Advances in neglected tropical disease vaccines: Developing relative potency and functional assays for the Na-GST-1/Alhydrogel hookworm vaccine

Clinical formulation development of Plasmodium falciparum malaria vaccine candidates based on Pfs48/45, Pfs230, and PfCSP

Two malaria transmission-blocking vaccine (TBV) candidates, R0.6C and ProC6C, have completed preclinical development including the selection of adjuvants, Alhydrogel® with or without the saponin based adjuvant Matrix-M™. Here, we report on the final drug product (formulation) design of R0.6C and ProC6C and evaluate their safety and biochemical stability in preparation for preclinical and clinical pharmacy handling. The point-of-injection stability studies demonstrated that both the R0.6C and ProC6C antigens are stable on Alhydrogel in the presence or absence of Matrix-M for up to 24 h at room temperature. As this is the first study to combine Alhydrogel and Matrix-M for clinical use, we also evaluated their potential interactions. Matrix-M adsorbs to Alhydrogel, while not displacing the > 95 % adsorbed protein. The R0.6C and ProC6C formulations were found to be safe and well tolerated in repeated dose toxicity studies in rabbits generating high levels of functional antibodies that blocked infection of mosquitoes. Further, the R0.6C and ProC6C drug products were found to be stable for minimally 24 months when stored at 2-8 °C, with studies ongoing through 36 months. Together, this data demonstrates the safety and suitability of the L. lactis expression system as well as supports the clinical testing of the R0.6C and ProC6C malaria vaccine candidates in First-In-Human clinical trials.

A Journey in Science: Molecular vaccines for global child health in troubled times of anti-science

My scientific life in translational medicine runs in two parallel, yet often converging paths. The first, is four-decade-long commitment to develop new vaccines for parasitic and neglected tropical diseases, as well as pandemic threats. This includes a vaccine for human hookworm infection that I began as an MD-PhD student in New York City in the 1980s, and a new low-cost COVID vaccine that reached almost 100 million people in low- and middle-income countries. Alongside this life in scientific research, is one in public engagement for vaccine and neglected disease diplomacy to ensure that people who live in extreme poverty can benefit from access to biomedical innovations. A troubling element has been the daunting task of countering rising antivaccine activism, which threatens to undermine our global vaccine ecosystem. Yet, this activity may turn out to become just as important for saving lives as developing new vaccines.

Establishing a controlled hookworm human infection (CHHI) model for Africa: A report from the stakeholders meeting held in Lambaréné, Gabon, November 10-11, 2019

BACKGROUND

Hookworm is a major contributor to worldwide disease burden with over 230 million people infected. It has been identified as one of the Neglected Tropical Diseases that can be controlled and even eliminated through mass drug administration and other effective interventions. Mathematical models have shown that hookworm can only be eliminated via a vaccine. Controlled Hookworm Human Infection (CHHI) models can facilitate rapid development of vaccines and drugs.

METHODS

As a first step towards the establishment of CHHI in Africa, we held a stakeholders meeting in Lamberene, Gabon from 10 to 11 November 2019.

RESULTS

Discussions revolved around the roles of the different regulatory institutions concerned; the need to strengthen existing regulatory capacity and the role of legislation; creating Gabon-specific ethical guidelines to govern Controlled Human Infection (CHI) studies; development of a study protocol; consideration of cultural and social peculiarities; the need for regular joint review meetings between interested parties throughout the process of protocol implementation; and participant compensation. Moreover, operational considerations concerning the introduction of CHHI in Gabon include the use of the local strain of hookworm for the challenge infections, capacity building for the local production of challenge material, and the establishment of adequate quality assurance procedures.

CONCLUSION

The workshop addressed several of the anticipated hurdles to the successful implementation of CHHI in Gabon. It is our aim that this report will stimulate interest in the implementation of this model in the sub-Saharan African setting.

