Adjuvant activity of polymer microparticles and Montanide ISA 720 on immune responses to Plasmodium falciparum MSP2 long synthetic peptides in mice

Polymeric Nanoparticle Based Diagnosis and Nanomedicine for Treatment and Development of Vaccines for Cerebral Malaria: A Review on Recent Advancement

Cerebral malaria occurs due to Plasmodium falciparum infection, which causes 228 million infections and 450,000 deaths worldwide every year. African people are mostly affected with nearly 91% cases, of which 86% are pregnant women and infants. India and Brazil are the other two countries severely suffering from malaria endemicity. Commonly used drugs have severe side effects, and unfortunately no suitable vaccine is available in the market today. In this line, this review is focused on polymeric nanomaterials and nanocapsules that can be used for the development of effective diagnostic strategies, nanomedicines, and vaccines in the management of cerebral malaria. Further, this review will help scientists and medical professionals by updating the status on the development stages of polymeric nanoparticle based diagnostics, nanomedicines, and vaccines and strategies to eradicate cerebral malaria. In addition to this, the predominant focus of this review is antimalarial agents based on polymer nanomedicines that are currently in the preclinical and clinical trial stages, and potential developments are suggested as well. This review further will have an important social and commercial impact worldwide for the development of polymeric nanomedicines and strategies for the treatment of cerebral malaria.

Immunization with merozoite surface protein 2 fused to a Plasmodium-specific carrier protein elicits strain-specific and strain-transcending, opsonizing antibody

Vaccine trials and cohort studies in Plasmodium falciparum endemic areas indicate that naturally-acquired and vaccine-induced antibodies to merozoite surface protein 2 (MSP2) are associated with resistance to malaria. These data indicate that PfMSP2 has significant potential as a component of a multi-antigen malaria vaccine. To overcome challenges encountered with subunit malaria vaccines, we established that the use of highly immunogenic rPfMSP8 as a carrier protein for leading vaccine candidates rPfMSP1₁₉ and rPfs25 facilitated antigen production, minimized antigenic competition and enhanced induction of functional antibodies. We applied this strategy to optimize a rPfMSP2 (3D7)-based subunit vaccine by producing unfused rPfMSP2 or chimeric rPfMSP2/8 in Escherichia coli. rPfMSP2 formed fibrils, which induced splenocyte proliferation in an antigen receptor-independent, TLR2-dependent manner. However, fusion to rPfMSP8 prevented rPfMSP2 amyloid-like fibril formation. Immunization of rabbits elicited high-titer anti-PfMSP2 antibodies that recognized rPfMSP2 of the 3D7 and FC27 alleles, as well as native PfMSP2. Competition assays revealed a difference in the specificity of antibodies induced by the two rPfMSP2-based vaccines, with evidence of epitope masking by rPfMSP2-associated fibrils. Rabbit anti-PfMSP2/8 was superior to rPfMSP2-elicited antibody at opsonizing P. falciparum merozoites for phagocytosis. These data establish rPfMSP8 as an effective carrier for a PfMSP2-based subunit malaria vaccine.

The Use of Synthetic Carriers in Malaria Vaccine Design

Malaria vaccine research has been ongoing since the 1980s with limited success. However, recent improvements in our understanding of the immune responses required to combat each stage of infection will allow for intelligent design of both antigens and their associated delivery vaccine vehicles/vectors. Synthetic carriers (also known as vectors) are usually particulate and have multiple properties, which can be varied to control how an associated vaccine interacts with the host, and consequently how the immune response develops. This review comprehensively analyzes both historical and recent studies in which synthetic carriers are used to deliver malaria vaccines. Furthermore, the requirements for a synthetic carrier, such as size, charge, and surface chemistry are reviewed in order to understand the design of effective particle-based vaccines against malaria, as well as providing general insights. Synthetic carriers have the ability to alter and direct the immune response, and a better control of particle properties will facilitate improved vaccine design in the near future.

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.

