Biomedical subjects

Susan W Barnett

Publications and source records attributed to Susan W Barnett.

At least 19 recordsLinked to original sources

PubMed2006

Efficient protein boosting after plasmid DNA or recombinant adenovirus immunization with HIV-1 vaccine constructs.

DNA plasmids and recombinant adenovirus serotype-5 (rAd5) vectors are being studied in human clinical trials as HIV-1 vaccine candidates. Each elicits robust T-cell responses and modest antibody levels. Since protein immunization alone elicits antibody but not CD8 T-cell responses, we studied protein boosting of DNA and rAd5 HIV-1 vaccine vectors. A single Env protein immunization provided a marked boost in antibody titer in guinea pigs primed with either DNA or rAd5 vaccines, and the resulting antibody binding and neutralization levels were similar to those attained after thee sequential protein immunizations. Since both T-cell immunity and neutralizing antibodies are thought to be required for protection against HIV-1, it may be possible to establish a balanced T-cell and antibody response with appropriate vectored vaccines and improve the neutralizing antibody titer with protein boosting.

AIDS Vaccines↗

PubMed2006

An adenovirus-based HIV subtype B prime/boost vaccine regimen elicits antibodies mediating broad antibody-dependent cellular cytotoxicity against non-subtype B HIV strains.

Although HIV subtype B predominates in North America and Western Europe, most HIV infections worldwide are non-subtype B. Globally effective AIDS vaccines need to elicit broad immunity against multiple HIV strains. In this study, 10 chimpanzees were intranasally primed sequentially with adenovirus type 5 (Ad5)- and Ad7-HIVMNenv/rev recombinants and boosted twice intramuscularly with heterologous oligomeric HIVSF162 gp140DeltaV2 protein in MF59 adjuvant. Sera were evaluated for binding, neutralizing, and antibody-dependent cellular cytotoxicity (ADCC) against HIV clades A, B, C, and CRF01_AE. The vaccine regimen elicited high-titered HIV subtype A, B, C and CRF01_AE gp120-binding antibodies. Sera from 7 of 10 vaccinated chimpanzees cross-neutralized the heterologous South African subtype C primary HIVTV-1 isolate. Significant cross-clade neutralization against other subtype A, C and E isolates was not observed. Sera from all animals mediated ADCC of cells coated with gp120 from HIV subtypes A and B. Nine of 10 animals also exhibited ADCC activity against HIV subtype C and CRF01_AE gp120-coated targets. This subtype B Ad-HIV recombinant prime/envelope protein boost regimen is a promising approach for eliciting broad ADCC activity against diverse HIV clades. Incorporating additional non-subtype B envelope genes and protein boosts in a multivalent strategy may be required to elicit broader neutralizing antibodies against non-subtype B HIV strains.

AIDS Vaccines↗

PubMed2006

Viral evolution in macaques coinfected with CCR5- and CXCR4-tropic SHIVs in the presence or absence of vaccine-elicited anti-CCR5 SHIV neutralizing antibodies.

Macaques were immunized with SF162 Env-based gp140 immunogens and challenged simultaneously with the CCR5-tropic homologous SHIV(SF162P4) and the CXCR4-tropic heterologous SHIV(SF33A) viruses. Both mock-immunized and immunized animals became dually infected. Prior immunization preferentially reduced the viral replication of the homologous virus during primary infection but the relative replication of the two coinfecting viruses during chronic infection was unaffected by prior immunization, despite the fact that five of six immunized animals maintained a significantly lower overall viral replication that the control animals. Neutralizing antibodies participated in controlling the replication of SHIV(SF162P4), but not that of SHIV(SF33A). Dual infection resulted in the emergence and predominance within the circulating CCR5 virus pool, of a variant with a distinct neutralization phenotype. The signature of this variant was the presence of three amino acid changes in gp120, two of which were located in the receptor and coreceptor binding sites. Also, a significant fraction of the viruses circulating in the blood, as early as two weeks post-infection, was recombinants and prior immunization did not prevent their emergence. These findings provide new insights into the dynamic interaction of CCR5- and CXCR4-tropic HIV isolates that are potentially relevant in better understanding HIV-mediated pathogenesis.

