The generation and evaluation of two panels of epitope-matched mouse IgG1, IgG2a, IgG2b and IgG3 antibodies specific for Plasmodium falciparum and Plasmodium yoelii merozoite surface protein 1-19 (MSP1(19))

A non-classical view of antibody properties: Allosteric effect between variable and constant regions

Historically, antibodies have been divided into two functionally independent domains, the variable (V) region for antigen binding and the constant (C) region for mediating effector functions. However, this classical view of antibody function has been severely challenged by a large and growing number of studies, which reveal long-range conformational interactions and allosteric links between the V and C regions. This review comprehensively summarizes the existing studies on antibody allostery, including allosteric conformational changes induced by covalent modifications or noncovalent ligand binding. In addition, we discuss how intramolecular allosteric signals are transmitted from the V to C regions and vice versa. This review argues that there is sufficient evidence to revisit the structure-function relationship of antibodies. These advances in antibody allostery will provide a blueprint for regulating antibody functions in a simple and highly predictable manner. More focus on antibody allostery will definitely benefit antibody engineering and vaccine design in the field of biotechnology.

Bioinformatic features and immunological response of recombinant antigen CTLA4-IgV-EgG1Y162 against Echinococcus granulosus

Cystic echinococcosis (CE) is a zoonotic disease caused by the infection of Echinococcus granulosus (E. granulosus) larva. Currently, blocking the pathogenic cycle chain through immunoprophylaxis has become the main research direction. EgG1Y162 protein has good antigenicity and immunogenicity and is therefore a good candidate molecule for E. granulosus vaccine. Mature T cells express CTLA-4 on their surface, and its extracellular IgV region binds efficiently to the B7 molecules on antigen-presenting cells to deliver negative signals. We designed and prepared a recombinant vaccine by fusing CTLA-4IgV to the EgG1Y162 protein to exploit its binding properties. Bioinformatic methods were used to analyze the structure and epitopes of the proposed recombinant vaccine. The placement of 16 amino acids (GTDDDDKAMADIGSEF) between the CTLA-4IgV and EgG1Y162 using the skeleton structure of pET30a plasmid did not affect the correct folding of the proteins. When the recombinant proteins were co-cultured with bone marrow-induced dendritic cells (DC), the protein CTLA-4IgV-EgG1Y162 promoted its binding to DC and increased the percentage of DC maturation compared with protein EgG1Y162 in vitro and in vivo. Compared to EgG1Y162, CTLA-4IgV-EgG1Y162 promoted the proliferation of lymphocytes in spleen and the release of interferon (IFN)-γ and interleukin (IL)-4 by those lymphocytes in vitro, while it also promoted the release of protective antibodies in the serum of immunized mice in vivo. These findings indicated that the designed recombinant vaccine, CTLA-4IgV-EgG1Y162, can provide new ideas for the optimization and improvement of vaccines against E. granulosus.

Immunogenicity of PvCyRPA, PvCelTOS and Pvs25 chimeric recombinant protein of Plasmodium vivax in murine model

In the Americas, P. vivax is the predominant causative species of malaria, a debilitating and economically significant disease. Due to the complexity of the malaria parasite life cycle, a vaccine formulation with multiple antigens expressed in various parasite stages may represent an effective approach. Based on this, we previously designed and constructed a chimeric recombinant protein, PvRMC-1, composed by PvCyRPA, PvCelTOS, and Pvs25 epitopes. This chimeric protein was strongly recognized by naturally acquired antibodies from exposed population in the Brazilian Amazon. However, there was no investigation about the induced immune response of PvRMC-1. Therefore, in this work, we evaluated the immunogenicity of this chimeric antigen formulated in three distinct adjuvants: Stimune, AddaVax or Aluminum hydroxide (Al(OH)3) in BALB/c mice. Our results suggested that the chimeric protein PvRMC-1 were capable to generate humoral and cellular responses across all three formulations. Antibodies recognized full-length PvRMC-1 and linear B-cell epitopes from PvCyRPA, PvCelTOS, and Pvs25 individually. Moreover, mice's splenocytes were activated, producing IFN-γ in response to PvCelTOS and PvCyRPA peptide epitopes, affirming T-cell epitopes in the antigen. While aluminum hydroxide showed notable cellular response, Stimune and Addavax induced a more comprehensive immune response, encompassing both cellular and humoral components. Thus, our findings indicate that PvRMC-1 would be a promising multistage vaccine candidate that could advance to further preclinical studies.

