Safety and immunogenicity of the Na-APR-1 hookworm vaccine in infection-naïve adults

Bioinformatics-guided decoding of the Ancylostoma duodenale genome for the identification of potential vaccine targets

Ancylostoma duodenale, a parasitic nematode worm, is found to be involved in various infections, including intestinal blood loss, protein malnutrition, and anemia. Antimicrobial resistance to the available therapeutics has prompted the search for new drug and vaccine targets against A. duodenale. Despite significant advances in vaccine development against A. duodenale, no commercial and FDA-approved vaccine exists to safeguard humans from infections caused by this pathogen. In this investigation, a stringent bioinformatics analysis identified 36 unique essential and host-interacting proteins. Based on their subcellular localization, 6 proteins located in the extracellular space and outer membrane were categorized as vaccine targets, while the remaining proteins were predicted to act as potential drug candidates. These vaccine candidates were further assessed for antigenicity, allergenicity, and physicochemical analysis to determine their suitability for the designing of a multi-epitope vaccine. Two candidate proteins were chosen as optimal targets in the development of vaccine design. The identified T- and B-cell epitopes from these proteins were then combined with appropriate linkers and adjuvants to design chimeric vaccine constructs aimed at inducing both cellular and humoral immune responses. Molecular docking, molecular dynamic simulations, PCA analysis, DCCM analysis, and binding free energy calculations proved stable interactions of the designed vaccine with human immune cell receptors. Within a bacterial cloning system, the vaccine constructs demonstrated the ability to be cloned and expressed. The immunological stimulation elicited significant immunological responses to the proposed vaccine. Our investigation identified new therapeutic targets and developed a peptide-based multi-epitope vaccine against A. duodenale infection. Additional experimental verification will open up new therapeutic alternatives for this emerging resistant pathogen.

Plant-Made Vaccines Targeting Enteric Pathogens-Safe Alternatives for Vaccination in Developing Countries

Enteric diseases by pathogenic organisms are one of the leading causes of death worldwide, particularly in low-income countries. Despite antibiotics, access to clean water and vaccination are the most economically affordable options to prevent those infections and their health consequences. Vaccines, such as those approved for rotavirus and cholera, have played a key role in preventing several enteric diseases. However, vaccines for other pathogens are still in clinical trials. Distribution and cost remain significant barriers to vaccine access in developing regions due to poor healthcare infrastructure, cold-chain requirements, and high production costs. Plant-made vaccines offer a promising alternative to address these challenges. Plants can be easily grown, lowering production costs, and can be administered in oral forms, potentially eliminating cold-chain dependency. Although there are some promising prototypes of vaccines produced in plants, challenges remain, including yields and achieving sufficient immunogenicity. This review aims to describe common enteric pathogens and available vaccines, followed by a strategic summary of plant-made vaccine development and a discussion of plant-made enteric vaccine prototypes. Trends to overcome the key challenges for plant-made vaccines are identified and placed in perspective for the development of affordable and effective vaccines for populations at the highest risk of enteric diseases.

Antibody Responses and the Vaccine Efficacy of Recombinant Glycosyltransferase and Nicastrin Against Schistosoma japonicum

Schistosomiasis is a neglected tropical disease and the second most common parasitic disease after malaria. While praziquantel remains the primary treatment, concerns about drug resistance highlight the urgent need for new drugs and effective vaccines to achieve sustainable control. Previous proteomic studies from our group revealed that the expression of Schistosoma japonicum glycosyltransferase and nicastrin as proteins was higher in single-sex males than mated males, suggesting their critical roles in parasite reproduction and their potential as vaccine candidates. In this study, bioinformatic tools were employed to analyze the structural and functional properties of these proteins, including their signal peptide regions, transmembrane domains, tertiary structures, and protein interaction networks. Recombinant forms of glycosyltransferase and nicastrin were expressed and purified, followed by immunization experiments in BALB/c mice. Immunized mice exhibited significantly elevated specific IgG antibody levels after three immunizations compared to adjuvant and PBS controls. Furthermore, immunization with recombinant glycosyltransferase and nicastrin significantly reduced the reproductive capacity of female worms and liver egg burden, though egg hatchability and adult worm survival were unaffected. These findings demonstrate that recombinant glycosyltransferase and nicastrin are immunogenic and reduce female worm fecundity, supporting their potential as vaccine candidates against schistosomiasis.

Altering the intracellular trafficking of Necator americanus GST-1 antigen yields novel hookworm mRNA vaccine candidates

BACKGROUND

The antigen Na-GST-1, expressed by the hookworm Necator americanus, plays crucial biochemical roles in parasite survival. This study explores the development of mRNA vaccine candidates based on Na-GST-1, building on the success of recombinant Na-GST-1 (rNa-GST-1) protein, currently assessed as a subunit vaccine candidate, which has shown promise in preclinical and clinical studies.