AIDS Vaccines↗

PubMed2006

Immunization with HIV-1 SF162-derived Envelope gp140 proteins does not protect macaques from heterologous simian-human immunodeficiency virus SHIV89.6P infection.

Immunization by the SF162gp140 or the DeltaV2gp140 HIV-1 envelope proteins results in the generation of strong homologous neutralizing antibodies (NAbs) that offer similar degree of protection from disease-development to macaques challenged with homologous virus. These two immunogens elicit weak cross-reactive NAbs and their effectiveness against heterologous challenge is currently unknown. To examine this issue, we immunized macaques with SIVGag p55 and either the SF162gp140 or the DeltaV2gp140 and challenged them intravenously with SHIV-89.6P. All animals became infected but previous immunization with SF162gp140 accelerated the development of anti-SHIV89.6P neutralizing antibody responses following infection. DeltaV2gp140 is derived from SF162gp140 following the deletion of 30 amino acids and one N-linked glycosylation site from the V2 loop. Our results suggest that even small differences in HIV Envelope immunogen structure can affect the neutralizing antibody responses generated following infection.

AIDS Vaccines↗

PubMed2006

Evaluation of human immunodeficiency virus type 1 subtype C gag, pol, and gagpol DNA and alphavirus replicon vaccines.

The worldwide HIV-1 vaccine research endeavor is focused increasingly on subtype C, which is now the predominant strain of the present HIV/AIDS epidemic. Expression cassettes of HIV-1 subtype C gag, pol and versions of gagpol fusion cassettes were constructed and evaluated for their relative abilities to induce cellular immune responses in mice. Animals were vaccinated with DNA or alphavirus replicon particle-based vaccines and cellular immune responses were measured by flow cytometry. Five new major histocompatibility complex (MHC) class I-restricted T cell epitopes in subtype C Gag and Pol were identified. Although two CD8(+) T cell epitopes within Gag were immunodominant in BALB/c and CB6F1 mice, the overall breadth of the T cell responses in mice immunized with plasmids or recombinant alphavirus replicon particles encoding gagpol fusion genes was improved over single antigen genes (i.e. gag or pol alone). The patterns of epitope dominance were consistent among mice although there were variations observed between different animals in the relative contributions of the various epitopes to the total response. These data are consistent with observations in non-human primates (Otten GR, Schaefer M, Doe B, Liu H, Magede JZ, Donnelly J, et al. Potent immunogenicity of an HIV-1 gag-pol fusion DNA vaccine delivered by in vivo electroporation. Vaccine 2005, in press) and support a subtype C in-frame gagpol fusion gene vaccine.

AIDS Vaccines↗

PubMed2006

Characterization of immune responses elicited in macaques immunized sequentially with chimeric VEE/SIN alphavirus replicon particles expressing SIVGag and/or HIVEnv and with recombinant HIVgp140Env protein.

In the present study, macaques were coimmunized with VEErep/SINenv chimeric alphavirus replicon particles expressing SIVp55Gag and HIVDeltaV2gp140Env or only with replicon particles expressing HIVDeltaV2gp140Env. All animals were subsequently immunized with recombinant trimeric HIVDeltaV2gp140Env protein. During alphavirus immunization, anti-SIVGag and anti-HIVEnv-specific interferon (IFN)-gamma responses, as well as high titers of anti-HIVEnv binding (gp120 but not gp41 specific) and anti-HIV neutralizing antibodies, were generated. The subsequent immunization with recombinant HIVDeltaV2gp140 enhanced the neutralizing antibody titers and Env-specific IFN-gamma responses. Following intravenous challenge with the R5- tropic SHIV(SF162P4) virus, significantly lower primary plasma viremia levels were recorded in the immunized animals, as compared to control animals immunized with replicon particles expressing influenza virus HA. Our results show that this method of immunization elicits both strong cellular immunity and neutralizing antibodies in primates and, thus, merits further investigation.

AIDS Vaccines↗

PubMed2006

Antibody responses against HIV in rhesus macaques following combinations of mucosal and systemic immunizations with chimeric alphavirus-based replicon particles.

