Toward an AIDS vaccine

Transcriptional profiling of experimental CD8(+) lymphocyte depletion in rhesus macaques infected with simian immunodeficiency virus SIVmac239

CD8(+) T cells inhibit virus replication in SIV-infected rhesus macaques. However, it is unclear to what extent the viral suppression mediated by CD8(+) T cells reflects direct killing of infected cells as opposed to indirect, noncytolytic mechanisms. In this study, we used functional genomics to investigate noncytolytic mechanisms of in vivo viral suppression mediated by CD8(+) lymphocytes. Eight chronically SIVmac239-infected rhesus macaques underwent CD8(+) lymphocyte depletion, and RNA from whole blood was obtained prior to depletion, during the nadir of CD8(+) cell depletion, and after CD8(+) lymphocyte numbers had rebounded. We observed significant downregulation of the expression of genes encoding factors that can suppress SIV replication, including the CCR5-binding chemokine CCL5/RANTES and CCL4 and several members of the tripartite motif-containing (TRIM) family. Surprisingly, we also noted a strong, widespread downregulation of α- and θ-defensins with anti-HIV activity, which are not expressed by CD8(+) T cells. After cessation of depleting antibody treatment, we observed induction of a transcriptional signature indicative of B lymphocyte activation. Validation experiments demonstrated that animals during this period had elevated levels of B cells coupled with higher expression of the proliferative marker Ki67, indicating that CD8(+) depletion triggered a potent expansion of B cell numbers. Collectively, these data identify antiviral pathways perturbed by in vivo CD8(+) T cell depletion that may contribute to noncytolytic control of SIV replication.

Finding the sweet spots of inhibition: understanding the targets of a functional antibody against Plasmodium vivax Duffy binding protein

Plasmodium vivax Duffy binding protein region II (DBPII) is an essential ligand for reticulocyte invasion, thereby making this molecule an attractive vaccine candidate against asexual blood-stage P. vivax. Similar to other Plasmodium blood-stage vaccine candidates, strain-specific immunity due to DBPII allelic variation may complicate vaccine efficacy. Targeting immune responses to more conserved epitopes that are potential targets of strain-transcending neutralising immunity is necessary to avoid induction of strain-specific responses to dominant variant epitopes. In this article, we focus on different approaches to optimise the design of DBP immunogenicity to target conserved epitopes, which is important for developing a broadly effective vaccine against P. vivax.

Animal models in virus research: their utility and limitations

Viral diseases are important threats to public health worldwide. With the number of emerging viral diseases increasing the last decades, there is a growing need for appropriate animal models for virus studies. The relevance of animal models can be limited in terms of mimicking human pathophysiology. In this review, we discuss the utility of animal models for studies of influenza A viruses, HIV and SARS-CoV in light of viral emergence, assessment of infection and transmission risks, and regulatory decision making. We address their relevance and limitations. The susceptibility, immune responses, pathogenesis, and pharmacokinetics may differ between the various animal models. These complexities may thwart translating results from animal experiments to the humans. Within these constraints, animal models are very informative for studying virus immunopathology and transmission modes and for translation of virus research into clinical benefit. Insight in the limitations of the various models may facilitate further improvements of the models.

Stochastic simulations suggest that HIV-1 survives close to its error threshold

The use of mutagenic drugs to drive HIV-1 past its error threshold presents a novel intervention strategy, as suggested by the quasispecies theory, that may be less susceptible to failure via viral mutation-induced emergence of drug resistance than current strategies. The error threshold of HIV-1, , however, is not known. Application of the quasispecies theory to determine poses significant challenges: Whereas the quasispecies theory considers the asexual reproduction of an infinitely large population of haploid individuals, HIV-1 is diploid, undergoes recombination, and is estimated to have a small effective population size in vivo. We performed population genetics-based stochastic simulations of the within-host evolution of HIV-1 and estimated the structure of the HIV-1 quasispecies and . We found that with small mutation rates, the quasispecies was dominated by genomes with few mutations. Upon increasing the mutation rate, a sharp error catastrophe occurred where the quasispecies became delocalized in sequence space. Using parameter values that quantitatively captured data of viral diversification in HIV-1 patients, we estimated to be substitutions/site/replication, ∼2–6 fold higher than the natural mutation rate of HIV-1, suggesting that HIV-1 survives close to its error threshold and may be readily susceptible to mutagenic drugs. The latter estimate was weakly dependent on the within-host effective population size of HIV-1. With large population sizes and in the absence of recombination, our simulations converged to the quasispecies theory, bridging the gap between quasispecies theory and population genetics-based approaches to describing HIV-1 evolution. Further, increased with the recombination rate, rendering HIV-1 less susceptible to error catastrophe, thus elucidating an added benefit of recombination to HIV-1. Our estimate of may serve as a quantitative guideline for the use of mutagenic drugs against HIV-1.

Currently available antiretroviral drugs curtail HIV infection but fail to eradicate the virus. A strategy of intervention radically different from that employed by current drugs has been proposed by the molecular quasispecies theory. The theory predicts that increasing the viral mutation rate beyond a critical value, called the error threshold, would cause a severe loss of genetic information, potentially leading to viral clearance. Several chemical mutagens are now being developed that can increase the mutation rate of HIV-1. Their success depends on reliable estimates of the error threshold of HIV-1, which are currently lacking. The quasispecies theory cannot be applied directly to HIV-1: the theory considers an infinitely large population of asexually reproducing haploid individuals, whereas HIV-1 is diploid, undergoes recombination, and is estimated to have a small effective population size in vivo. We employed detailed stochastic simulations that overcome the limitations of the quasispecies theory and accurately mimic HIV-1 evolution in vivo. With these simulations, we estimated the error threshold of HIV-1 to be ∼2–6-fold higher than its natural mutation rate, suggesting that HIV-1 survives close to its error threshold and may be readily susceptible to mutagenic drugs.

A mouse model for HIV-1 entry

Passive transfer of neutralizing antibodies against HIV-1 can prevent infection in macaques and seems to delay HIV-1 rebound in humans. Anti-HIV antibodies are therefore of great interest for vaccine design. However, the basis for their in vivo activity has been difficult to evaluate systematically because of a paucity of small animal models for HIV infection. Here we report a genetically humanized mouse model that incorporates a luciferase reporter for rapid quantitation of HIV entry. An antibody's ability to block viral entry in this in vivo model is a function of its bioavailability, direct neutralizing activity, and effector functions.

A phase I double blind, placebo-controlled, randomized study of a multigenic HIV-1 adenovirus subtype 35 vector vaccine in healthy uninfected adults

Background

We conducted a phase I, randomized, double-blind, placebo-controlled trial to assess the safety and immunogenicity of escalating doses of two recombinant replication defective adenovirus serotype 35 (Ad35) vectors containing gag, reverse transcriptase, integrase and nef (Ad35-GRIN) and env (Ad35-ENV), both derived from HIV-1 subtype A isolates. The trial enrolled 56 healthy HIV-uninfected adults.

Methods

Ad35-GRIN/ENV (Ad35-GRIN and Ad35-ENV mixed in the same vial in equal proportions) or Ad35-GRIN was administered intramuscularly at 0 and 6 months. Participants were randomized to receive either vaccine or placebo (10/4 per group, respectively) within one of four dosage groups: Ad35-GRIN/ENV 2×10⁹ (A), 2×10¹⁰ (B), 2×10¹¹ (C), or Ad35-GRIN 1×10¹⁰ (D) viral particles.