Immune System Modulation by the Adjuvants Poly (I:C) and Montanide ISA 720

Adjuvants are essential for vaccine development, especially subunit-based vaccines such as those containing recombinant proteins. Increasing the knowledge of the immune response mechanisms generated by adjuvants should facilitate the formulation of vaccines in the future. The present work describes the immune phenotypes induced by Poly (I:C) and Montanide ISA 720 in the context of mice immunization with a recombinant protein based on the Plasmodium vivax circumsporozoite protein (PvCSP) sequence. Mice immunized with the recombinant protein plus Montanide ISA 720 showed an overall more robust humoral response, inducing antibodies with greater avidity to the antigen. A general trend for mixed Th1/Th2 inflammatory cytokine profile was increased in Montanide-adjuvanted mice, while a balanced profile was observed in Poly (I:C)-adjuvanted mice. Montanide ISA 720 induced a gene signature in B lymphocytes characteristic of heme biosynthesis, suggesting increased differentiation to Plasma Cells. On the other hand, Poly (I:C) provoked more perturbations in T cell transcriptome. These results extend the understanding of the modulation of specific immune responses induced by different classes of adjuvants, and could support the optimization of subunit-based vaccines.

Influenza virus-like particle vaccine containing both apical membrane antigen 1 and microneme-associated antigen proteins of Plasmodium berghei confers protection in mice

Background

Apical membrane antigen 1 (AMA1) and microneme-associated antigen (MIC) of Plasmodium parasites are important factors involved in host cell invasion.

Methods

In this study, influenza VLP vaccines containing both codon-optimized AMA1 and MIC were generated and the vaccine efficacy was evaluated in mice.

Results

VLPs vaccine immunization elicited higher levels of parasite-specific IgG and IgG2a antibody responses in sera. CD4⁺ and CD8⁺ T cells and germinal center B cells in blood, inguinal lymph nodes (ILN) and spleen were found to be significantly increased. Importantly, VLPs vaccination significantly reduced the levels of pro-inflammatory cytokines IFN-γ and TNF-α, decreased parasitemia in blood, resulting in lower body weight loss and longer survival time compared to control.

Conclusion

These results indicated that VLPs containing P. berghei AMA1 and MIC could be a candidate for malaria blood-stage vaccine design.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-022-00494-4.

Optimizing TNFR2 antagonism for immunotherapy with tumor microenvironment specificity

Most approved cancer immunotherapies lack T-regulatory (Treg) or tumor specificity. TNF receptor 2 (TNFR2) antibody antagonism is emerging as an attractive immunotherapy due to its tumor microenvironment (TME) specificity. Here we show that the human TNFR2 receptor is overexpressed on both human tumor cells and on human tumor-residing Tregs, but negligibly expressed on beneficial T effectors (Teffs). Further, we found widespread, if variable, TNFR2 expression on 788 human tumor cell lines from diverse cancer tissues. These findings provided strong rationale for developing a targeted immunotherapy using a TNFR2 antibody antagonist. We designed a novel, human-directed TNFR2 antibody antagonist and tested it for function using three cell-based TME assays. The antagonist showed TME specificity by killing of TNFR2-expressing tumor cells and Tregs, but sparing Teffs, which proliferated. However, the antagonist shuffled between five isoforms, only one of which showed the desirable function. We designed and tested several new chimeric human versions of the antagonist, finding that the IgG2 isotype functioned better than the IgG1 isotype. To further improve function, we introduced targeted mutations to its amino acid sequence to stabilize the natural variability of the IgG2 isotype's hinge. Altogether, our findings suggest that optimal TNFR2 antagonists are of the human IgG2 isotype, have hinge stabilization, and have wide separation of antibody arms to bind to newly synthesized TNFR2 on rapidly growing tumor cells. Antagonistic antibodies with these characteristics, when bound to TNFR2, can form a nonsignaling cell surface dimer that functions with high TME specificity.

