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Biomedical subjects

B M Bhat

Publications and source records attributed to B M Bhat.

At least 19 recordsLinked to original sources
PubMed1999

Enhanced immunogenicity of hepatitis B surface antigen by insertion of a helper T cell epitope from tetanus toxoid.

The currently marketed hepatitis B vaccines in the U.S. are based on the recombinant major hepatitis B surface antigen (HBsAg) of hepatitis B virus. Although a large majority of individuals develop protective immunity to HBV-induced disease after three immunizations, routinely a small but a significant percentage of the human population does not respond well to these vaccines. In this report, we describe the generation of a novel HBsAg molecule containing a Th epitope derived from tetanus toxoid (TT). Using recombinant DNA technology. the TT Th epitope (TTe) was inserted into the HBsAg coding sequence. Using a recombinant adenovirus expression system, HBsAg TTe chimeric protein was produced in A549 cells and found to be secreted into culture medium as 22 nm particles. The chimeric HBsAg particles were readily purified by immunoaffinity chromatography and their immunogenicity was evaluated relative to native HBsAg produced in an adenovirus expression system. When evaluated in inbred and outbred strains of mice, HBsAg TTe was shown to enhance several-fold the anti-HBs response relative to native HBsAg. Further enhanced responses were observed in mice primed with TT. This highly immunogenic form of HBsAg has promise as an improved HBsAg subunit vaccine.

Animals↗
PubMed1997

Replication and immunogenicity of Ad7-, Ad4-, and Ad5-hepatitis B virus surface antigen recombinants, with or without a portion of E3 region, in chimpanzees.

Human adenovirus vectors containing intact or largely deleted E3 region were used to construct adenovirus-hepatitis B recombinant viruses (Ad-HepB) and shown to produce substantial amount of recombinant protein, hepatitis B surface antigen (HBsAg), in tissue culture. Previously we showed that these viruses were able to elicit good anti-HBs antibodies in a dog model. In the present study, the Ad-HepB viruses were evaluated for replication and immunogenicity in chimpanzees which sustain permissive infection by human adenoviruses. Recombinants containing entire E3 region showed better replication pattern than their E3 deleted counterparts as evidenced by longer duration and high titers of virus shedding. The effect of E3 region was also seen in the antibody titers against HBsAg in that the E3 containing viruses showed better response than the E3 deleted viruses. The importance of E3 region for the development of adenovirus vectored vaccines is further discussed.

Adenovirus E3 Proteins↗
PubMed1994

Efficacy of adenovirus-vectored respiratory syncytial virus vaccines in a new ferret model.

In the absence of an adequate small animal model for testing the efficacy of adenovirus-vectored respiratory syncytial virus (RSV) vaccines, a ferret model was established for this purpose. Recombinant adenovirus types 4, 5 and 7 expressing the RSV fusion glycoprotein (F), the attachment glycoprotein (G) or both F and G were constructed previously. These recombinants contain a deletion of a large portion of the E3 region of the respective adenovirus vector. In addition, an Ad7(E3+)F recombinant virus which contains an intact E3 region was constructed to assess whether E3 region functions might enhance vaccine immunogenicity. Evaluation of these viruses in the ferret model demonstrated that Ad4 and Ad5 recombinants, administered intranasally to ferrets, induce stronger seroresponses to RSV than do Ad7 recombinant viruses. Ad7(E3+)F did not show enhanced immunogenicity relative to E3-deleted recombinant viruses. However, measurement of RSV infectivity in nasal washes, following intranasal RSV challenge, showed that five different vaccination regimens, Ad7F/Ad4F, Ad7G/Ad4G, Ad7FG/Ad4FG, Ad4F/Ad7(E3+)F and Ad5F/Ad4F, protected ferrets from RSV infection in a dose-dependent manner.

Animals↗
PubMed1994

Immunogenicity of recombinant adenovirus-human immunodeficiency virus vaccines in chimpanzees following intranasal administration.

