Portia Gillespie

New vaccines for neglected parasitic diseases and dengue

Neglected tropical diseases (NTDs) are a significant source of morbidity and socioeconomic burden among the worlds poor. Virtually all of the 2.4 billion people who live on less than

Molecular Cloning, Biochemical Characterization, and Partial Protective Immunity of the Heme-Binding Glutathione S-Transferases from the Human Hookworm Necator americanus

2 per d, more than a third of the worlds population, are at risk for these debilitating NTDs. Although chemotherapeutic measures exist for many of these pathogens, they are not sustainable countermeasures on their own because of rates of reinfection, risk of drug resistance, and inconsistent maintenance of drug treatment programs. Preventative and therapeutic NTD vaccines are needed as long-term solutions. Because there is no market in the for-profit sector of vaccine development for these pathogens, much of the effort to develop vaccines is driven by nonprofit entities, mostly through product development partnerships. This review describes the progress of vaccines under development for many of the NTDs, with a specific focus on those about to enter or that are currently in human clinical trials. Specifically, we report on the progress on dengue, hookworm, leishmaniasis, schistosomiasis, Chagas disease, and onchocerciasis vaccines. These products will be some of the first with specific objectives to aid the worlds poorest populations.

Status of vaccine research and development of vaccines for leishmaniasis.

ABSTRACT Hookworm glutathione S-transferases (GSTs) are critical for parasite blood feeding and survival and represent potential targets for vaccination. Three cDNAs, each encoding a full-length GST protein from the human hookworm Necator americanus (and designated Na-GST-1, Na-GST-2, and Na-GST-3, respectively) were isolated from cDNA based on their sequence similarity to Ac-GST-1, a GST from the dog hookworm Ancylostoma caninum. The open reading frames of the three N. americanus GSTs each contain 206 amino acids with 51% to 69% sequence identity between each other and Ac-GST-1. Sequence alignment with GSTs from other organisms shows that the three Na-GSTs belong to a nematode-specific nu-class GST family. All three Na-GSTs, when expressed in Pichia pastoris, exhibited low lipid peroxidase and glutathione-conjugating enzymatic activities but high heme-binding capacities, and they may be involved in the detoxification and/or transport of heme. In two separate vaccine trials, recombinant Na-GST-1 formulated with Alhydrogel elicited 32 and 39% reductions in adult hookworm burdens (P < 0.05) following N. americanus larval challenge relative to the results for a group immunized with Alhydrogel alone. In contrast, no protection was observed in vaccine trials with Na-GST-2 or Na-GST-3. On the basis of these and other preclinical data, Na-GST-1 is under possible consideration for further vaccine development.

Expression, immunogenicity, histopathology, and potency of a mosquito-based malaria transmission-blocking recombinant vaccine

A number of leishmaniasis vaccine candidates are at various stages of pre-clinical and clinical development. Leishmaniasis is a vector-borne neglected tropical disease (NTD) caused by a protozoan parasite of the genus Leishmania and transmitted to humans by the bite of a sand fly. Visceral leishmaniasis (VL, kala-azar) is a high mortality NTD found mostly in South Asia and East Africa, while cutaneous leishmaniasis (CL) is a disfiguring NTD highly endemic in the Middle East, Central Asia, North Africa, and the Americas. Estimates attribute 50,000 annual deaths and 3.3 million disability-adjusted life years to leishmaniasis. There are only a few approved drug treatments, no prophylactic drug and no vaccine. Ideally, an effective vaccine against leishmaniasis will elicit long-lasting immunity and protect broadly against VL and CL. Vaccines such as Leish-F1, F2 and F3, developed at IDRI and designed based on selected Leishmania antigen epitopes, have been in clinical trials. Other groups, including the Sabin Vaccine Institute in collaboration with the National Institutes of Health are investigating recombinant Leishmania antigens in combination with selected sand fly salivary gland antigens in order to augment host immunity. To date, both VL and CL vaccines have been shown to be cost-effective in economic modeling studies.

Expression, purification, and molecular analysis of the Necator americanus glutathione S-transferase 1 (Na-GST-1): A production process developed for a lead candidate recombinant hookworm vaccine antigen

ABSTRACT Vaccines have been at the forefront of global research efforts to combat malaria, yet despite several vaccine candidates, this goal has yet to be realized. A potentially effective approach to disrupting the spread of malaria is the use of transmission-blocking vaccines (TBV), which prevent the development of malarial parasites within their mosquito vector, thereby abrogating the cascade of secondary infections in humans. Since malaria is transmitted to human hosts by the bite of an obligate insect vector, mosquito species in the genus Anopheles, targeting mosquito midgut antigens that serve as ligands for Plasmodium parasites represents a promising approach to breaking the transmission cycle. The midgut-specific anopheline alanyl aminopeptidase N (AnAPN1) is highly conserved across Anopheles vectors and is a putative ligand for Plasmodium ookinete invasion. We have developed a scalable, high-yield Escherichia coli expression and purification platform for the recombinant AnAPN1 TBV antigen and report on its marked vaccine potency and immunogenicity, its capacity for eliciting transmission-blocking antibodies, and its apparent lack of immunization-associated histopathologies in a small-animal model.

