Adjuvant-enhanced antibody and cellular responses to inclusion bodies expressing FhSAP2 correlates with protection of mice to Fasciola hepatica

Protein purification strategies must consider downstream applications and individual biological characteristics

BACKGROUND

Proteins are used as reagents in a broad range of scientific fields. The reliability and reproducibility of experimental data will largely depend on the quality of the (recombinant) proteins and, consequently, these should undergo thorough structural and functional controls. Depending on the downstream application and the biochemical characteristics of the protein, different sets of specific features will need to be checked.

RESULTS

A number of examples, representative of recurrent issues and previously published strategies, has been reported that illustrate real cases of recombinant protein production in which careful strategy design at the start of the project combined with quality controls throughout the production process was imperative to obtain high-quality samples compatible with the planned downstream applications. Some proteins possess intrinsic properties (e.g., prone to aggregation, rich in cysteines, or a high affinity for nucleic acids) that require certain precautions during the expression and purification process. For other proteins, the downstream application might demand specific conditions, such as for proteins intended for animal use that need to be endotoxin-free.

CONCLUSIONS

This review has been designed to act as a practical reference list for researchers who wish to produce and evaluate recombinant proteins with certain specific requirements or that need particular care for their preparation and storage.

Intranasal vaccination with protein bodies elicit strong protection against Streptococcus pneumoniae colonization

Protein bodies (PBs) are particles consisting of insoluble, aggregated proteins with potential as a vaccine formulation. PBs can contain high concentrations of antigen, are stable and relatively resistant to proteases, release antigen slowly and are cost-effective to manufacture. Yet, the capacity of PBs to provoke immune responses and protection in the upper respiratory tract, a major entry route of respiratory pathogens, is largely unknown. In this study, we vaccinated mice intranasally with PBs comprising antigens from Streptococcus pneumoniae and evaluated the level of protection against nasopharyngeal colonization. PBs composed of the α-helical domain of pneumococcal surface protein A (PspAα) provided superior protection against colonization with S. pneumoniae compared to soluble PspAα. Immunization with soluble protein or PBs induced differences in antibody binding to pneumococci as well as a highly distinct antigen-specific nasal cytokine profile upon in vivo stimulation with inactivated S. pneumoniae. Moreover, immunization with PBs composed of conserved putative pneumococcal antigens reduced colonization by S. pneumoniae in mice, both as a single- and as a multi-antigen formulation. In conclusion, PBs represent a vaccine formulation that elicits strong mucosal immune responses and protection. The versatility of this platform offers opportunities for development of next-generation vaccine formulations.

Prospects for liver fluke vaccines

Fasciola spp., Opisthorchis spp. and Clonorchis sinensis are common liver flukes that can cause a variety of diseases, mainly cholangiocarcinoma induced by clonorchiasis and liver damage and associated pathology induced by fascioliasis. Because these trematodes are parasites of humans and domestic animals, they have greatly affected the economy of agricultural industries and public health worldwide. Due to the emergence of drug resistance and the living habits of flukes, among other reasons, a possibility of reinfection remains even when antiparasitic drugs are used. Therefore, developing a safe, efficient and cost-effective vaccine against trematodes is an important goal. Here, we briefly describe the progress in the development of vaccines against liver flukes. Related innovations may provide effective protection against these helminths and the diseases that they cause.

Promising Technologies in the Field of Helminth Vaccines

Helminths contribute a larger global burden of disease than both malaria and tuberculosis. These eukaryotes have caused human infections since before our earliest recorded history (i.e.: earlier than 1200 B.C. for Schistosoma spp.). Despite the prevalence and importance of these infections, helminths are considered a neglected tropical disease for which there are no vaccines approved for human use. Similar to other parasites, helminths are complex organisms which employ a plethora of features such as: complex life cycles, chronic infections, and antigenic mimicry to name a few, making them difficult to target by conventional vaccine strategies. With novel vaccine strategies such as viral vectors and genetic elements, numerous constructs are being defined for a wide range of helminth parasites; however, it has yet to be discussed which of these approaches may be the most effective. With human trials being conducted, and a pipeline of potential anti-helminthic antigens, greater understanding of helminth vaccine-induced immunity is necessary for the development of potent vaccine platforms and their optimal design. This review outlines the conventional and the most promising approaches in clinical and preclinical helminth vaccinology.