Application of red clover isoflavone extract as an adjuvant in mice

In the present study, the safety of red clover isoflavone extract (RCIE) and its potential adjuvant effects on the cellular and humoral immune responses to ovalbumin (OVA) were evaluated using an ICR mouse model. On day 1, the mice were first subcutaneously immunized with 100 µg OVA, 100 µg OVA + 200 µg aluminum hydroxide gel (alum) or OVA + 50, 100 or 200 µg RCIE (RCIE + OVA), following which booster immunization was performed on day 15. After 2 weeks, the stimulation of splenocyte proliferation and levels of serum antibodies were measured. No notable stress responses were observed after the initial and booster immunization. Splenocyte proliferation was significantly increased in mice immunized with OVA + 100 µg RCIE (P<0.01). The levels of IgG, IgG1 and IgG2a antibodies in serum were also significantly increased in OVA + RCIE groups compared with the OVA control group (P<0.05). In the OVA + RCIE groups, serum levels of interleukin (IL)-2, interferon-γ (IFN-γ) and IL-10 were increased, and the mRNA expression levels of IL-2, IFN-γ, IL-4, IL-10, T-bet and GATA-3 were also significantly increased compared with the OVA control group (P<0.05) in splenocytes. In addition, as an adjuvant, RCIE significantly increased the survival rates of mice inoculated with an E. coli vaccine and enhanced the early immune protection against pathogenic E. coli. In conclusion, these findings suggest that RCIE can be used as a safe vaccine adjuvant and supports its use in clinical applications.

Protection induced by malaria virus-like particles containing codon-optimized AMA-1 of Plasmodium berghei

Background

Despite the extensive endeavours, developing an effective malaria vaccine remains as a great challenge. Apical membrane antigen 1 (AMA-1) located on the merozoite surface of parasites belonging to the genus Plasmodium is involved in red blood cell invasion.

Methods

Influenza virus-like particle (VLP) vaccines containing codon-optimized or native (non-codon optimized) AMA-1 from Plasmodium berghei were generated. VLP-induced protective immunity was evaluated in a mouse model.

Results

Mice immunized with VLP vaccine containing the codon-optimized AMA-1 elicited higher levels of P. berghei-specific IgG and IgG2a antibody responses compared to VLPs containing non-codon optimized AMA-1 before and after challenge infection. Codon-optimized AMA-1 VLP vaccination induced higher levels of CD4⁺ T cells, CD8⁺ T cells, B cells, and germinal centre cell responses compared to non-codon optimized AMA-1 VLPs. Importantly, the codon-optimized AMA-1 VLP vaccination showed lower body weight loss, longer survival and a significant decrease in parasitaemia compared to non-codon optimized VLP vaccination.

Conclusion

Overall, VLP vaccine expressing codon-optimized AMA-1 induced better protective efficacy than VLPs expressing the non-codon optimized AMA-1. Current findings highlight the importance of codon-optimization for vaccine use and its potential involvement in future malaria vaccine design strategies.

A Synthetic Nanoparticle Based Vaccine Approach Targeting MSP4/5 Is Immunogenic and Induces Moderate Protection Against Murine Blood-Stage Malaria