METHODOLOGY/FINDINGS

By leveraging the flexible design of RNA vaccines and protein intracellular trafficking signal sequences, we developed three variants of Na-GST-1 as native (cytosolic), secretory, and plasma membrane-anchored (PM) antigens. After one immunization in mice, mRNA vaccines induced an earlier onset of antigen-specific antibodies compared to rNa-GST-1. Following two immunizations, mRNA vaccines induced similar or superior levels of antigen-specific antibodies compared to rNa-GST-1. Secretory Na-GST-1 was comparable to rNa-GST1 in producing neutralizing antibodies against Na-GST-1's thiol transferase activity, while native Na-GST-1 induced a more robust CD8+ T cell response due to its intracellular accumulation. Although PM Na-GST-1 elicited one of highest titers of antigen-specific antibody and a diverse set of memory T-cell populations, it resulted in a lower ratio of neutralizing antibodies after IgG purification compared to the other vaccine candidates.

CONCLUSIONS/SIGNIFICANCE

These findings emphasize the importance of antigen localization in tailoring immune responses and suggest that extracellular antigens are more effective for inducing humoral responses, whereas cytosolic antigen accumulation enhances MHC-1 peptide presentation. Future studies will determine if these in vitro and immunogenicity findings translate to in vivo efficacy. Altogether, mRNA vaccines offer numerous possibilities in the development of multivalent vaccines with single or multiple antigens.

Safety and immunogenicity of the co-administered Na-APR-1 and Na-GST-1 hookworm vaccines in school-aged children in Gabon: a randomised, controlled, observer-blind, phase 1, dose-escalation trial

BACKGROUND

A human hookworm vaccine is being developed to protect children against iron deficiency and anaemia associated with chronic infection with hookworms. Necator americanus aspartic protease-1 (Na-APR-1) and N americanus glutathione S-transferase-1 (Na-GST-1) are components of the blood digestion pathway critical to hookworm survival in the host. Recombinant Na-GST-1 and catalytically inactive Na-APR-1 (Na-APR-1[M74]) adsorbed to Alhydrogel were safe and immunogenic when delivered separately or co-administered to adults in phase 1 trials in non-endemic and endemic areas. We aimed to investigate the safety and immunogenicity of these antigens in healthy children in a hookworm-endemic area.

METHODS

This was a randomised, controlled, observer-blind, phase 1, dose-escalation trial, conducted in a clinical research centre, in 60 children aged six to ten years in Lambaréné, a hookworm-endemic region of Gabon. Healthy children (determined by clinical examination and safety laboratory testing) were randomised 4:1 to receive co-administered Na-GST-1 on Alhydrogel plus Na-APR-1(M74) on Alhydrogel and glucopyranosyl lipid A in aqueous formulation (GLA-AF), or co-administered ENGERIX-B hepatitis B vaccine (HBV) and saline placebo, injected into the deltoid of each arm. Allocation to vaccine groups was observer-masked. In each vaccine group, children were randomised 1:1 to receive intramuscular injections into each deltoid on two vaccine schedules, one at months 0, 2, and 4 or at months 0, 2, and 6. 10 μg, 30 μg, and 100 μg of each antigen were administered in the first, second, and third cohorts, respectively. The intention-to-treat population was used for safety analyses; while for immunogenicity analyses, the per-protocol population was used (children who received all scheduled vaccinations). The primary outcome was to evaluate the vaccines' safety and reactogenicity in healthy children aged between six and ten years. The secondary outcome was to measure antigen-specific serum IgG antibody levels at pre-vaccination and post-vaccination timepoints by qualified ELISAs. The trial is registered with ClinicalTrials.gov, NCT02839161, and is completed.

FINDINGS

Between Jan 23 and Oct 3, 2017, 137 children were screened, of whom 76 were eligible for this trial. 60 children were recruited, and allocated to either 10 μg of the co-administered antigens (n=8 for each injection schedule), 30 μg (n=8 for each schedule), 100 μg (n=8 for each schedule), or HBV and placebo (n=6 for each schedule) in three sequential cohorts. Co-administration of the vaccines was well tolerated; the most frequent solicited adverse events were mild-to-moderate injection-site pain, observed in up to 12 (75%) of 16 participants per vaccine group, and mild headache (12 [25%] of 48) and fever (11 [23%] of 48). No vaccine-related serious adverse events were observed. Significant anti-Na-APR-1(M74) and anti-Na-GST-1 IgG levels were induced in a dose-dependent manner, with peaks seen 14 days after the third vaccinations, regardless of dose (for Na-APR-1[M74], geometric mean levels [GML]=2295·97 arbitrary units [AU] and 726·89 AU, while for Na-GST-1, GMLs=331·2 AU and 21·4 AU for the month 0, 2, and 6 and month 0, 2, and 4 schedules, respectively). The month 0, 2, and 6 schedule induced significantly higher IgG responses to both antigens (p=0·01 and p=0·04 for Na-APR-1[M74] and Na-GST-1, respectively).

