Effect of particulation on the immunogenic and protective properties of the recombinant Bm86 antigen expressed in Pichia pastoris

Efficacy of the Vaccine Candidate Based on the P0 Peptide against Dermacentor nitens and Ixodes ricinus Ticks

The control of ticks through vaccination offers a sustainable alternative to the use of chemicals that cause contamination and the selection of resistant tick strains. However, only a limited number of anti-tick vaccines have reached commercial realization. In this sense, an antigen effective against different tick species is a desirable target for developing such vaccines. A peptide derived from the tick P0 protein (pP0) conjugated to a carrier protein has been demonstrated to be effective against the Rhipicephalus microplus, Rhipicephalus sanguineus, and Amblyomma mixtum tick species. The aim of this work was to assess the efficacy of this peptide when conjugated to the Bm86 protein against Dermacentor nitens and Ixodes ricinus ticks. An RNAi experiment using P0 dsRNA from I. ricinus showed a dramatic reduction in the feeding of injected female ticks on guinea pigs. In the follow-up vaccination experiments, rabbits were immunized with the pP0-Bm86 conjugate and challenged simultaneously with larvae, nymphs, and the adults of I. ricinus ticks. In the same way, horses were immunized with the pP0-Bm86 conjugate and challenged with D. nitens larva. The pP0-Bm86 conjugate showed efficacies of 63% and 55% against I. ricinus and D. nitens ticks, respectively. These results, combined with previous reports of efficacy for this conjugate, show the promising potential for its development as a broad-spectrum anti-tick vaccine.

Synthesis, LC-MS/MS analysis, and biological evaluation of two vaccine candidates against ticks based on the antigenic P0 peptide from R. sanguineus linked to the p64K carrier protein from Neisseria meningitidis

A peptide from the P0 acidic ribosomal protein (pP0) of ticks conjugated to keyhole limpet hemocyanin from Megathura crenulata has shown to be effective against different tick species when used in host vaccination. Turning this peptide into a commercial anti-tick vaccine will depend on finding the appropriate, technically and economically feasible way to present it to the host immune system. Two conjugates (p64K-Cys¹pP0 and p64K-βAla¹pP0) were synthesized using the p64K carrier protein from Neisseria meningitidis produced in Escherichia coli, the same cross-linking reagent, and two analogues of pP0. The SDS-PAGE analysis of p64K-Cys¹pP0 showed a heterogeneous conjugate compared to p64K-βAla¹pP0 that was detected as a protein band at 91kDa. The pP0/p64K ratio determined by MALDI-MS for p64K-Cys¹pP0 ranged from 1 to 8, being 3-5 the predominant ratio, while in the case of p64K-βAla¹pP0 this ratio was 5-7. Cys¹pP0 was partially linked to 35 out of 39 Lys residues and the N-terminal end, while βAla¹pP0 was mostly linked to the six free cysteine residues, to the N-terminal end, and, in a lesser extent, to Lys residues. The assignment of the conjugation sites and side reactions were based on the identification of type 2 peptides. Rabbit immunizations showed the best anti-pP0 titers and the highest efficacy against Rhipicephalus sanguineus ticks when the p64K-Cys¹pP0 was used as vaccine antigen. The presence of high molecular mass aggregates observed in the SDS-PAGE analysis of p64K-Cys¹pP0 could be responsible for a better immune response against pP0 and consequently for its better efficacy as an anti-tick vaccine.