Malaria vaccine adjuvants: latest update and challenges in preclinical and clinical research

There is no malaria vaccine currently available, and the most advanced candidate has recently reported a modest 30% efficacy against clinical malaria. Although many efforts have been dedicated to achieve this goal, the research was mainly directed to identify antigenic targets. Nevertheless, the latest progresses on understanding how immune system works and the data recovered from vaccination studies have conferred to the vaccine formulation its deserved relevance. Additionally to the antigen nature, the manner in which it is presented (delivery adjuvants) as well as the immunostimulatory effect of the formulation components (immunostimulants) modulates the immune response elicited. Protective immunity against malaria requires the induction of humoral, antibody-dependent cellular inhibition (ADCI) and effector and memory cell responses. This review summarizes the status of adjuvants that have been or are being employed in the malaria vaccine development, focusing on the pharmaceutical and immunological aspects, as well as on their immunization outcomings at clinical and preclinical stages.

Evaluation of Montanide™ ISA 71 VG adjuvant during profilin vaccination against experimental coccidiosis

Chickens were immunized subcutaneously with an Eimeria recombinant profilin protein plus Montanide™ ISA 70 VG (ISA 70) or Montanide™ ISA 71 VG (ISA 71) water-in-oil adjuvants, or with profilin alone, and comparative RNA microarray hybridizations were performed to ascertain global transcriptome changes induced by profilin/ISA 70 vs. profilin alone and by profilin/ISA 71 vs. profilin alone. While immunization with profilin/ISA 70 vs. profilin alone altered the levels of more total transcripts compared with profilin/ISA 71 vs. profilin alone (509 vs. 296), the latter was associated with a greater number of unique biological functions, and a larger number of genes within these functions, compared with the former. Further, canonical pathway analysis identified 10 pathways that were associated with genes encoding the altered transcripts in animals immunized with profilin/ISA 71 vs. profilin alone, compared with only 2 pathways in profilin/ISA 70 vs. profilin alone. Therefore, ISA 71 was selected as a candidate adjuvant in conjunction with profilin vaccination for in vivo disease protection studies. Vaccination with profilin/ISA 71 was associated with greater body weight gain following E. acervulina infection, and decreased parasite fecal shedding after E. maxima infection, compared with profilin alone. Anti-profilin antibody levels were higher in sera of E. maxima- and E. tenella-infected chickens vaccinated with profilin/ISA 71 compared with profilin alone. Finally, the levels of transcripts encoding interferon-γ, interleukin (IL)-2, IL-10, and IL-17A were increased in intestinal lymphocytes from E. acervulina-, E. maxima-, and/or E. tenella-infected chickens vaccinated with profilin/ISA 71 compared with profilin alone. None of these effects were seen in chickens injected with ISA 71 alone indicating that the adjuvant was not conferring non-specific immune stimulation. These results suggest that profilin plus ISA 71 augments protective immunity against selective Eimeria species in chickens.

Plasmodium falciparum synthetic LbL microparticle vaccine elicits protective neutralizing antibody and parasite-specific cellular immune responses

Epitopes of the circumsporozoite (CS) protein of Plasmodium falciparum, the most pathogenic species of the malaria parasite, have been shown to elicit protective immunity in experimental animals and human volunteers. The mechanisms of immunity include parasite-neutralizing antibodies that can inhibit parasite motility in the skin at the site of infection and in the bloodstream during transit to the hepatocyte host cell and also block interaction with host cell receptors on hepatocytes. In addition, specific CD4+ and CD8+ cellular mechanisms target the intracellular hepatic forms, thus preventing release of erythrocytic stage parasites from the infected hepatocyte and the ensuing blood stage cycle responsible for clinical disease. An innovative method for producing particle vaccines, layer-by-layer (LbL) fabrication of polypeptide films on solid CaCO3 cores, was used to produce synthetic malaria vaccines containing a tri-epitope CS peptide T1BT comprising the antibody epitope of the CS repeat region (B) and two T-cell epitopes, the highly conserved T1 epitope and the universal epitope T. Mice immunized with microparticles loaded with T1BT peptide developed parasite-neutralizing antibodies and malaria-specific T-cell responses including cytotoxic effector T-cells. Protection from liver stage infection following challenge with live sporozoites from infected mosquitoes correlated with neutralizing antibody levels. Although some immunized mice with low or undetectable neutralizing antibodies were also protected, depletion of T-cells prior to challenge resulted in the majority of mice remaining resistant to challenge. In addition, mice immunized with microparticles bearing only T-cell epitopes were not protected, demonstrating that cellular immunity alone was not sufficient for protective immunity. Although the microparticles without adjuvant were immunogenic and protective, a simple modification with the lipopeptide TLR2 agonist Pam3Cys increased the potency and efficacy of the LbL vaccine candidate. This study demonstrates the potential of LbL particles as promising malaria vaccine candidates using the T1BT epitopes from the P. falciparum CS protein.

