A candidate HIV/AIDS vaccine (MVA-B) lacking vaccinia virus gene C6L enhances memory HIV-1-specific T-cell responses

The vaccinia virus (VACV) C6 protein has sequence similarities with the poxvirus family Pox_A46, involved in regulation of host immune responses, but its role is unknown. Here, we have characterized the C6 protein and its effects in virus replication, innate immune sensing and immunogenicity in vivo. C6 is a 18.2 kDa protein, which is expressed early during virus infection and localizes to the cytoplasm of infected cells. Deletion of the C6L gene from the poxvirus vector MVA-B expressing HIV-1 Env, Gag, Pol and Nef antigens from clade B (MVA-B ΔC6L) had no effect on virus growth kinetics; therefore C6 protein is not essential for virus replication. The innate immune signals elicited by MVA-B ΔC6L in human macrophages and monocyte-derived dendritic cells (moDCs) are characterized by the up-regulation of the expression of IFN-β and IFN-α/β-inducible genes. In a DNA prime/MVA boost immunization protocol in mice, flow cytometry analysis revealed that MVA-B ΔC6L enhanced the magnitude and polyfunctionality of the HIV-1-specific CD4+ and CD8+ T-cell memory immune responses, with most of the HIV-1 responses mediated by the CD8+ T-cell compartment with an effector phenotype. Significantly, while MVA-B induced preferentially Env- and Gag-specific CD8+ T-cell responses, MVA-B ΔC6L induced more Gag-Pol-Nef-specific CD8+ T-cell responses. Furthermore, MVA-B ΔC6L enhanced the levels of antibodies against Env in comparison with MVA-B. These findings revealed that C6 can be considered as an immunomodulator and that deleting C6L gene in MVA-B confers an immunological benefit by enhancing IFN-β-dependent responses and increasing the magnitude and quality of the T-cell memory immune responses to HIV-1 antigens. Our observations are relevant for the improvement of MVA vectors as HIV-1 vaccines.

B cell depletion in HIV-1 subtype A infected Ugandan adults: relationship to CD4 T cell count, viral load and humoral immune responses

To better understand the nature of B cell dysfunctions in subjects infected with HIV-1 subtype A, a rural cohort of 50 treatment-naïve Ugandan patients chronically infected with HIV-1 subtype A was studied, and the relationship between B cell depletion and HIV disease was assessed. B cell absolute counts were found to be significantly lower in HIV-1+ patients, when compared to community matched negative controls (p<0.0001). HIV-1-infected patients displayed variable functional and binding antibody titers that showed no correlation with viral load or CD4+ T cell count. However, B cell absolute counts were found to correlate inversely with neutralizing antibody (NAb) titers against subtype A (p = 0.05) and subtype CRF02_AG (p = 0.02) viruses. A positive correlation was observed between subtype A gp120 binding antibody titers and NAb breadth (p = 0.02) and mean titer against the 10 viruses (p = 0.0002). In addition, HIV-1 subtype A sera showed preferential neutralization of the 5 subtype A or CRF02_AG pseudoviruses, as compared with 5 pseudoviruses from subtypes B, C or D (p<0.001). These data demonstrate that in patients with chronic HIV-1 subtype A infection, significant B cell depletion can be observed, the degree of which does not appear to be associated with a decrease in functional antibodies. These findings also highlight the potential importance of subtype in the specificity of cross-clade neutralization in HIV-1 infection.

Isolation of a monoclonal antibody that targets the alpha-2 helix of gp120 and represents the initial autologous neutralizing-antibody response in an HIV-1 subtype C-infected individual

The C3-V4 region is a major target of autologous neutralizing antibodies in HIV-1 subtype C infection. We previously identified a Center for AIDS Program of Research in South Africa (CAPRISA) participant, CAP88, who developed a potent neutralizing-antibody response within 3 months of infection that targeted an epitope in the C3 region of the HIV-1 envelope (P. L. Moore et al., PLoS Pathog. 5:e1000598, 2009). Here we showed that these type-specific antibodies could be adsorbed using recombinant gp120 from the transmitted/founder virus from CAP88 but not by gp120 made from other isolates. Furthermore, this activity could be depleted using a chimeric gp120 protein that contained only the C3 region from the CAP88 viral envelope engrafted onto the unrelated CAP63 viral envelope (called 63-88C3). On the basis of this, a differential sorting of memory B cells was performed using gp120s made from 63-88C3 and CAP63 labeled with different fluorochromes as positive and negative probes, respectively. This strategy resulted in the isolation of a highly specific monoclonal antibody (MAb), called CAP88-CH06, that neutralized the CAP88 transmitted/founder virus and viruses from acute infection but was unable to neutralize CAP88 viruses isolated at 6 and 12 months postinfection. The latter viruses contained 2 amino acid changes in the alpha-2 helix of C3 that mediated escape from this MAb. One of these changes involved the introduction of an N-linked glycan at position 339 that occluded the epitope, while the other mutation (either E343K or E350K) was a charge change. Our data validate the use of differential sorting to isolate a MAb targeting a specific epitope in the envelope glycoprotein and provided insights into the mechanisms of autologous neutralization escape.

Broad-spectrum inhibition of HIV-1 by a monoclonal antibody directed against a gp120-induced epitope of CD4

To penetrate susceptible cells, HIV-1 sequentially interacts with two highly conserved cellular receptors, CD4 and a chemokine receptor like CCR5 or CXCR4. Monoclonal antibodies (MAbs) directed against such receptors are currently under clinical investigation as potential preventive or therapeutic agents. We immunized Balb/c mice with molecular complexes of the native, trimeric HIV-1 envelope (Env) bound to a soluble form of the human CD4 receptor. Sera from immunized mice were found to contain gp120-CD4 complex-enhanced antibodies and showed broad-spectrum HIV-1-inhibitory activity. A proportion of MAbs derived from these mice preferentially recognized complex-enhanced epitopes. In particular, a CD4-specific MAb designated DB81 (IgG1Κ) was found to preferentially bind to a complex-enhanced epitope on the D2 domain of human CD4. MAb DB81 also recognized chimpanzee CD4, but not baboon or macaque CD4, which exhibit sequence divergence in the D2 domain. Functionally, MAb DB81 displayed broad HIV-1-inhibitory activity, but it did not exert suppressive effects on T-cell activation in vitro. The variable regions of the heavy and light chains of MAb DB81 were sequenced. Due to its broad-spectrum anti-HIV-1 activity and lack of immunosuppressive effects, a humanized derivative of MAb DB81 could provide a useful complement to current preventive or therapeutic strategies against HIV-1.

Synthesis, gp120 binding and anti-HIV activity of fatty acid esters of 1,1-linked disaccharides

Inspired by the anti-human immunodeficiency virus (HIV) activity of analogues of β-galactosylceramide (GalCer), a set of mono- and di-saccharide fatty acid esters were designed as GalCer mimetics and their binding to the V3 loop peptide of HIV-1 and anti-HIV activity evaluated. 1,1-linked Gal-Man and Glu-Man disaccharides with an ester on the Man subunit bound the V3 loop peptide and inhibited HIV infectivity in single round infection assays with the TZM-bl cell line. IC(50)'s were in the 50 μM range with no toxicity to the cells at concentrations up to 200 μM. These compounds appear to inhibit virus entry at early steps in viral infection since they were inactive if added post viral entry. Although these compounds were found to bind to the V3 loop peptide of gp120, it is not clear that this interaction is responsible for their anti-HIV activity because the relative binding affinity of closely related analogues did not correlate with their antiviral behavior. The low cytotoxicity of these 1,1-linked disaccharide fatty acid esters, combined with the easy accessibility to structurally diverse analogues make these molecules attractive leads for new topical anti-viral agents.

[Experimental study of candidate vaccines against variable or quasi-species pathogenes: multiepitopic synthetic peptide antigenes and new receptor-guiding adjuvants]

The short multiepitopic synthetic peptides from the sequences of hypervariable area of V3-loope of gp120 of HIV don't induce anti-peptides antibodies production in mice themselves. We prepared the potent immunogen by noncovalent conjugations of the multitude peptides with pure peptidoglycans from cell wall of Salmonella typhi. The sera from immunized mice have the anti-peptides antibody titers (3-5) x 10(5) in ELISA, as high as Freund's adjuvant is of use.