Functional and Mass Spectrometric Evaluation of an Anti-Tick Antigen Based on the P0 Peptide Conjugated to Bm86 Protein

A synthetic 20 amino acid peptide of the ribosomal protein P0 from ticks, when conjugated to keyhole limpet hemocyanin from Megathura crenulata and used as an immunogen against Rhipicephalus microplus and Rhipicephalus sanguineus s.l. species, has shown efficacies of around 90%. There is also experimental evidence of a high efficacy of this conjugate against Amblyomma mixtum and Ixodes ricinus species, which suggest that this antigen could be a good broad-spectrum anti-tick vaccine candidate. In this study, the P0 peptide (pP0) was chemically conjugated to Bm86 as a carrier protein. SDS-PAGE analysis of this conjugate demonstrated that it is highly heterogeneous in size, carrying from 1 to 18 molecules of pP0 per molecule of Bm86. Forty-nine out of the 54 lysine residues and the N-terminal end of Bm86 were found partially linked to pP0 by using LC-MS/MS analysis and the combination of four different softwares. Several post-translational modifications of Bm86 protein were also identified by mass spectrometry. High immunogenicity and efficacy were achieved when dogs and cattle were vaccinated with the pP0-Bm86 conjugate and challenged with R. sanguineus s.l. and R. microplus, respectively. These results encourage the development of this antigen with promising possibilities as an anti-tick vaccine.

Transmembrane proteins--Mining the cattle tick transcriptome

Managing the spread and load of pathogen-transmitting ticks is an important task worldwide. The cattle tick, Rhipicephalus microplus, not only impacts the economy through losses in dairy and meat production, but also raises concerns for human health in regards to the potential of certain transmitted pathogens becoming zoonotic. However, novel strategies to control R. microplus are hindered by lack of understanding tick biology and the discovery of suitable vaccine or acaricide targets. The importance of transmembrane proteins as vaccine targets are well known, as is the case in tick vaccines with Bm86 as antigen. In this study, we describe the localization and functional annotation of 878 putative transmembrane proteins. Thirty proteins could be confirmed in the R. microplus gut using LC-MS/MS analysis and their roles in tick biology are discussed. To the best of our knowledge, 19 targets have not been reported before in any proteomics study in various tick species and the possibility of using the identified proteins as targets for tick control are discussed. Although tissue expression of identified putative proteins through expansive proteomics is necessary, this study demonstrates the possibility of using bioinformatics for the identification of targets for further evaluation in tick control strategies.

Advances in the identification and characterization of protective antigens for recombinant vaccines against tick infestations

Ticks are economically important ectoparasites of domestic and wild animals and are considered to be second worldwide to mosquitoes as vectors of human pathogens. Current control methods for ticks, based primarily on the use of acaricides, have had limited efficacy in the reduction of tick infestations and the use of acaricides is often accompanied by serious drawbacks, including selection of acaricide-resistant ticks and environmental contamination. Development of improved vaccines against tick infestations offers a cost-effective and environmentally sound control method. Commercial vaccines currently marketed for control of cattle ticks have been effective in field studies when used in concert with integrated control strategies. However, new antigens are needed to increase the efficacy of tick vaccines. Although a limited number of protective antigens against tick infestations have been identified and characterized, discovery of new antigens remains the limiting step for improving the efficacy of tick vaccines. Recent technologies developed for gene discovery, including expression library immunization and evaluation of expressed sequence tags, show promise for rapid, systematic and global antigen screening and should provide a comprehensive approach to selection of candidate vaccine antigens. Design of future tick vaccines should target multiple tick species, as well as interfere with the transmission of pathogens.

Improved vaccines through targeted manipulation of the body's immunological risk-assessment?

Recent advances have highlighted the outstanding role of the innate immune system for instructing adaptive immunity. Translating this knowledge into successful immunotherapies like vaccines, however, has proven to be a difficult task. This essay is based on the hypothesis that immune responses are tightly scaled to the infectious threat posed by a given microbial stimulus. A meticulous immunological risk-assessment process is therefore instrumental for eliciting well-balanced responses and maintaining immune homeostasis. The immune system makes fine distinctions, for example, between live and dead bacteria, or pathogenic and non-pathogenic microorganisms. Here, I discuss recent evidence for some of the mechanisms underlying these distinctions and speculate on strategies for therapeutically targeting the immunological risk-assessment machinery.