Potency testing for a recombinant protein vaccine early in clinical development: Lessons from the Schistosoma mansoni Tetraspanin 2 vaccine

Introduction

As a primary stability-indicating parameter, potency should be strategically evaluated during each phase of vaccine development. Herein, we present potency testing during the early clinical development of the Schistosoma mansoni (Sm) Tetraspanin-2 vaccine formulated on Alhydrogel (Sm-TSP-2/Al). As Sm-TSP-2/Al does not induce sterilizing immunity against its target pathogen (Sm) in animal models, potency is measured by “serological substitution”, a method that can add significant variation to the potency metric, especially when used in a compliance (or ‘single data point’) approach.

Methods

Potency data were analyzed using the compliance approach to determine if two clinical lots of Sm-TSP-2/Al retained potency over 84 and 36 months post-release, respectively. These same data were also analyzed by: i) least-squares regression with a joinpoint regression analysis; ii) control charting of stability slopes; and iii) bootstrap modeling. Nested-regression and bootstrapping were used to compare the potency of the first (#11-69F-003) and second (#1975) clinical lots of Sm-TSP-2/Al.

Results

Despite significant variability in the immune assay, both clinical lots of Sm-TSP-2/Al remained potent for 84 and 36 months, respectively, in all four statistical approaches. The first lot of Sm-TSP-2/Al showed a gain in potency starting at 36 months post-release as captured by joinpoint regression. The two clinical lots of Sm-TSP-2/Al had comparable long-term potency.

Conclusion

While a compliance approach can monitor the long-term stability of Sm-TSP-2/Al, it risks putting this critical stability-indicating parameter out of specification with each time point tested due to statistical multiplicity. Alternative statistical methods, such as joinpoint regression or bootstrapping, do not have this limitation and offer even more precise estimations of potency, with the added benefit of also providing predictive analytics. Nested regression and bootstrapping were shown to be a viable alternatives for lot-to-lot comparisons of the stability of Sm-TSP-2/Al. Instructions for implementing both these potency testing approaches are provided.

Twenty-five-year research progress in hookworm excretory/secretory products

Hookworm infection is a major public health problem that threatens about 500 million people throughout tropical areas of the world. Adult hookworms survive for many years in the host intestine, where they suck blood, causing iron deficiency anemia and malnutrition. Numerous molecules, named excretory/secretory (ES) products, are secreted by hookworm adults and/or larvae to aid in parasite survival and pathobiology. Although the molecular cloning and characterization of hookworm ES products began 25 years ago, the biological role and molecular nature of many of them are still unclear. Hookworm ES products, with distinct structures and functions, have been linked to many essential events in the disease pathogenesis. These events include host invasion and tissue migration, parasite nourishment and reproduction, and immune modulation. Several of these products represent promising vaccine targets for controlling hookworm disease and therapeutic targets for many inflammatory diseases. This review aims to summarize our present knowledge about hookworm ES products, including their role in parasite biology, host-parasite interactions, and as vaccine and pharmaceutical targets and to identify research gaps and future research directions in this field.

Human hookworm infection: Is effective control possible? A review of hookworm control efforts and future directions

Human hookworm, a soil-transmitted helminth (STH) infection caused by either Necator americanus or Anclystoma duodenale, is a major cause of morbidity globally and predominantly affects the world's poorest populations. Transmitted primarily by larval invasion of exposed skin, the adults inhabit the host small intestine, where they consume host blood. The resultant chronic iron deficiency anemia can lead to stunted growth and cognitive deficits in children, reduced work capacity in adults, and a variety of pregnancy complications. Historically, successful STH elimination has only been achieved in regions with concomitant significant economic growth. Since 2001, control of the STHs has been attempted via single-dose mass deworming of at-risk school-aged and preschool-aged children within STH-endemic countries, with the goal of morbidity reduction. Research questioning this strategy has grown in recent years, and current studies are evaluating the effectiveness of novel deworming strategies, including multidrug regimens and expansion of deworming to entire communities. While footwear campaigns may be associated with reduced odds of hookworm infection, the evidence supporting the impact of water, sanitation, and hygiene (WASH) interventions upon hookworm is mixed. Progress towards a human hookworm vaccine continues, with promising results from recent Phase 1 trials and several others ongoing. Integrated STH control programs, which combine mass deworming with WASH interventions, are relatively unstudied but may be a promising advancement. Whether interruption of STH transmission can be achieved apart from significant economic growth remains unanswered, but likely the implementation of intensive, integrated control programs will be necessary to achieve that goal.