Recombinant adenovirus (Ad)-human immunodeficiency virus (HIV) vaccines expressing HIVIIIB Env and Gag proteins were evaluated for immunogenicity in chimpanzees following intranasal administration. When Ad7-, Ad4-, and Ad5-vectored vaccines were administered sequentially at 0, 24, and 52 weeks, respectively, to three chimpanzees, the inoculations resulted in limited virus replication in the nasopharynx, but extensive Ad-HIV replication occurred in the intestine. High-titered IgG serum antibody responses to Env and Gag that were nonneutralizing were induced following booster administration of Ad4-HIV recombinant viruses. Following the Ad5-HIV booster, low levels of neutralizing antibodies as well as V3 loop antibodies were induced in all three chimpanzees that persisted for several months. Administration of a gp160 subunit vaccine (baculovirus derived) in SAF-m 24 weeks later boosted broadly neutralizing serum antibodies that peaked within 1 month of the injection. Two additional subunit boosters 19 and 37 weeks later were progressively less effective at stimulating serum neutralizing antibody responses. Substantial local immune responses were induced in nasal, vaginal, and salivary secretions following the third Ad-HIV intranasal immunization. These responses were further boosted with the gp160 subunit vaccine, which also stimulated production of rectal antibodies. The predominant responses in all secretions tested were of the IgG isotype, although some IgA responses were also detected. Strong blastogenic responses to HIV recombinant Env and Gag proteins were induced after each immunization.

AIDS Vaccines↗
PubMed1994

Immunogenicity of high expression adenovirus-hepatitis B virus recombinant vaccines in dogs.

High yielding adenovirus (Ad)-hepatitis B recombinant (Ad-Hep B) viruses were prepared by insertion of the hepatitis B surface antigen (HBsAg) gene into the early region 3 (E3 region) of Ad4 or Ad7 vectors containing intact or largely deleted E3 regions. Both E3-deleted and non-deleted recombinants produced about six- to eight-fold higher amounts of HBsAg than previously reported recombinants. These recombinant viruses were evaluated for immunogenicity in dogs which sustain abortive lung infections by Ad4 and Ad7. Recombinants containing E3 deletions elicited 10- to 12-fold stronger anti-HBs primary responses than previously evaluated low yield recombinants. Further immunizations with heterotypic Ad-Hep B recombinants induced substantial anti-HBs booster responses as well as anti-'a' epitope responses. In contrast, recombinant viruses containing intact E3 regions induced only weak or negligible anti-HBs responses, although such viruses induced strong antibody responses to the Ad vectors. The immunogenicity of high-yielding Ad recombinants correlated with temporal expression of HBsAg and thus the dog represents a valuable model for evaluation of immune responses to heterologous proteins that are expressed early and that do not require efficient DNA replication. Recombinants expressing HBsAg late in the infectious cycle require further testing in the fully permissive chimpanzee model. This study establishes that the E3-deleted high yield Ad4 and Ad7 recombinants represent promising live oral hepatitis B vaccine candidates.

Adenovirus E3 Proteins↗
PubMed1994

Adenovirus vectored vaccines.

Human recombinant adenoviruses (Ad) have been employed to develop experimental vaccines against a number of infectious agents. Ad-vectored vaccines express recombinant proteins, including any post-translational modifications, into functioning replicas of the native proteins capable of eliciting neutralizing antibodies in both abortive and permissive animal models. Human Ad types 4, 5, and 7 were used to construct recombinant viruses that express the respiratory syncytial virus F or G glycoproteins, the hepatitis B surface antigen, and the HIV env or gag genes. The recombinant Ad-HIV viruses are of particular interest and have been examined for their immunogenicity in dogs and chimpanzees. Dogs were immunized intratracheally with Ad-env recombinants (10(9) pfu/dog). Excellent humoral anti-HIV responses, including neutralizing antibodies, were detected in the sera following booster immunization (12-18 weeks after primary immunization) with a second Ad-env recombinant made in a different Ad serotype (heterotypic booster). Chimpanzees were immunized in two ways, orally with lyophilized virus (10(9) to 10(10) pfu/virus) in enteric-coated capsules or intranasally (10(7) pfu/virus). Intranasal immunization was superior to oral immunization with respect to replication of recombinant viruses as well as induction of anti-Ad and anti-HIV antibodies. Administration by both routes resulted in stimulation of cellular immune responses, as measured by antigen proliferation assays. Anti-HIV antibodies were detected in chimpanzee secretions (salivary, nasal, rectal, vaginal) taken from animals following intranasal immunization with a heterotypic recombinant. Intranasal administration effectively primed chimpanzees to produce high-titred (320-640) serum neutralizing antibodies to HIV following boosting with a baculovirus-derived env (gp160) subunit vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)

AIDS Vaccines↗
PubMed1992

Adenovirus-human immunodeficiency virus (HIV) envelope recombinant vaccines elicit high-titered HIV-neutralizing antibodies in the dog model.