Malaria remains a significant health problem in many tropical and sub-tropical regions. The development of vaccines against the clinically active blood-stage of infection needs to consider variability and polymorphism in target antigens, and an adjuvant system able to induce broad spectrum immunity comprising both antibodies and helper T cells. Moreover, recent studies have shown some conventional pro-inflammatory adjuvants can also promote expansion of immunosuppressive regulatory T cells (Treg) and myeloid derived suppressor cells (MDSC), both of which could negatively impact malaria disease progression. Herein, we explore the ability of a model nanoparticle delivery system (polystyrene nanoparticles; PSNPs), previously proven to not induce conventional inflammation, Treg or MDSC, to induce immunity to MSP4/5 from Plasmodium yoelii, a member of the MSP4 and MSP5 family of proteins which are highly conserved across diverse malaria species including P. falciparum. The results show PSNPs-MSP4/5 conjugates are highly immunogenic, inducing immune responses comprising both T helper 1 (Th1) and Th2 cellular immunity, and a spectrum of antibody subclasses including IgG1, IgG2a, and IgG2b. Benchmarked against Alum and Complete Freund's Adjuvant (CFA), the immune responses that were induced were of comparable or higher magnitude, for both T cell frequencies by ELISpot and antibody responses in terms of ELISA end titer. Importantly, immunization with PSNPs-MSP4/5 induced partial protection against malaria blood-stage infection (50–80%) shown to be mechanistically dependent on interferon gamma (IFN-γ) production. These results expand the scope of adjuvants considered for malaria blood-stage vaccine development to those that do not use conventional adjuvant pathways and emphasizes the critical role of cellular immunity and specifically IFN-γ producing cells in providing moderate protection against blood-stage malaria comparable to Freunds adjuvant.

Neutrophils and Malaria

Neutrophils are abundant in the circulation and are one of the immune system's first lines of defense against infection. There has been substantial work carried out investigating the role of neutrophils in malaria and it is clear that during infection neutrophils are activated and are capable of clearing malaria parasites by a number of mechanisms. This review focuses on neutrophil responses to human malarias, summarizing evidence which helps us understand where neutrophils are, what they are doing, how they interact with parasites as well as their potential role in vaccine mediated immunity. We also outline future research priorities for these, the most abundant of leukocytes.

Immune-Informatic Analysis and Design of Peptide Vaccine From Multi-epitopes Against Corynebacterium pseudotuberculosis

Caseous lymphadenitis (CLA) is a disease caused by Corynebacterium pseudotuberculosis bacteria that affects sheep and goats. The absence of a serologic diagnose is a factor that contributes for the disease dissemination, and due to the formation of granuloma, the treatment is very expensive. Therefore, prophylaxis is the approach with best cost-benefit relation; however, it still lacks an effective vaccine. In this sense, this work seeks to apply bioinformatic tools to design an effective vaccine against CLA, using CP40 protein as standard for the design of immunodominant epitopes, from which a total of 6 sequences were obtained, varying from 10 to 16 amino acid residues. The evaluation of different properties of the vaccines showed that the vaccine is a potent and nonallergenic antigen remaining stable in a wide range of temperatures. The initial tertiary structure of the vaccine was then predicted and a model selected. Later, the process of CP40 protein and TLR2 receptor binding was performed, presenting interaction with this receptor, which plays an important role in the activation of the immune response.

Poly(I:C) adjuvant strongly enhances parasite-inhibitory antibodies and Th1 response against Plasmodium falciparum merozoite surface protein-1 (42-kDa fragment) in BALB/c mice

Malaria vaccine development has been confronted with various challenges such as poor immunogenicity of malaria vaccine candidate antigens, which is considered as the main challenge. However, this problem can be managed using appropriate formulations of antigens and adjuvants. Poly(I:C) is a potent Th1 inducer and a human compatible adjuvant capable of stimulating both B- and T-cell immunity. Plasmodium falciparum merozoite surface protein 142 (PfMSP-142) is a promising vaccine candidate for blood stage of malaria that has faced several difficulties in clinical trials, mainly due to improper adjuvants. Therefore, in the current study, poly(I:C), as a potent Th1 inducer adjuvant, was evaluated to improve the immunogenicity of recombinant PfMSP-142, when compared to CFA/IFA, as reference adjuvant. Poly(I:C) produced high level and titers of anti-PfMSP-142 IgG antibodies in which was comparable to CFA/IFA adjuvant. In addition, PfMSP-142 formulated with poly(I:C) elicited a higher ratio of IFN-γ/IL-4 (23.9) and IgG2a/IgG1 (3.77) with more persistent, higher avidity, and titer of IgG2a relative to CFA/IFA, indicating a potent Th1 immune response. Poly(I:C) could also help to induce anti-PfMSP-142 antibodies with higher growth-inhibitory activity than CFA/IFA. Altogether, the results of the current study demonstrated that poly(I:C) is a potent adjuvant that can be appropriate for being used in PfMSP-142-based vaccine formulations.

