Stable expression of Mycobacterium bovis antigen 85B in auxotrophic M. bovis bacillus Calmette-Guérin

BACKGROUND Bovine tuberculosis (TB) is a zoonotic disease caused by Mycobacterium bovis, responsible for causing major losses in livestock. A cost effective alternative to control the disease could be herd vaccination. The bacillus Calmette-Guérin (BCG) vaccine has a limited efficacy against bovine TB, but can improved by over-expression of protective antigens. The M. bovis antigen 85B demonstrates ability to induce protective immune response against bovine TB in animal models. However, current systems for the construction of recombinant BCG expressing multiple copies of the gene result in strains of low genetic stability that rapidly lose the plasmid in vivo. Employing antibiotic resistance as selective markers, these systems also compromise vaccine safety. We previously reported the construction of a stable BCG expression system using auxotrophic complementation as a selectable marker. OBJECTIVES The fundamental aim of this study was to construct strains of M. bovis BCG Pasteur and the auxotrophic M. bovis BCG ΔleuD expressing Ag85B and determine their stability in vivo. METHODS Employing the auxotrophic system, we constructed rBCG strains that expressed M. bovis Ag85B and compared their stability with a conventional BCG strain in mice. Stability was measured in terms of bacterial growth on the selective medium and retention of antigen expression. FINDINGS The auxotrophic complementation system was highly stable after 18 weeks, even during in vivo growth, as the selective pressure and expression of antigen were maintained comparing to the conventional vector. MAIN CONCLUSION The Ag85B continuous expression within the host may generate a stronger and long-lasting immune response compared to conventional systems.

Stable expression of Leptospira interrogans antigens in auxotrophic Mycobacterium bovis BCG

Mycobacterium bovis BCG has been proposed as an effective live vector for multivalent vaccines. The development of mycobacterial genetic systems to express foreign antigens and the adjuvanticity of BCG are the basis for the potential use of this attenuated mycobacterium as a recombinant vaccine vector. Stable plasmid vectors without antibiotic resistance markers are needed for heterologous antigen expression in BCG. Our group recently described the construction of a BCG expression system using auxotrophic complementation as a selectable marker. In this work, LipL32 and LigAni antigens of Leptospira interrogans were cloned and expressed in M. bovis BCG Pasteur and in the auxotrophic M. bovis BCG ΔleuD strains under the control of the M. leprae 18kDa promoter. Stability of the plasmids during in vitro growth and after inoculation of the recombinant BCG strains in hamsters was compared. The auxotrophic complementation system was highly stable, even during in vivo growth, as the selective pressure was maintained, whereas the conventional vector was unstable in the absence of selective pressure. These results confirm the usefulness of the new expression system, which represents a huge improvement over previously described expression systems for the development of BCG into an effective vaccine vector.

Avaliação da imunização de hamsters com plasmídeos que codificam componentes salivares de Lutzomiya longipalpis (LJM19) e/ou antígeno parasitário (KMP11) contra a infecção com Leishmania chagasi / Evaluation of immunization of hamsters with plasmids encoding salivary components of Lutzomyia longipalpis (LJM19) and / or parasite antigen (KMP11) against infection with Leishmania chagasi

Hamsters têm sido utilizados como modelos experimentais visando compreender os mecanismos de respostas imunes contra espécies de Leishmania do complexo donovani. Estes modelos são capazes de reproduzir muitas das manifestações clínicas da leishmaniose visceral humana. Estudos recentes demonstraram que a imunização de hamsters com plasmídeos codificantes para proteínas salivares (LJM19) de Lutzomyia longipalpis, vetor de L. chagasi, bem como antígenos parasitários (KMPl1) protege hamsters contra um desafio letal com Leishmania chagasi. Neste trabalho, hamsters foram utilizados para avaliar o efeito protetor contra uma infecção por L. chagasi utilizando imunização com os plasmídeos que codificam as proteínas LJM19 e KMP11 administrados em conjunto. A imunização com os plasmídeos induziu a produção de IFN-y nos linfonodos drenantes do local das imunizações quando os animais foram avaliados 7, 14 e 21 dias após a última imunização. Uma vez imunizados e desafiados com L. chagasi mais saliva do vetor, os animais mostraram maiores relações (...) nos linfonodos drenantes quando mensuradas 7 e 14 dias após o desafio. Quando avaliados 2 e 5 meses após o desafio, os animais imunizados mostraram menores cargas parasitárias no baço e no fígado e maiores relações (...) no baço 2 meses após o desafio. Além disso, os hamsters imunizados apresentaram maior conservação da arquitetura histológica do baço e do fígado nos tempos avaliados e não desenvolveram distúrbios hematológicos quando comparados com animais controles sadios.