Mucosal and systemic transmission of HIV is prevalent. Therefore, mucosal followed by parenteral immunizations with chimeric vs. complete alphavirus-based replicon particles, encoding an HIV envelope glycoprotein, were tested. Female rhesus macaques were immunized intranasally and then intramuscularly. Following the immunizations, enhanced mucosal and systemic antibody responses were detected with the chimeric compared to the complete replicon particles. Although similar proportions of the same peripheral blood monocyte lineage target cells were infected with the chimeric vs. the complete replicon particles, the latter resulted in enhanced expression of the gene of interest, suggesting a possible mechanism of the enhanced immunogenicity.

Administration, Intranasal↗

PubMed2006

Antibody responses elicited in macaques immunized with human immunodeficiency virus type 1 (HIV-1) SF162-derived gp140 envelope immunogens: comparison with those elicited during homologous simian/human immunodeficiency virus SHIVSF162P4 and heterologous HIV-1 infection.

The antibody responses elicited in rhesus macaques immunized with soluble human immunodeficiency virus (HIV) Env gp140 proteins derived from the R5-tropic HIV-1 SF162 virus were analyzed and compared to the broadly reactive neutralizing antibody responses elicited during chronic infection of a macaque with a simian/human immunodeficiency virus (SHIV) expressing the HIV-1 SF162 Env, SHIV(SF162P4), and humans infected with heterologous HIV-1 isolates. Four gp140 immunogens were evaluated: SF162gp140, DeltaV2gp140 (lacking the crown of the V2 loop), DeltaV3gp140 (lacking the crown of the V3 loop), and DeltaV2DeltaV3gp140 (lacking both the V2 and V3 loop crowns). SF162gp140 and DeltaV2gp140 have been previously evaluated by our group in a pilot study, but here, a more comprehensive analysis of their immunogenic properties was performed. All four gp140 immunogens elicited stronger anti-gp120 than anti-gp41 antibodies and potent homologous neutralizing antibodies (NAbs) that primarily targeted the first hypervariable region (V1 loop) of gp120, although SF162gp140 also elicited anti-V3 NAbs. Heterologous NAbs were elicited by SF162gp140 and DeltaV2gp140 but were weak in potency and narrow in specificity. No heterologous NAbs were elicited by DeltaV3gp140 or DeltaV2DeltaV3gp140. In contrast, the SHIV(SF162P4)-infected macaque and HIV-infected humans generated similar titers of anti-gp120 and anti-gp41 antibodies and NAbs of significant breadth against primary HIV-1 isolates, which did not target the V1 loop. The difference in V1 loop immunogenicity between soluble gp140 and virion-associated gp160 Env proteins derived from SF162 may be the basis for the observed difference in the breadth of neutralization in sera from the immunized and infected animals studied here.

AIDS Vaccines↗

PubMed2005

Development of V2-deleted trimeric envelope vaccine candidates from human immunodeficiency virus type 1 (HIV-1) subtypes B and C.

The urgent need for a vaccine against HIV/AIDS requires that multiple strategies be employed and evaluated in a clinical setting. V2-loop deleted trimeric envelope (Env) immunogens (protein and DNA) from subtypes B and C human immunodeficiency virus type 1 (HIV-1) strains were produced for ongoing and future clinical evaluations with other HIV antigens, adjuvants and deliveries.

AIDS Vaccines↗

PubMed2005

Role of neutralizing antibodies in protective immunity against HIV.