Results

No vaccine-related serious adverse event was reported. Reactogenicity events reported were dose-dependent, mostly mild or moderate, some severe in Group C volunteers, all transient and resolving spontaneously. IFN-γ ELISPOT responses to any vaccine antigen were detected in 50, 56, 70 and 90% after the first vaccination, and in 75, 100, 88 and 86% of Groups A–D vaccine recipients after the second vaccination, respectively. The median spot forming cells (SFC) per 10⁶ PBMC to any antigen was 78–139 across Groups A–C and 158–174 in Group D, after each of the vaccinations with a maximum of 2991 SFC. Four to five HIV proteins were commonly recognized across all the groups and over multiple timepoints. CD4+ and CD8+ T-cell responses were polyfunctional. Env antibodies were detected in all Group A–C vaccinees and Gag antibodies in most vaccinees after the second immunization. Ad35 neutralizing titers remained low after the second vaccination.

Conclusion/Significance

Ad35-GRIN/ENV reactogenicity was dose-related. HIV-specific cellular and humoral responses were seen in the majority of volunteers immunized with Ad35-GRIN/ENV or Ad35-GRIN and increased after the second vaccination. T-cell responses were broad and polyfunctional.

Trial Registration

ClinicalTrials.gov NCT00851383

Vaccines expressing the innate immune modulator EAT-2 elicit potent effector memory T lymphocyte responses despite pre-existing vaccine immunity

The mixed results from recent vaccine clinical trials targeting HIV-1 justify the need to enhance the potency of HIV-1 vaccine platforms in general. Use of first-generation recombinant adenovirus serotype 5 (rAd5) platforms failed to protect vaccinees from HIV-1 infection. One hypothesis is that the rAd5-based vaccine failed due to the presence of pre-existing Ad5 immunity in many vaccines. We recently confirmed that EAT-2-expressing rAd5 vectors uniquely activate the innate immune system and improve cellular immune responses against rAd5-expressed Ags, inclusive of HIV/Gag. In this study, we report that use of the rAd5-EAT-2 vaccine can also induce potent cellular immune responses to HIV-1 Ags despite the presence of Ad5-specific immunity. Compared to controls expressing a mutant SH2 domain form of EAT-2, Ad5 immune mice vaccinated with an rAd5-wild-type EAT-2 HIV/Gag-specific vaccine formulation significantly facilitated the induction of several arms of the innate immune system. These responses positively correlated with an improved ability of the vaccine to induce stronger effector memory T cell-biased, cellular immune responses to a coexpressed Ag despite pre-existing anti-Ad5 immunity. Moreover, inclusion of EAT-2 in the vaccine mixture improves the generation of polyfunctional cytolytic CD8(+) T cell responses as characterized by enhanced production of IFN-γ, TNF-α, cytotoxic degranulation, and increased in vivo cytolytic activity. These data suggest a new approach whereby inclusion of EAT-2 expression in stringent human vaccination applications can provide a more effective vaccine against HIV-1 specifically in Ad5 immune subjects.

Vault nanocapsules as adjuvants favor cell-mediated over antibody-mediated immune responses following immunization of mice

Background

Modifications of adjuvants that induce cell-mediated over antibody-mediated immunity is desired for development of vaccines. Nanocapsules have been found to be viable adjuvants and are amenable to engineering for desired immune responses. We previously showed that natural nanocapsules called vaults can be genetically engineered to elicit Th1 immunity and protection from a mucosal bacterial infection. The purpose of our study was to characterize immunity produced in response to OVA within vault nanoparticles and compare it to another nanocarrier.

Methodology and Principal Findings

We characterized immunity resulting from immunization with the model antigen, ovalbumin (OVA) encased in vault nanocapsules and liposomes. We measured OVA responsive CD8⁺ and CD4⁺ memory T cell responses, cytokine production and antibody titers in vitro and in vivo. We found that immunization with OVA contain in vaults induced a greater number of anti-OVA CD8⁺ memory T cells and production of IFNγ plus CD4⁺ memory T cells. Also, modification of the vault body could change the immune response compared to OVA encased in liposomes.

Conclusions/Significance

These experiments show that vault nanocapsules induced strong anti-OVA CD8⁺ and CD4⁺ T cell memory responses and modest antibody production, which markedly differed from the immune response induced by liposomes. We also found that the vault nanocapsule could be modified to change antibody isotypes in vivo. Thus it is possible to create a vault nanocapsule vaccine that can result in the unique combination of immunogen-responsive CD8⁺ and CD4⁺ T cell immunity coupled with an IgG1 response for future development of vault nanocapsule-based vaccines against antigens for human pathogens and cancer.

Characterization of circulating HIV type 1 env genes in plasma of two antiretroviral-naive slow progressing patients with broad neutralizing antibody response with evidence of recombination

In the present study, we investigated genetic divergence between complete autologous HIV-1 env genes amplified directly from plasma of two antiretroviral-naive, slow progressing Indian patients with broad neutralizing antibody response. All the envelope (Env) clones obtained from one patient (LT1) belonged to subtype C; the second patient (LT5) harbored quasispecies comprised of pure B, C, and B/C recombinants with distinct breakpoints indicative of dual infection with genetically distinct strains. Further characterization of these Envs would provide insight into the biological properties under strong humoral immune response.

Mapping of antigenic determinants on a SAT2 foot-and-mouth disease virus using chicken single-chain antibody fragments

Recombinant single-chain variable fragments (scFvs) of antibodies make it possible to localize antigenic and immunogenic determinants, identify protective epitopes and can be exploited for the design of improved diagnostic tests and vaccines. A neutralizing epitope, as well as other potential antigenic sites of a SAT2 foot-and-mouth disease virus (FMDV) were identified using phage-displayed scFvs. Three unique ZIM/7/83-specific scFvs, designated scFv1, scFv2 and scFv3, were isolated. Further characterization of these scFvs revealed that only scFv2 was capable of neutralizing the ZIM/7/83 virus and was used to generate neutralization-resistant virus variants. Sequence analysis of the P1 region of virus escaping neutralization revealed a residue change from His to Arg at position 159 of the VP1 protein. Residue 159 is not only surface exposed but is also located at the C-terminal base of the G-H loop, a known immunogenic region of FMDV. A synthetic peptide, of which the sequence corresponded to the predicted antigenic site of the VP1 G-H loop of ZIM/7/83, inhibited binding of scFv2 to ZIM/7/83 in a concentration-dependent manner. This region can therefore be considered in the design of SAT2 vaccine seed viruses for the regional control of FMD in Africa.

Influence of cytokines on HIV-specific antibody-dependent cellular cytotoxicity activation profile of natural killer cells

There is growing interest in HIV-specific antibody-dependent cellular cytotoxicity (ADCC) as an effective immune response to prevent or control HIV infection. ADCC relies on innate immune effector cells, particularly NK cells, to mediate control of virus-infected cells. The activation of NK cells (i.e., expression of cytokines and/or degranulation) by ADCC antibodies in serum is likely subject to the influence of other factors that are also present. We observed that the HIV-specific ADCC antibodies, within serum samples from a panel of HIV-infected individuals induced divergent activation profiles of NK cells from the same donor. Some serum samples primarily induced NK cell cytokine expression (i.e., IFNγ), some primarily initiated NK cell expression of a degranulation marker (CD107a) and others initiated a similar magnitude of responses across both effector functions. We therefore evaluated a number of HIV-relevant soluble factors for their influence on the activation of NK cells by HIV-specific ADCC antibodies. Key findings were that the cytokines IL-15 and IL-10 consistently enhanced the ability of NK cells to respond to HIV-specific ADCC antibodies. Furthermore, IL-15 was demonstrated to potently activate “educated” KIR3DL1⁺ NK cells from individuals carrying its HLA-Bw4 ligand. The cytokine was also demonstrated to activate “uneducated” KIR3DL1⁺ NK cells from HLA-Bw6 homozygotes, but to a lesser extent. Our results show that cytokines influence the ability of NK cells to respond to ADCC antibodies in vitro. Manipulating the immunological environment to enhance the potency of NK cell-mediated HIV-specific ADCC effector functions could be a promising immunotherapy or vaccine strategy.

