Targeted Isolation of Antibodies Directed against Major Sites of SIV Env Vulnerability.

The simian immunodeficiency virus (SIV) challenge model of lentiviral infection is often used as a model to human immunodeficiency virus type 1 (HIV-1) for studying vaccine mediated and immune correlates of protection. However, knowledge of the structure of the SIV envelope (Env) glycoprotein is limited, as is knowledge of binding specificity, function and potential efficacy of SIV antibody responses. In this study we describe the use of a competitive probe binding sort strategy as well as scaffolded probes for targeted isolation of SIV Env-specific monoclonal antibodies (mAbs). We isolated nearly 70 SIV-specific mAbs directed against major sites of SIV Env vulnerability analogous to broadly neutralizing antibody (bnAb) targets of HIV-1, namely, the CD4 binding site (CD4bs), CD4-induced (CD4i)-site, peptide epitopes in variable loops 1, 2 and 3 (V1, V2, V3) and potentially glycan targets of SIV Env. The range of SIV mAbs isolated includes those exhibiting varying degrees of neutralization breadth and potency as well as others that demonstrated binding but not neutralization. Several SIV mAbs displayed broad and potent neutralization of a diverse panel of 20 SIV viral isolates with some also neutralizing HIV-2(7312A). This extensive panel of SIV mAbs will facilitate more effective use of the SIV non-human primate (NHP) model for understanding the variables in development of a HIV vaccine or immunotherapy.

Determinants in V2C2 region of HIV-1 clade C primary envelopes conferred altered neutralization susceptibilities to IgG1b12 and PG9 monoclonal antibodies in a context-dependent manner.

In the present study by examining pseudoviruses expressing patient chimeric envelopes (Envs) made between an IgG1b12 (b12)-sensitive (2-5.J3) and a b12-resistant (4.J22) HIV-1 clade C envelope, we identified determinants in the V2C2 region that governed susceptibility to b12 monoclonal antibody, but not to other CD4 binding site antibodies. Interestingly, when the V2C2 sequence of the 2-5.J3 Env was transferred to other b12-resistant primary clade C Envs, their susceptibility to b12 varied, indicating that this effect was context dependent. In addition, we identified determinants within the V2 region in the b12-resistant envelope that significantly modulated the neutralization of Env-pseudotyped viruses to PG9/PG16 MAbs. The enhanced neutralization susceptibilities of Envs to b12 and PG9 MAbs were correlated with increased exposure of their corresponding epitopes highlighting vulnerabilities in the V2C2 region that altered Env conformation necessary for the efficient accessibility of b12 and PG9 antibodies.

Phase 1 safety and immunogenicity evaluation of a multiclade HIV-1 candidate vaccine delivered by a replication-defective recombinant adenovirus vector.

BACKGROUND: The development of an effective human immunodeficiency virus (HIV) vaccine is a high global priority. Here, we report the safety, tolerability, and immunogenicity of a replication-defective recombinant adenovirus serotype 5 (rAd5) vector HIV-1 candidate vaccine. METHODS: The vaccine is a mixture of 4 rAd5 vectors that express HIV-1 subtype B Gag-Pol fusion protein and envelope (Env) from subtypes A, B, and C. Healthy, uninfected adults were randomized to receive 1 intramuscular injection of placebo (n=6) or vaccine at dose levels of 10(9) (n=10), 10(10) (n=10), or 10(11) (n=10) particle units and were followed for 24 weeks to assess immunogenicity and safety. RESULTS: The vaccine was well tolerated but was associated with more reactogenicity at the highest dose. At week 4, vaccine antigen-specific T cell responses were detected in 28 (93.3%) and 18 (60%) of 30 vaccine recipients for CD4(+) and CD8(+) T cells, respectively, by intracellular cytokine staining assay and in 22 (73%) of 30 vaccine recipients by enzyme-linked immunospot assay. Env-specific antibody responses were detected in 15 (50%) of 30 vaccine recipients by enzyme-linked immunosorbant assay and in 28 (93.3%) of 30 vaccine recipients by immunoprecipitation followed by Western blotting. No neutralizing antibody was detected. CONCLUSIONS: A single injection induced HIV-1 antigen-specific CD4(+) T cell, CD8(+) T cell, and antibody responses in the majority of vaccine recipients. This multiclade rAd5 HIV-1 vaccine is now being evaluated in combination with a multiclade HIV-1 DNA plasmid vaccine.

Phase 1 safety and immunogenicity evaluation of a multiclade HIV-1 DNA candidate vaccine.