HIV continues to be a major health problem world wide, however the situation is particularly serious in Asian and Sub-Saharan countries. Therefore, development of an effective HIV vaccine could help to reduce the severity of the disease and prevent infection. Over the last two decades significant efforts have been made towards inducing potent humoral and cellular immune responses by vaccination, however antibodies and CTL responses alone are likely not sufficient for inducing sterilizing immunity or long-term control of viral replication. Therefore, it is generally believed that both humoral and cellular responses will be needed for an effective HIV vaccine. In support of humoral immunity, monoclonal antibodies that recognize critical neutralizing epitopes have shown to be effective at passive transfer experiments in conferring protection against challenge infection. However, antibodies to similar epitope specificities are difficult to induce by vaccination. Therefore, optimization of Env structure is needed for exposing appropriate neutralizing epitopes and masking non-neutralizing epitopes. Since the crystal structure of the core of Env glycoprotein has been solved, efforts are in progress to design novel Env immunogens that may induce effective neutralizing responses. Furthermore, there are HIV-1 strains that are resistant to neutralization by monoclonal antibodies, yet neutralized by pooled sera from HIV-1 patients. Therefore, efforts should be made to identify these novel epitopes and to design strategies to incorporate them in potential vaccines. To facilitate comparative evaluation of vaccine immunogens for their ability to induce cross clade neutralizing antibodies, efforts should be made to use standardized neutralization assays and standard virus panels. Once potent HIV Env structure have been identified, their effectiveness may be enhanced through the use of adjuvants, delivery systems and prime and boost strategies to improve the quality and magnitude of neutralizing responses.

AIDS Vaccines↗

PubMed2005

Functionally-inactive and immunogenic Tat, Rev and Nef DNA vaccines derived from sub-Saharan subtype C human immunodeficiency virus type 1 consensus sequences.

The efficacy of cellular immune responses elicited by HIV vaccines is dependent on their strength, durability and antigenic breadth. The regulatory proteins are abundantly expressed early in the viral life cycle and CTL recognition may bring about early killing of infected cells. We synthesised DNA vaccine constructs that encode consensus HIV-1 subtype C Tat, Rev and Nef proteins. Proteins carrying inactivating mutations were tested for functional activity and highly expressing, inactive Tat, Rev and Nef mutants were identified and their reading frames fused into a TatRevNef cassette. Single- and polygene Tat, Rev and/or Nef constructs were immunogenic in BALB/c mice. These constructs may serve to increase the antigenic breadth for an HIV-1 vaccine that is relevant for sub-Saharan Africa.

AIDS Vaccines↗

PubMed2005

Replicating rather than nonreplicating adenovirus-human immunodeficiency virus recombinant vaccines are better at eliciting potent cellular immunity and priming high-titer antibodies.

A major challenge in combating the human immunodeficiency virus (HIV) epidemic is the development of vaccines capable of inducing potent, persistent cellular immunity and broadly reactive neutralizing antibody responses to HIV type 1 (HIV-1). We report here the results of a preclinical trial using the chimpanzee model to investigate a combination vaccine strategy involving sequential priming immunizations with different serotypes of adenovirus (Ad)/HIV-1(MN)env/rev recombinants and boosting with an HIV envelope subunit protein, oligomeric HIV(SF162) gp140deltaV2. The immunogenicities of replicating and nonreplicating Ad/HIV-1(MN)env/rev recombinants were compared. Replicating Ad/HIV recombinants were better at eliciting HIV-specific cellular immune responses and better at priming humoral immunity against HIV than nonreplicating Ad-HIV recombinants carrying the same gene insert. Enhanced cellular immunity was manifested by a greater frequency of HIV envelope-specific gamma interferon-secreting peripheral blood lymphocytes and better priming of T-cell proliferative responses. Enhanced humoral immunity was seen in higher anti-envelope binding and neutralizing antibody titers and better induction of antibody-dependent cellular cytotoxicity. More animals primed with replicating Ad recombinants mounted neutralizing antibodies against heterologous R5 viruses after one or two booster immunizations with the mismatched oligomeric HIV-1(SF162) gp140deltaV2 protein. These results support continued development of the replicating Ad-HIV recombinant vaccine approach and suggest that the use of replicating vectors for other vaccines may prove fruitful.

AIDS Vaccines↗

PubMed2005

Evaluation of envelope vaccines derived from the South African subtype C human immunodeficiency virus type 1 TV1 strain.

