Process Development of Sj-p80: A Low-Cost Transmission-Blocking Veterinary Vaccine for Asiatic Schistosomiasis

An assessment of a GMP schistosomiasis vaccine (SchistoShield®)

Introduction

Schistosomiasis is a neglected tropical disease that puts over 200 million people at risk, and prevention options are sparse with no approved vaccine. Our vaccine candidate, SchistoShield®, is based on an approximately 87 kDa large subunit of calcium activated neutral protease - termed Sm-p80 - combined with a potent TLR4 agonist-based adjuvant. SchistoShield® has been shown to prevent disease throughout the parasitic life cycle - including egg, juvenile, and adult worm stages - in numerous animal models up to and including baboons. SchistoShield® has been shown safe in both preclinical toxicology studies in rabbits and in a Phase 1 clinical trial in the USA. A Phase 1b trial was initiated in 2023 in endemic regions of Africa, and to date no serious safety signals have been reported.

Methods

In preparation for large-scale Phase 2 clinical trials and eventual vaccine deployment, the Sm-p80 antigen production process has been transferred to a manufacturing organization, Quratis Corporation in South Korea, which specializes in preparation of vaccines for large-scale European and African trials. The process of scaling from our current production level of ~2000 vaccine doses, to a process that will generate more than 100 million doses has required multiple improvement steps in the process including fermentation, downstream purification of the protein antigen, lyophilization, and fill and finish.

Results

In this study, we detail the large-scale production process of the SchistoShield® protein product by Quratis. In addition, an effort was made to analyze and compare the Quratis-made lot of Sm-p80, referred to as QTP-105, to the cGMP lot of Sm-p80 which is in use in human trials in the USA and Africa, referred to as Sm-p80 DP (made in USA). We show that QTP-105 demonstrates excellent potency, purity, identity, and endotoxin levels compared to our Phase 1 Sm-p80 DP and is suitable for use in Phase 2 studies and beyond.

Transmission-Blocking Vaccines against Schistosomiasis Japonica

Control of schistosomiasis japonica, endemic in Asia, including the Philippines, China, and Indonesia, is extremely challenging. Schistosoma japonicum is a highly pathogenic helminth parasite, with disease arising predominantly from an immune reaction to entrapped parasite eggs in tissues. Females of this species can generate 1000-2200 eggs per day, which is about 3- to 15-fold greater than the egg output of other schistosome species. Bovines (water buffalo and cattle) are the predominant definitive hosts and are estimated to generate up to 90% of parasite eggs released into the environment in rural endemic areas where these hosts and humans are present. Here, we highlight the necessity of developing veterinary transmission-blocking vaccines for bovines to better control the disease and review potential vaccine candidates. We also point out that the approach to producing efficacious transmission-blocking animal-based vaccines before moving on to human vaccines is crucial. This will result in effective and feasible public health outcomes in agreement with the One Health concept to achieve optimum health for people, animals, and the environment. Indeed, incorporating a veterinary-based transmission vaccine, coupled with interventions such as human mass drug administration, improved sanitation and hygiene, health education, and snail control, would be invaluable to eliminating zoonotic schistosomiasis.

Evaluation of the Immunomodulatory Effect of the Recombinant 14-3-3 and Major Antigen Proteins of Strongyloides stercoralis against an Infection by S. venezuelensis