A phase 1 study of the safety, reactogenicity, and immunogenicity of a Schistosoma mansoni vaccine with or without glucopyranosyl lipid A aqueous formulation (GLA-AF) in healthy adults from a non-endemic area

BACKGROUND

Schistosomiasis caused by Schistosoma mansoni (Sm) is a chronic, debilitating and potentially deadly neglected tropical disease. The licensure of a vaccine to prevent schistosomiasis would represent a major breakthrough in public health.

METHODS

The safety and immunogenicity of a candidate Sm vaccine were assessed in this phase I, double-blind, dose-escalation trial. Seventy-two healthy Sm-naïve 18-50 year olds were randomized to receive 3 doses ∼ 8 weeks apart of saline placebo, or 10 µg, 30 µg, or 100 µg of recombinant Sm-Tetraspanin-2 vaccine formulated on aluminum hydroxide adjuvant (Sm-TSP-2/Al) with or without 5 µg of glucopyranosyl lipid A aqueous formulation (GLA-AF). Clinical and serologic responses were assessed for 1 year after dose 3.

RESULTS

Vaccines were safe and well-tolerated. The most common reactions were injection site tenderness and pain, and headache and fatigue. Tenderness and pain were more frequent in groups receiving vaccine with GLA-AF than placebo (p = 0.0036 and p = 0.0014, respectively). Injection site reactions among those given Sm-TSP-2/Al with GLA-AF lasted 1.22 and 1.33 days longer than those receiving Sm-TSP-2/Al without GLA-AF or placebo (p < 0.001 for both). Dose- and adjuvant-related increases in serum IgG against Sm-TSP-2 were observed. Peak IgG levels occurred 14 days after dose 3. Seroresponse frequencies were low among recipients of Sm-TSP-2/Al without GLA-AF, but higher among subjects receiving 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF. More seroresponses were observed among those given 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF compared to placebo (p = 0.023 and p < 0.001, respectively). Seroresponse frequencies were 0%, 30%, 50%, and 89%, respectively, among those given placebo, or 10 µg, 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF, suggesting a dose-response relationship for Sm-TSP-2/Al with GLA-AF (p = 0.0001).

CONCLUSIONS

Sm-TSP-2/Al with or without GLA-AF was safe and well tolerated in a Sm-naïve population. A vaccine like the one under development may represent our best hope to eliminating this neglected tropical disease.

A highly expressed intestinal cysteine protease of Ancylostoma ceylanicum protects vaccinated hamsters from hookworm infection

BACKGROUND

Human hookworms (Necator americanus, Ancylostoma duodenale, and Ancylostoma ceylanicum) are intestinal blood-feeding parasites that infect ~500 million people worldwide and are among the leading causes of iron-deficiency anemia in the developing world. Drugs are useful against hookworm infections, but hookworms rapidly reinfect people, and the parasites can develop drug resistance. Therefore, having a hookworm vaccine would be of tremendous benefit.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the vaccine efficacy in outbred Syrian hamsters of three A. ceylanicum hookworm antigen candidates from two classes of proteins previously identified as promising vaccine candidates. These include two intestinally-enriched, putatively secreted cathepsin B cysteine proteases (AceyCP1, AceyCPL) and one small Kunitz-type protease inhibitor (AceySKPI3). Recombinant proteins were produced in Pichia pastoris, and adsorbed to Alhydrogel. Recombinant AceyCPL (rAceyCPL)/Alhydrogel and rAceySKPI3/Alhydrogel induced high serum immunoglobulin G (IgG) titers in 8/8 vaccinates, but were not protective. rAceyCP1/Alhydrogel induced intermediate serum IgG titers in ~60% of vaccinates in two different trials. rAceyCP1 serum IgG responders had highly significantly decreased hookworm burdens, fecal egg counts and clinical pathology compared to Alhydrogel controls and nonresponders. Protection was highly correlated with rAceyCP1 serum IgG titer. Antisera from rAceyCP1 serum IgG responders, but not nonresponders or rAceyCPL/Alhydrogel vaccinates, significantly reduced adult A. ceylanicum motility in vitro. Furthermore, rAceyCP1 serum IgG responders had canonical Th2-specific recall responses (IL4, IL5, IL13) in splenocytes stimulated ex vivo.