A directed molecular evolution approach to improved immunogenicity of the HIV-1 envelope glycoprotein

A prophylactic vaccine is needed to slow the spread of HIV-1 infection. Optimization of the wild-type envelope glycoproteins to create immunogens that can elicit effective neutralizing antibodies is a high priority. Starting with ten genes encoding subtype B HIV-1 gp120 envelope glycoproteins and using in vitro homologous DNA recombination, we created chimeric gp120 variants that were screened for their ability to bind neutralizing monoclonal antibodies. Hundreds of variants were identified with novel antigenic phenotypes that exhibit considerable sequence diversity. Immunization of rabbits with these gp120 variants demonstrated that the majority can induce neutralizing antibodies to HIV-1. One novel variant, called ST-008, induced significantly improved neutralizing antibody responses when assayed against a large panel of primary HIV-1 isolates. Further study of various deletion constructs of ST-008 showed that the enhanced immunogenicity results from a combination of effective DNA priming, an enhanced V3-based response, and an improved response to the constant backbone sequences.

Can natural antibodies to VIP or VIP-like HIV-1 glycoprotein facilitate prevention and supportive treatment of breast cancer?

OBJECTIVES

The incidence of non-AIDS-defining cancer is remarkably higher in HIV-infected than in the general population. In contrast, breast cancer risk is significantly reduced in the HIV-infected population. The molecular mechanisms underlying the phenomenon of suppression of breast cancer in the HIV-infected population may serve as a basis for development of a new platform for prevention and treatment of breast cancer.

HYPOTHESIS

Various evidences indicate that vasoactive intestinal peptide (VIP) plays an important role in growth, and differentiation of breast cancer. We previously showed (i) that natural antibodies recognizing VIP and the gp120-derived peptide NTM significantly contribute to the control of HIV disease progression by suppression of VIP-like activity of HIV-1 gp120 and (ii) that physical exercise stimulates production of these natural antibodies. These findings suggest that natural anti-VIP/NTM antibodies could contribute to a decrease of breast cancer in the HIV-infected population by suppression of VIP, which may play a pro/oncogenic function. Aerobic exercise which stimulates production of anti-VIP/NTM antibodies could be used as prevention and supportive treatment of breast cancer.

IMPACT

Immunotherapy based on natural anti-VIP/NTM antibodies could serve as an effective adjunct therapy for the treatment of breast cancer. Similarly, aerobic exercise, which stimulates production of these antibodies, should be considered as an inexpensive and safe preventive and supportive breast cancer therapy. Natural anti-VIP/NTM antibodies also represent promising prognostic marker for breast cancer.

Signaling through the P38 and ERK pathways: a common link between HIV replication and the immune response

One of the defining characteristics of HIV is its ability to manipulate the human immune response to promote its own replication. Since the beginning of the epidemic, there has been controversy whether a robust immune response to the virus is beneficial or detrimental for the host. Therefore, the effects of HIV on signaling pathways and cytokine production need to be characterized in order to distinguish between protective immune responses and inappropriate immune activation. Cytokine and biomarker expression during HIV infection results from the combined effects of intracellular signaling pathways orchestrated by kinases like P38 and ERK. The P38 and ERK Mitogen-Activated Protein Kinase (MAPK) pathways govern the regulation of cytokines (IL-2, IL-10, and TNF-α) as well biomarkers (PD-1, Fas/FasL, among others) that are skewed in chronic HIV infection. HIV utilizes the P38 and ERK pathways to produce new virions and to deplete CD4+ T cells from the host's immune system. Understanding the interplay between HIV and the cytokines induced by activation of the P38 and ERK pathways may provide insights into HIV immunopathogenesis and the development of a protective vaccine.

R5-SHIV induces multiple defects in T cell function during early infection of rhesus macaques including accumulation of T reg cells in lymph nodes

Background

HIV-1 is a pathogen that T cell responses fail to control. HIV-1gp120 is the surface viral envelope glycoprotein that interacts with CD4 T cells and mediates entry. HIV-1gp120 has been implicated in immune dysregulatory functions that may limit anti-HIV antigen-specific T cell responses. We hypothesized that in the context of early SHIV infection, immune dysregulation of antigen-specific T-effector cell and regulatory functions would be detectable and that these would be associated or correlated with measurable concentrations of HIV-1gp120 in lymphoid tissues.

Methods

Rhesus macaques were intravaginally inoculated with a Clade C CCR5-tropic simian-human immunodeficiency virus, SHIV-1157ipd3N4. HIV-1gp120 levels, antigen-specificity, levels of apoptosis/anergy and frequency and function of Tregs were examined in lymph node and blood derived T cells at 5 and 12 weeks post inoculation.

Results/Conclusions

We observed reduced responses to Gag in CD4 and gp120 in CD8 lymph node-derived T cells compared to the peripheral blood at 5 weeks post-inoculation. Reduced antigen-specific responses were associated with higher levels of PD-1 on lymph node-derived CD4 T cells as compared to peripheral blood and uninfected lymph node-derived CD4 T cells. Lymph nodes contained increased numbers of Tregs as compared to peripheral blood, which positively correlated with gp120 levels; T regulatory cell depletion restored CD8 T cell responses to Gag but not to gp120. HIV gp120 was also able to induce T regulatory cell chemotaxis in a dose-dependent, CCR5-mediated manner. These studies contribute to our broader understanding of the ways in which HIV-1 dysregulates T cell function and localization during early infection.

B cell responses to HIV-1 infection and vaccination: pathways to preventing infection

The B cell arm of the immune response becomes activated soon after HIV-1 transmission, yet the initial antibody response does not control HIV-1 replication, and it takes months for neutralizing antibodies to develop against the autologous virus. Antibodies that can be broadly protective are made only in a minority of subjects and take years to develop--too late to affect the course of disease. New studies of the earliest stages of HIV-1 infection, new techniques to probe the human B cell repertoire, the modest degree of efficacy in a vaccine trial and new studies of human monoclonal antibodies that represent the types of immune responses an HIV-1 vaccine should induce are collectively illuminating paths that a successful HIV-1 vaccine might take.

A novel strategy for inducing enhanced mucosal HIV-1 antibody responses in an anti-inflammatory environment

Prophylactic vaccination against HIV-1 sexual transmission will probably require antibody elicitation at genital mucosal surfaces. However, HIV-1 envelope glycoprotein (Env)-based antigens are weakly immunogenic, particularly when applied mucosally. The polyanion PRO 2000 is safe for human vaginal application, and thus may represent a potential formulating agent for vaginal delivery of experimental vaccine immunogens. Based upon its biochemical properties, we hypothesized that PRO 2000 might enhance mucosal immunogenicity of HIV-1 envelope glycoprotein (Env)-based antigens, promoting local and systemic immune responses. Vaginal immunization with Env-PRO 2000 resulted in significantly increased titres of Env-specific mucosal IgA and IgG in mice and rabbits, respectively, compared to Env alone, revealing modest but significant mucosal adjuvant activity for PRO 2000. In vitro, PRO 2000 associated with Env, protecting the glycoprotein from proteolytic degradation in human vaginal lavage. Unexpectedly, PRO 2000 antagonized TLR4 activation, suppressing local production of inflammatory cytokines. Since inflammation-mediated recruitment of viral target cells is a major risk factor in HIV-1 transmission, the immune modulatory and anti-inflammatory activities of PRO 2000 combined with its intravaginal safety profile suggests promise as an HIV-1 mucosal vaccine formulating agent.

The B cell response is redundant and highly focused on V1V2 during early subtype C infection in a Zambian seroconverter

High-titer autologous neutralizing antibody responses have been demonstrated during early subtype C human immunodeficiency virus type 1 (HIV-1) infection. However, characterization of this response against autologous virus at the monoclonal antibody (MAb) level has only recently begun to be elucidated. Here we describe five monoclonal antibodies derived from a subtype C-infected seroconverter and their neutralizing activities against pseudoviruses that carry envelope glycoproteins from 48 days (0 month), 2 months, and 8 months after the estimated time of infection. Sequence analysis indicated that the MAbs arose from three distinct B cell clones, and their pattern of neutralization compared to that in patient plasma suggested that they circulated between 2 and 8 months after infection. Neutralization by MAbs representative of each B cell clone was mapped to two residues: position 134 in V1 and position 189 in V2. Mutational analysis revealed cooperative effects between glycans and residues at these two positions, arguing that they contribute to a single epitope. Analysis of the cognate gp120 sequence through homology modeling places this potential epitope near the interface between the V1 and V2 loops. Additionally, the escape mutation R189S in V2, which conferred resistance against all three MAbs, had no detrimental effect on virus replication in vitro. Taken together, our data demonstrate that independent B cells repeatedly targeted a single structure in V1V2 during early infection. Despite this assault, a single amino acid change was sufficient to confer complete escape with minimal impact on replication fitness.