Immunomics-Guided Antigen Discovery for Praziquantel-Induced Vaccination in Urogenital Human Schistosomiasis

Despite the enormous morbidity attributed to schistosomiasis, there is still no vaccine to combat the disease for the hundreds of millions of infected people. The anthelmintic drug, praziquantel, is the mainstay treatment option, although its molecular mechanism of action remains poorly defined. Praziquantel treatment damages the outermost surface of the parasite, the tegument, liberating surface antigens from dying worms that invoke a robust immune response which in some subjects results in immunologic resistance to reinfection. Herein we term this phenomenon Drug-Induced Vaccination (DIV). To identify the antigenic targets of DIV antibodies in urogenital schistosomiasis, we constructed a recombinant proteome array consisting of approximately 1,000 proteins informed by various secretome datasets including validated proteomes and bioinformatic predictions. Arrays were screened with sera from human subjects treated with praziquantel and shown 18 months later to be either reinfected (chronically infected subjects, CI) or resistant to reinfection (DIV). IgG responses to numerous antigens were significantly elevated in DIV compared to CI subjects, and indeed IgG responses to some antigens were completely undetectable in CI subjects but robustly recognized by DIV subjects. One antigen in particular, a cystatin cysteine protease inhibitor stood out as a unique target of DIV IgG, so recombinant cystatin was produced, and its vaccine efficacy assessed in a heterologous Schistosoma mansoni mouse challenge model. While there was no significant impact of vaccination with adjuvanted cystatin on adult worm numbers, highly significant reductions in liver egg burdens (45-55%, P<0.0001) and intestinal egg burdens (50-54%, P<0.0003) were achieved in mice vaccinated with cystatin in two independent trials. This study has revealed numerous antigens that are targets of DIV antibodies in urogenital schistosomiasis and offer promise as subunit vaccine targets for a drug-linked vaccination approach to controlling schistosomiasis.

Als3-Th-cell-epitopes plus the novel combined adjuvants of CpG, MDP, and FIA synergistically enhanced the immune response of recombinant TRAP derived from Staphylococcus aureus in mice

INTRODUCTION

Staphylococcus aureus (S. aureus) is a gram-positive opportunistic pathogen, there are currently no high effective vaccine against S. aureus in humans and animals, the development of an efficient vaccine remains an important challenge to prevent S. aureus infection. Here, we prepared Als3-Th-cell-epitope-Target of RNAIII Activating Protein (TRAP) (ATT) proteins plus the novel combined adjuvants to develop a promising vaccine candidate against S. aureus.

METHODS

The recombinant pET-28a (+)-att plasmids were constructed, and the ATT proteins were expressed and obtained, then, ATT plus Freund's adjuvant or the novel combined adjuvants of cytosine-phosphate-guanosine oligodeoxynucleotides (CpG), muramyl dipeptides (MDP), and FIA were immunized in mice. After booster immunization, the levels of interferon-γ (IFN-γ), interleukin-4 (IL-4), IL-10 and IL-17A cytokine were evaluated, the humoral immune responses against TRAP were detected in mice, and the survival rate of mice was confirmed by challenge assay.

RESULTS

The mice immunized with ATT plus Freund's adjuvant exhibited significantly higher level of IFN-γ, IL-4, IL-10, and IL-17A, and displayed the stronger humoral immune response against TRAP than control groups, importantly, the survival rate of these mice was significantly higher than control groups. In addition, compared with the control groups, ATT + CpG + MDP + FIA group was elicited significantly higher level of IFN-γ, IL-4, IL-10, and IL-17A and was triggered the stronger humoral immune responses against TRAP, moreover, generated the higher survival rate of mice.

