaccine development; however, none has been approved for human use. Antigenic variation, complex life cycle, and inadequate understanding of the mechanisms of parasite-host interaction and of host immune response all contribute to the lack of an effective vaccine for malaria control. In a recent search of genome-wide polymorphism in Plasmodium falciparum, several molecules were found to be recognized by sera from patients infected with the P. falciparum parasite. Here, we have expressed a 350-amino acid N terminus from one of the homologous candidate antigen genes from the rodent malaria parasite Plasmodium yoelii (Py01157, a putative dentin phosphorin) in bacteria and evaluated the immune response and protection generated after immunization with the recombinant protein. We showed that the recombinant protein was recognized by sera from both mice and humans infected with malaria parasites. Partial protection was observed after challenge with non-lethal P. yoelii 17XNL but not with the lethal P. yoelii 17XL parasite. Further tests using a full-length protein or the conserved C terminus may provide additional information on whether this protein has the potential for being a malaria vaccine.

Multiple antigenic peptides of human heparanase elicit a much more potent immune response against tumors

Peptide vaccination for cancer immunotherapy requires an ideal immune response induced by epitope peptides derived from tumor-associated antigens (TAA). Heparanase is broadly expressed in various advanced tumors. Accumulating evidence suggests that heparanase can serve as a universal TAA for tumor immunotherapy. However, due to the low immunogenicity of peptide vaccines, an ideal immune response against tumors usually cannot be elicited in patients. To increase the immunogenicity of peptide vaccines, we designed three 4-branched multiple antigenic peptides (MAP) on the basis of the human leukocyte antigen (HLA)-A2-restricted cytotoxic T lymphocyte (CTL) epitopes of human heparanase that we identified previously as antigen carriers. Our results show that MAP vaccines based on the HLA-A2-restricted CLT epitopes of human heparanase were capable of inducing HLA-A2-restricted and heparanase-specific CTL in vitro and in mice. Moreover, compared with their corresponding linear peptides, heparanase MAP vaccines elicited much stronger lysis of tumor cells by activating CD8(+) T lymphocytes and increasing the releasing of IFN-γ. However, these heparanase-specific CTLs did not lyse heparanase-expressing autologous lymphocytes and dendritic cells, which confirm the safety of these MAP vaccines. Therefore, our findings indicate that MAP vaccines based on CTL epitopes of human heparanase can be used as potent immunogens for tumor immunotherapy because of advantages such as broad spectrum, high effectiveness, high specificity, and safety.

Identification and characterization of protective epitope of Trichinella spiralis paramyosin

Trichinella spiralis paramyosin (Ts-Pmy) is a protective antigen that induces partial immunity against T. spiralis infection in mice. To identify protective epitope of Ts-Pmy, a monoclonal antibody (mAb) 7E2 against the recombinant protein was generated, which partially protected against T. spiralis infection following passive transfer. The mAb was used to screen a random phage-displayed peptide library. Ten positive clones were identified, most of which matched amino acids 88-107 or 108-127 of Ts-Pmy. Expression of overlapping fragments of Ts-Pmy in E. coli confirmed that region 88-107 was specifically recognized by 7E2. A peptide based on this epitope region (YX1) was synthesized and shown to compete with native Ts-Pmy for binding to 7E2. Mice immunized with KLH-conjugated YX1 were protected against T. spiralis larval challenge. The identification of a protective epitope within Ts-Pmy highlights the possibility of developing a subunit vaccine against T. spiralis infection.