BACKGROUND: Gene-based vaccine delivery is an important strategy in the development of a preventive vaccine for acquired immunodeficiency syndrome (AIDS). Vaccine Research Center (VRC) 004 is the first phase 1 dose-escalation study of a multiclade HIV-1 DNA vaccine. METHODS: VRC-HIVDNA009-00-VP is a 4-plasmid mixture encoding subtype B Gag-Pol-Nef fusion protein and modified envelope (Env) constructs from subtypes A, B, and C. Fifty healthy, uninfected adults were randomized to receive either placebo (n=10) or study vaccine at 2 mg (n=5), 4 mg (n=20), or 8 mg (n=15) by needle-free intramuscular injection. Humoral responses (measured by enzyme-linked immunosorbant assay, Western blotting, and neutralization assay) and T cell responses (measured by enzyme-linked immunospot assay and intracellular cytokine staining after stimulation with antigen-specific peptide pools) were measured. RESULTS: The vaccine was well tolerated and induced cellular and humoral responses. The maximal CD4(+) and CD8(+) T cell responses occurred after 3 injections and were in response to Env peptide pools. The pattern of cytokine expression by vaccine-induced HIV-specific T cells evolved over time, with a diminished frequency of interferon- gamma -producing T cells and an increased frequency of interleukin-2-producing T cells at 1 year. CONCLUSIONS: DNA vaccination induced antibody to and T cell responses against 3 major HIV-1 subtypes and will be further evaluated as a potential component of a preventive AIDS vaccine regimen.

A DNA vaccine for Ebola virus is safe and immunogenic in a phase I clinical trial.

Ebola viruses represent a class of filoviruses that causes severe hemorrhagic fever with high mortality. Recognized first in 1976 in the Democratic Republic of Congo, outbreaks continue to occur in equatorial Africa. A safe and effective Ebola virus vaccine is needed because of its continued emergence and its potential for use for biodefense. We report the safety and immunogenicity of an Ebola virus vaccine in its first phase I human study. A three-plasmid DNA vaccine encoding the envelope glycoproteins (GP) from the Zaire and Sudan/Gulu species as well as the nucleoprotein was evaluated in a randomized, placebo-controlled, double-blinded, dose escalation study. Healthy adults, ages 18 to 44 years, were randomized to receive three injections of vaccine at 2 mg (n = 5), 4 mg (n = 8), or 8 mg (n = 8) or placebo (n = 6). Immunogenicity was assessed by enzyme-linked immunosorbent assay (ELISA), immunoprecipitation-Western blotting, intracellular cytokine staining (ICS), and enzyme-linked immunospot assay. The vaccine was well-tolerated, with no significant adverse events or coagulation abnormalities. Specific antibody responses to at least one of the three antigens encoded by the vaccine as assessed by ELISA and CD4(+) T-cell GP-specific responses as assessed by ICS were detected in 20/20 vaccinees. CD8(+) T-cell GP-specific responses were detected by ICS assay in 6/20 vaccinees. This Ebola virus DNA vaccine was safe and immunogenic in humans. Further assessment of the DNA platform alone and in combination with replication-defective adenoviral vector vaccines, in concert with challenge and immune data from nonhuman primates, will facilitate evaluation and potential licensure of an Ebola virus vaccine under the Animal Rule.

Replication-defective adenovirus serotype 5 vectors elicit durable cellular and humoral immune responses in nonhuman primates.

The magnitude and durability of immune responses induced by replication-defective adenovirus serotype 5 (ADV5) vector-based vaccines were evaluated in the simian-human immunodeficiency virus/rhesus monkey model. A single inoculation of recombinant ADV5 vector constructs induced cellular and humoral immunity, but the rapid generation of neutralizing anti-Ad5 antibodies limited the immunity induced by repeated vector administration. The magnitude and durability of the immune responses elicited by these vaccines were greater when they were delivered as boosting immunogens in plasmid DNA-primed monkeys than when they were used as single-modality immunogens. Therefore, administration of ADV5-based vectors in DNA-primed subjects may be a preferred use of this vaccine modality for generating long-term immune protection.

Expanded breadth of virus neutralization after immunization with a multiclade envelope HIV vaccine candidate.