Vaccination Strategies against Malaria: novel carrier(s) more than a tour de force

The introduction of vaccine technology has facilitated an unprecedented multi-antigen approach to develop an effective vaccine against complex systemic inflammatory pathogens such as Plasmodium spp. that cause severe malaria. The capacity of multi subunit DNA vaccine encoding different stage Plasmodium antigens to induce CD8(+) cytotoxic T lymphocytes and interferon-γ responses in mice, monkeys and humans has been observed. Moreover, genetic vaccination may be capable of eliciting both cell mediated and humoral immune responses. The cytotoxic T cell responses are categorically needed against intracellular hepatic stage and humoral response with antibodies targeted against antigens from all stages of malaria parasite life cycle. Therefore, the key to success for any DNA based vaccine is to design a vector able to serve as a safe and efficient delivery system. This has encouraged the development of non-viral DNA-mediated gene transfer techniques such as liposome, virosomes, microsphere and nanoparticles. Efficient and relatively safe DNA transfection using lipoplexes makes them an appealing alternative to be explored for gene delivery. Also, liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells (APC). Another recent technology using cationic lipids has been deployed and has generated substantial interest in this approach to gene transfer. In this review we discussed various aspects that could be decisive in the formulation of efficient and stable carrier system(s) for the development of malaria vaccine.

An overview on the field of micro- and nanotechnologies for synthetic Peptide-based vaccines

The development of synthetic peptide-based vaccines has many advantages in comparison with vaccines based on live attenuated organisms, inactivated or killed organism, or toxins. Peptide-based vaccines cannot revert to a virulent form, allow a better conservation, and are produced more easily and safely. However, they generate a weaker immune response than other vaccines, and the inclusion of adjuvants and/or the use of vaccine delivery systems is almost always needed. Among vaccine delivery systems, micro- and nanoparticulated ones are attractive, because their particulate nature can increase cross-presentation of the peptide. In addition, they can be passively or actively targeted to antigen presenting cells. Furthermore, particulate adjuvants are able to directly activate innate immune system in vivo. Here, we summarize micro- and nanoparticulated vaccine delivery systems used in the field of synthetic peptide-based vaccines as well as strategies to increase their immunogenicity.

Design of a composite drug delivery system to prolong functionality of cell-based scaffolds

Cell encapsulation technology raises hopes in medicine and biotechnology. However, despite important advances in the field in the past three decades, several challenges associated with the biocompatibility are still remaining. In the present study, the effect of a temporary release of an anti-inflammatory agent on co-administered encapsulated allogeneic cells was investigated. The aim was to determine the biocompatibility and efficacy of the approach to prevent the inflammatory response. A composite delivery system comprised of alginate-poly-l-lysine-alginate (APA)-microencapsulated Epo-secreting myoblasts and dexamethasone (DXM)-releasing poly(lactic-co-glycolic acid) (PLGA) microspheres was implanted in the subcutaneous space of Balb/c mice for 45 days. The use of independently co-implanted DXM-loaded PLGA microspheres resulted in an improved functionality of the cell-based graft, evidenced by significantly higher hematocrit levels found in the cell-implanted groups by day 45, which was found to be more pronounced when higher cell-doses (100 μL) were employed. Moreover, no major host reaction was observed upon implantation of the systems, showing good biocompatibility and capability to partially avoid the inflammatory response, probably due to the immunosuppressive effects related to DXM. The findings of this study imply that DXM-loaded PLGA microspheres show promise as release systems to enhance biocompatibility and offer advantage in the development of long-lasting and effective implantable microencapsulated cells by generating a potential immunopriviledged local environment and an effective method to limit the structural ensheathing layer caused by inflammation.

Antibody responses to 43 and 48 kDa antigens of blood-stage Plasmodium berghei in Balb/c mice

Progress towards a vaccine against malaria is advancing rapidly with several candidate antigens being tested for their safety and efficacy. In present investigation, two polypeptides (43 and 48 kDa) of Plasmodium berghei (NK-65) were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Immunogenicity and protective efficacy of both these polypeptides formulated in saponin has been compared in Balb/c mice against challenge infection with P. berghei. Antibody responses were evaluated by indirect fluorescent antibody test and enzyme-linked immunosorbent assay. Merozoite invasion inhibition assay and challenge infections revealed that 48 kDa antigen is better immunogen as compared to 43 kDa and provide better protection against rodent malaria infection.