B-cell-lineage immunogen design in vaccine development with HIV-1 as a case study

Failure of immunization with the HIV-1 envelope to induce broadly neutralizing antibodies against conserved epitopes is a major barrier to producing a preventive HIV-1 vaccine. Broadly neutralizing monoclonal antibodies (BnAbs) from those subjects who do produce them after years of chronic HIV-1 infection have one or more unusual characteristics, including polyreactivity for host antigens, extensive somatic hypermutation and long, variable heavy-chain third complementarity-determining regions, factors that may limit their expression by host immunoregulatory mechanisms. The isolation of BnAbs from HIV-1-infected subjects and the use of computationally derived clonal lineages as templates provide a new path for HIV-1 vaccine immunogen design. This approach, which should be applicable to many infectious agents, holds promise for the construction of vaccines that can drive B cells along rare but desirable maturation pathways.

Induction of mucosal HIV-specific B and T cell responses after oral immunization with live coxsackievirus B4 recombinants

Given the limited success of clinical HIV vaccine trials, new vaccine strategies are needed for the HIV pipeline. The present study explored the novel concept that a live enteric virus, with limited disease potential, is a suitable vaccine vector to elicit HIV-specific immune responses in the gut mucosa of immunized mice. Two coxsackievirus B4 (CVB4) vaccine vectors were designed to induce HIV-specific B or T cell responses. A B cell immunogen, CVB4/gp41(2F5), was constructed by expressing an epitope from the membrane proximal external region (MPER) of gp41 as a structural peptide within a surface loop of a capsid protein of CVB4. The T cell immunogen, CVB4/p24(73(3)), was constructed previously by expressing a gag p24 sequence as a non-structural peptide at the amino-terminus of the CVB4 polyprotein. The CVB4/gp41(2F5) recombinant was antigenic in mice and elicited anti-gp41 antibodies in both the mucosal and systemic compartments. The route of immunization affected the antibody response since oral delivery of CVB4/gp41(2F5) induced anti-gp41 antibodies in the mucosal but not in the systemic compartment while parenteral delivery induced anti-gp41 antibodies in both compartments. In contrast, oral immunization with CVB4/p24(73(3)) elicited both mucosal and systemic gag p24-specific T cell responses. Since coxsackieviruses are ubiquitous in the human population, a key question is whether pre-existing vector immunity will inhibit the ability of a CVB4-based vaccine to induce HIV-specific immune responses. We show that pre-existing vector immunity did not preclude the development of mucosal anti-gp41 antibodies or gag p24-specific T cell responses after oral immunization with the CVB4/HIV recombinants. We suggest that the CVB4/HIV recombinants have the potential to be a viable vaccine product because of ease of delivery, safety, immunogenicity, ease of large-scale production, and storage conditions requiring cold-chain temperatures provided by refrigeration.

Polymeric multilayer capsule-mediated vaccination induces protective immunity against cancer and viral infection

Recombinant antigens hold high potential to develop vaccines against lethal intracellular pathogens and cancer. However, they are poorly immunogenic and fail to induce potent cellular immunity. In this paper, we demonstrate that polymeric multilayer capsules (PMLC) strongly increase antigen delivery toward professional antigen-presenting cells in vivo, including dendritic cells (DCs), macrophages, and B cells, thereby enforcing antigen presentation and stimulating T cell proliferation. A thorough analysis of the T cell response demonstrated their capacity to induce IFN-γ secreting CD4 and CD8 T cells, in addition to follicular T-helper cells, a recently identified CD4 T cell subset supporting antibody responses. On the B cell level, PMLC-mediated antigen delivery promoted the formation of germinal centers, resulting in increased numbers of antibody-secreting plasma cells and elevated antibody titers. The functional relevance of the induced immune responses was validated in murine models of influenza and melanoma. On a mechanistic level, we have demonstrated the capacity of PMLC to activate the NALP3 inflammasome and trigger the release of the potent pro-inflammatory cytokine IL-1β. Finally, using DC-depleted mice, we have identified DCs as the key mediators of the immunogenic properties of PMLC.

Use of a polyanionic carbomer, Carbopol971P, in combination with MF59, improves antibody responses to HIV-1 envelope glycoprotein

Identification of optimal antigen(s) and adjuvant combination(s) to elicit potent, protective, and long-lasting immunity has been a major challenge for the development of effective vaccines against chronic viral pathogens, such as HIV-1, for which there are not yet any licensed vaccines. Here we describe the use of a novel adjuvant approach employing Carbopol 971P(®) NF (hereafter referred to as Carbopol971P), a cross-linked polyanionic carbomer, in combination with the Novartis proprietary oil-in-water adjuvant, MF59, as a potentially safe and effective adjuvant to augment humoral immune responses to the HIV-1 envelope glycoprotein (Env). Intramuscular immunization of small animals with recombinant Env glycoprotein (gp140) formulated in Carbopol971P plus MF59 gave significantly higher titers of binding and virus neutralizing antibodies as compared to immunization using gp140 with either MF59 or Carbopol971P alone. In addition, the antibodies generated were of higher avidity. Importantly, the use of Carbopol971P plus MF59 did not cause any serious adverse reactions or any obvious health problems in animals upon intramuscular administration. Hence, the Carbopol971P plus MF59 adjuvant formulation may provide a benefit for future vaccine applications.

Clustering of HIV-1 Subtypes Based on gp120 V3 Loop electrostatic properties

BACKGROUND

The V3 loop of the glycoprotein gp120 of HIV-1 plays an important role in viral entry into cells by utilizing as coreceptor CCR5 or CXCR4, and is implicated in the phenotypic tropisms of HIV viruses. It has been hypothesized that the interaction between the V3 loop and CCR5 or CXCR4 is mediated by electrostatics. We have performed hierarchical clustering analysis of the spatial distributions of electrostatic potentials and charges of V3 loop structures containing consensus sequences of HIV-1 subtypes.

RESULTS

Although the majority of consensus sequences have a net charge of +3, the spatial distribution of their electrostatic potentials and charges may be a discriminating factor for binding and infectivity. This is demonstrated by the formation of several small subclusters, within major clusters, which indicates common origin but distinct spatial details of electrostatic properties. Some of this information may be present, in a coarse manner, in clustering of sequences, but the spatial details are largely lost. We show the effect of ionic strength on clustering of electrostatic potentials, information that is not present in clustering of charges or sequences. We also make correlations between clustering of electrostatic potentials and net charge, coreceptor selectivity, global prevalence, and geographic distribution. Finally, we interpret coreceptor selectivity based on the N6X7T8|S8X9 sequence glycosylation motif, the specific positive charge location according to the 11/24/25 rule, and the overall charge and electrostatic potential distribution.

CONCLUSIONS

We propose that in addition to the sequence and the net charge of the V3 loop of each subtype, the spatial distributions of electrostatic potentials and charges may also be important factors for receptor recognition and binding and subsequent viral entry into cells. This implies that the overall electrostatic potential is responsible for long-range recognition of the V3 loop with coreceptors CCR5/CXCR4, whereas the charge distribution contributes to the specific short-range interactions responsible for the formation of the bound complex. We also propose a scheme for coreceptor selectivity based on the sequence glycosylation motif, the 11/24/25 rule, and net charge.