Human immunodeficiency virus type 1 (HIV-1) subtype C infections are on the rise in Sub-Saharan Africa and Asia. Therefore, there is a need to develop an HIV vaccine capable of eliciting broadly reactive immune responses against members of this subtype. We show here that modified HIV envelope (env) DNA vaccines derived from the South African subtype C TV1 strain are able to prime for humoral responses in rabbits and rhesus macaques. Priming rabbits with DNA plasmids encoding V2-deleted TV1 gp140 (gp140TV1DeltaV2), followed by boosting with oligomeric protein (o-gp140TV1DeltaV2) in MF59 adjuvant, elicited higher titers of env-binding and autologous neutralizing antibodies than priming with DNA vaccines encoding the full-length TV1 env (gp160) or the intact TV1 gp140. Immunization with V2-deleted subtype B SF162 env and V2-deleted TV1 env together using a multivalent vaccine approach induced high titers of oligomeric env-binding antibodies and autologous neutralizing antibodies against both the subtypes B and C vaccine strains, HIV-1 SF162 and TV1, respectively. Low-level neutralizing activity against the heterologous South African subtype C TV2 strain, as well as a small subset of viruses in a panel of 13 heterologous primary isolates, was observed in some rabbits immunized with the V2-deleted vaccines. Immunization of rhesus macaques with the V2-deleted TV1 DNA prime/protein boost also elicited high titers of env-binding antibodies and moderate titers of autologous TV1 neutralizing antibodies. The pilot-scale production of the various TV1 DNA vaccine constructs and env proteins described here should provide an initial platform upon which to improve the immunogenicity of these subtype C HIV envelope vaccines.

AIDS Vaccines↗

PubMed2004

Immunogenicity of HIV-1 Env and Gag in baboons using a DNA prime/protein boost regimen.

OBJECTIVES: To evaluate the immunogenicity of sequence-modified HIV env and gag in baboons using DNA prime and protein boost strategy. METHODS: Synthetic sequence-modified HIV gene cassettes were constructed that expressed three different forms of Env proteins, gp140, gp140mut and gp140TM, plus or minus a mutation in the protease-cleavage site. These plasmids were used to immunize baboons (Papio cynocephalus). A group of baboons was also immunized with both env and gag DNA followed by p55Gag virus-like particles (VLP) boost. RESULTS: Modest antibody responses and low or no lymphoproliferative responses were observed following multiple DNA immunizations. In contrast, strong antibodies and substantial antigen-specific lymphoproliferative responses were seen following booster immunizations with oligomeric Env protein (o-gp140US4) in MF59. Neutralizing antibody responses were scored against T cell line adapted HIV-1 strains after the protein boosters, but neutralizing responses were low or absent against homologous and heterologous primary isolate strains. In the group receiving both gag and env vaccines, modest antigen-specific antibody and lymphoproliferative responses were scored after the DNA immunizations; these responses were enhanced several-fold upon boosting with the VLP preparations. The addition of Gag antigen did not interfere with Env-specific antibody responses, but there was a negative effect on the levels of Env-specific lymphoproliferation. CONCLUSIONS: These results highlight the importance of improving the potency of HIV DNA vaccines by enhanced DNA delivery and prime-boost vaccine technologies to generate more robust immune responses in larger animal models. In addition, care must be taken when immunizations with Env and Gag antigens are performed together.

AIDS Vaccines↗

PubMed2004

Priming B cell-mediated anti-HIV envelope responses by vaccination allows for the long-term control of infection in macaques exposed to a R5-tropic SHIV.

The potential of vaccine-elicited anti-HIV envelope antibodies to control HIV-infection was evaluated by immunizing macaques with the HIV envelope protein and transiently depleting them of their CD8+ cells before intravenous challenge with the pathogenic CCR5-tropic SIV/HIV chimeric virus, SHIV(SF162P4). Although sterilizing immunity was not achieved, all vaccinated animals effectively controlled infection and remained free of disease for the duration of observation (over 3 years). In contrast, during the same period, the control animals progressed to disease. Both the vaccinees and the controls developed robust cell-mediated antiviral and neutralizing antibody responses following infection. A comparative analysis of these responses suggests that the more effective long-term control of infection by the vaccinated animals is due to the more rapid development of anti-HIV envelope antibodies. These studies suggest that priming by vaccination of B cell anti-HIV envelope responses maybe crucial for the long-term control of HIV infection.

AIDS Vaccines↗

PubMed2004

Neutralizing antibody responses to HIV: role in protective immunity and challenges for vaccine design.

