A scalable method for biochemical purification of Salmonella flagellin.

Flagellins are the main structural proteins of bacterial flagella and potent stimulators of innate and adaptive immunity in mammals. The flagellins of Salmonella are virulence factors and protective antigens, and form the basis of promising vaccines. Despite broad interest in flagellins as antigens and adjuvants in vaccine formulations, there have been few advances towards the development of scalable and economical purification methods for these proteins. We report here a simple and robust strategy to purify flagellin monomers from the supernatants of liquid growth culture. Phase 1 flagellins from Salmonella enterica serovars Typhimurium (i epitope) and Enteritidis (g,m epitopes) were purified directly from conditioned fermentation growth media using sequential cation- and anion-exchange chromatography coupled with a final tangential flow-filtration step. Conventional porous chromatography resin was markedly less efficient than membrane chromatography for flagellin purification. Recovery after each process step was robust, with endotoxin, nucleic acid and residual host-cell protein effectively removed. The final yield was 200-300 mg/L fermentation culture supernatant, with ∼45-50% overall recovery. A final pH 2 treatment step was instituted to ensure uniformity of flagellin in the monomeric form. Flagellins purified by this method were recognized by monoclonal anti-flagellin antibodies and maintained capacity to activate Toll-like Receptor 5. The process described is simple, readily scalable, uses standard bioprocess methods, and requires only a few steps to obtain highly purified material.

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.

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.

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.

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.

Molecular cloning, biochemical characterization, and partial protective immunity of the heme-binding glutathione S-transferases from the human hookworm Necator americanus.

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.

Crystallization and preliminary X-ray analysis of Na-SAA-2 from the human hookworm parasite Necator americanus.

Human hookworms are among the most pathogenic soil-transmitted helminths. These parasitic nematodes have co-evolved with the host and are able to maintain a high worm burden for decades without killing the human host. However, it is possible to develop vaccines against laboratory-challenge hookworm infections using either irradiated third-state infective larvae (L3) or enzymes from the adult parasites. In an effort to control hookworm infection globally, the Human Hookworm Vaccine Initiative, a product-development partnership with the Sabin Vaccine Institute to develop new control tools including vaccines, has identified a battery of protein antigens, including surface-associated antigens (SAAs) from L3. SAA proteins are characterized by a 13 kDa conserved domain of unknown function. SAA proteins are found on the surface of infective L3 stages (and some adult stages) of different nematode parasites, suggesting that they may play important roles in these organisms. The atomic structures and function of SAA proteins remain undetermined and in an effort to remedy this situation recombinant Na-SAA-2 from the most prevalent human hookworm parasite Necator americanus has been expressed, purified and crystallized. Useful X-ray data have been collected to 2.3 A resolution from a crystal that belonged to the monoclinic space group C2 with unit-cell parameters a = 73.88, b = 35.58, c = 42.75 A, beta = 116.1 degrees .

The evaluation of recombinant hookworm antigens as vaccines in hamsters (Mesocricetus auratus) challenged with human hookworm, Necator americanus.

We have previously reported the successful adaptation of human hookworm Necator americanus in the golden hamster, Mesocricetus auratus. This animal model was used to test a battery of hookworm (N. americanus and Ancylostoma caninum) recombinant antigens as potential vaccine antigens. Hamsters immunized a leading vaccine candidate N. americanus-Ancylostoma secreted protein 2 (Na-ASP-2) and challenged with N. americanus infective larvae (L3), resulted in 30-46.2% worm reduction over the course of three vaccine trials, relative to adjuvant controls. In addition, significant reduction of worm burdens was also observed in the hamsters immunized with adult hookworm antigens A. caninum aspartic protease 1 (Ac-APR-1); A. caninum-glutathione-S transferase 1 (Ac-GST-1) and Necator cysteine proteases 2 (Na-CP-2) (44.4%, 50.6%, and 29.3%, respectively). Our data on the worm burden reductions afforded by these hookworm antigens approximate the level of protection reported previously from dogs challenged with A. caninum L3, and provide additional evidence to support these hookworm antigens as vaccine candidates for human hookworm infection. The hamster model of N. americanus provides useful information for the selection of antigens to be tested in downstream vaccine development.