Elicitation of neutralizing antibodies directed against CD4-induced epitope(s) using a CD4 mimetic cross-linked to a HIV-1 envelope glycoprotein

The identification of HIV-1 envelope glycoprotein (Env) structures that can generate broadly neutralizing antibodies (BNAbs) is pivotal to the development of a successful vaccine against HIV-1 aimed at eliciting effective humoral immune responses. To that end, the production of novel Env structure(s) that might induce BNAbs by presentation of conserved epitopes, which are otherwise occluded, is critical. Here, we focus on a structure that stabilizes Env in a conformation representative of its primary (CD4) receptor-bound state, thereby exposing highly conserved "CD4 induced" (CD4i) epitope(s) known to be important for co-receptor binding and subsequent virus infection. A CD4-mimetic miniprotein, miniCD4 (M64U1-SH), was produced and covalently complexed to recombinant, trimeric gp140 envelope glycoprotein (gp140) using site-specific disulfide linkages. The resulting gp140-miniCD4 (gp140-S-S-M64U1) complex was recognized by CD4i antibodies and the HIV-1 co-receptor, CCR5. The gp140-miniCD4 complex elicited the highest titers of CD4i binding antibodies as well as enhanced neutralizing antibodies against Tier 1 viruses as compared to gp140 protein alone following immunization of rabbits. Neutralization against HIV-2(7312/V434M) and additional serum mapping confirm the specific elicitation of antibodies directed to the CD4i epitope(s). These results demonstrate the utility of structure-based approach in improving immunogenic response against specific region, such as the CD4i epitope(s) here, and its potential role in vaccine application.

Two mucosal-parenteral schedules to coadminister a multiantigenic formulation against HIV-1 in Balb/c mice

Previous studies showed that simultaneous immunization through the nasal (IN) and subcutaneous (SC) route of a multiantigenic formulation induced a Th1 anti-HIV humoral and cellular immune responses. The formulation was comprised of a recombinant protein of HIV-1 (named CR3; Cellular Response number 3) and the surface and nucleocapsid antigens of hepatitis B virus. This study asks whether four times simultaneous administration through the IN and SC routes (SC+IN) of the multiantigenic formulation induces a similar systemic and mucosal immune responses than two sequential IN priming and two SC boosting (2IN&2SC) inoculations in mice. To answer this question, we tested the same total dose of each antigen per animal in both schedules of inoculation. We found that SC+IN and 2IN&2SC coadministration induced comparable levels of CR3(HIV)-specific IFN-γ-secreting cells and CD8+ cells proliferation in the systemic compartment of animals. Consistent with these findings, a similar Th1 profile considering anti-CR3 IgG1:IGg2a ratio was observed. Additionally, the level of IgG antibodies and the frequency of seroconverting animals in vagina were not different. However, in the case of IgA antibodies the same parameters were significantly higher in the SC+IN group. We also found important level of HBsAg-specific antibodies in serum and vaginal washes.

Control of M184V HIV-1 mutants by CD8 T-cell responses

Antiretroviral treatment directed against HIV is highly effective, yet limited by drug resistance mutations. We hypothesized that CD8 T cells targeting drug-resistant HIV mutants are able to inhibit viral replication in the setting of a failing therapeutic regimen. We evaluated CD8 T-cell responses and mapped epitopes in HIV-infected patients by interferon-gamma Elispot and intracellular cytokine staining. Autologous virus was sequenced by RT-PCR. Viral replication inhibition assays were performed using M184V mutant virus and CD8 T cell lines. CD8 T-cell responses toward the regions of viral drug resistance mutations in Pol are frequent. Focusing on the M184V mutation, A*02:01-YQYVDDLYV and A*02:01-VIYQYVDDLYV were identified as optimal epitopes for the majority of study subjects. Viral replication of M184V HIV mutants was inhibited by CD8 T cell lines in vitro. In case of a failing lamivudine/emtricitabine containing regimen, individuals with a CD8 T-cell response toward M184V had a significant lower viral load than those without a CD8 response (p = 0.005). Two study subjects even achieved an undetectable viral load. Our data suggest that control of M184V mutant virus by CD8 T-cell responses is possible in vitro and in vivo. This control has important implications for therapeutic vaccination strategies.

Progress in the rational design of an AIDS vaccine

Human immunodeficiency virus-1 (HIV-1) has a high degree of genetic and antigenic diversity that has impeded the development of an effective vaccine using traditional methods. We are attempting to develop an AIDS vaccine by employing strategies that include structural biology and computational modelling, in an effort to develop immunogens capable of eliciting neutralizing antibodies of the requisite breadth and potency against circulating strains of HIV-1.

Safety and reactogenicity of canarypox ALVAC-HIV (vCP1521) and HIV-1 gp120 AIDSVAX B/E vaccination in an efficacy trial in Thailand

Background

A prime-boost vaccination regimen with ALVAC-HIV (vCP1521) administered intramuscularly at 0, 4, 12, and 24 weeks and gp120 AIDSVAX B/E at 12 and 24 weeks demonstrated modest efficacy of 31.2% for prevention of HIV acquisition in HIV-uninfected adults participating in a community-based efficacy trial in Thailand.

Methodology/Principal Findings

Reactogenicity was recorded for 3 days following vaccination. Adverse events were monitored every 6 months for 3.5 years, during which pregnancy outcomes were recorded. Of the 16,402 volunteers, 69% of the participants reported an adverse event any time after the first dose. Only 32.9% experienced an AE within 30 days following any vaccination. Overall adverse event rates and attribution of relatedness did not differ between groups. The frequency of serious adverse events was similar in vaccine (14.3%) and placebo (14.9%) recipients (p = 0.33). None of the 160 deaths (85 in vaccine and 75 in placebo recipients, p = 0.43) was assessed as related to vaccine. The most common cause of death was trauma or traffic accident. Approximately 30% of female participants reported a pregnancy during the study. Abnormal pregnancy outcomes were experienced in 17.1% of vaccine and 14.6% (p = 0.13) of placebo recipients. When the conception occurred within 3 months (estimated) of a vaccination, the majority of these abnormal outcomes were spontaneous or elective abortions among 22.2% and 15.3% of vaccine and placebo pregnant recipients, respectively (p = 0.08). Local reactions occurred in 88.0% of vaccine and 61.0% of placebo recipients (p<0.001) and were more frequent after ALVAC-HIV than AIDSVAX B/E vaccination. Systemic reactions were more frequent in vaccine than placebo recipients (77.2% vs. 59.8%, p<0.001). Local and systemic reactions were mostly mild to moderate, resolving within 3 days.

Conclusions/Significance

The ALVAC-HIV and AIDSVAX B/E vaccine regimen was found to be safe, well tolerated and suitable for potential large-scale use in Thailand.

Trial Registration

ClinicalTrials.govNCT00223080

Defining epitope coverage requirements for T cell-based HIV vaccines: theoretical considerations and practical applications

Background

HIV vaccine development must address the genetic diversity and plasticity of the virus that permits the presentation of diverse genetic forms to the immune system and subsequent escape from immune pressure. Assessment of potential HIV strain coverage by candidate T cell-based vaccines (whether natural sequence or computationally optimized products) is now a critical component in interpreting candidate vaccine suitability.