IgG opsonization of merozoites: multiple immune mechanisms for malaria vaccine development

Global eradication of the human-infecting malaria parasite Plasmodium falciparum, the major cause of malaria mortality, is unlikely to be achieved without an effective vaccine. However, our limited understanding of how protective immune responses target malaria parasites in humans, and how to best elicit these immune responses through vaccination, has hampered vaccine development. The red blood cell invading stage of the parasite lifecycle (merozoite) displays antigens that are attractive vaccine candidates as they are accessible to antibodies and raise high antibody titres in naturally immune individuals. The number of merozoite antigens that elicit an immune response, and their structural and functional diversity, has led to a large number of lead antigens being pursued as vaccine candidates. Despite being seemingly spoilt for choice in terms of vaccine candidates, there is still a lack of consensus on exactly how merozoite antibodies reduce parasitemia and malaria disease. In this review we describe the various immune mechanisms that can result from IgG opsonization of merozoites, and highlight recent developments that support a role for these functional antibodies in naturally acquired and vaccine-induced immunity.

IgE-tailpiece associates with α-1-antitrypsin (A1AT) to protect IgE from proteolysis without compromising its ability to interact with FcεRI

Several splice variants of IgE exist in human plasma, including a variant called IgE-tailpiece (IgE-tp) that differs from classical IgE by the replacement of two carboxy-terminal amino acids with eight novel residues that include an ultimate cysteine. To date, the role of the secreted IgE-tp isoform in human immunity is unknown. We show that levels of IgE-tp are raised in helminth-infected donors, and that both the classical form of IgE (IgE-c) and IgE-tp interact with polymers of the serine protease inhibitor alpha-1-antitrypsin (A1AT). The association of IgE-tp with A1AT polymers in plasma protects the antibody from serine protease-mediated degradation, without affecting the functional interaction of IgE-tp with important receptors, including FcεR1. That polymers of A1AT protect IgE from degradation by helminth proteases may explain why these common and normally non-disease causing polymorphic variants of A1AT have been retained by natural selection. The observation that IgE can be complexed with polymeric forms of A1AT may therefore have important consequences for our understanding of the pathophysiology of pulmonary diseases that arise either as a consequence of A1AT-deficiency or through IgE-mediated type 1 hypersensitivity responses.

Ig Constant Region Effects on Variable Region Structure and Function

The adaptive humoral immune response is responsible for the generation of antimicrobial proteins known as immunoglobulin molecules or antibodies. Immunoglobulins provide a defense system against pathogenic microbes and toxins by targeting them for removal and/or destruction. Historically, antibodies have been thought to be composed of distinct structural domains known as the variable and constant regions that are responsible for antigen binding and mediating effector functions such as opsonization and complement activation, respectively. These domains were thought to be structurally and functionally independent. Recent work has revealed however, that in some families of antibodies, the two regions can influence each other. We will discuss the body of work that led to these observations, as well as the mechanisms that have been proposed to explain how these two different antibody regions may interact in the function of antigen binding.

Recombinant CP40 from Corynebacterium pseudotuberculosis confers protection in mice after challenge with a virulent strain

BACKGROUND

Caseous Lymphadenitis (CLA) is a contagious, infectious, chronic disease caused by Corynebacterium pseudotuberculosis, which affects mainly sheep and goats. The clinical prevalence of CLA in Brazil is 30%, resulting in decreased milk production, weight loss, and unusable meat and leather. Prophylaxis is based on vaccination; however, current vaccinations do not offer effective protection against the infection, which makes the development of a new vaccine essential to control this disease.

EXPERIMENTAL APPROACH

Here, we developed a recombinant vaccine based on CP40 protein (rCP40) combined with an adjuvant (Freund's complete adjuvant or saponin) and evaluated its efficacy in a murine model of CLA. Female BALB/c mice were used in an immunization assay.