Strongyloidiasis, caused by Strongyloides stercoralis, is a neglected parasitic disease that represents a serious public health problem. In immunocompromised patients, this parasitosis can result in hyperinfection or disseminated disease with high levels of mortality. In previous studies, the mRNAs encoding for the 14-3-3 and major antigen proteins were found to be expressed at high levels in S. stercoralis L3 larvae, suggesting potential key roles in parasite-host interactions. We have produced them as recombinant proteins (rSs14-3-3 and rSsMA) in a bacterial protein expression system. The serum levels of anti-rSs14-3-3 and anti-rSsMA IgGs are increased upon infection with S. venezuelensis, validating the use of the mouse model since the native 14-3-3 and MA proteins induce an immune response. Each recombinant protein was formulated in the adjuvant adaptation (ADAD) vaccination system and injected twice, subcutaneously, in CD1 mice that were experimentally infected with 3000 S. venezuelensis L3 to evaluate their protective and immunomodulatory activity. Our results, including the number of parthenogenetic females, number of eggs in stool samples and the analysis of the splenic and intestinal indexes, show that the vaccines did not protect against infection. The immunization with rSs14-3-3 induced changes in the cytokine profile in mice, producing higher expression of IL-10, TGF-β, IL-13 and TNF-α in the spleen, suggesting a Th2/Treg-type response with an increase in TNF-α levels, confirming its role as an immunomodulator.

Protective immune potential of multiple antigenic peptide (MAP) constructs comprising peptides that are shared by several cysteine peptidases against Schistosoma mansoni infection in mice

In vaccine trials, Schistosoma mansoni cathepsin B1 (SmCB1), helminth cathepsins of the L family (e.g., SmCL3), and papain consistently induce highly significant reductions in challenge worm burden and egg viability, but generated no additive protective effects when used in combination. The protective capacity of the cysteine peptidases is associated with modest (SmCB1) and poor (cathepsins L) production of cytokines and antibodies, essentially of the type 2 axis, and is only marginally reduced upon use of proteolytically inactive enzymes. In this work, peptides shared by SmCB1, cathepsins of the L family, papain and other allergens were selected, synthesized as tetrabranched multiple antigen peptide constructs (MAP-1 and MAP-2), and used in two independent experiments to immunize outbred mice, in parallel with papain. The two peptides elicited significant (P <  0.05) reduction in challenge worm burden when compared to unimmunized mice, albeit lower than that achieved by papain. Protection was associated with modest serum type 2 cytokines and antibody levels in MAP-, and papain-immunized mice. Immunization with papain also elicited a reduction in parasite egg load, viability, and granuloma numbers in liver and intestine. MAP-1 and MAP-2 immunogens displayed some opposite effects- MAP-1 leading to higher egg numbers with poor vitality, whereas MAP-2 immunization yielded fewer eggs. Cysteine peptidase thus appear to carry peptides that elicit opposing outcomes, highlighting the difficulty of reaching fully fledged protection, unless a vaccine is based on carefully selected peptides and combined with an effective adjuvant.

Recent Advances and Methodological Considerations on Vaccine Candidates for Human Schistosomiasis

Schistosomiasis remains a neglected tropical disease of major public health concern with high levels of morbidity in various parts of the world. Although considerable efforts in implementing mass drug administration programs utilizing praziquantel have been deployed, schistosomiasis is still not contained. A vaccine may therefore be an essential part of multifaceted prevention control efforts. In the 1990s, a joint United Nations committee promoting parasite vaccines shortlisted promising candidates including for schistosomiasis discussed below. After examining the complexity of immune responses in human hosts infected with schistosomes, we review and discuss the antigen design and preclinical and clinical development of the four leading vaccine candidates: Sm-TSP-2 in Phase 1b/2b, Sm14 in Phase 2a/2b, Sm-p80 in Phase 1 preparation, and Sh28GST in Phase 3. Our assessment of currently leading vaccine candidates revealed some methodological issues that preclude a fair comparison between candidates and the rationale to advance in clinical development. These include (1) variability in animal models - in particular non-human primate studies - and predictive values of each for protection in humans; (2) lack of consensus on the assessment of parasitological and immunological parameters; (3) absence of reliable surrogate markers of protection; (4) lack of well-designed parasitological and immunological natural history studies in the context of mass drug administration with praziquantel. The controlled human infection model - while promising and unique - requires validation against efficacy outcomes in endemic settings. Further research is also needed on the impact of advanced adjuvants targeting specific parts of the innate immune system that may induce potent, protective and durable immune responses with the ultimate goal of achieving meaningful worm reduction.