Although the V3 loop of the human immunodeficiency virus type 1 (HIV-1) envelope (Env) effectively elicits potent neutralizing antibody responses, the specificity of the antibody response is often restricted to T cell line adapted (TCLA) strains and a small subset of primary isolates, limiting its utility for an AIDS vaccine. In this study, we have compared Env immunogens with substituted V3 regions to combinations of strains from different clades and evaluated their ability to expand the breadth of the neutralizing antibody response. When the V3 region from HIV BaL was substituted for HIV HXB2, an effective neutralizing antibody response against several clade B primary isolates was elicited, but it remained restricted to neutralization of most clade B isolates. In an attempt to expand this response further, a linear epitope recognized by the broadly neutralizing 2F5 antibody was inserted into V3. A V3 2F5 epitope was identified that bound to 2F5 and elicited a potent 2F5 antibody response as an immunogen, but the antisera neutralized only a lab-adapted strain and not primary isolates. In contrast, combinations of Envs from clades A, B, and C, elicited neutralizing antibodies to a more diverse group of primary HIV-1 isolates. These studies suggest that combinations of Env immunogens, despite the limited reactivity of the V3 from each component, can be used to expand the breadth of the neutralizing antibody response.

Multiclade human immunodeficiency virus type 1 envelope immunogens elicit broad cellular and humoral immunity in rhesus monkeys.

The development of a human immunodeficiency virus type 1 (HIV-1) vaccine that elicits potent cellular and humoral immune responses recognizing divergent strains of HIV-1 will be critical for combating the global AIDS epidemic. The present studies were initiated to examine the magnitude and breadth of envelope (Env)-specific T-lymphocyte and antibody responses generated by vaccines containing either a single or multiple genetically distant HIV-1 Env immunogens. Rhesus monkeys were immunized with DNA prime-recombinant adenovirus boost vaccines encoding a Gag-Pol-Nef polyprotein in combination with either a single Env or a mixture of clade-A, clade-B, and clade-C Envs. Monkeys receiving the multiclade Env immunization developed robust immune responses to all vaccine antigens and, importantly, a greater breadth of Env recognition than monkeys immunized with vaccines including a single Env immunogen. All groups of vaccinated monkeys demonstrated equivalent immune protection following challenge with the pathogenic simian-human immunodeficiency virus 89.6P. These data suggest that a multicomponent vaccine encoding Env proteins from multiple clades of HIV-1 can generate broad Env-specific T-lymphocyte and antibody responses without antigenic interference. This study demonstrates that it is possible to generate protective immune responses by vaccination with genetically diverse isolates of HIV-1.

Neutralizing antibodies elicited by immunization of monkeys with DNA plasmids and recombinant adenoviral vectors expressing human immunodeficiency virus type 1 proteins.

Immunization with recombinant serotype 5 adenoviral (rAd5) vectors or a combination of DNA plasmid priming and rAd5 boosting is known to elicit potent immune responses. However, little data exist regarding these immunization strategies and the development of anti-human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies. We used DNA plasmids and rAd5 vectors encoding the HIV-1 89.6P or chimeric HxB2/BaL envelope glycoprotein to immunize macaque monkeys. A single rAd5 immunization elicited anti-Env antibody responses, but there was little boosting with subsequent rAd5 immunizations. In contrast, rAd5 boosting of DNA-primed monkeys resulted in a rapid rise in antibody titers, including the development of anti-HIV-1 neutralizing antibodies. The potency and breadth of neutralization were evaluated by testing plasma against a panel of 14 clade B primary isolates. Moderate levels of plasma neutralizing activity were detected against about one-third of the viruses tested, and immunoglobulin G fractionation demonstrated that virus neutralization was antibody mediated. After a challenge with a chimeric simian-human immunodeficiency virus (SHIV89.6P), an anamnestic neutralizing antibody response was observed, although the breadth of the response was limited to the subset of viruses that were neutralized after the primary immunization. These data are the first detailed description of the anti-HIV-1 neutralizing antibody response in nonhuman primates elicited by DNA and rAd5 immunization. In addition to the well-established ability of DNA priming and rAd5 boosting to elicit potent anti-HIV-1 cellular immune responses, this immunization strategy elicits anti-HIV-1 neutralizing antibodies and therefore can be used to study novel Env immunogens designed to elicit more potent neutralizing antibodies.

Heterologous envelope immunogens contribute to AIDS vaccine protection in rhesus monkeys.