CONCLUSION

Als3 epitopes significantly enhanced TRAP immunogenicity. ATT plus the novel combined adjuvants of CpG, MDP, and FIA induced the strong immune response and protection against S. aureus, revealing the combination of CpG, MDP, and FIA adjuvant acts the synergistic effect.

Efficacy of a multivalent vaccine against Fasciola hepatica infection in sheep

In this work we report the protection found in a vaccination trial performed in sheep with two different vaccines composed each one by a cocktail of antigens (rCL1, rPrx, rHDM and rLAP) formulated in two different adjuvants (Montanide ISA 61 VG (G1) and Alhydrogel®(G2)). The parameters of protection tested were fluke burden, faecal egg count and evaluation of hepatic lesions. In vaccinated group 1 we found a significant decrease in fluke burden in comparison to both unimmunised and infected control group (37.2%; p = 0.002) and to vaccinated group 2 (Alhydrogel®) (27.08%; p = 0.016). The lower fluke burden found in G1 was accompanied by a decrease in egg output of 28.71% in comparison with the infected control group. Additionally, gross hepatic lesions found in vaccine 1 group showed a significant decrease (p = 0.03) in comparison with unimmunised-infected group. The serological study showed the highest level for both IgG1 and IgG2 in animals from group 1. All these data support the hypothesis of protection found in vaccine 1 group.

Moderate protection is induced by a chimeric protein composed of leucine aminopeptidase and cathepsin L1 against Fasciola hepatica challenge in sheep

Leucine aminopeptidase (FhLAP) and cathepsin L1 (FhCL1) of Fasciola hepatica play a critical role in parasite feeding, migration through host tissue, and immune evasion. These antigens have been tested for immune protection as single components with variable degrees of success. The chimeric-protein approach could improve protection levels against fasciolosis. Previously, we reported the design and construction of a chimeric protein composed of antigenic sequences of FhLAP and FhCL1 of F. hepatica. The goal of the present study was to express and evaluate the immune-protective capacity of this chimeric protein (rFhLAP-CL1) in sheep. Animals were randomly allocated into five groups with five animals in each group. Groups 1, 2 and 3 were immunized twice with 100 μg, 200 μg and 400 μg of rFhLAP-CL1 emulsified with Quil A adjuvant, whereas groups 4 and 5 were the adjuvant control and infection control groups, respectively. The animals were then challenged with 200 metacercariae two weeks after the rFhLAP-CL1 booster. The fluke burden was reduced by 25.5%, 30.7% (p < 0.05) and 46.5% (p < 0.01) in sheep immunized with 100 μg, 200 μg and 400 μg of chimeric protein, respectively, in comparison to the infection control group. There was a reduction of 22.7% (p < 0.05) and 24.4% (p < 0.01) in fecal egg count in groups 2 and 3, respectively, compared to the infection control group. Sheep immunized with chimeric protein produced F. hepatica excretion-secretion product-specific total IgG antibody, which were increased after challenge. Moreover, the levels of rFhLAP-CL1-specific IgG1 and IgG2 isotypes in immunized sheep increased rapidly two weeks after the first immunization and were significantly more elevated than those of the control groups, indicating a mixed Th1/Th2 response. This is a preliminary evaluation of the chimeric protein rFhLAP-CL1 as a possible immunogen against F. hepatica infection in sheep.