X-ray structures of Na-GST-1 and Na-GST-2 two glutathione S-transferase from the human hookworm Necator americanus.

BACKGROUND: Human hookworm infection is a major cause of anemia and malnutrition of adults and children in the developing world. As part of on-going efforts to control hookworm infection, The Human Hookworm Vaccine Initiative has identified candidate vaccine antigens from the infective L3 larval stages and adult stages of the parasite. Adult stage antigens include the cytosolic glutathione-S-transferases (GSTs). Nematode GSTs facilitate the inactivation and degradation of a variety of electrophilic substrates (drugs) via the nucleophilic addition of reduced glutathione. Parasite GSTs also play significant roles in multi-drug resistance and the modulation of host-immune defense mechanisms. RESULTS: The crystal structures of Na-GST-1 and Na-GST-2, two major GSTs from Necator americanus the main human hookworm parasite, have been solved at the resolution limits of 2.4 A and 1.9 A respectively. The structure of Na-GST-1 was refined to R-factor 18.9% (R-free 28.3%) while that of Na-GST-2 was refined to R-factor 17.1% (R-free 21.7%). Glutathione usurped during the fermentation process in bound in the glutathione binding site (G-site) of each monomer of Na-GST-2. Na-GST-1 is uncomplexed and its G-site is abrogated by Gln 50. These first structures of human hookworm parasite GSTs could aid the design of novel hookworm drugs. CONCLUSION: The 3-dimensional structures of Na-GST-1 and Na-GST-2 show two views of human hookworm GSTs. While the GST-complex structure of Na-GST-2 reveals a typical GST G-site that of Na-GST-1 suggests that there is some conformational flexibility required in order to bind the substrate GST. In addition, the overall binding cavities for both are larger, more open, as well as more accessible to diverse ligands than those of GSTs from organisms that have other major detoxifying mechanisms. The results from this study could aid in the design of novel drugs and vaccine antigens.

Ancylostoma caninum MTP-1, an astacin-like metalloprotease secreted by infective hookworm larvae, is involved in tissue migration.

Infective larvae (L3) of nematodes secrete macromolecules that are critical to infection and establishment of the parasite in the host. The dog hookworm Ancylostoma caninum secretes an astacin-like metalloprotease, Ac-MTP-1, upon activation in vitro with host serum. Recombinant Ac-MTP-1 was expressed in the baculovirus/insect cell system as a secreted protein and was purified from culture medium by two separate methods, cation-exchange fast-performance liquid chromatography and gelatin-affinity chromatography. Recombinant MTP-1 was catalytically active and digested a range of native and denatured connective tissue substrates, including gelatin, collagen, laminin, and fibronectin. A dog was immunized with recombinant Ac-MTP-1 formulated with AS03 adjuvant, and the antiserum was used to immunolocalize the anatomic sites of expression within A. caninum L3 to secretory granules in the glandular esophagus and the channels that connect the esophagus to the L3 surface and to the cuticle. Antiserum inhibited the ability of recombinant MTP-1 to digest collagen by 85% and inhibited larval migration through tissue in vitro by 70 to 75%, in contrast to just 5 to 10% inhibition obtained with preimmunization serum. The metalloprotease inhibitors EDTA and 1,10-phenanthroline also reduced the penetration of L3 through skin in vitro by 43 to 61%. The data strongly suggest that Ac-MTP-1 is critical for the invasion process of hookworm larvae, and moreover, that antibodies against the enzyme can neutralize its function and inhibit migration.

Expression of the Necator americanus hookworm larval antigen Na-ASP-2 in Pichia pastoris and purification of the recombinant protein for use in human clinical trials.

The ASP-2 protein secreted by infective larvae of the human hookworm, Necator americanus, is under development as a recombinant vaccine. Recombinant Na-ASP-2 was expressed in Pichia pastoris, and the purified protein was characterized. At the 60 L scale, the 21.3 kDa recombinant protein was produced at a yield of 0.4 g/L. When formulated with Alhydrogel and injected into rats to determine immunological potency, three 50 microg doses of the formulated recombinant protein elicited geometric mean antibody titers up to 1:234,881. Rat anti-Na-ASP-2 antibody recognized larval-derived ASP-2 and also inhibited larval migration through skin in vitro. The processes developed and tested for the high yield production of recombinant Na-ASP-2 provide a foundation for clinical vaccine development.

