Anjali Yadava

Enhancing humoral responses to a malaria antigen with nanoparticle vaccines that expand Tfh cells and promote germinal center induction.

For subunit vaccines, adjuvants play a key role in shaping immunological memory. Nanoparticle (NP) delivery systems for antigens and/or molecular danger signals are promising adjuvants capable of promoting both cellular and humoral immune responses, but in most cases the mechanisms of action of these materials are poorly understood. Here, we studied the immune response elicited by NPs composed of multilamellar “stapled” lipid vesicles carrying a recombinant Plasmodium vivax circumsporozoite antigen, VMP001, both entrapped in the aqueous core and anchored to the lipid bilayer surfaces. Immunization with these particles and monophosphoryl lipid A (MPLA), a US Food and Drug Administration–approved immunostimulatory agonist for Toll-like receptor-4, promoted high-titer, high-avidity antibody responses against VMP001, lasting more than 1 y in mice at 10-fold lower doses than conventional adjuvants. Compared to soluble VMP001 mixed with MPLA, VMP001-NPs promoted broader humoral responses, targeting multiple epitopes of the protein and a more balanced Th1/Th2 cytokine profile from antigen-specific T cells. To begin to understand the underlying mechanisms, we examined components of the B-cell response and found that NPs promoted robust germinal center (GC) formation at low doses of antigen where no GC induction occurred with soluble protein immunization, and that GCs nucleated near depots of NPs accumulating in the draining lymph nodes over time. In parallel, NP vaccination enhanced the expansion of antigen-specific follicular helper T cells (Tfh), compared to vaccinations with soluble VMP001 or alum. Thus, NP vaccines may be a promising strategy to enhance the durability, breadth, and potency of humoral immunity by enhancing key elements of the B-cell response.

Effect of Codon Optimization on Expression Levels of a Functionally Folded Malaria Vaccine Candidate in Prokaryotic and Eukaryotic Expression Systems

ABSTRACT We have produced two synthetic genes that code for the F2 domain located within region II of the 175-kDa Plasmodium falciparum erythrocyte binding antigen (EBA-175) to determine the effects of codon alteration on protein expression in homologous and heterologous host systems. EBA-175 plays a key role in the process of merozoite invasion into erythrocytes through a specific receptor-ligand interaction. The F2 domain of EBA-175 is the ligand that binds to the glycophorin A receptor on human erythrocytes and is therefore a target of vaccine development efforts. We designed synthetic genes based on P. falciparum, Escherichia coli, and Pichia codon usage and expressed recombinant F2 in E. coli and Pichia pastoris. Compared to the expression of the native F2 sequence, conversion to prokaryote (E. coli)- or eukaryote (Pichia)-based codon usage dramatically improved the levels of recombinant protein expression in both E. coli and P. pastoris. The majority of the protein expressed in E. coli, however, was produced as inclusion bodies. The protein expressed in P. pastoris, on the other hand, was expressed as a secreted, soluble protein. The P. pastoris-produced protein was superior to that produced in E. coli based on its ability to bind to red blood cells. Consistent with these observations, the antibodies generated against the Pichia-produced protein prevented the binding of recombinant EBA to red blood cells. These antibodies recognize EBA-175 present on merozoites as well as in sporozoites by immunofluorescence. Our results suggest that the Pichia-based EBA-F2 vaccine construct has further potential to be developed for clinical use.

Primaquine failure and cytochrome P-450 2D6 in Plasmodium vivax malaria.

Primaquine is used to eradicate the hepatic or hypnozoite form of Plasmodium vivax that may lead to relapse of infection. Host genetic factors may play a role in the activity of primaquine therapy.

Immunogenicity and Efficacy in Aotus Monkeys of Four Recombinant Plasmodium falciparum Vaccines in Multiple Adjuvant Formulations Based on the 19-Kilodalton C Terminus of Merozoite Surface Protein 1

ABSTRACT The immunogenicity and protective efficacy of four versions of recombinant C-terminal 19-kDa epidermal growth factor-like region of the major surface protein 1 (rMSP119) of Plasmodium falciparum was studied in Aotus monkeys. Vaccination with each of the four rMSP119 constructs elicited high levels of antibodies to MSP119 but only one construct, the 19-kDa fragment expressed as a secreted fusion protein fromSaccharomyces cerevisiae (yP30P2MSP119), induced a high degree of protective immunity in Aotus nancymai against lethal P. falciparum challenge. Protective formulation required Freunds adjuvant; vaccination with yP30P2MSP119 in six other adjuvants that are suitable for human use induced lower levels of antibody response and no protection. These results emphasize the need to continue the search for an adjuvant that is comparable to Freunds adjuvant in potency and is safe for use in humans.

Antigen-Displaying Lipid-Enveloped PLGA Nanoparticles as Delivery Agents for a Plasmodium vivax Malaria Vaccine

The parasite Plasmodium vivax is the most frequent cause of malaria outside of sub-Saharan Africa, but efforts to develop viable vaccines against P. vivax so far have been inadequate. We recently developed pathogen-mimicking polymeric vaccine nanoparticles composed of the FDA-approved biodegradable polymer poly(lactide-co-glycolide) acid (PLGA) “enveloped” by a lipid membrane. In this study, we sought to determine whether this vaccine delivery platform could be applied to enhance the immune response against P. vivax sporozoites. A candidate malaria antigen, VMP001, was conjugated to the lipid membrane of the particles, and an immunostimulatory molecule, monophosphoryl lipid A (MPLA), was incorporated into the lipid membranes, creating pathogen-mimicking nanoparticle vaccines (VMP001-NPs). Vaccination with VMP001-NPs promoted germinal center formation and elicited durable antigen-specific antibodies with significantly higher titers and more balanced Th1/Th2 responses in vivo, compared with vaccines composed of soluble protein mixed with MPLA. Antibodies raised by NP vaccinations also exhibited enhanced avidity and affinity toward the domains within the circumsporozoite protein implicated in protection and were able to agglutinate live P. vivax sporozoites. These results demonstrate that these VMP001-NPs are promising vaccines candidates that may elicit protective immunity against P. vivax sporozoites.