CONCLUSIONS/SIGNIFICANCE

These findings indicate that rAceyCP1 is a promising vaccine candidate and validates a genomic/transcriptomic approach to human hookworm vaccine discovery.

Lessons along the Critical Path: Developing Vaccines against Human Helminths

Helminthic parasites are important targets for vaccine research as they infect an estimated 1 billion people worldwide. Despite significant progress in the discovery of defined antigens as candidates for vaccines, the potential of a helminth vaccine advancing to an investigational product to be tested in humans remains as challenging as it did 50 years ago. Candidate helminth vaccines must still advance along a 'critical path' of preclinical research, vaccine process development (which includes 'chemistry, manufacturing, and controls' or CMC), current good manufacturing practice (cGMP) production of the vaccine, and clinical trials. This path is highly targeted towards meeting the safety, immunogenicity, and efficacy criteria of regulatory bodies such as the US Food and Drug Administration (FDA). For nearly 20 years our product development partnership (PDP), the Texas Children's Hospital Center for Vaccine Development (TCH-CVD), has followed the critical paths of several novel subunit vaccines for the human hookworm Necator americanus and the intestinal trematode Schistosoma mansoni. Herein, we describe the critical lessons learned along this critical path.

Advances in neglected tropical disease vaccines: Developing relative potency and functional assays for the Na-GST-1/Alhydrogel hookworm vaccine

A new generation of vaccines for the neglected tropical diseases (NTDs) have now advanced into clinical development, with the Na-GST-1/Alhydrogel Hookworm Vaccine already being tested in Phase 1 studies in healthy adults. The current manuscript focuses on the often overlooked critical aspects of NTD vaccine product development, more specifically, vaccine stability testing programs. A key measure of vaccine stability testing is "relative potency" or the immunogenicity of the vaccine during storage. As with most NTD vaccines, the Na-GST-1/Alhydrogel Hookworm Vaccine was not developed by attenuation or inactivation of the pathogen (Necator americanus), so conventional methods for measuring relative potency are not relevant for this investigational product. Herein, we describe a novel relative potency testing program and report for the first time on the clinical lot of this NTD vaccine during its first 60 months of storage at 2–8°C. We also describe the development of a complementary functional assay that measures the ability of IgG from animals or humans immunized with Na-GST-1/Alhydrogel to neutralize this important hookworm enzyme. While 90% inhibition of the catalytic activity of Na-GST-1 was achieved in animals immunized with Na-GST-1/Alhydrogel, lower levels of inhibition were observed in immunized humans. Moreover, anti-Na-GST-1 antibodies from volunteers in non-hookworm endemic areas were better able to inhibit catalytic activity than anti-Na-GST-1 antibodies from volunteers resident in hookworm endemic areas. The results described herein provide the critical tools for the product development of NTD vaccines.

As vaccines targeting NTDs advance into clinical trials, product development and vaccine maintenance become critical activities for the success of these vaccines. A key activity during this phase of vaccine development is the “relative potency” of a vaccine or the quality of the immune response that the vaccine elicits in an animal model during storage to ensure its immunogenicity is maintained. As with most NTD vaccines, the Na-GST-1/Alhydrogel Hookworm Vaccine was not developed using traditional methods of attenuating the pathogen (Necator americanus), so traditional measures of relative potency, such as testing the vaccine’s ability to protect against lethal challenge, could not be used. For the first time, we describe the development of a relative potency testing program for an NTD vaccine during five years of storage at 2–8°C. We also describe the development of a complementary functional assay that measures the ability of IgG from animals or humans immunized with Na-GST-1/Alhydrogel to neutralize this important hookworm enzyme. The results described herein provide, for the first time in an open access format, critical tools for the development of future NTD vaccines.