Because a strategy to elicit broadly neutralizing anti-human immunodeficiency virus type 1 (HIV-1) antibodies has not yet been found, the role of an Env immunogen in HIV-1 vaccine candidates remains undefined. We sought to determine whether an HIV-1 Env immunogen genetically disparate from the Env of the challenge virus can contribute to protective immunity. We vaccinated Indian-origin rhesus monkeys with Gag-Pol-Nef immunogens, alone or in combination with Env immunogens that were either matched or mismatched with the challenge virus. These animals were then challenged with a pathogenic simian-human immunodeficiency virus. The vaccine regimen included a plasmid DNA prime and replication-defective adenoviral vector boost. Vaccine regimens that included the matched or mismatched Env immunogens conferred better protection against CD4(+) T-lymphocyte loss than that seen with comparable regimens that did not include Env immunogens. This increment in protective immunity was associated with anamnestic Env-specific cellular immunity that developed in the early days following viral challenge. These data suggest that T-lymphocyte immunity to Env can broaden the protective cellular immune response to HIV despite significant sequence diversity of the strains of the Env immunogens and can contribute to immune protection in this AIDS vaccine model.

Selective modification of variable loops alters tropism and enhances immunogenicity of human immunodeficiency virus type 1 envelope.

Although the B clade of human immunodeficiency virus type 1 (HIV-1) envelopes (Env) includes five highly variable regions, each of these domains contains a subset of sequences that remain conserved. The V3 loop has been much studied for its ability to elicit neutralizing antibodies, which are often restricted to a limited number of closely related strains, likely because a large number of antigenic structures are generated from the diverse amino acid sequences in this region. Despite these strain-specific determinants, subregions of V3 are highly conserved, and the effects of different portions of the V3 loop on Env tropism and immunogenicity have not been well delineated. For this report, selective deletions in V3 were introduced by shortening of the stem of the V3 loop. These mutations were explored in combination with deletions of selected V regions. Progressive shortening of the stem of V3 abolished the immunogenicity as well as the functional activity of HIV Env; however, two small deletions on both arms of the V3 stem altered the tropism of the dualtropic 89.6P viral strain so that it infected only CXCR4(+) cells. When this smaller deletion was combined with removal of the V1 and V2 loops and used as an immunogen in guinea pigs, the antisera were able to neutralize multiple independent clade B isolates with a higher potency. These findings suggest that highly conserved subregions within V3 may be relevant targets for eliciting neutralizing antibody responses, affecting HIV tropism, and increasing the immunogenicity of AIDS vaccines.

Enhanced mucosal immunoglobulin A response of intranasal adenoviral vector human immunodeficiency virus vaccine and localization in the central nervous system.

Replication-defective adenovirus (ADV) vectors represent a promising potential platform for the development of a vaccine for AIDS. Although this vector is typically administered intramuscularly, it would be desirable to induce mucosal immunity by delivery through alternative routes. In this study, the immune response and biodistribution of ADV vectors delivered by different routes were evaluated. ADV vectors expressing human immunodeficiency virus type 1 (HIV-1) Gag, Pol, and Env were delivered intramuscularly or intranasally into mice. Intranasal immunization induced greater HIV-specific immunoglobulin A (IgA) responses in mucosal secretions and sera than in animals with intramuscular injection, which showed stronger systemic cellular and IgG responses. Administration of the vaccine through an intranasal route failed to overcome prior ADV immunity. Animals exposed to ADV prior to vaccination displayed substantially reduced cellular and humoral immune responses to HIV antigens in both groups, though the reduction was greater in animals immunized intranasally. This inhibition was partially overcome by priming with a DNA expression vector expressing HIV-1 Gag, Pol, and Env before boosting with the viral vector. Biodistribution of recombinant adenovirus (rADV) vectors administered intranasally revealed infection of the central nervous system, specifically in the olfactory bulb, possibly via retrograde transport by olfactory neurons in the nasal epithelium, which may limit the utility of this route of delivery of ADV vector-based vaccines.

Plasmid chemokines and colony-stimulating factors enhance the immunogenicity of DNA priming-viral vector boosting human immunodeficiency virus type 1 vaccines.

Heterologous "prime-boost" regimens that involve priming with plasmid DNA vaccines and boosting with recombinant viral vectors have been shown to elicit potent virus-specific cytotoxic T-lymphocyte responses. Increasing evidence, however, suggests that the utility of recombinant viral vectors in human populations will be significantly limited by preexisting antivector immunity. Here we demonstrate that the coadministration of plasmid chemokines and colony-stimulating factors with plasmid DNA vaccines markedly increases the immunogenicity of DNA prime-recombinant adenovirus serotype 5 (rAd5) boost and DNA prime-recombinant vaccinia virus (rVac) boost vaccine regimens in BALB/c mice. In mice with preexisting anti-Ad5 immunity, priming with the DNA vaccine alone followed by rAd5 boosting elicited only marginal immune responses. In contrast, cytokine-augmented DNA vaccine priming followed by rAd5 vector boosting was able to generate potent immune responses in mice with preexisting anti-Ad5 immunity. These data demonstrate that plasmid cytokines can markedly improve the immunogenicity of DNA prime-viral vector boost vaccine strategies and can partially compensate for antivector immunity.