Methods

We have utilized an N-mer identity algorithm to represent T cell epitopes and explore potential coverage of the global HIV pandemic using natural sequences derived from candidate HIV vaccines. Breadth (the number of T cell epitopes generated) and depth (the variant coverage within a T cell epitope) analyses have been incorporated into the model to explore vaccine coverage requirements in terms of the number of discrete T cell epitopes generated.

Results

We show that when multiple epitope generation by a vaccine product is considered a far more nuanced appraisal of the potential HIV strain coverage of the vaccine product emerges. By considering epitope breadth and depth several important observations were made: (1) epitope breadth requirements to reach particular levels of vaccine coverage, even for natural sequence-based vaccine products is not necessarily an intractable problem for the immune system; (2) increasing the valency (number of T cell epitope variants present) of vaccine products dramatically decreases the epitope requirements to reach particular coverage levels for any epidemic; (3) considering multiple-hit models (more than one exact epitope match with an incoming HIV strain) places a significantly higher requirement upon epitope breadth in order to reach a given level of coverage, to the point where low valency natural sequence based products would not practically be able to generate sufficient epitopes.

Conclusions

When HIV vaccine sequences are compared against datasets of potential incoming viruses important metrics such as the minimum epitope count required to reach a desired level of coverage can be easily calculated. We propose that such analyses can be applied early in the planning stages and during the execution phase of a vaccine trial to explore theoretical and empirical suitability of a vaccine product to a particular epidemic setting.

Vaccine protection against simian immunodeficiency virus in monkeys using recombinant gamma-2 herpesvirus

Recombinant strains of replication-competent rhesus monkey rhadinovirus (RRV) were constructed in which strong promoter/enhancer elements were used to drive expression of simian immunodeficiency virus (SIV) Env or Gag or a Rev-Tat-Nef fusion protein. Cultured rhesus monkey fibroblasts infected with each recombinant strain were shown to express the expected protein. Three RRV-negative and two RRV-positive rhesus monkeys were inoculated intravenously with a mixture of these three recombinant RRVs. Expression of SIV Gag was readily detected in lymph node biopsy specimens taken at 3 weeks postimmunization. Impressive anti-SIV cellular immune responses were elicited on the basis of major histocompatibility complex (MHC) tetramer staining and gamma interferon enzyme-linked immunospot (ELISPOT) assays. Responses were much greater in magnitude in the monkeys that were initially RRV negative but were still readily detected in the two monkeys that were naturally infected with RRV at the time of immunization. By 3 weeks postimmunization, responses measured by MHC tetramer staining in the two Mamu-A*01(+) RRV-negative monkeys reached 9.3% and 13.1% of all CD8(+) T cells in peripheral blood to the Gag CM9 epitope and 2.3% and 7.3% of all CD8(+) T cells in peripheral blood to the Tat SL8 epitope. Virus-specific CD8(+) T cell responses persisted at high levels up to the time of challenge at 18 weeks postimmunization, and responding cells maintained an effector memory phenotype. Despite the ability of the RRVenv recombinant to express high levels of Env in cultured cells, and despite the appearance of strong anti-RRV antibody responses in immunized monkeys, anti-Env antibody responses were below our ability to detect them. Immunized monkeys, together with three unimmunized controls, were challenged intravenously with 10 monkey infectious doses of SIVmac239. All five immunized monkeys and all three controls became infected with SIV, but peak viral loads were 1.2 to 3.0 log(10) units lower and chronic-phase viral loads were 1.0 to 3.0 log(10) units lower in immunized animals than the geometric mean of unimmunized controls. These differences were statistically significant. Anti-Env antibody responses following challenge indicated an anamnestic response in the vaccinated monkeys. These findings further demonstrate the potential of recombinant herpesviruses as preventive vaccines for AIDS. We hypothesize that this live, replication-competent, persistent herpesvirus vector could match, or come close to matching, live attenuated strains of SIV in the degree of protection if the difficulty with elicitation of anti-Env antibody responses can be overcome.

Design and immunogenicity of a novel synthetic antigen based on the ligand domain of the Plasmodium vivax duffy binding protein

The Duffy binding protein is considered a leading vaccine candidate against asexual blood-stage Plasmodium vivax. The interaction of P. vivax merozoites with human reticulocytes through Duffy binding protein (DBP) and its cognate receptor is vital for parasite infection. The ligand domain of DBP (DBPII) is polymorphic, showing a diversity characteristic of selective immune pressure that tends to compromise vaccine efficacy associated with strain-specific immunity. A previous study resolved that a polymorphic region of DBPII was a dominant B-cell epitope target of human inhibitory anti-DBP antibodies, which we refer to as the DEK epitope for the amino acids in the SalI allele. We hypothesized that the polymorphic residues, which are not functionally important for erythrocyte binding but flank the receptor binding motif of DBPII, comprise variant epitopes that tend to divert the immune response away from more conserved epitopes. In this study, we designed, expressed, and evaluated the immunogenicity of a novel artificial DBPII allele, termed DEKnull, having nonpolar amino acids in the naturally occurring polymorphic charged residues of the DEK epitope. The DEKnull antigen retained erythrocyte-binding activity and elicited antibodies to shared epitopes of SalI DBPII from which it was derived. Our results confirmed that removal of the dominant variant epitope in the DEKnull vaccine lowered immunogenicity of DBPII, but inhibitory anti-DBPII antibodies were elicited against shared neutralizing epitopes on SalI. Focusing immune responses toward more conserved DBP epitopes may avoid development of a strain-specific immunity and enhance functional inhibition against broader range of DBPII variants.

The ins and outs of HIV-1 Tat

HIV-1 encodes for the small basic protein Tat (86-101 residues) that drastically enhances the efficiency of viral transcription. The mechanism enabling Tat nuclear import is not yet clear, but studies using reporter proteins fused to the Tat basic domain indicate that Tat could reach the nucleus by passive diffusion. Tat also uses an unusual transcellular transport pathway. The first step of this pathway involves high-affinity binding of Tat to phosphatidylinositol (4,5) bisphosphate (PI(4,5)P(2)), a phospholipid that is concentrated in the inner leaflet of the plasma membrane and enables Tat recruitment at this level. Tat then crosses the plasma membrane to reach the outside medium. Although unconventional, Tat secretion by infected cells is highly active, and export is the major destination for HIV-1 Tat. Secreted Tat can bind to a variety of cell types using several different receptors. Most of them will allow Tat endocytosis. Upon internalization, low endosomal pH triggers a conformational change in Tat that results in membrane insertion. Later steps of Tat translocation to the target-cell cytosol are assisted by Hsp90, a general cytosolic chaperone. Cytosolic Tat can trigger various cell responses. Indeed, accumulating evidence suggests that extracellular Tat acts as a viral toxin that affects the biological activity of different cell types and has a key role in acquired immune-deficiency syndrome development. This review focuses on some of the recently identified molecular details underlying the unusual transcellular transport pathway used by Tat, such as the role of the single Trp in Tat for its membrane insertion and translocation.

Characterization of an effective CTL response against HIV and SIV infections

A vaccine inducing protective immunity in mucosal tissues and secretions may stop or limit HIV infection. Although cytotoxic T lymphocytes (CTLs) are clearly associated with control of viral replication in HIV and simian immunodeficiency virus (SIV) infections, there are examples of uncontrolled viral replication in the face of strong CD8⁺ T-cell responses. The number of functions, breadth, avidity, and magnitude of CTL response are likely to be important factors in the effectiveness of anti-HIV T-cell response, but the location and persistence of effector CD8⁺ T cells are also critical factors. Although the only HIV vaccine clinical trial targeting cellular immunity to prevent HIV infection failed, vaccine strategies using persistent agents against pathogenic mucosal challenge in macaque models are showing unique success. Thus, the key to control the initial focus of viral replication at the portal of entry may rely on the continuous generation of effector CTL responses at mucosal level.