KEY RESULTS

rCP40 induced high levels of IgG2a and IgG2b antibodies. After challenge with a virulent strain of C. pseudotuberculosis C57 (10(4)CFU/mL), the levels of IgG2a and IgG2b were sustained, indicating a Th1 response. The groups immunized with rCP40 protein (GES and GEF groups) showed 100% protection and was statistically significant in the GES and GEF groups (p<0.037 and p<0.0952, respectively).

CONCLUSIONS

The results indicated the recombinant protein CP40 induced an specific immune response in mice that was able to afford protection after challenge, regardless the adjuvant used in the formulation.

Corynebacterium pseudotuberculosis cp09 mutant and cp40 recombinant protein partially protect mice against caseous lymphadenitis

Background

Caseous lymphadenitis (CLA) is an infectious disease that affects small ruminants and is caused by Corynebacterium pseudotuberculosis. This disease is responsible for high economic losses due to condemnation and trim of infected carcasses, decreased leather and wool yield, loss of sales of breeding stock and deaths from internal involvement. Treatment is costly and ineffective; the most cost-effective strategy is timely immunisation. Various vaccine strategies have been tested, and recombinant vaccines are a promising alternative. Thus, in this study, different vaccine formulations using a recombinant protein (rCP40) and the CP09 live recombinant strain were evaluated. Five groups of 10 mice each were immunised with saline (G1), rCP40 (G2), CP09 (G3), a combination of CP09 and rCP40 (G4) and a heterologous prime-boost strategy (G5). Mice received two immunisations within 15 days. On day 30 after primary immunisation, all groups were challenged with a C. pseudotuberculosis virulent strain. Mice were monitored and mortality was recorded for 30 days after challenge.

Results

The G2, G4 and G5 groups showed high levels of IgG1 and IgG2a; G2 presented significant IgG2a production after virulent challenge in the absence of IgG1 and IgG3 induction. Thirty days after challenge, the mice survival rates were 20 (G1), 90 (G2), 50 (G3), 70 (G4) and 60% (G5).

Conclusions

rCP40 is a promising target in the development of vaccines against caseous lymphadenitis.

Assessment of the neutrophilic antibody-dependent respiratory burst (ADRB) response to Plasmodium falciparum

Semi-immunity against Pf malaria is based on a combination of cellular and humoral immune responses. PMNs and IgGs are considered important components of this process, but the underlying mechanisms are unclear. We investigated the neutrophilic ADRB by analyzing the production of ROS in response to Pf antigen-specific IgGs bound to solid-phase immobilized antigens (sADRB) or whole merozoites (mADRB). We found that the PMN stimulations in each assay were based on different underlying mechanisms, demonstrating the importance of the assay set-up for the evaluation of antibody-triggered PMN responses. In the sADRB assay, ROS were produced externally, and by specific blocking of CD32(a)/FcγRII(a), the immediate neutrophilic response was abolished, whereas the removal of CD16(b)/FcγRIII(b) had no substantial effect. The key role of CD32(a) was confirmed using CD16(b)-deficient PMNs, in which similar changes of neutrophilic ADRB profiles were recorded after treatment. In the mADRB assay, ROS were produced almost exclusively within the cell, suggesting that the underlying mechanism was phagocytosis. This was confirmed using an additional phagocytosis assay, in which PMNs specifically ingested merozoites opsonized with Ghanaian plasma IgGs, seven times more often than merozoites opsonized with European plasma IgGs (P<0.001). Our data show that assay set-ups used to evaluate the responses of PMNs and perhaps other effector cells must be chosen carefully to evaluate the appropriate cellular responses. Our robust, stable, and well-characterized methods could therefore be useful in malaria vaccine studies to analyze the antimalarial effector function of antibodies.