HIV-1 envelope subregion length variation during disease progression

The V3 loop of the HIV-1 Env protein is the primary determinant of viral coreceptor usage, whereas the V1V2 loop region is thought to influence coreceptor binding and participate in shielding of neutralization-sensitive regions of the Env glycoprotein gp120 from antibody responses. The functional properties and antigenicity of V1V2 are influenced by changes in amino acid sequence, sequence length and patterns of N-linked glycosylation. However, how these polymorphisms relate to HIV pathogenesis is not fully understood. We examined 5185 HIV-1 gp120 nucleotide sequence fragments and clinical data from 154 individuals (152 were infected with HIV-1 Subtype B). Sequences were aligned, translated, manually edited and separated into V1V2, C2, V3, C3, V4, C4 and V5 subregions. V1-V5 and subregion lengths were calculated, and potential N-linked glycosylation sites (PNLGS) counted. Loop lengths and PNLGS were examined as a function of time since infection, CD4 count, viral load, and calendar year in cross-sectional and longitudinal analyses. V1V2 length and PNLGS increased significantly through chronic infection before declining in late-stage infection. In cross-sectional analyses, V1V2 length also increased by calendar year between 1984 and 2004 in subjects with early and mid-stage illness. Our observations suggest that there is little selection for loop length at the time of transmission; following infection, HIV-1 adapts to host immune responses through increased V1V2 length and/or addition of carbohydrate moieties at N-linked glycosylation sites. V1V2 shortening during early and late-stage infection may reflect ineffective host immunity. Transmission from donors with chronic illness may have caused the modest increase in V1V2 length observed during the course of the pandemic.

The HIV envelope gene (env) encodes viral surface proteins (Env) that are vital to the basic processes used by the virus to infect and cause disease in humans. Adaptations in env determine which cells the virus can infect, and permit the virus to avoid elimination by the immune system. Env is one of the most variable genes known, and it can change dramatically over time in a single individual. However, Env-host cell interactions are complex and incompletely understood, and changes in this viral protein during infection have not yet been systematically described. We examined a large number of env sequences from 154 individuals at various stages of HIV infection but who had never received antiretroviral treatment. We found that the env V1V2 region lengthens during chronic infection and becomes more heavily glycosylated. However, these changes partially reverse during late-stage illness, possibly in response to a weakening host immune system. V1V2 lengths are also increasing over time in the epidemic at large, possibly related to the epidemiology of HIV transmission within the subtype B epidemic. These results provide fundamental insights into the biology of HIV.

[Immunogenicity of plasmid DNA and adenoviral vectors encoding HIV-1 subtype B env gene]

OBJECTIVE

To construct DNA and recombinant adenovirus vector vaccines containing an env gene from the prevalent subtype B strain in China and try to use them for therapeutic and prophylactic vaccines.

METHODS

The candidate plasmid DNA vaccine pVR-gp160 and recombinant adenovirus vaccine rAdV-gp160 were constructed separately. BALB/c mice were immunized with these two vaccines in different administration schemes. HIV-1 Gp120-specific cellular responses and antibody levels were detected by ELISPOT and ELISA respectively.

RESULTS

DNA vaccine alone and combined vaccines in a DNA prime/rAdV-gp160 boost vaccination regimen induced high level of Gp120-specific cellular responses. While low level of Gp120-specific antibodies were elicited in all groups.

CONCLUSION

DNA and rAdV vaccines could efficiently express Gp160 protein and activate specific cellular responses.

Profiles of human serum antibody responses elicited by three leading HIV vaccines focusing on the induction of Env-specific antibodies

In the current report, we compared the specificities of antibody responses in sera from volunteers enrolled in three US NIH-supported HIV vaccine trials using different immunization regimens. HIV-1 Env-specific binding antibody, neutralizing antibody, antibody-dependent cell-mediated cytotoxicity (ADCC), and profiles of antibody specificity were analyzed for human immune sera collected from vaccinees enrolled in the NIH HIV Vaccine Trial Network (HVTN) Study #041 (recombinant protein alone), HVTN Study #203 (poxviral vector prime-protein boost), and the DP6-001 study (DNA prime-protein boost). Vaccinees from HVTN Study #041 had the highest neutralizing antibody activities against the sensitive virus along with the highest binding antibody responses, particularly those directed toward the V3 loop. DP6-001 sera showed a higher frequency of positive neutralizing antibody activities against more resistant viral isolate with a significantly higher CD4 binding site (CD4bs) antibody response compared to both HVTN studies #041 and #203. No differences were found in CD4-induced (CD4i) antibody responses, ADCC activity, or complement activation by Env-specific antibody among these sera. Given recent renewed interest in realizing the importance of antibody responses for next generation HIV vaccine development, different antibody profiles shown in the current report, based on the analysis of a wide range of antibody parameters, provide critical biomarker information for the selection of HIV vaccines for more advanced human studies and, in particular, those that can elicit antibodies targeting conformational-sensitive and functionally conserved epitopes.

Induction of immunity to human immunodeficiency virus type-1 by vaccination

Recent findings have brought optimism that development of a successful human immunodeficiency virus type-1 (HIV-1) vaccine lies within reach. Studies of early events in HIV-1 infection have revealed when and where HIV-1 is potentially vulnerable to vaccine-targeted immune responses. With technical advances in human antibody production, clues about how antibodies recognize HIV-1 envelope proteins have uncovered new targets for immunogen design. A recent vaccine regimen has shown modest efficacy against HIV-1 acquisition. However, inducing long-term T and B cell memory and coping with HIV-1 diversity remain high priorities. Mediators of innate immunity may play pivotal roles in blocking infection and shaping immunity; vaccine strategies to capture these activities are under investigation. Challenges remain in integrating basic, preclinical and clinical research to improve predictions of types of immunity associated with vaccine efficacy, to apply these insights to immunogen design, and to accelerate evaluation of vaccine efficacy in persons at-risk for infection.

Direct observation to chemokine receptor 5 on T-lymphocyte cell surface using fluorescent metal nanoprobes

Chemokine receptor 5 (CCR5) is a cell surface protein required for HIV-1 infection. It is important to detect the amount and observe the spatial distribution of the CCR5 receptors on the cell surfaces. In this report, we describes the metal nanoparticles which were specially designed as molecular fluorescent probes for imaging of CCR5 receptors on the T-lymphocytic PM1 cell surfaces. These CCR5 monoclonal antibodies (mAbs) metal complexes were prepared by labeling mAbs with Alexa Fluor 680 followed by covalent binding the labeled mAbs on the 20 nm silver nanoparticles. Compared with the labeled mAbs without metal, the mAb-metal complexes were found to display enhanced emission intensity and shortened lifetime due to interactions between fluorophores and metal. The mAb-metal complexes were incubated with the PM1 cell lines. The confocal fluorescent intensity and lifetime cell images were recorded on single cells. It was observed that the mAb-metal complexes could be clearly distinguished from the cellular autofluorescence. By analyzing a pool of cell images, we observed that most CCR5 receptors appeared as clusters on the cell surfaces. The fluorophore-metal complexes developed in this report are generally useful for detection of cell surface receptors and provide a new class of probe to study the interaction between the CCR5 receptors with viral gp120 during HIV infections.

