Application of equine infectious anemia virus core proteins produced in a baculovirus expression system to serological diagnosis

Preventive, Diagnostic and Therapeutic Applications of Baculovirus Expression Vector System

Different strategies are being worked out for engineering the original baculovirus expression vector (BEV) system to produce cost-effective clinical biologics at commercial scale. To date, thousands of highly variable molecules in the form of heterologous proteins, virus-like particles, surface display proteins/antigen carriers, heterologous viral vectors and gene delivery vehicles have been produced using this system. These products are being used in vaccine production, tissue engineering, stem cell transduction, viral vector production, gene therapy, cancer treatment and development of biosensors. Recombinant proteins that are expressed and post-translationally modified using this system are also suitable for functional, crystallographic studies, microarray and drug discovery-based applications. Till now, four BEV-based commercial products (Cervarix^®, Provenge^®, Glybera^® and Flublok^®) have been approved for humans, and myriad of others are in different stages of preclinical or clinical trials. Five products (Porcilis^® Pesti, BAYOVAC CSF E2^®, Circumvent^® PCV, Ingelvac CircoFLEX^® and Porcilis^® PCV) got approval for veterinary use, and many more are in the pipeline. In the present chapter, we have emphasized on both approved and other baculovirus-based products produced in insect cells or larvae that are important from clinical perspective and are being developed as preventive, diagnostic or therapeutic agents. Further, the potential of recombinant adeno-associated virus (rAAV) as gene delivery vector has been described. This system, due to its relatively extended gene expression, lack of pathogenicity and the ability to transduce a wide variety of cells, gained extensive popularity just after the approval of first AAV-based gene therapy drug alipogene tiparvovec (Glybera^®). Numerous products based on AAV which are presently in different clinical trials have also been highlighted.

Recombinant protein-based viral disease diagnostics in veterinary medicine

Identification of pathogens or antibody response to pathogens in human and animals modulates the treatment strategies for naive population and subsequent infections. Diseases can be controlled and even eradicated based on the epidemiology and effective prophylaxis, which often depends on development of efficient diagnostics. In addition, combating newly emerging diseases in human as well as animal healthcare is challenging and is dependent on developing safe and efficient diagnostics. Detection of antibodies directed against specific antigens has been the method of choice for documenting prior infection. Other than zoonosis, development of inexpensive vaccines and diagnostics is a unique problem in animal healthcare. The advent of recombinant DNA technology and its application in the biotechnology industry has revolutionized animal healthcare. The use of recombinant DNA technology in animal disease diagnosis has improved the rapidity, specificity and sensitivity of various diagnostic assays. This is because of the absence of host cellular proteins in the recombinant derived antigen preparations that dramatically decrease the rate of false-positive reactions. Various recombinant products are used for disease diagnosis in veterinary medicine and this article discusses recombinant-based viral disease diagnostics currently used for detection of pathogens in livestock and poultry.

Systematic epitope analysis of the p26 EIAV core protein

The major core protein of equine infectious anemia virus (EIAV), p26, is one of the primary immunogenic structural proteins during a persistent infection of horses and is highly conserved among antigenically variants of viral isolates. In order to investigate its immune profile in more detail for a better diagnostic, an epitope mapping was carried out by means of two libraries of overlapping peptide fragments prepared by simultaneous and parallel SPPS on derivatized cellulose membranes (SPOT synthesis). Polyclonal equine sera from infected horses were used for the biological assay. Particularly two promising continuous epitopes (NAMRHL and MYACRD) were localized on the C-terminal extreme of p26, region 194-222. A cyclic synthetic fragment of 29 amino acid residues containing the identified epitopes was designed and studied. A significant conformational change towards a helical structure was observed when the peptide was cyclized by a bridge between Cys198 and Cys218. This observation correlated with an improvement of its ability to be recognized by specific antibodies in an EIA (Enzyme-linked Immunosorbent assay). These results suggest that the conformationally restricted synthetic antigen adequately mimics the native structure of this region of p26 core protein.

Serodiagnosis of equine infectious anemia by agar gel immunodiffusion and ELISA using a recombinant p26 viral protein expressed in Escherichia coli as antigen

We used a p26 recombinant protein (p26r) from equine infectious-anemia virus (EIAV) expressed in Escherichia coli as antigen to standardize an agar-gel immunodiffusion (AGIDp26r) test and an indirect ELISA (ELISAp26r) for the detection of antibodies against EIAV in 720 equine sera from Brazil. We evaluated the tests's relative diagnostic sensitivities (relSe) and relative diagnostic specificities (relSp) against a commercial AGID kit (Idexx, USA). We used three sera panels: panel A--196 AGID-negative sera from an AIE non-endemic controlled area; panel B--194 AGID-negative sera from an AIE endemic area and panel C--330 AGID-positive sera from an AIE endemic area. ELISAp26r cut-off value was defined with TG-ROC using sera from panels A and C. AGIDp26r showed an agreement of 100% with the commercial kit. When applied to sera from panels A and C, ELISAp26r showed an agreement of 100% with the kit, but, although relSe was 100% for panel C, the ELISAp26r had relSp of 93.3%.