Understanding the role of antibodies in murine infections with Heligmosomoides (polygyrus) bakeri: 35 years ago, now and 35 years ahead

The rodent intestinal nematode H.p.bakeri has played an important role in the exploration of the host-parasite relationship of chronic nematode infections for over six decades, since the parasite was first isolated in the 1950s by Ehrenford. It soon became a popular laboratory model providing a tractable experimental system that is easy to maintain in the laboratory and far more cost-effective than other laboratory nematode-rodent model systems. Immunity to this parasite is complex, dependent on antibodies, but confounded by the parasite's potent immunosuppressive secretions that facilitate chronic survival in murine hosts. In this review, we remind readers of the state of knowledge in the 1970s, when the first volume of Parasite Immunology was published, focusing on the role of antibodies in protective immunity. We show how our understanding of the host-parasite relationship then developed over the following 35 years to date, we propose testable hypotheses for future researchers to tackle, and we speculate on how the new technologies will be applied to enable an increasingly refined understanding of the role of antibodies in host-protective immunity, and its evasion, to be achieved in the longer term.

Designing improved poly lactic-co-glycolic acid microspheres for a malarial vaccine: incorporation of alginate and polyinosinic-polycytidilic acid

Vaccination using proteins and peptides is currently gaining importance. One of the major drawbacks of this approach is the lack of an efficient immune response when the antigens are administered without adjuvants. In this study, we have taken the advantage of a combined adjuvant system in order to improve the immunogenicity of the SPf66 malarial antigen. For that purpose, we have combined poly (lactic-co-glycolic) acid microspheres, alginate, and polyinosinic polycytidilic acid. Our results show that microspheres can enhance the IgG production obtained with Freund's complete adjuvant. We have attributed this improvement to the presence of polyinosinic polycytidilic acid, since formulations comprising this adjuvant overcame the immune response from the others. In addition, our microspheres produced both IgG1 and IgG2a, leading to mixed Th1/Th2 activation, optimal for malaria vaccination. In conclusion, we have designed a preliminary formulation with a high potential for the treatment of malaria.

Assessment of antibody-dependent respiratory burst activity from mouse neutrophils on Plasmodium yoelii malaria challenge outcome

New tools are required to expedite the development of an effective vaccine against the blood-stage infection with the human malaria parasite Plasmodium falciparum. This work describes the assessment of the ADRB assay in a mouse model, characterizing the functional interaction between antimalarial serum antibodies and FcRs upon neutrophils. We describe a reproducible, antigen-specific assay, dependent on functional FcR signaling, and show that ADRB activity is induced equally by IgG1 and IgG2a isotypes and is modulated by blocking FcR function. However, following immunization of mice with the blood-stage vaccine candidate antigen MSP142, no measurable ADRB activity was induced against PEMS and neither was vaccine efficacy modulated against Plasmodium yoelii blood-stage challenge in γ(-/-) mice compared with WT mice. In contrast, following a primary, nonlethal P. yoelii parasite challenge, serum from vaccinated mice and nonimmunized controls showed anti-PEMS ADRB activity. Upon secondary challenge, nonimmunized γ(-/-) mice showed a reduced ability to control blood-stage parasitemia compared with immunized γ(-/-) mice; however, WT mice, depleted of their neutrophils, did not lose their ability to control infection. Thus, whereas neutrophil-induced ADRB against PEMS does not appear to play a role in protection against P. yoelii rodent malaria, induction of ADRB activity after challenge suggests that antigen targets of anti-PEMS ADRB activity remain to be established, as well as further supporting the observation that ADRB activity to P. falciparum arises following repeated natural exposure.

The utility of Plasmodium berghei as a rodent model for anti-merozoite malaria vaccine assessment

Rodent malaria species Plasmodium yoelii and P. chabaudi have been widely used to validate vaccine approaches targeting blood-stage merozoite antigens. However, increasing data suggest the P. berghei rodent malaria may be able to circumvent vaccine-induced anti-merozoite responses. Here we confirm a failure to protect against P. berghei, despite successful antibody induction against leading merozoite antigens using protein-in-adjuvant or viral vectored vaccine delivery. No subunit vaccine approach showed efficacy in mice following immunization and challenge with the wild-type P. berghei strains ANKA or NK65, or against a chimeric parasite line encoding a merozoite antigen from P. falciparum. Protection was not improved in knockout mice lacking the inhibitory Fc receptor CD32b, nor against a Δsmac P. berghei parasite line with a non-sequestering phenotype. An improved understanding of the mechanisms responsible for protection, or failure of protection, against P. berghei merozoites could guide the development of an efficacious vaccine against P. falciparum.