Design of a non-glycosylated outer domain-derived HIV-1 gp120 immunogen that binds to CD4 and induces neutralizing antibodies

The outer domain (OD) of the HIV-1 envelope glycoprotein gp120 is an important target for vaccine design as it contains a number of conserved epitopes, including a large fraction of the CD4 binding site. Attempts to design OD-based immunogens in the past have met with little success. We report the design and characterization of an Escherichia coli-expressed OD-based immunogen (OD(EC)), based on the sequence of the HxBc2 strain. The OD(EC)-designed immunogen lacks the variable loops V1V2 and V3 and incorporates 11 designed mutations at the interface of the inner and the outer domains of gp120. Biophysical studies showed that OD(EC) is folded and protease-resistant, whereas OD(EC) lacking the designed mutations is highly aggregation-prone. In contrast to previously characterized OD constructs, OD(EC) bound CD4 and the broadly neutralizing antibody b12 but not the non-neutralizing antibodies b6 and F105. Upon immunization in rabbits, OD(EC) was highly immunogenic, and the sera showed measurable neutralization for four subtype B and one subtype C virus including two b12-resistant viruses. In contrast, sera from rabbits immunized with gp120 did not neutralize any of the viruses. OD(EC) is the first example of a gp120 fragment-based immunogen that yields significant neutralizing antibodies.

Immunogenic profiling in mice of a HIV/AIDS vaccine candidate (MVA-B) expressing four HIV-1 antigens and potentiation by specific gene deletions

Background

The immune parameters of HIV/AIDS vaccine candidates that might be relevant in protection against HIV-1 infection are still undefined. The highly attenuated poxvirus strain MVA is one of the most promising vectors to be use as HIV-1 vaccine. We have previously described a recombinant MVA expressing HIV-1 Env, Gag, Pol and Nef antigens from clade B (referred as MVA-B), that induced HIV-1-specific immune responses in different animal models and gene signatures in human dendritic cells (DCs) with immunoregulatory function.

Methodology/Principal Findings

In an effort to characterize in more detail the immunogenic profile of MVA-B and to improve its immunogenicity we have generated a new vector lacking two genes (A41L and B16R), known to counteract host immune responses by blocking the action of CC-chemokines and of interleukin 1β, respectively (referred as MVA-B ΔA41L/ΔB16R). A DNA prime/MVA boost immunization protocol was used to compare the adaptive and memory HIV-1 specific immune responses induced in mice by the parental MVA-B and by the double deletion mutant MVA-B ΔA41L/ΔB16R. Flow cytometry analysis revealed that both vectors triggered HIV-1-specific CD4⁺ and CD8⁺ T cells, with the CD8⁺ T-cell compartment responsible for >91.9% of the total HIV-1 responses in both immunization groups. However, MVA-B ΔA41L/ΔB16R enhanced the magnitude and polyfunctionality of the HIV-1-specific CD4⁺ and CD8⁺ T-cell immune responses. HIV-1-specific CD4⁺ T-cell responses were polyfunctional and preferentially Env-specific in both immunization groups. Significantly, while MVA-B induced preferentially Env-specific CD8⁺ T-cell responses, MVA-B ΔA41L/ΔB16R induced more GPN-specific CD8⁺ T-cell responses, with an enhanced polyfunctional pattern. Both vectors were capable of producing similar levels of antibodies against Env.

Conclusions/Significance

These findings revealed that MVA-B and MVA-B ΔA41L/ΔB16R induced in mice robust, polyfunctional and durable T-cell responses to HIV-1 antigens, but the double deletion mutant showed enhanced magnitude and quality of HIV-1 adaptive and memory responses. Our observations are relevant in the immune evaluation of MVA-B and on improvements of MVA vectors as HIV-1 vaccines.

Structural basis for broad and potent neutralization of HIV-1 by antibody VRC01

During HIV-1 infection, antibodies are generated against the region of the viral gp120 envelope glycoprotein that binds CD4, the primary receptor for HIV-1. Among these antibodies, VRC01 achieves broad neutralization of diverse viral strains. We determined the crystal structure of VRC01 in complex with a human immunodeficiency virus HIV-1 gp120 core. VRC01 partially mimics CD4 interaction with gp120. A shift from the CD4-defined orientation, however, focuses VRC01 onto the vulnerable site of initial CD4 attachment, allowing it to overcome the glycan and conformational masking that diminishes the neutralization potency of most CD4-binding-site antibodies. To achieve this recognition, VRC01 contacts gp120 mainly through immunoglobulin V-gene regions substantially altered from their genomic precursors. Partial receptor mimicry and extensive affinity maturation thus facilitate neutralization of HIV-1 by natural human antibodies.

Comparative immunogenicity of HIV-1 clade C envelope proteins for prime/boost studies

Background

Previous clinical efficacy trials failed to support the continued development of recombinant gp120 (rgp120) as a candidate HIV vaccine. However, the recent RV144 HIV vaccine trial in Thailand showed that a prime/boost immunization strategy involving priming with canarypox vCP1521 followed by boosting with rgp120 could provide significant, although modest, protection from HIV infection. Based on these results, there is renewed interest in the development of rgp120 based antigens for follow up vaccine trials, where this immunization approach can be applied to other cohorts at high risk for HIV infection. Of particular interest are cohorts in Africa, India, and China that are infected with clade C viruses.

Methodology/Principal Findings

A panel of 10 clade C rgp120 envelope proteins was expressed in 293 cells, purified by immunoaffinity chromatography, and used to immunize guinea pigs. The resulting sera were collected and analyzed in checkerboard experiments for rgp120 binding, V3 peptide binding, and CD4 blocking activity. Virus neutralization studies were carried out with two different assays and two different panels of clade C viruses. A high degree of cross reactivity against clade C and clade B viruses and viral proteins was observed. Most, but not all of the immunogens tested elicited antibodies that neutralized tier 1 clade B viruses, and some sera neutralized multiple clade C viruses. Immunization with rgp120 from the CN97001 strain of HIV appeared to elicit higher cross neutralizing antibody titers than the other antigens tested.

Conclusions/Significance

While all of the clade C antigens tested were immunogenic, some were more effective than others in eliciting virus neutralizing antibodies. Neutralization titers did not correlate with rgp120 binding, V3 peptide binding, or CD4 blocking activity. CN97001 rgp120 elicited the highest level of neutralizing antibodies, and should be considered for further HIV vaccine development studies.

Selective induction of host genes by MVA-B, a candidate vaccine against HIV/AIDS

The aim of this study was to define the effects on antigen-presenting cells of the expression of HIV antigens from an attenuated poxvirus vector. We have analyzed the transcriptional changes in gene expression following infection of human immature monocyte-derived dendritic cells (DC) with recombinant modified vaccinia virus Ankara (MVA) expressing the genes encoding the gp120 and Gag-Pol-Nef antigens of HIV type 1 clade B (referred to as MVA-B) versus parental MVA infection. Using microarray technology and real-time reverse transcription-PCR, we demonstrated that the HIV proteins induced the expression of cytokines, cytokine receptors, chemokines, chemokine receptors, and molecules involved in antigen uptake and processing, including major histocompatibility complex (MHC) genes. Levels of mRNAs for interleukin-1, beta interferon, CCR8, and SCYA20 were higher after HIV antigen production. MVA-B infection also modulated the expression of antigen processing and presentation genes: the gene for MICA was upregulated, whereas those for HLA-DRA and HSPA5 were downregulated. Indeed, the increased expression of the gene for MICA, a glycoprotein related to major histocompatibility complex class I molecules, was shown to enhance the interaction between MVA-B-infected target cells and cytotoxic lymphocytes. The expression profiles of the genes for protein kinases such as JAK1 and IRAK2 were activated after HIV antigen expression. Several genes included in the JAK-STAT and mitogen-activated protein kinase signaling pathways were regulated after HIV antigen expression. Our findings provide the first gene signatures in DC of a candidate MVA-B vaccine expressing four HIV antigens and identified the biological roles of some of the regulatory genes, like that for MICA, which will help in the design of more effective MVA-derived vaccines.

Clarifying the role of G protein signaling in HIV infection: new approaches to an old question

Whether or not HIV gp120-elicited signal transduction through the coreceptors CCR5 and CXCR4 is required for productive viral replication has long been a subject of controversy. The complexity and diversity of G protein signal transduction initiated by chemokine receptor activation has hindered efforts to understand the contributions of these pathways to the HIV life cycle. Several recent studies have demonstrated an important role for G proteins in mediating signaling events through both CCR5 and CXCR4 that are necessary for productive HIV infection. In addition to gp120-mediated G protein activation, there is still much to learn about the impact of G protein signaling during HIV infection, including the role of T-cell receptor/CXCR4 cross-talk, regulation of G protein expression during infection and the contribution of G protein subunit genetic polymorphisms to disease progression. This review will describe the effects of G protein signaling in immune cells, summarize the current understanding of CCR5 and CXCR4-initiated signal transduction in HIV replication, and discuss important gaps that still remain in our understanding of G protein signaling and its contribution to HIV pathogenesis.