A systematic, functional genomics, and reverse vaccinology approach to the identification of vaccine candidates in the cattle tick, Rhipicephalus microplus

In the post-genomic era, reverse vaccinology is proving promising in the development of vaccines against bacterial and viral diseases, with limited application in ectoparasite vaccine design. In this study, we present a systematic approach using a combination of functional genomics (DNA microarrays) techniques and a pipeline incorporating in silico prediction of subcellular localization and protective antigenicity using VaxiJen for the identification of novel anti-tick vaccine candidates. A total of 791 candidates were identified using this approach, of which 176 are membrane-associated and 86 secreted soluble proteins. A preliminary analysis on the antigenicity of selected membrane proteins using anti-gut antisera yielded candidates with an IgG binding capacity greater than previously identified epitopes of Bm86. Subsequent vaccination trials using recombinant proteins will not only validate this approach, but will also improve subsequent reverse vaccinology approaches for the identification of novel anti-tick vaccine candidates.

Expression of recombinant HAO3 from an Iranian isolate of Hyalomma anatolicum anatolicum in Pichia pastoris and evaluation of its antigenicity

Hyalomma anatolicum anatolicum tick is considered as one of the main problem of ruminants' productivity in endemic countries such as parts of Africa, the Middle East and India. The disease is economically important and hence, its control and eradication is a priority. This problem reinforces the need for alternative approach like vaccine to control tick infestations instead of continuous application of acaricide which led to the natural selection of the acaricide-resistant ticks. Therefore, the present study provided evidence for the construction of transformant containing the chromosomally integrated multi-copy expression cassettes of HAO3, its successful and efficient expression in Pichia pastoris yeast and purification of the secreted protein by ultrafiltration (UF) system in a high level yield and purity. The result of antigenicity assay for the rHAO3 protein pointed well toward its capability for the elicitation of antibody response in immunized rabbits. Interestingly, the results indicated that the expressed HAO3 protein reacted well with mid gut antigen (MGAg) and rBm86 (Gavac) antisera in ELISA and western blot assays making it evident that the epitopes present in expressed protein are well recognized by the antibodies against MGAg and rBm86 proteins. Moreover, the presence of cross-reactive epitopes between rHAO3 protein with its native antigen from mid gut cells was also determined.

Humoral immune response of dairy cattle immunized with rBm95 (KU-VAC1) derived from Thai Rhipicephalus microplus

Rhipicephalus (Boophilus) microplus is an important cause of economic losses in Thailand through direct effects of feeding on cattle and pathogen transmission. Current tick control methods rely on expensive chemical acaricides that result in environmental contamination, residues in food animal products and acaricide-resistant ticks. Anti-tick vaccines based on concealed antigens have shown promising results in the control of cattle tick. Thus, recombinant Bm95 (rBm95) from Thai R. microplus (KU-VAC1) was cloned and expressed to test as an anti-tick vaccine in Thailand. The objective of this study was to compare antibody responses induced by KU-VAC1 to that obtained after vaccination with Gavac that is based on the Bm86 homologue. Four groups of six cattle each were immunized with KU-VAC1, Gavac, adjuvant or phosphate-buffered saline, and boosted three times at 21-day intervals. Enzyme-linked-immunosorbent serologic assay were used to measure the humoral antibody responses specific to Thai rBm95. Cattle immunized with either KU-VAC1 or Gavac showed significantly greater antibody production than the controls. Antibody titres were detected after the first immunization and peaked after the seventh week. These results indicated that KU-VAC1 and Gavac are similarly immunogenic, and that further studies are warranted to compare performance parameters of ticks fed on immunized cattle.