New paradigms for HIV/AIDS vaccine development

HIV-1 and its simian counterpart SIV have been exquisitely tailored by evolution to evade host immunity. By virtue of specific adaptations that thwart individual innate or adaptive immune mechanisms, and an overall replication strategy that provides for rapid establishment of a large, systemic viral population, capable of dynamic adaptation to almost all immune selection pressures, these viruses, once established, almost invariably stay one step ahead of the host's immune system, and in the vast majority of infected individuals, replicate indefinitely. Although many vaccine approaches tested to date have been able to enhance the magnitude of the immune responses to HIV/SIV infection, most of these responses, whether cellular or humoral, have largely failed to be both effectively antiviral and targeted to prevent the emergence of fully functional escape variants. Recent advances, however, have provided strong evidence that the initial stages of infection following mucosal transmission of these viruses are more vulnerable to immune intervention, and have led to the development of vaccine strategies that elicit responses able to effectively intervene in these early stages of infection, either preventing acquisition of infection or establishing early, stringent, and durable control. Here, we place HIV/AIDS vaccine development in the context of the basic immunobiology of HIV and SIV, review the evidence for their vulnerability to immune responses immediately after mucosal transmission, and discuss how this newly recognized vulnerability might be exploited for the development of an effective HIV/AIDS vaccine.

Heterologous prime-boost-boost immunisation of Chinese cynomolgus macaques using DNA and recombinant poxvirus vectors expressing HIV-1 virus-like particles

Background

There is renewed interest in the development of poxvirus vector-based HIV vaccines due to the protective effect observed with repeated recombinant canarypox priming with gp120 boosting in the recent Thai placebo-controlled trial. This study sought to investigate whether a heterologous prime-boost-boost vaccine regimen in Chinese cynomolgus macaques with a DNA vaccine and recombinant poxviral vectors expressing HIV virus-like particles bearing envelopes derived from the most prevalent clades circulating in sub-Saharan Africa, focused the antibody response to shared neutralising epitopes.

Methods

Three Chinese cynomolgus macaques were immunised via intramuscular injections using a regimen composed of a prime with two DNA vaccines expressing clade A Env/clade B Gag followed by boosting with recombinant fowlpox virus expressing HIV-1 clade D Gag, Env and cholera toxin B subunit followed by the final boost with recombinant modified vaccinia virus Ankara expressing HIV-1 clade C Env, Gag and human complement protein C3d. We measured the macaque serum antibody responses by ELISA, enumerated T cell responses by IFN-γ ELISpot and assessed seroneutralisation of HIV-1 using the TZM-bl β-galactosidase assay with primary isolates of HIV-1.

Results

This study shows that large and complex synthetic DNA sequences can be successfully cloned in a single step into two poxvirus vectors: MVA and FPV and the recombinant poxviruses could be grown to high titres. The vaccine candidates showed appropriate expression of recombinant proteins with the formation of authentic HIV virus-like particles seen on transmission electron microscopy. In addition the b12 epitope was shown to be held in common by the vaccine candidates using confocal immunofluorescent microscopy. The vaccine candidates were safely administered to Chinese cynomolgus macaques which elicited modest T cell responses at the end of the study but only one out of the three macaques elicited an HIV-specific antibody response. However, the antibodies did not neutralise primary isolates of HIV-1 or the V3-sensitive isolate SF162 using the TZM-bl β-galactosidase assay.

Conclusions

MVA and FP9 are ideal replication-deficient viral vectors for HIV-1 vaccines due to their excellent safety profile for use in humans. This study shows this novel prime-boost-boost regimen was poorly immunogenic in Chinese cynomolgus macaques.

Host immune responses that promote initial HIV spread

The host inflammatory response to HIV invasion is a necessary component of the innate antiviral activity that vaccines and early interventions seek to exploit/enhance. However, the response is dependent on CD4+ T-helper cell 1 (Th1) recruitment and activation. It is this very recruitment of HIV-susceptible target cells that is associated with the initial viral proliferation. Hence, global enhancement of the inflammatory response by T-cells and dendritic cells will likely feed viral propagation. Mucosal entry sites contain inherent pathways, in the form of natural regulatory T-cells (nTreg), that globally dampen the inflammatory response. We created a model of this inflammatory response to virus as well as inherent nTreg-mediated regulation of Th1 recruitment and activation. With simulations using this model we sought to address the net effect of nTreg activation and its specific functions as well as identify mechanisms of the natural inflammatory response that are best targeted to inhibit viral spread without compromising initial antiviral activity. Simulation results provide multiple insights that are relevant to developing intervention strategies that seek to exploit natural immune processes: (i) induction of the regulatory response through nTreg activation expedites viral proliferation due to viral production by nTreg itself and not to reduced Natural Killer (NK) cell activity; (ii) at the same time, induction of the inflammation response through either DC activation or Th1 activation expedites viral proliferation; (iii) within the inflammatory pathway, the NK response is an effective controller of viral proliferation while DC-mediated stimulation of T-cells is a significant driver of viral proliferation; and (iv) nTreg-mediated DC deactivation plays a significant role in slowing viral proliferation by inhibiting T-cell stimulation, making this function an aide to the antiviral immune response.

HIV-mediated phosphatidylinositol 3-kinase/serine-threonine kinase activation in APCs leads to programmed death-1 ligand upregulation and suppression of HIV-specific CD8 T cells

Recent evidence demonstrates that HIV-1 infection leads to the attenuation of cellular immune responses, which has been correlated with the increased expression of programmed death (PD)-1 on virus-specific CD8(+) T cells. PD-1 is induced upon T cell activation, and its prolonged expression facilitates CD8(+) T cell inhibitory signals when bound to its B7 family ligands, PD-ligand (L)1/2, which are expressed on APCs. Importantly, early reports demonstrated that blockade of the PD-1/PD-L interaction by Abs may help to counter the development of immune exhaustion driven by HIV viral persistence. To better understand the regulation of the PD-1 pathway during HIV infection, we examined the ability of the virus to induce PD-L expression on macrophages and dendritic cells. We found a direct relationship between the infection of APCs and the expression of PD-L1 in which virus-mediated upregulation induced a state of nonresponsiveness in uninfected HIV-specific T cells. Furthermore, this exhaustion phenotype was revitalized by the blockade of PD-L1, after which T cells regained their capacity for proliferation and the secretion of proinflammatory cytokines IFN-γ, IL-2, and IL-12 upon restimulation. In addition, we identify a critical role for the PI3K/serine-threonine kinase signaling pathway in PD-L1 upregulation of APCs by HIV, because inhibition of these intracellular signal transducer enzymes significantly reduced PD-L1 induction by infection. These data identify a novel mechanism by which HIV exploits the immunosuppressive PD-1 pathway and suggest a new role for virus-infected cells in the local corruption of immune responses required for viral suppression.