A novel trifunctional IgG-like bispecific antibody to inhibit HIV-1 infection and enhance lysis of HIV by targeting activation of complement

BACKGROUND

The complement system is not only a key component of innate immunity but also provides a first line of defense against invading pathogens, especially for viral pathogens. Human immunodeficiency virus (HIV), however, possesses several mechanisms to evade complement-mediated lysis (CoML) and exploit the complement system to enhance viral infectivity. Responsible for this intrinsic resistance against complement-mediated virolysis are complement regulatory membrane proteins derived from the host cell that inherently downregulates complement activation at several stages of the cascade. In addition, HIV is protected from complement-mediated lysis by binding soluble factor H (fH) through the viral envelope proteins, gp120 and gp41. Whereas inhibition of complement activity is the desired outcome in the vast majority of therapeutic approaches, there is a broader potential for complement-mediated inhibition of HIV by complement local stimulation.

PRESENTATION OF THE HYPOTHESIS

Our previous studies have proven that the complement-mediated antibody-dependent enhancement of HIV infection is mediated by the association of complement receptor type 2 bound to the C3 fragment and deposited on the surface of HIV virions. Thus, we hypothesize that another new activator of complement, consisting of two dsFv (against gp120 and against C3d respectively) linked to a complement-activating human IgG1 Fc domain ((anti-gp120 x anti-C3d)-Fc), can not only target and amplify complement activation on HIV virions for enhancing the efficiency of HIV lysis, but also reduce the infectivity of HIV through blocking the gp120 and C3d on the surface of HIV.

TESTING THE HYPOTHESIS

Our hypothesis was tested using cell-free HIV-1 virions cultivated in vitro and assessment of virus opsonization was performed by incubating appropriate dilutions of virus with medium containing normal human serum and purified (anti-gp120 x anti-C3d)-Fc proteins. As a control group, viruses were incubated with normal human serum under the same conditions. Virus neutralization assays were used to estimate the degree of (anti-gp120 x anti-C3d)-Fc lysis of HIV compared to untreated virus.

IMPLICATIONS OF THE HYPOTHESIS

The targeted complement activator, (anti-gp120 x anti-C3d)-Fc, can be used as a novel approach to HIV therapy by abrogating the complement-enhanced HIV infection of cells.

Subtype-specific conservation of isoleucine 309 in the envelope V3 domain is linked to immune evasion in subtype C HIV-1 infection

The V3 region of the HIV-1 envelope (Env) glycoprotein gp120 is a key functional domain yet it exhibits distinct mutational patterns across subtypes. Here an invariant residue (Ile 309) was replaced with Leu in 7 subtype C patient-derived Envs from recent infection and 4 related neutralizing antibody escape variants that emerged later. For these 11 Envs, I309L did not alter replication in primary CD4 T cells; however, replication in monocyte-derived macrophages was enhanced. Infection of cell lines with low CD4 or CCR5 revealed that I309L enhanced utilization of CD4 but did not affect the ability to use CCR5. This CD4-enhanced phenotype tracked with sensitivity to sCD4, indicating increased exposure of the CD4 binding site. The results suggest that Ile 309 preserves a V3-mediated masking function that occludes the CD4 binding site. The findings point to an immune evasion strategy in subtype C Env to protect this vulnerable immune target.

Trp-26 imparts functional versatility to human alpha-defensin HNP1

We performed a comprehensive alanine scan of human alpha-defensin HNP1 and tested the ability of the resulting analogs to kill Staphylococcus aureus, inhibit anthrax lethal factor, and bind human immunodeficiency virus-1 gp120. By far, the most deleterious mutation for all of these functions was W26A. The activities lost by W26A-HNP1 were restored progressively by replacing W26 with non-coded, straight-chain aliphatic amino acids of increasing chain length. The hydrophobicity of residue 26 also correlated with the ability of the analogs to bind immobilized wild type HNP1 and to undergo further self-association. Thus, the hydrophobicity of residue 26 is not only a key determinant of the direct interactions of HNP1 with target molecules, but it also governs the ability of this peptide to form dimers and more complex quaternary structures at micromolar concentrations. Although all defensin peptides are cationic, their amphipathicity is at least as important as their positive charge in enabling them to participate in innate host defense.

Crystal structure of the neutralizing Llama V(HH) D7 and its mode of HIV-1 gp120 interaction

HIV-1 entry into host cells is mediated by the sequential binding of the envelope glycoprotein gp120 to CD4 and a chemokine receptor. Antibodies binding to epitopes overlapping the CD4-binding site on gp120 are potent inhibitors of HIV entry, such as the llama heavy chain antibody fragment V(HH) D7, which has cross-clade neutralizing properties and competes with CD4 and mAb b12 for high affinity binding to gp120. We report the crystal structure of the D7 V(HH) at 1.5 A resolution, which reveals the molecular details of the complementarity determining regions (CDR) and substantial flexibility of CDR3 that could facilitate an induced fit interaction with gp120. Structural comparison of CDRs from other CD4 binding site antibodies suggests diverse modes of interaction. Mutational analysis identified CDR3 as a key component of gp120 interaction as determined by surface plasmon resonance. A decrease in affinity is directly coupled to the neutralization efficiency since mutations that decrease gp120 interaction increase the IC50 required for HIV-1 IIIB neutralization. Thus the structural study identifies the long CDR3 of D7 as the key determinant of interaction and HIV-1 neutralization. Furthermore, our data confirm that the structural plasticity of gp120 can accommodate multiple modes of antibody binding within the CD4 binding site.

Anti-V3 monoclonal antibodies display broad neutralizing activities against multiple HIV-1 subtypes

Background

The V3 loop of the HIV-1 envelope (Env) glycoprotein gp120 was identified as the “principal neutralizing domain” of HIV-1, but has been considered too variable to serve as a neutralizing antibody (Ab) target. Structural and immunochemical data suggest, however, that V3 contains conserved elements which explain its role in binding to virus co-receptors despite its sequence variability. Despite this evidence of V3 conservation, the ability of anti-V3 Abs to neutralize a significant proportion of HIV-1 isolates from different subtypes (clades) has remained controversial.

Methods

HIV-1 neutralization experiments were conducted in two independent laboratories to test human anti-V3 monoclonal Abs (mAbs) against pseudoviruses (psVs) expressing Envs of diverse HIV-1 subtypes from subjects with acute and chronic infections. Neutralization was defined by 50% inhibitory concentrations (IC₅₀), and was statistically assessed based on the area under the neutralization titration curves (AUC).

Results

Using AUC analyses, statistically significant neutralization was observed by ≥1 anti-V3 mAbs against 56/98 (57%) psVs expressing Envs of diverse subtypes, including subtypes A, AG, B, C and D. Even when the 10 Tier 1 psVs tested were excluded from the analysis, significant neutralization was detected by ≥1 anti-V3 mAbs against 46/88 (52%) psVs from diverse HIV-1 subtypes. Furthermore, 9/24 (37.5%) Tier 2 viruses from the clade B and C standard reference panels were neutralized by ≥1 anti-V3 mAbs. Each anti-V3 mAb tested was able to neutralize 28–42% of the psVs tested. By IC₅₀ criteria, 40/98 (41%) psVs were neutralized by ≥1 anti-V3 mAbs.

Conclusions

Using standard and new statistical methods of data analysis, 6/7 anti-V3 human mAbs displayed cross-clade neutralizing activity and revealed that a significant proportion of viruses can be neutralized by anti-V3 Abs. The new statistical method for analysis of neutralization data provides many advantages to previously used analyses.