Two initial vaccinations with the Bm86-based Gavacplus vaccine against Rhipicephalus (Boophilus) microplus induce similar reproductive suppression to three initial vaccinations under production conditions

BACKGROUND

The cattle tick, Rhipicephalus (Boophilus) microplus, affects livestock production in many regions of the world. Up to now, the widespread use of chemical acaricides has led to the selection of acaricide-resistant ticks and to environmental contamination. Gavacplus is a subunit vaccine based on the recombinant Bm86 tick antigen expressed in yeast, capable to control infestations of R. microplus under controlled and production conditions. The vaccine constitutes the core element of broad control programs against this ectoparasite, in which acquired immunity in cattle to Bm86 is combined with a rational use of acaricides. At present, the conventional vaccine scheme consists of three doses that should be administered at weeks 0, 4 and 7, followed by a booster every six months.

RESULTS

In this study we assayed a reduction in the number of the initial doses of Gavacplus, evaluated the time course and the level of bovine anti-Bm86 antibodies elicited, and analyzed the vaccine effect on ticks engorging on immunized cattle under production conditions. Following three different immunization schemes, the bovines developed a strong and specific immune response characterized by elevated anti-Bm86 IgG titers. A reduction in the weight of engorging female ticks, in the weight of the eggs laid and also in R. microplus viable eggs percentage was obtained by using only two doses of Gavacplus administered at weeks 0 and 4, followed by a booster six months later. This reduction did not differ from the results obtained on ticks engorging on cattle immunized at weeks 0, 4 and 7. It was also demonstrated that anti-Bm86 antibody titers over 1:640, measured in bovines immunized at weeks 0 and 4, were sufficient to affect weight and reproductive potential of female ticks as compared with ticks engorging on unvaccinated animals. In addition, no statistically significant differences were detected in the average weight of eggs laid by ticks engorged on immunized cattle that showed anti-Bm86 specific titers in the range of 1:640 to 1:81920.

CONCLUSION

The administration of two initial doses of Gavacplus containing 100 μg of Bm86 antigen to non-immunized cattle under production conditions is sufficient to affect the weight and the reproductive capacity of R. microplus engorging females. According to these results, cattle herds' manipulation and vaccine costs could be potentially reduced with a positive impact on the implementation of integrated control programs against R. microplus.

Efficacy of the Bm86 antigen against immature instars and adults of the dog tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae)

The Bm86 antigen has been used to control ticks of the Boophilus genera in integrated programs that also include the use of acaricides. Because of recent phylogenetic studies have lead to the inclusion of all Boophilus species within the Rhipicephalus genera, we aimed to investigate the efficacy of the Bm86 antigen on the biotic potential of Rhipicephalus sanguineus. Domestic dogs were vaccinated with Bm86 and challenged with the three instars of R. sanguineus. Male and female mongrel dogs were divided into two groups of four animals each, comprising non-vaccinated and vaccinated animals. Immunized dogs were given two doses of an experimental formulation containing 50mug of recombinant Bm86, at 21 days interval while the other group was given placebo, consisting of the same preparation without Bm86. Each dog was challenged 21 days after the last dose with 250 larvae, 100 nymphs and 55 adults (25 females and 30 males) released inside feeding chambers (one per instar) glued to their shaved flank. The effect of the vaccination was evaluated by determining biological parameters of ticks including the yield rates of larvae, nymphs and adult females. Adult females engorged weight, egg mass weight, efficiency rate of conversion to eggs (ERCE) and hatchability. In addition, sera were collected from dogs at 0, 21, 36, 45 and 75 days after the vaccination and used for the detection of specific antibodies by ELISA. Collection rates of larvae, nymphs and adult females fed on vaccinated dogs were significantly (p<0.05) reduced by 38%, 29% and 31%, respectively, as compared with non-vaccinated controls. Significant reductions were also observed in weight of engorged females and egg mass, in ERCE, but not in the hatch rate of ticks fed on immunized dogs. ELISA data revealed a marked and significant increase in optical densities of sera from vaccinated animals after the second dose of Bm86. We concluded that the Bm86 antigen used as a vaccine for dogs reduced the viability and biotic potential of the R. sanguineus.