Recombinant human adenoviruses (Ads) (types 4, 5, and 7) expressing the HIV-1 envelope membrane glycoprotein (gp160) were tested for immunogenicity in the dog. Administration of recombinant Ad7-env by intratracheal inoculation resulted in a low serum antibody response to gp160, which developed over several weeks. A strong neutralizing antibody response to the Ad7 vector developed within 1 week of infection. A subsequent booster inoculation 12 weeks later with the heterotypic Ad4-env recombinant virus resulted in significantly enhanced humoral responses directed at the envelope antigen, as measured by both ELISA and Western blot analysis as well as high-titer type-specific neutralizing antibodies, with some animals achieving neutralization titers approaching 1000. Recombinant HIV envelope glycoprotein derived from Ad-HIV-infected cell cultures was used as a subunit booster injection for dogs that had previously received sequential immunizations with heterotypic recombinant Ads. Significant immune responses against the envelope developed as measured by ELISA, Western blot analysis, and neutralization assays. These data indicate that live recombinant Ad-HIV vaccines are capable of inducing high-titer type-specific neutralizing antibodies to gp160 in vivo. Recombinant HIV envelope glycoprotein subunit vaccines, prepared from Ad-env-infected cells, are capable of boosting these responses.

AIDS Vaccines↗
PubMed1992

Immunogenicity of recombinant adenovirus-respiratory syncytial virus vaccines with adenovirus types 4, 5, and 7 vectors in dogs and a chimpanzee.

Recombinant adenovirus type 4, 5, and 7 expressing the fusion glycoprotein (F) gene, the attachment glycoprotein (G) gene, or both F and G genes of respiratory syncytial virus (RSV) was constructed. Intratracheal immunization of dogs with Ad7F induced moderate titers of RSV-neutralizing antibodies. After booster immunization with Ad4F, the dogs developed high titers of RSV-specific antibody. Subsequently, three two-dose vaccination regimens, Ad4F/Ad5F, Ad7G/Ad4G, and Ad7FG/Ad4FG, were compared with Ad7F/Ad4F for immunogenicity and protective efficacy. The results indicated that Ad4F/Ad5F was equal or greater in immunogenicity to Ad7F/Ad4F, but Ad7G/Ad4G and Ad7FG/Ad4FG were less effective than Ad7F/Ad4F in inducing RSV-neutralizing antibody. All vaccination regimens completely protected the lungs of dogs from RSV infection. A chimpanzee was sequentially immunized orally with Ad7F, Ad4F, and Ad5F. A low-level antibody response to RSV was induced after the primary immunization, but no significant increases were observed after booster immunizations.

Adenoviruses, Human↗
PubMed1991

Adenovirus vectors for gene expression.

Adenoviruses possess a combination of features that make them highly suitable as vectors for expression of heterologous genes. Non-conditional and non-defective adeno-vectors have been constructed to obtain high level expression of a number of foreign genes and some of them have been shown in animal models to exhibit excellent promise as vaccine candidates.

Adenoviridae↗
PubMed1990

High level expression of the envelope glycoproteins of the human immunodeficiency virus type I in presence of rev gene using helper-independent adenovirus type 7 recombinants.

The effect of rev (art/trs) gene on the level of HIV-1 envelope (env) expression using recombinant adenovirus was investigated. Recombinant adenoviruses expressing either the envelope or the rev gene of the human immunodeficiency virus type 1 (HIV-1) were constructed by inserting the gene into an expression cassette. The expression cassette contained the adenovirus type 7 major late promoter, followed by leader 1 of the adenovirus tripartite leader and a portion of intron between leaders 1 and 2, leaders 2 and 3, and a hexon polyadenylation signal. The cassette was then inserted at the terminal region between the E4 and ITR regions of the adenovirus 7 genome with a concomitant E3 region deletion (80-87 m.u.). A549 cells infected with the recombinant virus containing the env gene produced the envelope glycoproteins gp160, gp120, and gp41. HIV-1 envelope gene expression was greatly enhanced (20- to 50-fold) in the cells that were simultaneously infected with the recombinant adenovirus containing the rev gene as measured by ELISA and Western blotting. Interestingly, this effect was observed despite the lack of the 5' down splice site for rev and seems to be post-transcriptional. Another recombinant adenovirus which contains both the rev and the env genes was constructed by inserting the rev gene in the deleted E3 region and the env gene in the terminal cassette. This double recombinant virus expressed high levels of env antigen in A549 cells similar to those attained upon co-infection with two separate recombinant viruses containing the rev or env gene. Furthermore, the rev gene nucleotide sequence could be altered without altering the amino acid sequence and its sequences truncated by 17 amino acids from the C-terminus had no effect of rev function.