HIV-DNA priming alters T cell responses to HIV-adenovirus vaccine even when responses to DNA are undetectable

Many candidate HIV vaccines are designed to primarily elicit T cell responses. Although repeated immunization with the same vaccine boosts Ab responses, the benefit for T cell responses is ill defined. We compared two immunization regimens that include the same recombinant adenoviral serotype 5 (rAd5) boost. Repeated homologous rAd5 immunization fails to increase T cell responses, but increases gp140 Ab responses 10-fold. DNA prime, as compared with rAd5 prime, directs long-term memory CD8(+) T cells toward a terminally differentiated effector memory phenotype with cytotoxic potential. Based on the kinetics of activated cells measured directly ex vivo, the DNA vaccination primes for both CD4(+) and CD8(+) T cells, despite the lack of detection of the latter until after the boost. These results suggest that heterologous prime-boost combinations have distinct immunological advantages over homologous prime-boosts and suggest that the effect of DNA on subsequent boosting may not be easily detectable directly after the DNA vaccination.

Immune-mediated attenuation of HIV-1

Immune escape mutations selected by human leukocyte antigen class I-restricted CD8(+) cytotoxic T lymphocytes (CTLs) can result in biologically and clinically relevant costs to HIV-1 replicative fitness. This phenomenon may be exploited to design an HIV-1 vaccine capable of stimulating effective CTL responses against highly conserved, mutationally constrained viral regions, where immune escape could occur only at substantial functional costs. Such a vaccine might 'channel' HIV-1 evolution towards a less-fit state, thus lowering viral load set points, attenuating the infection course and potentially reducing the risk of transmission. A major barrier to this approach, however, is the accumulation of immune escape variants at the population level, possibly leading to the loss of immunogenic CTL epitopes and diminished vaccine-induced cellular immune responses as the epidemic progresses. Here, we review the evidence supporting CTL-driven replicative defects in HIV-1 and consider the implications of this work for CTL-based vaccines designed to attenuate the infection course.

Coordinate linkage of HIV evolution reveals regions of immunological vulnerability

Cellular immune control of HIV is mediated, in part, by induction of single amino acid mutations that reduce viral fitness, but compensatory mutations limit this effect. Here, we sought to determine if higher order constraints on viral evolution exist, because some coordinately linked combinations of mutations may hurt viability. Immune targeting of multiple sites in such a multidimensionally conserved region might render the virus particularly vulnerable, because viable escape pathways would be greatly restricted. We analyzed available HIV sequences using a method from physics to reveal distinct groups of amino acids whose mutations are collectively coordinated ("HIV sectors"). From the standpoint of mutations at individual sites, one such group in Gag is as conserved as other collectively coevolving groups of sites in Gag. However, it exhibits higher order conservation indicating constraints on the viability of viral strains with multiple mutations. Mapping amino acids from this group onto protein structures shows that combined mutations likely destabilize multiprotein structural interactions critical for viral function. Persons who durably control HIV without medications preferentially target the sector in Gag predicted to be most vulnerable. By sequencing circulating viruses from these individuals, we find that individual mutations occur with similar frequency in this sector as in other targeted Gag sectors. However, multiple mutations within this sector are very rare, indicating previously unrecognized multidimensional constraints on HIV evolution. Targeting such regions with higher order evolutionary constraints provides a novel approach to immunogen design for a vaccine against HIV and other rapidly mutating viruses.

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.

Mosaic HIV-1 Gag antigens can be processed and presented to human HIV-specific CD8+ T cells

Polyvalent mosaic HIV immunogens offer a potential solution for generating vaccines that can elicit immune responses against genetically diverse viruses. However, it is unclear whether key T cell epitopes can be processed and presented from these synthetic Ags and recognized by epitope-specific human T cells. In this study, we tested the ability of mosaic HIV immunogens expressed by recombinant, replication-incompetent adenovirus serotype 26 vectors to process and present major HIV clade B and clade C CD8 T cell epitopes in human cells. A bivalent mosaic vaccine expressing HIV Gag sequences was used to transduce PBMCs from 12 HIV-1-infected individuals from the United States and 10 HIV-1-infected individuals from South Africa; intracellular cytokine staining, together with tetramer staining, was used to assess the ability of mosaic Gag Ags to stimulate pre-existing memory responses compared with natural clade B and C vectors. Mosaic Gag Ags expressed all eight clade B epitopes tested in 12 United States subjects and all 5 clade C epitopes tested in 10 South African subjects. Overall, the magnitude of cytokine production induced by stimulation with mosaic Ags was comparable to clade B and clade C Ags tested, but the mosaic Ags elicited greater cross-clade recognition. Additionally, mosaic Ags induced HIV-specific CD4 T cell responses. Our studies demonstrate that mosaic Ags express major clade B and clade C viral T cell epitopes in human cells, as well as support the evaluation of mosaic HIV-1 vaccines in humans.

AIDS vaccines and preexposure prophylaxis: is synergy possible?

While the long-term goal is to develop highly effective AIDS vaccines, first generation vaccines may be only partially effective. Other HIV prevention modalities such as preexposure prophylaxis with antiretrovirals (PrEP) may have limited efficacy as well. The combined administration of vaccine and PrEP (VAXPREP), however, may have a synergistic effect leading to an overall benefit that is greater than the sum of the individual effects. We propose two test-of-concept trial designs for an AIDS vaccine plus oral or topical ARV. In one design, evidence that PrEP reduces the risk of HIV acquisition is assumed to justify offering it to all participants. A two-arm study comparing PrEP alone to VAXPREP is proposed in which 30 to 60 incident infections are observed to assess the additional benefit of vaccination on risk of infection and setpoint viral load. The demonstrated superiority of VAXPREP does not imply vaccine alone is efficacious. Similarly, the lack of superiority does not imply vaccine alone is ineffective, as antagonism could exist between vaccine and PrEP. In the other design, PrEP is assumed not to be in general use. A 2 × 2 factorial design is proposed in which high-risk individuals are randomized to one of four arms: placebo vaccine given with placebo PrEP, placebo vaccine given with PrEP, vaccine given with placebo PrEP, or VAXPREP. Between 60 and 210 infections are required to detect a benefit of vaccination with or without PrEP on risk of HIV acquisition or setpoint viral load, with fewer infections needed when synergy is present.

HIV-specific CD8+ T-cell proliferation is prospectively associated with delayed disease progression

Human immunodeficiency virus (HIV)-specific CD8(+) T-cell proliferation is consistently correlated with enhanced host HIV immune control, but whether proliferative responses are a cause or consequence of immune protection is unclear. We measured Env-specific CD8(+) T-cell proliferation and interferon (IFN)-γ secretion in HIV-infected participants with CD4 counts >200, who then completed 121 person-years of prospective follow-up to monitor HIV disease progression. In all, 13 of 31 participants (42%) reached end point during longitudinal follow-up. Strong Env-specific CD8(+) T-cell proliferation (>10% of CD8(+) T cells) was observed in 14/31 participants at baseline, and this was associated with a longer time to HIV disease progression end point, stratified baseline CD4 count (P=0.016). No associations were observed for IFN-γ ELISPOT responses and progression (P>0.2). Strong proliferation remained significant in multivariate Cox regression analyses (P=0.044) as an independent predictor of delayed HIV disease progression, along with baseline CD4 count (P=0.04). Duration of HIV infection was associated with more rapid progression in univariate, but not multivariate, analysis (P=0.112). Age and baseline viral load were not predictive of progression. HIV-specific CD8(+) T-cell proliferation was a correlate of protective immunity in this prospective study; such responses may be important for HIV vaccine protection.