Preparation of porous PLGA microspheres with thermoreversible gel to modulate drug release profile of water-soluble drug: bleomycin sulphate

Bleomycin sulphate-loaded porous microspheres were prepared using modified solvent evaporation method (w/o/w) using PLGA50:50 as a polymeric system. The prepared microspheres were incorporated in pluronic (F127) based thermoreversible gel to develop a depot formulation. Various process parameters as solvent evaporation temperature and formulation parameters such as surfactant concentration, volume of internal and external phase and drug-to-polymer ratio were optimized for enhancing percentage drug entrapment, percentage drug loading and desired release profile by controlling size and porosity of the microspheres. Microspheres were characterized for particle size, zeta potential, surface morphology, percentage drug loading and in vitro drug release study after incorporated in gel. The formulated microspheres were porous in nature and showed biphasic in vitro drug release profile. The microspheres incorporated in pluronic (F127) gel showed sustained release up to 1 week and may be useful for treatment of squamous cell carcinoma with better therapeutic effect.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Immune responses of mice with different genetic backgrounds to improved multiepitope, multitarget malaria vaccine candidate antigen FALVAC-1A

FALVAC-1A is a second-generation multitarget, multiepitope synthetic candidate vaccine against Plasmodium falciparum, incorporating elements designed to yield a stable and immunogenic molecule. Characteristics of the immunogenicity of FALVAC-1A were evaluated in congenic (H-2(b), H-2(k), and H-2(d)) and outbred strains of mice. The influences of four adjuvants (aluminum phosphate, QS-21, Montanide ISA-720, and copolymer CRL-1005) on different aspects of the immune response were also assessed. FALVAC-1A generated strong antibody responses in all mouse strains. The highest mean enzyme-linked immunosorbent assay (ELISA) antibody concentrations against FALVAC-1A were observed in the outbred ICR mice, followed by B10.BR, B10.D2, and C57BL/6 mice, though this order varied for the different adjuvants, with no statistical differences between mouse strains. In all mouse strains, the highest anti-FALVAC-1A antibody titers in ELISAs were induced by FALVAC-1A in copolymer and ISA-720 formulations, followed by QS-21 and AlPO4. These antibodies were of all four subclasses, though immunoglobulin G1 (IgG1) predominated, with the exception of FALVAC-1A with the QS-21 adjuvant, which induced predominantly IgG2c responses. Both sporozoites and blood stages of P. falciparum were recognized by anti-FALVAC-1A sera in the immunofluorescence assay. In addition to antibody, cellular immune responses were detected; these responses were studied by examining spleen cells producing gamma interferon and interleukin-4 in enzyme-linked immunospot assays. In summary, FALVAC-1A was found to be highly immunogenic and elicited functionally relevant antibodies that can recognize sporozoites and blood-stage parasites in diverse genetic backgrounds.

Cell microencapsulation technology: towards clinical application

The pharmacokinetic properties of a drug can be significantly improved by the delivery process. Scientists have understood that developing suitable drug delivery systems that release the therapeutically active molecule at the level and dose it is needed and during the optimal time represents a major advance in the field. Cell microencapsulation is an alternative approach for the sustained delivery of therapeutic agents. This technology is based on the immobilization of different types of cells within a polymeric matrix surrounded by a semipermeable membrane for the long-term release of therapeutics. As a result, encapsulated cells are isolated from the host immune system while allowing exchange of nutrients and waste and release of the therapeutic agents. The versatility of this approach has stimulated its use in the treatment of numerous medical diseases including diabetes, cancer, central nervous system diseases and endocrinological disorders among others. The aim of this review article is to give an overview on the current state of the art of the use of cell encapsulation technology as a controlled drug delivery system. The most important advantages of this type of "living" drug release strategy are highlighted, but also its limitations pointed out, and the major challenges to be addressed in the forthcoming years are described.