Elicitation of simian immunodeficiency virus-specific cytotoxic T lymphocytes in mucosal compartments of rhesus monkeys by systemic vaccination.

Since most human immunodeficiency virus (HIV) infections are initiated following mucosal exposure to the virus, the anatomic containment or abortion of an HIV infection is likely to require vaccine-elicited cellular immune responses in those mucosal sites. Studying vaccine-elicited mucosal immune responses has been problematic because of the difficulties associated with sampling T lymphocytes from those anatomic compartments. In the present study, we demonstrate that mucosal cytotoxic T lymphocytes (CTL) specific for simian immunodeficiency virus (SIV) and simian HIV can be reproducibly sampled from intestinal mucosal tissue of rhesus monkeys obtained under endoscopic guidance. These lymphocytes recognize peptide-major histocompatibility complex class I complexes and express gamma interferon on exposure to peptide antigen. Interestingly, systemic immunization of monkeys with plasmid DNA immunogens followed by live recombinant attenuated poxviruses or adenoviruses with genes deleted elicits high-frequency SIV-specific CTL responses in these mucosal tissues. These studies therefore suggest that systemic delivery of potent HIV immunogens may suffice to elicit substantial mucosal CTL responses.

Modifications of the human immunodeficiency virus envelope glycoprotein enhance immunogenicity for genetic immunization.

In this study, we have investigated the effect of specific mutations in human immunodeficiency virus type 1 (HIV-1) envelope (Env) on antibody production in an effort to improve humoral immune responses to this glycoprotein by DNA vaccination. Mice were injected with plasmid expression vectors encoding HIV Env with modifications in regions that might affect this response. Elimination of conserved glycosylation sites did not substantially enhance humoral or cytotoxic-T-lymphocyte (CTL) immunity. In contrast, a modified gp140 with different COOH-terminal mutations intended to mimic a fusion intermediate and stabilize trimer formation enhanced humoral immunity without reducing the efficacy of the CTL response. This mutant, with deletions in the cleavage site, fusogenic domain, and spacing of heptad repeats 1 and 2, retained native antigenic conformational determinants as defined by binding to known monoclonal antibodies or CD4, oligomer formation, and virus neutralization in vitro. Importantly, this modified Env, gp140 Delta CFI, stimulated the antibody response to native gp160 while it retained its ability to induce a CTL response, a desirable feature for an AIDS vaccine.

Effects of antigen and genetic adjuvants on immune responses to human immunodeficiency virus DNA vaccines in mice.

The effects of genetic adjuvants on humoral and cell-mediated immunity to two human immunodeficiency virus antigens, Env and Nef, have been examined in mice. Despite similar levels of gene expression and the same gene delivery vector, the immune responses to these two gene products differed following DNA immunization. Intramuscular immunization with a Nef expression vector plasmid generated a humoral response and antigen-specific gamma interferon (IFN-gamma) production but little cytotoxic-T-lymphocyte (CTL) immunity. In contrast, immunization with an Env vector stimulated CTL activity but did not induce a high-titer antibody response. The ability to modify these antigen-specific immune responses was investigated by coinjection of DNA plasmids encoding cytokine and/or hematopoietic growth factors, interleukin-2 (IL-2), IL-12, IL-15, Flt3 ligand (FL), and granulocyte-macrophage colony-stimulating factor (GM-CSF). Coadministration of these genes largely altered the immune responses quantitatively but not qualitatively. IL-12 induced the greatest increase in IFN-gamma and immunoglobulin G responses to Nef, and GM-CSF induced the strongest IFN-gamma and CTL responses to Env. A dual approach of expanding innate immunity by administering the FL gene, together with a cytokine that enhances adaptive immune responses, IL-2, IL-12, or IL-15, generated the most potent immune response at the lowest doses of Nef antigen. These findings suggest that intrinsic properties of the antigen determine the character of immune reactivity for this method of immunization and that specific combination of innate and adaptive immune cytokine genes can increase the magnitude of the response to DNA vaccines.