A Novel Chimeric Plasmodium vivax Circumsporozoite Protein Induces Biologically Functional Antibodies That Recognize both VK210 and VK247 Sporozoites

ABSTRACT A successful vaccine against Plasmodium vivax malaria would significantly improve the health and quality of the lives of more than 1 billion people around the world. A subunit vaccine is the only option in the absence of long-term culture of P. vivax parasites. The circumsporozoite protein that covers the surface of Plasmodium sporozoites is one of the best-studied malarial antigens and the most promising vaccine in clinical trials. We report here the development of a novel “immunologically optimal” recombinant vaccine expressed in Escherichia coli that encodes a chimeric CS protein encompassing repeats from the two major alleles, VK210 and VK247. This molecule is widely recognized by sera from patients naturally exposed to P. vivax infection and induces a highly potent immune response in genetically disparate strains of mice. Antibodies from immunized animals recognize both VK210 and VK247 sporozoites. Furthermore, these antibodies appear to be protective in nature since they cause the agglutination of live sporozoites, an in vitro surrogate of sporozoite infectivity. These results strongly suggest that recombinant CS is biologically active and highly immunogenic across major histocompatibility complex strains and raises the prospect that in humans this vaccine may induce protective immune responses.

Evidence for the Transmission of Plasmodium vivax in the Republic of the Congo, West Central Africa

Plasmodium vivax is not thought to be transmitted in western and central Africa, because of the very high prevalence of the red blood cell Duffy-negative phenotype in local populations, a condition which is thought to confer complete resistance against blood infection with P. vivax. There are, however, persistent reports of travelers returning from this region with P. vivax infections. To investigate whether transmission occurs in this region, the presence of antibodies specific to P. vivax preerythrocytic-stage antigens was assessed in individuals from the Republic of the Congo. A total of 55 (13%) of 409 samples tested by enzyme-linked immunosorbent assay had antibodies to P. vivax-specific antigens.

Process development for the production of an E. coli produced clinical grade recombinant malaria vaccine for Plasmodium vivax

The global eradication of malaria will require the development of vaccines to prevent infection cause by Plasmodium vivax in addition to Plasmodium falciparum. In an attempt to contribute to this effort we have previously reported the cloning and expression of a vaccine based on the circumsporozoite protein of P. vivax. The synthetic vaccine encodes for a full-length molecule encompassing the N-terminal and C-terminal regions flanking a chimeric repeat region representing VK210 and VK247, the two major alleles of P. vivax CSP. The vaccine, designated vivax malaria protein 001 (VMP001), was purified to >95% homogeneity using a three-column purification scheme and had low endotoxin levels and passed the rabbit pyrogenicity assay. The protein is recognized by monoclonal antibodies directed against the two repeat motifs, as well as polyclonal antibodies. Immunization with VMP001 induced high titer antibodies in mice using Montanide ISA 720. We currently have more than 10,000 doses of purified bulk and 1800 vials of formulated bulk vaccine available for clinical testing and VMP001 is currently undergoing further development as a candidate vaccine to prevent malaria in humans.

Genome-Wide Expression Profiling in Malaria Infection Reveals Transcriptional Changes Associated with Lethal and Nonlethal Outcomes

ABSTRACT High-density oligonucleotide microarrays are widely used to study gene expression in cells exposed to a variety of pathogens. This study addressed the global genome-wide transcriptional activation of genes in hosts infected in vivo, which result in radically different clinical outcomes. We present an analysis of the gene expression profiles that identified a set of host biomarkers which distinguish between lethal and nonlethal blood stage Plasmodium yoelii malaria infections. Multiple biological replicates sampled during the course of infection were used to establish statistically valid sets of differentially expressed genes. These genes that correlated with the intensity of infection were used to identify pathways of cellular processes related to metabolic perturbations, erythropoiesis, and B-cell immune responses and other innate and cellular immune responses. The transcriptional apparatus that controls gene expression in erythropoiesis was also differentially expressed and regulated the expression of target genes involved in the hosts response to malaria anemia. The biological systems approach provides unprecedented opportunities to explore the pathophysiology of host-pathogen interactions in experimental malaria infection and to decipher functionally complex networks of gene and protein interactions.

Development of a Chimeric Plasmodium berghei Strain Expressing the Repeat Region of the P. vivax Circumsporozoite Protein for In Vivo Evaluation of Vaccine Efficacy

ABSTRACT The development of vaccine candidates against Plasmodium vivax—the most geographically widespread human malaria species—is challenged by technical difficulties, such as the lack of in vitro culture systems and availability of animal models. Chimeric rodent Plasmodium parasites are safe and useful tools for the preclinical evaluation of new vaccine formulations. We report the successful development and characterization of chimeric Plasmodium berghei parasites bearing the type I repeat region of P. vivax circumsporozoite protein (CSP). The P. berghei-P. vivax chimeric strain develops normally in mosquitoes and produces highly infectious sporozoites that produce patent infection in mice that are exposed to the bites of as few as 3 P. berghei-P. vivax-infected mosquitoes. Using this transgenic parasite, we demonstrate that monoclonal and polyclonal antibodies against P. vivax CSP strongly inhibit parasite infection and thus support the notion that these antibodies play an important role in protective immunity. The chimeric parasites we developed represent a robust model for evaluating protective immune responses against P. vivax vaccines based on CSP.