Antibody responses elicited through homologous or heterologous prime-boost DNA and protein vaccinations differ in functional activity and avidity

Using a gp120 envelope glycoprotein from the JR-FL strain of human immunodeficiency virus-1 (HIV-1) as a model antigen, the goal of the current study was to evaluate the level and quality of antibody responses elicited by different prime-boost vaccination regimens (protein only, DNA only, DNA plus protein) in rabbits. Our data demonstrated that incorporating DNA immunization as a prime in a heterologous prime-boost regimen was able to elicit a more diverse and conformational epitope profile, higher antibody avidity, and improved neutralizing activity than immunization with only protein. Additionally, this improved neutralizing activity was observed in spite of similar antibody specificities and avidities seen when only DNA vaccination was used, providing additional evidence that the use of a combination immunization regimen increases the protective antibody response. Insights gained from the current study confirmed that the heterologous DNA prime-protein boost approach is effective in eliciting not only high level but also improved quality of antigen-specific antibody responses, and thus may offer a new technology platform to develop better and safer subunit vaccines.

Mutant TNF-alpha, mTNF-K90R, is a novel candidate adjuvant for a mucosal vaccine against HIV

The development of a safe and effective mucosal vaccine adjuvant is a crucial step for the development of vaccines against human immunodeficiency virus type-1 (HIV). We have previously reported that a mutant tumor necrosis factor-alpha (TNF-alpha), mTNF-K90R, possessed strong mucosal vaccine adjuvant activities in mice. Here, we evaluated the potential of mTNF-K90R as a mucosal vaccine adjuvant for the induction of systemic and mucosal immune responses against HIV. Nasal immunization of BALB/c mice with 5 microg of an HIV gp120 env protein immunogen together with mTNF-K90R induced higher serum anti-HIV gp120 protein immunoglobulin G (IgG) responses than gp120 alone. Furthermore, mTNF-K90R induced anti-gp120 IgA responses in nasal as well as vaginal washes from immunized mice, although these were not administration sites. Again, responses with mTNF-K90R were higher than with gp120 alone. These results indicate that mTNF-K90R may be applicable as amucosal adjuvant for HIV vaccination to induce both systemic and mucosal immune responses.

[Immunogenicity of recombinant adeno-asscociated virus type 1 expressing HIV-1 gp120 gene in mice and Rhesus macaques]

To study the immunogenicity of recombinant adeno-asscociated virus type 1 expressing HIV-1 gp120 gene (rAAV2/1-gp120) in BALB/c mice and Rhesus macaques. The gp120 gene derived from Chinese HIV-1 isolates was constructed into rAAV2/1 and rAd5 vectors. Firstly, the immunogenicity of rAAV2/1-gp120 was compared with rAd5-gp120 in BALB/c mice when used once or twice in 3 weeks interval. Then the monkeys were immunized with rAAV2/1-gp120 once. The HIV-1 specific IgG levels and neutralization activity to pseudotyped HIV-1 virus were tested using ELISA and neutralization assay, and the cellular immune responses were analyzed by IFN-gamma enzyme-linked immunospot (ELISPOT) and in vivo CTL assays. Compared with rAd5-gp120 immunized mice, mice immunized with rAAV2/1-gp120 once in duced stronger gp120-specific IgG and were sustained for at least 21 weeks. rAd5-gp120 immunized mice generated stronger cellular immune responses than rAAV2/1-gp120 in spleen and draining lymph node. But only moderate gp120-specific in vivo CTL activity was observed in both rAAV2/1-gp120 and rAd5-gp120 immunized mice. Four of five monkeys vaccinated with rAAV2/1-gp120 generated gp120 specific IgG, the titer ranged from 1:100 to 1:400 with end-point dilution. Gp120 specific IgG could be detected 4 weeks after immunization and reached the peak at 10 weeks after immunization. No neutralization activity against pseudotyped HIV-1 virus expressing NL4-3 Env antigen was detected. In Conclusion, rAAV2/1-gp120 induced high level of HIV-1 specific IgG antibody and moderate cellular immune responses. No neutralizing antibody was elicited. It indicates that the env gene and immunization strategy should be optimized to elicit neutralizing antibody against HIV-1 in further studies.

A strategy for eliciting antibodies against cryptic, conserved, conformationally dependent epitopes of HIV envelope glycoprotein

Background

Novel strategies are needed for the elicitation of broadly neutralizing antibodies to the HIV envelope glycoprotein, gp120. Experimental evidence suggests that combinations of antibodies that are broadly neutralizing in vitro may protect against challenge with HIV in nonhuman primates, and a small number of these antibodies have been selected by repertoire sampling of B cells and by the fractionation of antiserum from some patients with prolonged disease. Yet no additional strategies for identifying conserved epitopes, eliciting antibodies to these epitopes, and determining whether these epitopes are accessible to antibodies have been successful to date. The defining of additional conserved, accessible epitopes against which one can elicit antibodies will increase the probability that some may be the targets of broadly neutralizing antibodies.

Methodology/Principal Findings

We postulate that additional cryptic epitopes of gp120 are present, against which neutralizing antibodies might be elicited even though these antibodies are not elicited by gp120, and that many of these epitopes may be accessible to antibodies should they be formed. We demonstrate a strategy for eliciting antibodies in mice against selected cryptic, conformationally dependent conserved epitopes of gp120 by immunizing with multiple identical copies of covalently linked peptides (MCPs). This has been achieved with MCPs representing 3 different domains of gp120. We show that some cryptic epitopes on gp120 are accessible to the elicited antibodies, and some epitopes in the CD4 binding region are not accessible. The antibodies bind to gp120 with relatively high affinity, and bind to oligomeric gp120 on the surface of infected cells.

Conclusions/Significance

Immunization with MCPs comprised of selected peptides of HIV gp120 is able to elicit antibodies against conserved, conformationally dependent epitopes of gp120 that are not immunogenic when presented as gp120. Some of these cryptic epitopes are accessible to the elicited antibodies.

Human immunodeficiency virus type 1 evasion of a neutralizing anti-V3 antibody involves acquisition of a potential glycosylation site in V2

It has been reported that the addition of a potential N-linked glycosylation site (PNGS) to the gp120 human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein provides protection against neutralizing antibodies (NAbs) by acting as a 'glycan shield'. In this study, we induced insertion of a PNGS into the V2 region of HIV-1(BaL) with the KD-247 anti-V3 neutralizing monoclonal antibody. In the presence of KD-247 (200 microg ml(-1)) at passage five, viruses with 3 aa mutations in the C2 (T240S and I283T) and V3 (T319A) regions expanded from pre-existing variants. After six passages with KD-247 (>300 microg ml(-1)), a PNGS emerged in the V2 region in addition to C2 (T240S) and V3 mutations (R315K and F317L). A variant with a PNGS insertion in V2, but no V3 mutations was sensitive to KD-247, whereas a clone with a V2 PNGS insertion and mutations in V3 demonstrated a high level of resistance to KD-247. Replication kinetic analysis revealed that the F317L mutation in V3 played a compensatory role for fitness-loss caused by the PNGS insertion in V2. The evading HIV-1 variant did not revert back to the wild-type virus after 14 passages without KD-247. These findings demonstrate that the virus with fitness-loss mutations can replicate equally as well as the wild-type virus to acquire some key mutations in the V3 stem and the C2 region, and the compensated variants containing PNGS do not revert back to the ancestral virus even in the absence of NAb.

Vaccination with ALVAC and AIDSVAX to prevent HIV-1 infection in Thailand

BACKGROUND

The development of a safe and effective vaccine against the human immunodeficiency virus type 1 (HIV-1) is critical to pandemic control.

METHODS

In a community-based, randomized, multicenter, double-blind, placebo-controlled efficacy trial, we evaluated four priming injections of a recombinant canarypox vector vaccine (ALVAC-HIV [vCP1521]) plus two booster injections of a recombinant glycoprotein 120 subunit vaccine (AIDSVAX B/E). The vaccine and placebo injections were administered to 16,402 healthy men and women between the ages of 18 and 30 years in Rayong and Chon Buri provinces in Thailand. The volunteers, primarily at heterosexual risk for HIV infection, were monitored for the coprimary end points: HIV-1 infection and early HIV-1 viremia, at the end of the 6-month vaccination series and every 6 months thereafter for 3 years.

RESULTS

In the intention-to-treat analysis involving 16,402 subjects, there was a trend toward the prevention of HIV-1 infection among the vaccine recipients, with a vaccine efficacy of 26.4% (95% confidence interval [CI], -4.0 to 47.9; P=0.08). In the per-protocol analysis involving 12,542 subjects, the vaccine efficacy was 26.2% (95% CI, -13.3 to 51.9; P=0.16). In the modified intention-to-treat analysis involving 16,395 subjects (with the exclusion of 7 subjects who were found to have had HIV-1 infection at baseline), the vaccine efficacy was 31.2% (95% CI, 1.1 to 52.1; P=0.04). Vaccination did not affect the degree of viremia or the CD4+ T-cell count in subjects in whom HIV-1 infection was subsequently diagnosed.