Expression of recombinant Rhipicephalus (Boophilus) microplus, R. annulatus and R. decoloratus Bm86 orthologs as secreted proteins in Pichia pastoris

Background

Rhipicephalus (Boophilus) spp. ticks economically impact on cattle production in Africa and other tropical and subtropical regions of the world. Tick vaccines constitute a cost-effective and environmentally friendly alternative to tick control. The R. microplus Bm86 protective antigen has been produced by recombinant DNA technology and shown to protect cattle against tick infestations.

Results

In this study, the genes for Bm86 (R. microplus), Ba86 (R. annulatus) and Bd86 (R. decoloratus) were cloned and characterized from African or Asian tick strains and the recombinant proteins were secreted and purified from P. pastoris. The secretion of recombinant Bm86 ortholog proteins in P. pastoris allowed for a simple purification process rendering a final product with high recovery (35–42%) and purity (80–85%) and likely to result in a more reproducible conformation closely resembling the native protein. Rabbit immunization experiments with recombinant proteins showed immune cross-reactivity between Bm86 ortholog proteins.

Conclusion

These experiments support the development and testing of vaccines containing recombinant Bm86, Ba86 and Bd86 secreted in P. pastoris for the control of tick infestations in Africa.

High-level expression and immunogenic properties of the recombinant rabbit hemorrhagic disease virus VP60 capsid protein obtained in Pichia pastoris

The VP60 capsid protein from rabbit hemorrhagic disease virus (RHDV) (Spanish isolate AST/89) was cloned and expressed in Pichia pastoris. The transformed yeast was grown at high cell density and an expression level of about 1.5 g VP60L(-1) culture was obtained. The protein was detected associated with the cell debris fraction of the recombinant yeast after mechanical disruption. It was purified by a simple method and was obtained N-glycosylated with purity of approximately 70% as deduced from densitometry scan analysis. The recombinant product was antigenically similar to the native capsid protein as determined with polyclonal antibodies obtained from rabbits vaccinated with VP60 protein purified from native virus. The immunogenicity of VP60 protein purified from P. pastoris was demonstrated by ELISA in a vaccination experiment conducted with two groups of rabbits subcutaneously immunized. Animals vaccinated with VP60 in Freund's incomplete adjuvant developed a significant (p<0.01) virus-specific antibody response while the group injected with placebo remained seronegative. Preliminary results showed that the antigen administered within the cell debris fraction of the transformed yeast protected rabbits immunized by the oral route against an intramuscular challenge with 100 LD50 (16,000 hemagglutination units) of homologous virus.

Protection of Dairy Cows Immunized with Tick Tissues against NaturalBoophilus microplusInfestations in Thailand

Boophilus microplus has a major impact on cattle production, and an antitick vaccine would be a valuable tool for control of this important ectoparasite in Thailand. Previous work has shown that immunization of hosts with different tick tissues has different implications regarding tick feeding and fecundity under experimental conditions. The purpose of this study was to assess the effects of immunization of dairy cattle with B. microplus salivary gland or midgut extracts on natural infestations by this tick species. The different antigen extracts (1 mg total protein) or equivalent amounts of adjuvant alone were injected intradermally every two weeks for a total of three times before allowing cattle to graze in a tick-contaminated pasture. Animals were checked daily, and engorged female ticks collected, counted, weighed, and maintained in tick incubators to observe tick performance parameters, including engorged weight, egg mass weight, nonviable eggs, mortality, oviposition period, egg incubation period, and F1 larval weight. After six months, each group was reimmunized with the same antigen and/or adjuvant, and ticks were again collected and evaluated. Immunization of cattle with salivary gland preparations resulted in reductions in mean tick counts and in engorged female weights. Immunization with midgut antigens reduced tick oviposition and reduced egg mass weights. In addition, more ticks recovered from midgut-immunized cows produce nonviable eggs. This investigation indicates that a vaccine based on these antigen preparations could induce a lasting, protective immune response against B. microplus that would be expected to provide a safe nontoxic means of tick control.