INTERPRETATION

Co-administration of recombinant Na-APR-1(M74) and Na-GST-1 to school-aged Gabonese children was well tolerated and induced significant IgG responses. These results justify further evaluation of this antigen combination in proof-of-concept controlled-infection and efficacy studies in hookworm-endemic areas.

FUNDING

European Union Seventh Framework Programme.

Hookworm genomics: dusk or dawn?

Hookworms are parasites, closely related to the model nematode Caenorhabditis elegans, that are a major economic and health burden worldwide. Primarily three hookworm species (Necator americanus, Ancylostoma duodenale, and Ancylostoma ceylanicum) infect humans. Another 100 hookworm species from 19 genera infect primates, ruminants, and carnivores. Genetic data exist for only seven of these species. Genome sequences are available from only four of these species in two genera, leaving 96 others (particularly those parasitizing wildlife) without any genomic data. The most recent hookworm genomes were published 5 years ago, leaving the field in a dusk. However, assembling genomes from single hookworms may bring a new dawn. Here we summarize advances, challenges, and opportunities for studying these neglected but important parasitic nematodes.

Astacin metalloproteases in human-parasitic nematodes

Parasitic nematodes infect over 2 billion individuals worldwide, primarily in low-resource areas, and are responsible for several chronic and potentially deadly diseases. Throughout their life cycle, these parasites are thought to use astacin metalloproteases, a subfamily of zinc-containing metalloendopeptidases, for processes such as skin penetration, molting, and tissue migration. Here, we review the known functions of astacins in human-infective, soil-transmitted parasitic nematodes - including the hookworms Necator americanus and Ancylostoma duodenale, the threadworm Strongyloides stercoralis, the giant roundworm Ascaris lumbricoides, and the whipworm Trichuris trichiura - as well as the human-infective, vector-borne filarial nematodes Wuchereria bancrofti, Onchocerca volvulus, and Brugia malayi. We also review astacin function in parasitic nematodes that infect other mammalian hosts and discuss the potential of astacins as anthelmintic drug targets. Finally, we highlight the molecular and genetic tools that are now available for further exploration of astacin function and discuss how a better understanding of astacin function in human-parasitic nematodes could lead to new avenues for nematode control and drug therapies.

Hookworm vaccines: current and future directions

INTRODUCTION

Hookworms infect about half a billion people worldwide and are responsible for the loss of more than two billion disability-adjusted life years. Mass drug administration (MDA) is the most popular preventive approach, but it does not prevent reinfection. An effective vaccine would be a major public health tool in hookworm-endemic areas.

AREAS COVERED

We highlight recent human studies where vaccination with irradiated larvae and repeated rounds of infection-treatment have induced partial protection. These studies have emphasized the importance of targeting the infective larvae to generate immunity to prevent adult worms from maturing in the gut. We summarize the current status of human and animal model vaccine trials.

EXPERT OPINION

Hookworm infection is endemic in resource-poor developing regions where polyparasitism is common, and vaccine cold chain logistics are complex. Humans do not develop sterile immunity to hookworms, and the elderly are frequently overlooked in MDA campaigns. For all these reasons, a vaccine is essential to create long-lasting protection. The lack of a robust animal model to mimic human hookworm infections is a barrier to the discovery and development of a vaccine, however, there have been major recent advances in human challenge studies which will accelerate the process.

The Roles of Various Immune Cell Populations in Immune Response against Helminths

Helminths are multicellular parasites that are a substantial problem for both human and veterinary medicine. According to estimates, 1.5 billion people suffer from their infection, resulting in decreased life quality and burdens for healthcare systems. On the other hand, these infections may alleviate autoimmune diseases and allergy symptoms. The immune system is programmed to combat infections; nevertheless, its effector mechanisms may result in immunopathologies and exacerbate clinical symptoms. This review summarizes the role of the immune response against worms, with an emphasis on the Th2 response, which is a hallmark of helminth infections. We characterize non-immune cells (enteric tuft cells-ETCs) responsible for detecting parasites, as well as the role of hematopoietic-derived cells (macrophages, basophils, eosinophils, neutrophils, innate lymphoid cells group 2-ILC2s, mast cells, T cells, and B cells) in initiating and sustaining the immune response, as well as the functions they play in granulomas. The aim of this paper is to review the existing knowledge regarding the immune response against helminths, to attempt to decipher the interactions between cells engaged in the response, and to indicate the gaps in the current knowledge.