Adenoviridae↗
PubMed1990

Adenovirus vaccine vectors expressing hepatitis B surface antigen: importance of regulatory elements in the adenovirus major late intron.

Adenovirus types 4 and 7 are currently used as live oral vaccines for prevention of acute respiratory disease caused by these adenovirus serotypes. To investigate the concept of producing live recombinant vaccines using these serotypes, adenovirus types 4 (Ad4) and 7 (Ad7) were constructed that produce HBsAg upon infection of cell cultures. Ad4 recombinants were constructed that express HBsAg from a cassette inserted 135 bp from the right-hand terminus of the viral genome. The cassette contained the Ad4 major late promoter followed by leader 1 of the tripartite leader, the first intervening sequence between leaders 1 and 2, leaders 2 and 3, the HBsAg gene, and tandem polyadenylation signals from the Ad4 E3B and hexon genes. Using this same cassette, a series of Ad4 recombinants expressing HBsAg were constructed with deletions in the intervening sequence between leaders 1 and 2 to evaluate the contribution of the downstream control elements more precisely. Inclusion of regions located between +82 and +148 as well as +148 and +232 resulted in increases in expression levels of HBsAg in A549-infected cells by 22-fold and 44-fold, respectively, over the levels attained by an adenovirus recombinant retaining only sequences from +1 to +82, showing the importance of these elements in the activation of the major late promoter during the course of a natural Ad4 viral infection. Parallel increases were also observed in steady-state levels of cytoplasmic HBsAg-specific mRNA. When similar Ad7 recombinant viruses were constructed, these viruses also expressed 20-fold more HBsAg due to the presence of the intron. All Ad4 and Ad7 recombinants produced HBsAg particles containing gp27 and p24 which were secreted in the medium. When dogs were immunized intratracheally with one of these Ad7 recombinants, they seroconverted to both Ad7 and HBsAg to a high level.

Adenoviruses, Human↗
PubMed1990

Identification and characterization of the herpes simplex virus type 2 gene encoding the essential capsid protein ICP32/VP19c.

We describe the characterization of the herpes simplex virus type 2 (HSV-2) gene encoding infected cell protein 32 (ICP32) and virion protein 19c (VP19c). We also demonstrate that the HSV-1 UL38/ORF.553 open reading frame (ORF), which has been shown to specify a viral protein essential for capsid formation (B. Pertuiset, M. Boccara, J. Cebrian, N. Berthelot, S. Chousterman, F. Puvian-Dutilleul, J. Sisman, and P. Sheldrick, J. Virol. 63: 2169-2179, 1989), must encode the cognate HSV type 1 (HSV-1) ICP32/VP19c protein. The region of the HSV-2 genome deduced to contain the gene specifying ICP32/VP19c was isolated and subcloned, and the nucleotide sequence of 2,158 base pairs of HSV-2 DNA mapping immediately upstream of the gene encoding the large subunit of the viral ribonucleotide reductase was determined. This region of the HSV-2 genome contains a large ORF capable of encoding two related 50,538- and 49,472-molecular-weight polypeptides. Direct evidence that this ORF encodes HSV-2 ICP32/VP19c was provided by immunoblotting experiments that utilized antisera directed against synthetic oligopeptides corresponding to internal portions of the predicted polypeptides encoded by the HSV-2 ORF or antisera directed against a TrpE/HSV-2 ORF fusion protein. The type-common immunoreactivity of the two antisera and comparison of the primary amino acid sequences of the predicted products of the HSV-2 ORF and the equivalent genomic region of HSV-1 provided evidence that the HSV-1 UL38 ORF encodes the HSV-1 ICP32/VP19c. Analysis of the expression of the HSV-1 and HSV-2 ICP32/VP19c cognate proteins indicated that there may be differences in their modes of synthesis. Comparison of the predicted structure of the HSV-2 ICP32/VP19c protein with the structures of related proteins encoded by other herpes viruses suggested that the internal capsid architecture of the herpes family of viruses varies substantially.