Saponins from Quillaja saponaria and Quillaja brasiliensis: Particular Chemical Characteristics and Biological Activities

Quillaja saponaria Molina represents the main source of saponins for industrial applications. Q. saponaria triterpenoids have been studied for more than four decades and their relevance is due to their biological activities, especially as a vaccine adjuvant and immunostimulant, which have led to important research in the field of vaccine development. These saponins, alone or incorporated into immunostimulating complexes (ISCOMs), are able to modulate immunity by increasing antigen uptake, stimulating cytotoxic T lymphocyte production (Th1) and cytokines (Th2) in response to different antigens. Furthermore, antiviral, antifungal, antibacterial, antiparasitic, and antitumor activities are also reported as important biological properties of Quillaja triterpenoids. Recently, other saponins from Q. brasiliensis (A. St.-Hill. & Tul.) Mart. were successfully tested and showed similar chemical and biological properties to those of Q. saponaria barks. The aim of this manuscript is to summarize the current advances in phytochemical and pharmacological knowledge of saponins from Quillaja plants, including the particular chemical characteristics of these triterpenoids. The potential applications of Quillaja saponins to stimulate further drug discovery research will be provided.

Cell-free expression, purification and immunoreactivity assessment of recombinant Fasciola hepatica saposin-like protein-2

Cell free protein synthesis has become a powerful method for the high-throughput production of proteins that are difficult to express in living cells. The protein SAP2 of Fasciola hepatica (FhSAP2), which has demonstrated to be both, an excellent vaccine candidate against experimental fascioliasis and a good antigen for serodiagnosis of human chronic fascioliasis, is a typical example of a molecule that is difficult to produce. This is mainly due to its tendency to get over-expressed in inclusion bodies by prokaryotes. FhSAP2 expressed in an Escherichia coli-based expression system is poorly glycosylated, insoluble and often undergoes improper folding leading it to reduced immunogenicity. In this work, FhSAP2 was expressed in vitro using the eukaryote cell free system, TNT T7 Quick coupled transcription/translation, that has been designed for the expression of PCR-generated DNA templates. FhSAP2 was expressed in micro-volumes and purified by an affinity chromatography method, which gave a protein yield of 500 µg/ml as determined by bicinchoninic acid assay method. Circular dichroism, Western blotting and enzyme-linked immunosorbent assay analysis were used to confirm the secondary structure, purity and integrity of protein. Results demonstrate that FhSAP2 can be expressed in a cell-free system retaining its main conformational and antigenic properties. The protein purified could be used in immunization experiments and immunodiagnostic techniques.

Characterization and vaccine potential of Fasciola gigantica saposin-like protein 1 (SAP-1)

The recombinant Fasciola gigantica Saposin-like protien-1 (rFgSAP-1) was cloned by polymerase chain reaction (PCR) from NEJ cDNA, expressed in Escherichia coli BL21 (DE3) and used for production of a polyclonal antibody in rabbits (anti-rFgSAP-1). By immunoblotting and immunohistochemistry, rabbit IgG anti-rFgSAP-1 reacted with rFgSAP-1 at a molecular weight 12kDa, but not with rFgSAP-2. The rFgSAP-1 reacted with antisera from mouse infected with F. gigantica metacercariae collected at 2, 4, and 6 weeks after infection. The FgSAP-1 protein was expressed at a high level in the caecal epithelium of metacercariae and NEJs. The vaccination was performed in Imprinting Control Region (ICR) mice (n=10) by subcutaneous injection with 50μg of rFgSAP-1 combined with Alum adjuvant. Two weeks after the second boost, mice were infected with 15 metacercariae per mouse by the oral route. The percents protection of rFgSAP-1 vaccine were estimated to be 73.2% and 74.3% when compared with non vaccinated-infected and adjuvant-infected controls, respectively. The levels of IgG1 and IgG2a specific to rFgSAP-1 in the immune sera, which are indicative of Th2 and Th1 immune responses, were inversely and significantly correlated with the numbers of worm recoveries. The rFgSAP-1-vaccinated mice showed significantly reduced levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and liver damage. These indicated that rFgSAP-1 has strong potential as a vaccine candidate against F. gigantica, whose efficacy will be studied further in large economic animals including cattle, sheep, and goat.