Expression at a 20L scale and purification of the extracellular domain of the Schistosoma mansoni TSP-2 recombinant protein: A vaccine candidate for human intestinal schistosomiasis

The enzyme Necator americanus glutathione S-transferase 1 (Na-GST-1) belongs to a unique Nu class of GSTs and is a lead candidate antigen in a bivalent human hookworm vaccine. Here we describe the expression of Na-GST-1 in the yeast Pichia pastoris at the 20 L manufacturing scale and its purification process performed by three chromatographic steps, comprised of a Q Sepharose XL anion exchange column, followed by a Butyl Sepharose HP hydrophobic affinity column and a Superdex 75 size-exclusion column. Approximately 1.5 g of recombinant protein was recovered at an overall process yield of 51%, with a purity grade of 98% and the absence of detectable host cell protein. By mass spectrometry the recombinant protein exhibits a mass of 23,676Da, which closely matches the predicted molecular mass of the protein. The expression and purification methods described here are suitable for further scale-up product development and for its use to design formulation processes suitable to generate a vaccine for clinical testing.

Status of vaccine research and development of vaccines for Chagas disease.

A novel recombinant protein vaccine for human schistosomiasis caused by Schistosoma mansoni is under development. The Sm-TSP-2 schistosomiasis vaccine is comprised of a 9 kDa recombinant protein corresponding to the extracellular domain of a unique S. mansoni tetraspanin. Here, we describe the cloning and the expression of the external loop of Sm-TSP-2 recombinant protein secreted by Pichia Pink™ the process development at 20L scale fermentation, and the two-steps purification, which resulted in a protein recovery yield of 31% and a protein purity of 97%. The developed processes are suitable for the production of purified protein for subsequent formulation and Phase 1 clinical studies.

Advancing a vaccine to prevent hookworm disease and anemia.

National School of Tropical Medicine, Baylor College of Medicine, Houston, TX, USA Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA Sabin Vaccine Institute and Texas Children’s Hospital Center for Vaccine Development, Houston, TX, USA Sabin Vaccine Institute, Washington, DC, USA Department of Biology, Baylor University, Waco, TX, USA Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA

Fusion of Na‐ASP‐2 with human immunoglobulin Fcγ abrogates histamine release from basophils sensitized with anti‐Na‐ASP‐2 IgE

A human hookworm vaccine is under development and in clinical trials in Africa and the Americas. The vaccine contains the Na-APR-1 and Na-GST-1 antigens. It elicits neutralizing antibodies that interfere with establishment of the adult hookworm in the gut and the ability of the parasite to feed on blood. The vaccine target product profile is focused on the immunization of children to prevent hookworm infection and anemia caused by Necator americanus. It is intended for use in low- and middle-income countries where hookworm is highly endemic and responsible for at least three million disability-adjusted life years. So far, the human hookworm vaccine is being developed in the non-profit sector through the Sabin Vaccine Institute Product Development Partnership (PDP), in collaboration with the HOOKVAC consortium of European and African partners. We envision the vaccine to be incorporated into health systems as part of an elimination strategy for hookworm infection and other neglected tropical diseases, and as a means to reduce global poverty and address the Sustainable Development Goals.

Ac-AP-12, a novel factor Xa anticoagulant peptide from the esophageal glands of adult Ancylostoma caninum ☆

Na‐ASP‐2 is a major protein secreted by infective third‐stage larvae (L3) of the human hookworm Necator americanus upon host entry. It was chosen as a lead vaccine candidate for its ability to elicit protective immune responses. However, clinical development of this antigen as a recombinant vaccine was halted because it caused allergic reactions among some of human volunteers previously infected with N. americanus. To prevent IgE‐mediated allergic reactions induced by Na‐ASP‐2 but keep its immunogenicity as a vaccine antigen, we designed and tested a genetically engineered fusion protein, Fcγ/Na‐ASP‐2, composed of full‐length Na‐ASP‐2 and truncated human IgG Fcγ1 that targets the negative signalling receptor FcγRIIb expressed on pro‐allergic cells. The chimeric recombinant Fcγ/Na‐ASP‐2 protein was expressed in Pichia pastoris and shared the similar antigenicity as native Na‐ASP‐2. Compared to Na‐ASP‐2, the chimeric fusion protein efficiently reduced the release of histamine in human basophils sensitized with anti‐Na‐ASP‐2 IgE obtained from individuals living in a hookworm‐endemic area. In dogs infected with canine hookworm, Fcγ/Na‐ASP‐2 resulted in significantly reduced immediate‐type skin reactivity when injected intradermally compared with Na‐ASP‐2. Hamsters vaccinated with Fcγ/Na‐ASP‐2 formulated with Alhydrogel® produced specific IgG that recognized Na‐ASP‐2 and elicited similar protection level against N. americanus L3 challenge as native Na‐ASP‐2.