CONCLUSIONS

This ALVAC-HIV and AIDSVAX B/E vaccine regimen may reduce the risk of HIV infection in a community-based population with largely heterosexual risk. Vaccination did not affect the viral load or CD4+ count in subjects with HIV infection. Although the results show only a modest benefit, they offer insight for future research. (ClinicalTrials.gov number, NCT00223080.)

Broad and potent neutralizing antibodies from an African donor reveal a new HIV-1 vaccine target

Broadly neutralizing antibodies (bNAbs), which develop over time in some HIV-1-infected individuals, define critical epitopes for HIV vaccine design. Using a systematic approach, we have examined neutralization breadth in the sera of about 1800 HIV-1-infected individuals, primarily infected with non-clade B viruses, and have selected donors for monoclonal antibody (mAb) generation. We then used a high-throughput neutralization screen of antibody-containing culture supernatants from about 30,000 activated memory B cells from a clade A-infected African donor to isolate two potent mAbs that target a broadly neutralizing epitope. This epitope is preferentially expressed on trimeric Envelope protein and spans conserved regions of variable loops of the gp120 subunit. The results provide a framework for the design of new vaccine candidates for the elicitation of bNAb responses.

Immunogenicities of Env glycoproteins from circulating HIV-1 isolates in China focusing on the strategy of "DNA prime plus protein boost"

BACKGROUND

The adenovirus-based HIV-1 vaccine developed by Merck Company suffered from an unexpected failure in September 2007. This generated a big shift in the strategy of HIV vaccine development with renewed focus on the induction of neutralizing antibodies. A major challenge in developing an HIV-1 vaccine is to identify immunogens and adopt delivery methods that can elicit broadly neutralizing antibodies against primary isolates of different genetic subtypes.

METHODS

Most circulating HIV-1 isolates in China are composed of clades Thai-B, CRF_BC and CRF01_AE. In order to construct DNA vaccines against these 3 HIV-1 subtypes, DNA vaccines carrying the gp120 regions from HIV-1 isolates of GX48(AE), GX79(AE), NX22(BC), GS22(BC), HN24(Thai-B) were constructed. Expression of gp120 from these DNA vaccines was detected by Western blotting in transiently transfected 293T cells. Pilot immunizations of New Zealand white rabbits were performed using the strategy of "DNA prime plus protein boost" and the neutralizing antibody response was detected in a Tzm-bl cell based assay against different HIV-1 strains.

RESULTS

Response of gp120-specific antibody was relatively low after DNA primes (mean titer = 10(4.72)); however, the titer of gp120-specific antibody went up with 2 protein boosts (mean titer = 10(6.81)). Above all, neutralizing antibody (Nab) titers induced by this combined approach were much better than those elicited by DNA or protein used alone (P < 0.01). Neutralizing activities of immunized rabbit sera against several pseudoviruses and laboratorial strains were evaluated, most rabbit sera primed with monovalent vaccine were capable of neutralizing only 1 of 5 viruses, however, sera primed with the polyvalent DNA vaccines were able to neutralize at least 2 of 5 viruses.

CONCLUSION

Polyvalent DNA prime plus protein boost is an effective immunization strategy to broaden the neutralization breadth and further research should be performed on the basis of this pilot study.

Escape from autologous neutralizing antibodies in acute/early subtype C HIV-1 infection requires multiple pathways

One aim for an HIV vaccine is to elicit neutralizing antibodies (Nab) that can limit replication of genetically diverse viruses and prevent establishment of a new infection. Thus, identifying the strengths and weaknesses of Nab during the early stages of natural infection could prove useful in achieving this goal. Here we demonstrate that viral escape readily occurred despite the development of high titer autologous Nab in two subjects with acute/early subtype C infection. To provide a detailed portrayal of the escape pathways, Nab resistant variants identified at multiple time points were used to create a series of envelope (Env) glycoprotein chimeras and mutants within the background of a corresponding newly transmitted Env. In one subject, Nab escape was driven predominantly by changes in the region of gp120 that extends from the beginning of the V3 domain to the end of the V5 domain (V3V5). However, Nab escape pathways in this subject oscillated and at times required cooperation between V1V2 and the gp41 ectodomain. In the second subject, escape was driven by changes in V1V2. This V1V2-dependent escape pathway was retained over time, and its utility was reflected in the virus's ability to escape from two distinct monoclonal antibodies (Mabs) derived from this same patient via introduction of a single potential N-linked glycosylation site in V2. Spatial representation of the sequence changes in gp120 suggested that selective pressure acted upon the same regions of Env in these two subjects, even though the Env domains that drove escape were different. Together the findings argue that a single mutational pathway is not sufficient to confer escape in early subtype C HIV-1 infection, and support a model in which multiple strategies, including potential glycan shifts, direct alteration of an epitope sequence, and cooperative Env domain conformational masking, are used to evade neutralization.

Limited neutralizing antibody specificities drive neutralization escape in early HIV-1 subtype C infection

We previously showed that HIV-1 subtype C viruses elicit potent but highly type-specific neutralizing antibodies (nAb) within the first year of infection. In order to determine the specificity and evolution of these autologous nAbs, we examined neutralization escape in four individuals whose responses against the earliest envelope differed in magnitude and potency. Neutralization escape occurred in all participants, with later viruses showing decreased sensitivity to contemporaneous sera, although they retained sensitivity to new nAb responses. Early nAb responses were very restricted, occurring sequentially and targeting only two regions of the envelope. In V1V2, limited amino acid changes often involving indels or glycans, mediated partial or complete escape, with nAbs targeting the V1V2 region directly in 2 cases. The alpha-2 helix of C3 was also a nAb target, with neutralization escape associated with changes to positively charged residues. In one individual, relatively high titers of anti-C3 nAbs were required to drive genetic escape, taking up to 7 weeks for the resistant variant to predominate. Thereafter titers waned but were still measurable. Development of this single anti-C3 nAb specificity was associated with a 7-fold drop in HIV-1 viral load and a 4-fold rebound as the escape mutation emerged. Overall, our data suggest the development of a very limited number of neutralizing antibody specificities during the early stages of HIV-1 subtype C infection, with temporal fluctuations in specificities as escape occurs. While the mechanism of neutralization escape appears to vary between individuals, the involvement of limited regions suggests there might be common vulnerabilities in the HIV-1 subtype C transmitted envelope.

Different vaccine vectors delivering the same antigen elicit CD8+ T cell responses with distinct clonotype and epitope specificity

Prime-boost immunization with gene-based vectors has been developed to generate more effective vaccines for AIDS, malaria, and tuberculosis. Although these vectors elicit potent T cell responses, the mechanisms by which they stimulate immunity are not well understood. In this study, we show that immunization by a single gene product, HIV-1 envelope, with alternative vector combinations elicits CD8(+) cells with different fine specificities and kinetics of mobilization. Vaccine-induced CD8(+) T cells recognized overlapping third V region loop peptides. Unexpectedly, two anchor variants bound H-2D(d) better than the native sequences, and clones with distinct specificities were elicited by alternative vectors. X-ray crystallography revealed major differences in solvent exposure of MHC-bound peptide epitopes, suggesting that processed HIV-1 envelope gave rise to MHC-I/peptide conformations recognized by distinct CD8(+) T cell populations. These findings suggest that different gene-based vectors generate peptides with alternative conformations within MHC-I that elicit distinct T cell responses after vaccination.