Serological method using recombinant S2 protein to differentiate equine infectious anemia virus (EIAV)-infected and EIAV-vaccinated horses

We recently reported a highly protective attenuated live virus vaccine for equine infectious anemia virus (EIAV) based on a proviral construct (EIAVUKDeltaS2) with a genetically engineered mutation in the viral S2 gene that eliminates expression of this accessory protein. While the EIAVUKDeltaS2 vaccine provides protection from detectable infection by experimental challenge with highly virulent virus, the potential for commercial application of this vaccine is complicated by the fact that horses inoculated with the EIAVUKDeltaS2 vaccine strain become seropositive in various reference diagnostic assays based on detection of antibodies to virion core or envelope proteins. To address this issue, we describe here the development and optimization of a new serologic EIAV diagnostic enzyme-linked immunosorbent assay (ELISA) to detect serum antibodies to the EIAV S2 protein that are produced in infected horses but not in horses inoculated with the EIAVUKDeltaS2 vaccine virus. The test S2 protein antigen was developed using the S2 gene sequence from the EIAVUK strain of virus and a series of modifications to facilitate production and purification of the diagnostic antigen, designated HS2G. Using this HS2G as antigen, we describe the development of an affinity ELISA that provides a sensitive and specific detection of S2-specific serum antibodies in experimentally and field-infected horses (22 of 24), without detectable reactivity with immune serum from uninfected (12 of 12) or vaccinated (29 of 29) horses. These data indicate that the S2-based diagnostic ELISA has the potential to accurately differentiate horses infected with EIAV from horses inoculated with an attenuated EIAV vaccine strain with a mutant S2 gene.

Cross reaction of recombinant equine infectious anemia virus antigen to heterologous strains and application for serological survey among horses in the field

Cross reactivity of equine infectious anemia virus (EIAV) antigen prepared using a recombinant baculovirus containing the p26 gene of strain P337-V70 was examined by the agar gel immunodiffusion (AGID) test and enzyme-linked immunosorbent assay (ELISA). Serum samples serially collected from 13 horses experimentally infected with six different EIAV strains (two or three horses per strain) were subjected to the test. Positive reactions were observed in the AGID test and ELISA before or soon after the first feverish period and continued persistently in most of the horses. The results with recombinant antigens were essentially the same as those with the virion antigen prepared from horse cell cultures both in the AGID test and ELISA. The reactivities of the antigens were further compared using serum samples collected from horses in 1999 in certain districts of Mongolia where equine infectious anemia has been prevalent, and from horses in Japan in 1973 when EIA had not been eliminated completely from Japanese horses. These results were completely concurrent. Generally, recombinant antigens have high specificity but low cross reactivity to heterologous strains. However, the present study showed that the recombinant EIAV p26 antigen has cross reactivity to the heterologous strain and is useful for diagnosis of EIA in the field.

Serological diagnosis of equine influenza using the hemagglutinin protein produced in a baculovirus expression system

The hemagglutinin (HA) protein of an equine influenza strain, A/equine/La Plata/1/93 (LP/93), was produced using a baculovirus expression system. Silkworm larvae inoculated with recombinant baculovirus expressed high quantities of the HA protein which was then purified to greater than 95% purity by fetuin-affinity chromatography. Purified HA protein was used subsequently in an ELISA for detection of antibodies in horse sera. Two hundred serum samples from vaccinated racehorses were reacted on ELISA plates coated with 40.0 ng/ml of purified HA protein. Subsequent optical density (OD) levels revealed titers which correlated highly with respective hemagglutinin inhibition (HI) antibody titers which ranged from <1:8 to 1:256 (correlation coefficient among them was 0.850). ELISA OD levels and HI titers increased at 5 and 7 days post-inoculation, respectively, in a horse inoculated intranasally with LP/93. Respective antibody levels were observed to change in an essentially parallel manner during a period of 1 month. Similarly, ELISA OD levels correlated with HI titers in horses during a period of 6 weeks following intramuscular inoculation with inactivated single-strain vaccines containing LP/93, A/equine/Kentucky/1/81 (H3N8) or A/equine/Rome/5/91 (H3N8). A similar pattern was also observed in eight horses throughout a 10-week period following inoculation with a commercially available inactivated trivalent vaccine containing A/equine/Newmarket/1/77(H7N7), A/equine/Kentucky/81 and LP/93. From these results, it is suggested that this ELISA system could be used for disease diagnosis and surveillance of HI antibody titers among vaccinated horses.

Serological evidence of an Australian bovine lentivirus

Recombinant 26 kDa capsid (CA) proteins of bovine lentiviruses, bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV), were expressed in Escherichia coli and utilised as antigens for an enzyme-linked immunosorbent assay (ELISA) and a western immunoblot (WIB) procedure for the detection of antibody in dairy cattle in Western Australia. A total of 690 serum samples, 30 from each of 23 farms, were tested by ELISA with a JDV CA protein antigen, and antibody was detected in 3.8% (p<0.05) of the sera. Nine sera from each farm were also tested by WIB with JDV CA protein antigens and antibody was detected in 15.9% of these samples. All ELISA-positive results were also WIB-positive, and all sera antibody-positive by WIB with JDV CA protein antigens were also antibody-positive by the WIB using recombinant BIV CA antigens. This study showed that recombinant protein antigens can be used for serological tests to detect bovine lentivirus infection in Australia.

Evaluation of equine infectious anemia virus core proteins produced in a baculovirus expression system in agar gel immunodiffusion test and enzyme-linked immunosorbent assay

Equine infectious anemia virus (EIAV) core proteins (Gag and p26) obtained from a baculovirus expression system were used in agar gel immunodiffusion (AGID) and enzyme-linked immunosorbent assay (ELISA) antigens to test seventy-six horse sera. Those sera showed false-positive reaction in AGID test using Nisseiken antigen. However, none of them showed false-positive reaction with both of the expressed antigens. The 76 horse sera were also tested by ELISA. The sera gave a high background in ELISA using Nisseiken antigen. Gag and p26 reacted strongly against positive sera from horses immunized with Nisseiken antigen.