Effect of combining the larval antigens Ancylostoma secreted protein 2 (ASP-2) and metalloprotease 1 (MTP-1) in protecting hamsters against hookworm infection and disease caused by Ancylostoma ceylanicum.

Syrian Golden hamsters were vaccinated with the recombinant fusion proteins Ay-ASP-2 and Ay-MTP-1 from the infective larvae of the hookworm Ancylostoma ceylanicum. Vaccines comprised each antigen alone or the combination of the two proteins. All vaccinated group developed high antibody titers (>1:40,000); coadministration of a second antigen did not significantly affect the magnitude of the antibody response. Following challenge, hamsters vaccinated with each single antigen exhibited reductions in worm burden (32% and 28% to Ay-ASP-2 and Ay-MTP-1, respectively) and fecal egg counts (56% and 43%, respectively). A vaccine cocktail, containing both antigens further reduced worm burden (36%) and fecal egg counts (59%) (p<0.001). Moreover, vaccination with the antigen cocktail significantly improved hemoglobin values (p=0.01) and body weights (p=0.001) compared to what achieved with either each antigen or adjuvant alone. Taken together, these data suggest that combination of two or more antigens may present an effective vaccine development strategy to improve protection and/or disease symptoms in affected individuals.

X-ray structure of Na-ASP-2, a pathogenesis-related-1 protein from the nematode parasite, Necator americanus, and a vaccine antigen for human hookworm infection.

Human hookworm infection is a major cause of anemia and malnutrition of adults and children in the developing world. As part of on-going efforts to control hookworm infection, The Human Hookworm Vaccine Initiative has identified candidate vaccine antigens from the infective L3 larval stages of the parasite, including a family of pathogenesis-related (PR) proteins known as the Ancylostoma-secreted proteins (ASPs). A novel crystal structure of Na-ASP-2, a PR-1 protein secreted by infective larvae of the human hookworm Necator americanus, has been solved to resolution limits of 1.68 A and to an R-factor of 17% using the recombinant protein expressed in and secreted by Pichia pastoris. The overall fold of Na-ASP-2 is a three-layer alphabetaalpha sandwich flanked by an N-terminal loop and a short, cysteine-rich C terminus. Our structure reveals a large central cavity that is flanked by His129 and Glu106, two residues that are well conserved in all parasitic nematode L3 ASPs. Na-ASP-2 has structural and charge similarities to chemokines, which suggests that Na-ASP-2 may be an extra-cellular ligand of an unknown receptor. Na-ASP-2 is a useful homology model for NIF, a natural antagonistic ligand of CR3 receptor. From these modeling studies, possible binding modes were predicted. In addition, this first structure of a PR-1 protein from parasitic helminths may shed light on the molecular basis of host-parasite interactions.

Cloning, yeast expression, isolation, and vaccine testing of recombinant Ancylostoma-secreted protein (ASP)-1 and ASP-2 from Ancylostoma ceylanicum.

cDNAs encoding 2 Ancylostoma-secreted proteins (ASPs), Ancylostoma ceylanicum (Ay)-ASP-1 and Ay-ASP-2, were cloned from infective third-stage larvae (L3) of the hookworm A. ceylanicum and were expressed as soluble recombinant fusion proteins secreted by the yeast Pichia pastoris. The recombinant fusion proteins were purified, adjuvant formulated, and injected intramuscularly into hamsters. Hamsters vaccinated either by oral vaccination with irradiated L3 (irL3) or by injections of the adjuvants alone served as positive and negative controls, respectively. Anti-ASP-1 and anti-ASP-2 antibody titers exceeded 1 : 100000. Each vaccinated hamster was challenged orally with 100 L3. Two groups of vaccinated hamsters (i.e., those vaccinated with either irL3 or ASP-2 formulated with Quil A) exhibited significant reductions in adult hookworm burdens, compared with control hamsters. The hookworms recovered from the hamsters vaccinated with ASP-2 plus Quil A were reduced in length. Splenomegaly, which was observed in control hamsters, was not seen in hamsters vaccinated with either irL3 or ASP-2 formulated with Quil A. These results indicate that ASP-2 is a promising molecule for the development of a hookworm vaccine.