Two HIV-1 variants resistant to small molecule CCR5 inhibitors differ in how they use CCR5 for entry

HIV-1 variants resistant to small molecule CCR5 inhibitors recognize the inhibitor-CCR5 complex, while also interacting with free CCR5. The most common genetic route to resistance involves sequence changes in the gp120 V3 region, a pathway followed when the primary isolate CC1/85 was cultured with the AD101 inhibitor in vitro, creating the CC101.19 resistant variant. However, the D1/86.16 escape mutant contains no V3 changes but has three substitutions in the gp41 fusion peptide. By using CCR5 point-mutants and gp120-targeting agents, we have investigated how infectious clonal viruses derived from the parental and both resistant isolates interact with CCR5. We conclude that the V3 sequence changes in CC101.19 cl.7 create a virus with an increased dependency on interactions with the CCR5 N-terminus. Elements of the CCR5 binding site associated with the V3 region and the CD4-induced (CD4i) epitope cluster in the gp120 bridging sheet are more exposed on the native Env complex of CC101.19 cl.7, which is sensitive to neutralization via these epitopes. However, D1/86.16 cl.23 does not have an increased dependency on the CCR5 N-terminus, and its CCR5 binding site has not become more exposed. How this virus interacts with the inhibitor-CCR5 complex remains to be understood.

Human immunodeficiency virus type 1 (HIV-1) is the causative agent of AIDS. HIV-1 entry into target cells is triggered by the interaction of the viral envelope glycoproteins with a cell-surface receptor (CD4) and a co-receptor (CCR5), and culminates in fusion of the viral and cell membranes. Small molecule inhibitors that bind to CCR5 are a new class of drug for treating HIV-1-infected people. However, HIV-1 can evolve ways to become resistant to these compounds, by acquiring mutations that alter how its envelope glycoproteins (gp120-gp41) interact with CCR5. In this study, we investigated how two resistant viruses gained the ability to use the inhibitor-bound form of CCR5 through two different mechanisms. In the first virus, four amino acid substitutions in the V3 region of gp120 created an increased dependency on interactions with the CCR5 N-terminus. These changes altered the configuration of gp120, increasing the exposure of antibody epitopes in the V3 region and the CD4i epitope cluster associated with the CCR5 binding site. In contrast, the second virus, which became resistant via three sequence changes in the gp41 subunit, did not become more dependent on the CCR5 N-terminus and remained resistant to neutralization by antibodies against elements of the CCR5 binding site.

SAFETY AND ETHICAL CONSIDERATION OF AIDS VACCINE

It has been demonstrated that HIV-1 gp120 resembles several important properties of immunoglobulins allowing it strong influence on the human immune system, especially through induction of the deceptive imprinting and deregulation of the immune network. On the other hand there are many unanswered questions concerning properties and control of the genetically modified viruses and bacteria used as vectors in AIDS vaccines. This situation opens a serious question about the safety of vectored AIDS vaccine and the ethics of their trials in humans.

HIV-1 gp120 AND IMMUNE NETWORK

It has been demonstrated that the immunodominant V3 loop of HIV-1 gp120 and its flanking regions bear sequence and structural homology to the framework and complementarity-determining regions of human immunoglobulins. It has been proposed that the Ig-like domain of gp120 might encode idiotypes and in this way permit HIV-1 entry into the immune regulatory network. This notion is strongly supported by results demonstrating that the anti-V3 loop and anti-Ig antibodies of healthy individuals share complementary structure and that V3 reactive antibodies are present in HIV-negative sera. This might be the mechanism by which HIV induces immunological abnormalities, and it should be taken into consideration in AIDS vaccine development.

APPLICATION OF VIP/NTM-REACTIVE NATURAL ANTIBODIES IN THERAPY OF HIV DISEASE

In sera of HIV-infected individuals natural antibodies recognizing nonimmunogenic C-terminal domain of the second conserved region of HIV-1 gp120 and the vasoactive intestinal peptide (VIP) were identified. It has been demonstrated that these antibodies are significantly more prevalent in asymptomatic carriers than in AIDS patients and that their titer strongly correlates with disease progression. These findings point out the VIP/C2-reactive natural antibodies as an important agent for immunotherapy of HIV disease.

AVOIDING DECEPTIVE IMPRINTING OF THE IMMUNE RESPONSE TO HIV-1 INFECTION IN VACCINE DEVELOPMENT

Lymphocyte clonal restriction is caused by priming the immune system with an antigen and has been referred to infectious disease study as "original antigenic sin" (OAS), described first for influenza by Francis. OAS is a dominant feature of a normal immune response. Benefits of OAS come from the initial contact with the pathogen, which induces immunological memory. Memory is achieved by priming B and T cells of an immunologically naïve host, and confers protection against infection with the antigen-related pathogen. Thus, a restricted antibody response to viral or parasite antigens is not per se pathogenic. However, the interplay between a "locked-in" immune response and the high genetic variation of the pathogenic agent can result in a deception of the immune system. In the following, clonal restriction of the immune response to HIV is described by giving examples of restricted anti-HIV antibody formation in maternally infected children. Clonal restriction results in host resistance of infected individuals to emerging HIV variants and quasispecies. The problems of classical approaches of vaccine design in AIDS and the lack of protection in vaccinated patients is reviewed.

Cross-clade neutralizing antibodies against HIV-1 induced in rabbits by focusing the immune response on a neutralizing epitope

Studies were performed to induce cross-clade neutralizing antibodies (Abs) by testing various combinations of prime and boost constructs that focus the immune response on structurally-conserved epitopes in the V3 loop of HIV-1 gp120. Rabbits were immunized with gp120 DNA containing a V3 loop characterized by the GPGR motif at its tip, and/or with gp120 DNA with a V3 loop carrying the GPGQ motif. Priming was followed by boosts with V3-fusion proteins (V3-FPs) carrying the V3 sequence from a subtype B virus (GPGR motif), and/or with V3 sequences from subtypes A and C (GPGQ motif). The broadest and most consistent neutralizing responses were generated when using a clade C gp120 DNA prime and with the V3(B)-FP boost. Immune sera displayed neutralizing activity in three assays against pseudoviruses and primary isolates from subtypes A, AG, B, C, and D. Polyclonal Abs in the immune rabbit sera neutralized viruses that were not neutralized by pools of human anti-V3 monoclonal Abs. Greater than 80% of the neutralizing Abs were specific for V3, showing that the immune response could be focused on a neutralizing epitope and that vaccine-induced anti-V3 Abs have cross-clade neutralizing activity.

Ethnic differences in the adaptation rate of HIV gp120 from a vaccine trial

Differences in HIV-1 gp120 sequence variation were examined in North American volunteers who became infected during a phase III vaccine trial using the rgp120 vaccine. Molecular adaptation of the virus in vaccine and placebo recipients from different ethnic subgroups was compared by estimating the dN/dS ratios in viruses sampled from each individual using three different methods. ANOVA analyses detected significant differences in d(N)/d(S) ratios among races (P < 0.02). gp120 sequences from the black individuals showed higher mean d(N)/d(S) ratios for all estimators (1.24-1.45) than in other races (0.66-1.35), and several pairwise comparisons involving blacks remained significant (P < 0.05) after correction for multiple tests. In addition, black-placebo individuals showed significantly (P < 0.02) higher mean d(N)/d(S) ratios (1.3-1.66) than placebo individuals from the other races (0.65-1.56). These results suggest intrinsic differences among races in immune response and highlight the need for including multiple ethnicities in the design of future HIV-1 vaccine studies and trials.

Structure and function of HIV-1 CRF01_AE envelope proteins from blood and genital fluid isolates

The recombinant envelope protein (gp120) of the human immunodeficiency virus type 1 (HIV-1) CRF01_AE env gene isolated from the corresponding blood (rgp120-F36PC) and genital fluid (rgp120-F36VC) specimens obtained from HIV infected individuals was successfully produced in both prokaryote and eukaryote cells. The yields of HIV-1 recombinant envelope proteins rgp120-F36PC and rgp120-F36VC produced in E. coli and in mammalian cells were 1.0 and 1.2, and 0.3 and 0.5 mg/ml, respectively. Antibody responses in mice immunized with rgp120-F36VC protein were not significantly higher than those with rgp120-F36PC protein. The level of antibody response in mice immunized with V3 deleted recombinant gp120 proteins from rgp120-F36VC and rgp120-F36PC was not significantly different from wild type rgp120 proteins. beta-strands at the tip of the V3 loop of the HIV-1 envelope protein were predicted for the wild type genital fluid isolate but not for the wild type blood isolate. The replication capacity of both F36PC and F36VC was quite efficient. The infectivity assay of the epithelial cell line for pNL4-3/gp120F36VC was better than for pNL4-3/gp120F36PC. The extra beta-strands in the V3 loop may be involved in cell tropism.