Contudo, efeito protetor adicional pela imunização com os diferentes plasmídeos administrados em conjunto não foi observado em relação às imunizações com os plasmídeos separados. Comparações entre rotas de administração de plasmídeos foram estudadas utilizando as vias intradérmica e intramuscular. Os grupos de animais que receberam a imunização intradérmica apresentaram uma proteção mais prolongada quando comparados aos animais imunizados intramuscularmente. Estes resultados mostram que apesar da combinação de plasmídeos não induzir maior proteção que os plasmídeos separados, a via de imunização intradérmica pode conferir uma proteção mais duradoura quando comparada com a imunização pela via intramuscular.

Poduction of PCB01, a plasmid for DNA immunization against the adhesin of Escherichia coli K88AB

Growth characteristics and plasmid yields of Escherichia coli JM109 transformed with pCB01, a plasmid that encodes genes for the fimbrial adhesin of E. coli K88ab and for ampicillin resistance, grown in two culture media in agitated flasks and in fermentor, are reported. The rate of plasmid loss during growth was estimated by the differential counts in media with and without ampicillin. Plasmid yields of cultures grown in flasks varied from 0.9 to 67 µg/ml of medium, while those grown in fermentor attained 62 µg/ml of medium after 8 hours of culture. Plasmid bearing cells were outgrown by plasmid free cells in proportions varying from 5 to 1.2 non-transformed for each transformed cell during growth. Generation times of total population and plasmid bearing cells were 33 and 61 minutes, and 36 and 121 minutes, for fermentor and flask grown cultures, respectively. The same culture grown in fermentor and in flasks produced 62 and 33 µg of plasmid DNA per ml of medium, respectively. Bacterial concentrations and plasmid yields were higher in BHI than in LB medium. Yields of plasmid DNA obtained from the same batch were 1,7 times higher with cesium chloride-ethidium bromide gradients than with commercial columns.

Vacunas de ADN desnudo / Naked DNA vaccines

Las vacunas génicas o de ADN desnudo, que aún se hallan en el campo experimental, constituyen el avance más importante en la historia de la vacunología. Los poderes inmunizantes y protectores que estas vacunas inducen están claramente establecidos, en ensayos preclínicos, en animales experimentales. Además se está estudiando su capacidad terapéutica. Se ha avanzado mucho en el conocimiento de las vías y los métodos de inmuzación, pero aún se desconocen los mecanismos de transfección del plásmido y, lo que es muy importante, cuál o cuáles son las células transfectadas capaces de provocar en el vacunado, una respuesta a células citotóxicas y anticuerpos. Hay evidencias experimentales que afirman la importancia de los miocitos, los queratinocitos o las células dendríticas como factores principales de esta respuesta inmune. Otros experimentos sugieren dudas sobre cada uno de estos participantes. El objeto de esta revisión es presentar el estado actual del conocimiento sobre los tipos de células que pueden ser transfectadas, que expresan el gen y presentan el antígeno vacunante en una respuesta inmune a ADN desnudo. Lo más probable es que no sea una y la misma célula, la transfectada y la que presenta el péptido inmunizante en MHC clase I y II. Un paso importante para el conocimiento del mecanismo de inmunización por ADN sería el esclarecimiento del mecanismo de transfección del plásmido de ADN bacteriano. ¿Habrá algún tipo celular con receptores específicos que incorporen el plásmido, lo expresen y transfieran su producto a las células presentadoras de antígeno?

DNA-mediated immunization of mice with plasmid encoding HBs antigen

In order to develop an experimental DNA vaccine for the prevention and treatment of hepatitis B virus infection, hepatitis B virus surface antigen (HBsAg) DNA was subcloned into an E. coli-eukaryotic cell shuttle vector and was expressed in the Baculovirus expression system. Intramuscular, intradermal, and intraperitoneal injections of 30 microg of the plasmid DNA expressing HBsAg induced humoral and cellular immune responses in ICR mice. The first IgG antibodies were detected after ten days and specific IgG antibody titers peaked after two months of a single intramuscular DNA injection. Anti-HBs antibody titers gradually increased and peaked at four months following intradermal DNA injection, and in case of intraperitoneal injection they peaked at seven months. Generation of HBs-specific helper T lymphocytes was also investigated through the production of interleukin-2 by T helper cells. Boosting effects of HBs DNA were investigated without much results. In general, DNA-mediated HBs immunization induced humoral and cellular immune responses in mice that appears to simulate immune responses in human during the course of HBV vaccination.

Detection of IgM antibody against region IV flagellin of Salmonella paratyphi A.