Recombinant protein expression in Pichia pastoris

The methylotrophic yeast Pichia pastoris is now one of the standard tools used in molecular biology for the generation of recombinant protein. P. pastoris has demonstrated its most powerful success as a large-scale (fermentation) recombinant protein production tool. What began more than 20 years ago as a program to convert abundant methanol to a protein source for animal feed has been developed into what is today two important biological tools: a model eukaryote used in cell biology research and a recombinant protein production system. To date well over 200 heterologous proteins have been expressed in P. pastoris. Significant advances in the development of new strains and vectors, improved techniques, and the commercial availability of these tools coupled with a better understanding of the biology of Pichia species have led to this microbe's value and power in commercial and research labs alike.

Control of ticks resistant to immunization with Bm86 in cattle vaccinated with the recombinant antigen Bm95 isolated from the cattle tick, Boophilus microplus

The recombinant Bm86-containing vaccine Gavac(TM) against the cattle tick Boophilus microplus has proved its efficacy in a number of experiments, especially when combined with acaricides in an integrated manner. However, tick isolates such as the Argentinean strain A, show low susceptibility to this vaccine. In this paper we report on the isolation of the Bm95 gene from the B. microplus strain A, which was cloned and expressed in the yeast Pichia pastoris producing a glycosylated and particulated recombinant protein. This new antigen was effective against different tick strains in a pen trial, including the B. microplus strain A, resistant to vaccination with Bm86. A Bm95-based vaccine was used to protect cattle against tick infestations under production conditions, lowering the number of ticks on vaccinated animals and, therefore, reducing the frequency of acaricide treatments. The Bm95 antigen from strain A was able to protect against infestations with Bm86-sensitive and Bm86-resistant tick strains, thus suggesting that Bm95 could be a more universal antigen to protect cattle against infestations by B. microplus strains from different geographical areas.

Evaluation of tickGARD(PLUS), a novel vaccine against Boophilus microplus, in lactating Holstein-Friesian cows

The effects of vaccination with the Bm 86 vaccine TickGARD(PLUS) against infestation with cattle tick (Boophilus microplus) and of holding cattle on a feedpad until 09:00 hours after the morning milking was tested on 40 mid lactation Holstein cattle using a factorial design. Vaccination resulted in a 56% reduction in tick numbers in the field over one generation, and a 72% reduction in laboratory measures of the reproductive efficiency of ticks. The liveweight gain of vaccinated cattle over 27 weeks was 18.6 kg higher than that of controls, and vaccinated cattle tended to have lower somatic cell count in milk (SCC). There were no other significant differences in measures of production. Cattle kept on the feedpad after the morning milking carried 26% more ticks than those returned immediately to their paddocks.

Heterologous protein expression in the methylotrophic yeast Pichia pastoris

During the past 15 years, the methylotrophic yeast Pichia pastoris has developed into a highly successful system for the production of a variety of heterologous proteins. The increasing popularity of this particular expression system can be attributed to several factors, most importantly: (1) the simplicity of techniques needed for the molecular genetic manipulation of P. pastoris and their similarity to those of Saccharomyces cerevisiae, one of the most well-characterized experimental systems in modern biology; (2) the ability of P. pastoris to produce foreign proteins at high levels, either intracellularly or extracellularly; (3) the capability of performing many eukaryotic post-translational modifications, such as glycosylation, disulfide bond formation and proteolytic processing; and (4) the availability of the expression system as a commercially available kit. In this paper, we review the P. pastoris expression system: how it was developed, how it works, and what proteins have been produced. We also describe new promoters and auxotrophic marker/host strain combinations which extend the usefulness of the system.