Various carrier system(s)- mediated genetic vaccination strategies against malaria

The introduction of vaccine technology has facilitated an unprecedented multiantigen approach to develop an effective vaccine against complex pathogens, such as Plasmodium spp., that cause severe malaria. The capacity of multisubunit DNA vaccines encoding different stage Plasmodium antigens to induce CD8(+) cytotoxic T lymphocytes and IFN-gamma responses in mice, monkeys and humans has been observed. Moreover, genetic vaccination may be multi-immune (i.e., capable of eliciting more than one type of immune response, including cell-mediated and humoral). In the case of malaria parasites, a cytotoxic T-lymphocyte response is categorically needed against the intracellular hepatocyte stage while a humoral response, with antibodies targeted against antigens from all stages of the life cycle, is also needed. Therefore, the key to success for any DNA-based therapy is to design a vector able to serve as a safe and efficient delivery system. This has encouraged the development of nonviral DNA-mediated gene-transfer techniques, such as liposomes, virosomes, microspheres and nanoparticles. Efficient and relatively safe DNA transfection using lipoplexes makes them an appealing alternative to be explored for gene delivery. In addition, liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells. Another recent technology using cationic lipids has been deployed and has generated substantial interest in this approach to gene transfer. This review comprises various aspects that could be decisive in the formulation of efficient and stable carrier system(s) for the development of malaria vaccines.

Gamma-irradiation effects on biopharmaceutical properties of PLGA microspheres loaded with SPf66 synthetic vaccine

Gamma-irradiation is currently the method of choice for terminal sterilization of drug delivery systems made from biodegradable polymers. However, the consequences of gamma-sterilization on the immune response induced by microencapsulated antigens have not yet been reported in the literature. The aim of the present work was to evaluate the effect of gamma-irradiation on the biopharmaceutical properties of PLGA microspheres containing SPf66 malarial antigen. Microspheres were prepared by a (w/o/w) double emulsion/solvent extraction method. Once prepared, part of the formulation was irradiated at a dose of 25 kGy using 60Co gamma as radiation source. The in vitro results obtained showed that the gamma-irradiation exposure had no apparent effect on SPf66 integrity and formulation properties such us morphology, size and peptide loading. Only the release rate of SPf66 was slightly faster after gamma-irradiation. Subcutaneous administration of irradiated and non-irradiated microspheres into mice induced a similar immune response (IgG, IgG1, IgG2a levels) and was comparable to that obtained with SPf66 emulsified with Freund's complete adjuvant. These observations illustrate the applicability of gamma-irradiation as a method of terminal sterilization of microparticulate delivery systems based on chemically synthesized antigens encapsulated into biodegradable PLGA microspheres.

Blood coagulation in falciparum malaria--a review

Falciparum malaria infection influences blood coagulation by various interacting pathobiological mechanisms, the most important being the overwhelming response of the host to sepsis resulting in a cytokine storm. In addition, the parasite infects the red cells leading to changes in the red cell phospholipid composition which supports blood coagulation. Red cells infected with Plasmodium falciparum also adhere to deeper tissue capillary endothelium leading to profound damage to endothelial cells leading to further activation. This results in widespread consumption of platelets and activation of blood coagulation which at times culminates in a clinically and pathologically detectable disseminated intravascular coagulation (DIC). Monocyte-macrophage system also gets activated in this infection compounding the hypercoagulable state. Heavy parasitaemia leading to occlusion of hepatic microcirculation leads to abnormalities in synthesis and secretion of coagulation factors and their inhibitors. Drugs used in the treatment for falciparum malaria can cause thrombocytopaenia, bone marrow suppression and haemolytic anaemia, all of which can interfere indirectly with blood coagulation. Microparticle formation from platelets, red cells and macrophages also causes widespread activation of blood coagulation, and this recently observed mechanism is the focus of intense research in many other inflammatory and neoplastic conditions where there is activation of blood coagulation system. Thus, in severe falciparum malaria, there is activation of blood coagulation system along with thrombocytopaenia, even before widespread DIC and coagulation failure occur.

Viral peptide immunogens: current challenges and opportunities

Synthetic peptide vaccines have potential to control viral infections. Successful experimental models using this approach include the protection of mice against the lethal Sendai virus infection by MHC class I binding CTL peptide epitope. The main benefit of vaccination with peptide epitopes is the ability to minimize the amount and complexity of a well-defined antigen. An appropriate peptide immunogen would also decrease the chance of stimulating a response against self-antigens, thereby providing a safer vaccine by avoiding autoimmunity. In general, the peptide vaccine strategy needs to dissect the specificity of antigen processing, the presence of B-and T-cell epitopes and the MHC restriction of the T-cell responses. This article briefly reviews the implications in the design of peptide vaccines and discusses the various approaches that are applied to improve their immunogenicity.

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

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