Salmonella paratyphi A is a pathogenic bacterium that causes paratyphoid fever. The current laboratory diagnostic techniques are unsatisfactory. To improve diagnosis, a plasmid (pSK-8E) encoding phase 1 flagellin gene nucleotide position 452-890 from S. paratyphi A has been constructed. The recombinant protein expressed from the plasmid has been used to develop an indirect ELISA for IgM antibody detection. Sera from patients with hemoculture positive for S. paratyphi A, S. typhi, other gram-positive and gram-negative bacteria, and dengue hemorrhagic fever as well as from healthy control subjects were tested. Sensitivity, specificity, positive and negative predictive values of the test were 56.9%, 98.8%, 90.6% and 92.1%, respectively. Since the sensitivity was low, the explanation for this result was investigated. It was found that the sensitivity of the test could be increased to 83.3% if the sera were obtained 9-12 days after onset of fever. The sera obtained earlier or later gave only 33.3% and 66.6% sensitivity, respectively. This result suggests that the IgM antibody detection assay which we have developed is a valuable tool for diagnosis of S. paratyphi A infection when the serum samples are taken at the appropriate time.

Immunization against the colonization factor antigen I of enterotoxigenic Escherichia coli by administration of a bivalent Salmonella typhimurium aroA strain

An expression plasmid (pCFA-1) carrying the cfaB gene that codes for the enterotoxigenic Escherichia coli (ETEC) fimbrial adhesin colonization factor antigen I(CFA/I) subunit was constructed and used to transform a derivative of the attenuated Salmonella typhimurium aroA vaccine strain SL3261 carrying an F'lacl(q). Treatment of the transformed strain with isopropyl-beta-D-thiogalactopyranoside (IPTG) resulted in elevated in vitro expression of the CFA/I subunit. Although flagellar function and lipopolysaccharide (LPS) synthesis were similar in both the parental and the recombinant strains, spleen colonization was reduced in the recombinant strain. AII BALB/c mice parenteally inoculated with the recombinant strain developed significant anti-CFA/I and anti-LPS serum antibody titers (P<0.05). Moreover, 2 of 5 mice orally inoculated with the engineered Salmonella strain developed anti-CFA/I intestinal IgA (P>0.05) while 4/5 of the same mice developed anti-LPS (P<0.05). The results indicate that the vaccine strain elicited an antibody response against the bacterial host both after oral and intravenous immunization while the response against the CFA/I antigen was significant only after inoculation by the intravenous route.

Diffuse adherence, ST-I enterotoxin and CFA/IV colonization factor are encoded by the same plasmid in the Escherichia coli O29: H21 strai

Escherichia coli O29:H21 is a human enterotoxigenic serotype that produces heat-stable (ST-I) enterotoxin, adheres diffusely to HeLa cells, and presents colonization factor antigen IV (CFA/IV) composed of CS5CS6 surface antigens. In one strain studied the genes for diffuse adherence and CFA/IV (CS5CS6) production were found to be present in the same plasmid encoding ST-I. The virulence plasmid (Ent) presented two unrelated basic replicons homologous to repFIC and repW. Gene(s) encoding diffuse adherence did not share homology with the probe for F1845 fimbrial adhesin which is responsible for this phenotype in other E. coli strains. Ent plasmid containing genes for diffuse adherence have not been described previously.

Dengue virus: detection and pathogeny

Sequences from a cDNA of dengue virus type 4 were cloned into transcription vectors. These sequences included the E, NS1, NS2A, NS2B, NS3 genes. RNA transcipts produced in vitro from these plasmids were used in hybridization assays to detect dengue viral sequences. With these RNA-probes we have been able to detect molecules of serotype-specific dengue 4 viral RNA. Moreover, the riboprobes detected viral sequences of other serotypes in the following order of sensitivity 4 > 2 > 3 > 1, and might be useful to differentiate serotypes

Characterization of plasmid-related antigen of Yersinia enterocolitica by immunological techniques

Yersínia enterocolitica tem sua virulência relacionada a plasmídeo de 40-48-MDa que codifica proteínas que podem ser expressas nas membranas ou excretadas no meio de cultura. Procurou-se determinar o perfil dessas proteínas em cepas de Y. enterocolitica com e sem o plasmídeo de 40-48-MDa, através de gel de poliacrilamida com SDS (SDS-PAGE). Procurou-se também estudar as condiçöes ótimas de cultura de bactérias para expressäo dessas proteínas e finalmente analisá-las empregando a técnica de Immunoblot e utilizando anti-soro preparado com a amostra com e sem plasmídeo. Esses estudos resultaram na demonstraçäo da ocorrência, entre outros, de uma proteína de 38-kDa, presente apenas na cepa com plasmídeo e que era excretada quando o cultivo era realizado a 37ºC em meio de MOX