AIDS continues to be a major health problem throughout the world with a high degree of mortality and morbidity. Therefore, there is an urgent need for an effective anti-HIV vaccine. Although the correlates of protective immunity against infection by HIV remain unidentified, recent studies have demonstrated that both humoral and cellular responses are required for controlling viral replication. Vaccine efforts should therefore aim at developing broad and potent humoral as well as cellular responses. Anti-HIV T-cell responses can be generated both in animals and humans by several vaccine modalities. In contrast, broadly neutralizing antibody responses against HIV have not been elicited by any strategy tested in the clinic thus far. The presence of such responses has the potential to prevent the establishment of infection. If not, the presence of neutralizing antibodies may significantly reduce the number of cells that become infected, therefore reducing the inoculum, which may delay viral spread and allow for a better control of viral replication in the infected host. Finally, cytotoxic T-lymphocytes may facilitate the clearance of virally infected cells. One of the biggest challenges in HIV vaccine development is to design a HIV envelope immunogen that can induce protective neutralizing antibodies effective against the diverse HIV-1 strains that characterize the global pandemic. The focus of this article is to review the importance of antibodies and the strategies that are currently being used for inducing such antibodies.

AIDS Vaccines↗

PubMed2003

Induction of broad and potent anti-human immunodeficiency virus immune responses in rhesus macaques by priming with a DNA vaccine and boosting with protein-adsorbed polylactide coglycolide microparticles.

Several vaccine technologies were evaluated for their abilities to induce anti-human immunodeficiency virus Gag immune responses in rhesus macaques. While no vaccine alone was able to induce broad and strong immune responses, these were achieved by priming with Gag DNA and boosting with Gag protein adsorbed to polylactide coglycolide microparticles. This regimen elicited strong antibodies, helper T cells, and cytotoxic T lymphocytes and thus holds promise as an effective vaccination scheme.

AIDS Vaccines↗

PubMed2003

Expression and immunogenicity of sequence-modified human immunodeficiency virus type 1 subtype B pol and gagpol DNA vaccines.

Control of the worldwide AIDS pandemic may require not only preventive but also therapeutic immunization strategies. To meet this challenge, the next generation of human immunodeficiency virus type 1 (HIV-1) vaccines must stimulate broad and durable cellular immune responses to multiple HIV antigens. Results of both natural history studies and virus challenge studies with macaques indicate that responses to both Gag and Pol antigens are important for the control of viremia. Previously, we reported increased Rev-independent expression and improved immunogenicity of DNA vaccines encoding sequence-modified Gag derived from the HIV-1(SF2) strain (J. zur Megede, M. C. Chen, B. Doe, M. Schaefer, C. E. Greer, M. Selby, G. R. Otten, and S. W. Barnett, J. Virol. 74: 2628-2635, 2000). Here we describe results of expression and immunogenicity studies conducted with novel sequence-modified HIV-1(SF2) GagPol and Pol vaccine antigens. These Pol antigens contain deletions in the integrase coding region and were mutated in the reverse transcriptase (RT) coding region to remove potentially deleterious enzymatic activities. The resulting Pol sequences were used alone or in combination with sequence-modified Gag. In the latter, the natural translational frameshift between the Gag and Pol coding sequences was either retained or removed. Smaller, in-frame fusion gene cassettes expressing Gag plus RT or protease plus RT also were evaluated. Expression of Gag and Pol from GagPol fusion gene cassettes appeared to be reduced when the HIV protease was active. Therefore, additional constructs were evaluated in which mutations were introduced to attenuate or inactivate the protease activity. Nevertheless, when these constructs were delivered to mice as DNA vaccines, similar levels of CD8(+) T-cell responses to Gag and Pol epitopes were observed regardless of the level of protease activity. Overall, the cellular immune responses against Gag induced in mice immunized with multigenic gagpol plasmids were similar to those observed in mice immunized with the plasmid encoding Gag alone. Furthermore, all of the sequence-modified pol and gagpol plasmids expressed high levels of Pol-specific antigens in a Rev-independent fashion and were able to induce potent Pol-specific T- and B-cell responses in mice. These results support the inclusion of a gagpol in-frame fusion gene in future HIV vaccine approaches.

AIDS Vaccines↗