Amino Acid Sequence↗
PubMed1990

Adenovirus vaccine strains genetically engineered to express HIV-1 or HBV antigens for use as live recombinant vaccines.

Types 4 and 7 adenovirus are currently used as live, oral vaccines for the prevention of adenovirus respiratory disease in military recruits. These vaccine strains have been genetically engineered in order to express HIV-1 or HBV antigens in infected cells. A dog model was developed to evaluate the immunogenicity of these recombinant vaccines. Dogs inoculated with live adenovirus-HBV recombinant vaccine produced antibody against hepatitis B surface antigen.

Adenoviridae↗
PubMed1989

Immunogenicity and efficacy testing in chimpanzees of an oral hepatitis B vaccine based on live recombinant adenovirus.

As a major cause of acute and chronic liver disease as well as hepatocellular carcinoma, hepatitis B virus (HBV) continues to pose significant health problems world-wide. Recombinant hepatitis B vaccines based on adenovirus vectors have been developed to address global needs for effective control of hepatitis B infection. Although considerable progress has been made in the construction of recombinant adenoviruses that express large amounts of HBV gene products, preclinical immunogenicity and efficacy testing of candidate vaccines has remained difficult due to the lack of a suitable animal model. We demonstrate here that chimpanzees are susceptible to enteric infection by human adenoviruses type 7 (Ad7) and type 4 (Ad4) following oral administration of live virus. Moreover, after sequential oral immunization with Ad7- and Ad4-vectored vaccines containing the hepatitis B surface antigen (HBsAg) gene, significant antibody responses to HBsAg (anti-HBs) were induced in two chimpanzees. After challenge with heterologous HBV, one chimpanzee was protected from acute hepatitis and the other chimpanzee experienced modified HBV-induced disease. These data demonstrate the feasibility of using orally administered recombinant adenoviruses as a general approach to vaccination.

Adenoviruses, Human↗
PubMed1987

A short sequence in the COOH-terminus makes an adenovirus membrane glycoprotein a resident of the endoplasmic reticulum.

The E19 protein of adenoviruses is a transmembrane protein that abrogates the intracellular transport of class I antigens by forming complexes with them in the ER. We show here that the E19 protein is retained in the ER even in the absence of class I antigens. To define the region conferring residency in the ER, we examined two mutant forms of the viral protein. A 5 amino acid extension of the 15-membered cytoplasmic tail of the protein reduces its interaction with class I antigens but does not change its intracellular distribution. Shortening the tail to 7 amino acids also diminishes the affinity for class I antigens; however, this mutant E19 protein becomes transported to the cell surface. Thus, we concluded that a small stretch of amino acids exposed on the cytoplasmic side of the ER membrane is responsible for the retention of the E19 protein in the ER.

Adenovirus Early Proteins↗
PubMed1987

A small deletion distant from a splice or polyadenylation site dramatically alters pre-mRNA processing in region E3 of adenovirus.

The E3 complex transcription unit of adenovirus encodes overlapping mRNAs (a to i) with different exon structures. The major mRNAs are a (approximately 40% of the total) and c (approximately 15%), which are spliced once, and f (approximately 15%) and h (approximately 25%), which are spliced twice. mRNA a uses the upstream E3A polyadenylation site, and the other mRNAs use the downstream E3B polyadenylation site. We analyzed virus deletion mutants to identify sequences important in alternative pre-mRNA processing in region E3. Our main finding is that a 64-base-pair deletion in dl742 causes mainly mRNAs f and h to be formed. mRNAs a and c are barely made. dl742 does not delete either a splice site or a polyadenylation site. Thus, the sequences deleted must function in alternative pre-mRNA processing independently of the signals at the actual splice and polyadenylation sites. The lack of synthesis of mRNA a by dl742 does not appear to result from a defect in the E3A polyadenylation signal but rather from an increase in splicing activity which results in the synthesis of doubly spliced mRNAs f and h at the expense of singly spliced mRNAs a and c. This suggests, in the wild-type situation, that the frequency of use of the E3A versus the E3B polyadenylation site may be determined by the rate of splicing, as well as, presumably, the rate of cleavage-polyadenylation at the E3A site.

Adenoviridae↗