Vaccination against ticks (Boophilus spp.): the experience with the Bm86-based vaccine Gavac

The control of tick infestations and the transmission of tick-borne diseases remain a challenge for the cattle industry in tropical and subtropical areas of the world. Traditional control methods have been only partially successful and the parasites continue to result in significant losses for the cattle industry. Recently, vaccines containing the recombinant B. microplus gut antigen Bm86 have been developed. Our vaccine formulation (Gavac, Heber Biotec S.A., Havana, Cuba) has been registered and is commercially available in Cuba, Colombia, Dominican Republic, Brazil and Mexico. In controlled pen trials, Gavac has been effective for the control of artificial infestations of B. annulatus, B. decoloratus and chemical-sensitive and resistant B. microplus strains from Australia, Africa, America and Iran. In controlled field trials in Cuba, Brazil, Argentina and Mexico, Gavac has shown a 55-100% efficacy in the control of B. microplus infestations in grazing cattle 12-36 weeks after the first vaccination. Field trials under production conditions have been conducted in Cuba, Colombia, Brazil and Mexico in pure and cross-bred cattle herds. The application of Gavac has increased the time between acaricide treatments by an average of 32 /-21 days (P = 0.0005) resulting in important savings for the cattle industry. In Cuba, a cost-effectiveness analysis was conducted in more than 260000 animals. The cost-effectiveness analysis showed a 60% reduction in the number of acaricide treatments, together with the control of tick infestations and transmission of babesiosis, which resulted in savings of 23.4 dollars animal(-1) year (-1). These results clearly demonstrate the advantage of vaccination and support the application of Gavac for the control of Boophilus spp. infestations.

Reproductive and safety assessment of vaccination with Gavac against the cattle tick (Boophilus microplus)

Recent developments in cattle tick control have incorporated the use of recombinant Bm86 vaccines against this ectoparasite. The vaccine developed by our group (Gavac) contains an antigen expressed in Pichia pastoris, and has been successfully employed for the control of tick infestations and transmission of tick-borne diseases. Here, we examined the safety and effect of the Gavac vaccine on reproductive parameters in cattle. Toxicity tests in mice and guinea pigs demonstrated the safety of Gavac. To study the adverse effects of vaccination on reproduction, a field trial involving 9,500 animals in Cuba was conducted. The cattle at 3 farms were vaccinated while those on a fourth farm were left unvaccinated and served as the control. Following vaccination, the control of tick infestation and the transmission of babesiosis were used to demonstrate the efficacy of the vaccine. No adverse effects were observed in any of the reproductive parameters studied when comparing the data before and after vaccination with Gavac and between the vaccinated farms and the control farm. These results demonstrate that under the conditions of our study vaccination with Gavac is safe for use on cattle.

Arthropod vaccines

Antigens located in the midgut of the tick are hidden from the host's immune system. Egg production of ticks can be reduced when ticks are fed on animals vaccinated with midgut antigens of the tick, and a subunit vaccine formulated with the recombinant antigen Bm86 is now available that can reduce the number of ticks infesting cattle grazing on pasture. Midgut antigens used in vaccines against insects that transmit pathogenic organisms to humans have not been as effective in reducing insect fecundity and an alternative approach may be necessary. Transmission-blocking vaccines directed at interfering with the vector-pathogen interaction could result in loss of vector competence and block the spread of disease-causing organisms.

Aggregation of recombinant hepatitis B surface antigen in Pichia pastoris

The combination of immunoaffinity and size-exclusion chromatography (SEC) is a powerful tool to analyze multiprotein particle assembly. This approach was used to investigate the source of aggregation of recombinant hepatitis B surface antigen (HBsAg) detected in purified material. As HBsAg aggregation does not originate in the stresses, such as the concentration of HBsAg solutions, temperature and chaotropic agents, it is less probable that the HBsAg aggregate is produced during the process. To test whether aggregation takes place in vivo, crude yeast extract containing the expressed HBsAg was fractioned on a Sephacryl S-400 column just after cell disruption, and each fraction immunopurified individually. As a result, the HBsAg aggregate was isolated from a fraction corresponding to the elution of large particle aggregates only, not native HBsAg particles. It was biologically active, which demonstrates aggregate formation by specific assembly of partially or wholly folded HBsAg intermediates.