Viral CTL escape mutants are generated in lymph nodes and subsequently become fixed in plasma and rectal mucosa during acute SIV infection of macaques

SIV_mac239 infection of rhesus macaques (RMs) results in AIDS despite the generation of a strong antiviral cytotoxic T lymphocyte (CTL) response, possibly due to the emergence of viral escape mutants that prevent recognition of infected cells by CTLs. To determine the anatomic origin of these SIV mutants, we longitudinally assessed the presence of CTL escape variants in two MamuA*01-restricted immunodominant epitopes (Tat-SL8 and Gag-CM9) in the plasma, PBMCs, lymph nodes (LN), and rectal biopsies (RB) of fifteen SIV_mac239-infected RMs. As expected, Gag-CM9 did not exhibit signs of escape before day 84 post infection. In contrast, Tat-SL8 escape mutants were apparent in all tissues by day 14 post infection. Interestingly LNs and plasma exhibited the highest level of escape at day 14 and day 28 post infection, respectively, with the rate of escape in the RB remaining lower throughout the acute infection. The possibility that CTL escape occurs in LNs before RBs is confirmed by the observation that the specific mutants found at high frequency in LNs at day 14 post infection became dominant at day 28 post infection in plasma, PBMC, and RB. Finally, the frequency of escape mutants in plasma at day 28 post infection correlated strongly with the level Tat-SL8-specific CD8 T cells in the LN and PBMC at day 14 post infection. These results indicate that LNs represent the primary source of CTL escape mutants during the acute phase of SIV_mac239 infection, suggesting that LNs are the main anatomic sites of virus replication and/or the tissues in which CTL pressure is most effective in selecting SIV escape variants.

Strong antiviral CD8+ T lymphocytes limit SIV replication by recognizing short pathogen-derived peptide epitopes. The cytotoxic CD8+ T cell responses specific for this highly mutable virus can select for viruses bearing mutations that prevent CD8+ T cell recognition of cells infected with these escape mutants. To determine the anatomic origin of these escape mutants, we tracked a particular escape mutant in multiple tissues (plasma virus, lymph nodes, rectal mucosa, and peripheral blood immune cells) during the early, acute phase of SIVmac239 infection of rhesus macaques. We found that escape mutants first reach high frequency in lymph nodes 2 weeks after infection, and the particular mutants generated in lymph nodes disseminate to other tissues by week 4. Furthermore, we found that epitope-specific CD8+ T lymphocyte responses in the lymph nodes and peripheral blood, but not the gut mucosa, are significantly correlated with the frequency of escape mutants in the plasma virus at week 4. This suggests that lymph nodes, and not the gut, are the primary site of anti-SIV CD8+ T cell responses and/or SIV replication during the acute phase of infection.

Induction of HIV neutralizing antibodies against the MPER of the HIV envelope protein by HA/gp41 chimeric protein-based DNA and VLP vaccines

Several conserved neutralizing epitopes have been identified in the HIV Env protein and among these, the MPER of gp41 has received great attention and is widely recognized as a promising target. However, little success has been achieved in eliciting MPER-specific HIV neutralizing antibodies by a number of different vaccine strategies. We investigated the ability of HA/gp41 chimeric protein-based vaccines, which were designed to enhance the exposure of the MPER in its native conformation, to induce MPER-specific HIV neutralizing antibodies. In characterization of the HA/gp41 chimeric protein, we found that by mutating an unpaired Cys residue (Cys-14) in its HA1 subunit to a Ser residue, the modified chimeric protein HA-C14S/gp41 showed increased reactivity to a conformation-sensitive monoclonal antibody against HA and formed more stable trimers in VLPs. On the other hand, HA-C14S/gp41 and HA/gp41 chimeric proteins expressed on the cell surfaces exhibited similar reactivity to monoclonal antibodies 2F5 and 4E10. Immunization of guinea pigs using the HA-C14S/gp41 DNA or VLP vaccines induced antibodies against the HIV gp41 as well as to a peptide corresponding to a segment of MPER at higher levels than immunization by standard HIV VLPs. Further, sera from vaccinated guinea pigs were found to exhibit HIV neutralizing activities. Moreover, sera from guinea pigs vaccinated by HA-C14S/gp41 DNA and VLP vaccines but not the standard HIV VLPs, were found to neutralize HIV pseudovirions containing a SIV-4E10 chimeric Env protein. The virus neutralization could be blocked by a MPER-specific peptide, thus demonstrating induction of MPER-specific HIV neutralizing antibodies by this novel vaccine strategy. These results show that induction of MPER-specific HIV neutralizing antibodies can be achieved through a rationally designed vaccine strategy.

Early events in sexual transmission of HIV and SIV and opportunities for interventions

To constrain the growth of the HIV/AIDS pandemic and ultimately end it, effective measures must be developed to prevent sexual mucosal transmission, the major route by which new infections are acquired. I review sexual mucosal transmission of HIV and SIV, with a focus on vaginal transmission in the SIV rhesus macaque animal model, and the evidence for small founder populations of infected cells and the local expansion at the portal of entry necessary to establish systemic infection. These early events represent windows of maximum opportunity for interventions to prevent systemic infection. I highlight the paradoxical role the innate immune response plays in actually facilitating transmission, and a novel microbicide strategy that targets this innate response to prevent systemic infection, and I conclude with an agenda for future research that emphasizes mucosal immunology, virology and pathogenesis studies at each anatomic site of entry.

Two closely related Env antigens from the same patient elicited different spectra of neutralizing antibodies against heterologous HIV-1 isolates

Identification of immunogens capable of eliciting broadly neutralizing antibody (NAb) responses against HIV-1 is a major goal toward the development of an AIDS vaccine. Despite significant progress in understanding the structural features of the HIV-1 envelope glycoprotein (Env) and the discovery of multiple broadly neutralizing monoclonal antibodies with defined antigenic structures, the design of optimal Env immunogens to elicit broad NAbs remains a major challenge. As the structural determinants of Env immunogenicity remain unclear, we assessed two closely related Env antigens isolated from the same HIV-1-infected patient with different phenotypic features to identify what may result in a favorable immunogenic profile. One Env, B33, isolated from brain, was highly macrophage tropic with a high CD4 affinity, while the other, LN40, isolated from the lymph nodes, was poorly macrophage tropic with a low CD4 affinity. Using a DNA prime-protein boost approach, rabbits primed with LN40 Env antigen had a NAb response against heterologous primary isolates, while B33 Env antigens were capable of eliciting NAbs against only homologous and sensitive viral isolates. Further analysis revealed that the specificity of NAbs elicited by the LN40 antigen mapped to limited residues within or flanking the CD4 binding site. Certain key structural determinants were identified that could differentiate primary Env immunogens based on their potential to elicit broader NAbs. This progress will facilitate the rational design of effective HIV-1 vaccine formulations with optimal Env antigens.

AFM force measurements of the gp120-sCD4 and gp120 or CD4 antigen-antibody interactions

Soluble CD4 (sCD4), anti-CD4 antibody, and anti-gp120 antibody have long been regarded as entry inhibitors in human immunodeficiency virus (HIV) therapy. However, the interactions between these HIV entry inhibitors and corresponding target molecules are still poorly understood. In this study, atomic force microscopy (AFM) was utilized to investigate the interaction forces among them. We found that the unbinding forces of sCD4-gp120 interaction, CD4 antigen-antibody interaction, and gp120 antigen-antibody interaction were 25.45 ± 20.46, 51.2 2 ± 34.64, and 89.87 ± 44.63 pN, respectively, which may provide important mechanical information for understanding the effects of viral entry inhibitors on HIV infection. Moreover, we found that the functionalization of an interaction pair on AFM tip or substrate significantly influenced the results, implying that we must perform AFM force measurement and analyze the data with more caution.

Intercompartmental recombination of HIV-1 contributes to env intrahost diversity and modulates viral tropism and sensitivity to entry inhibitors

HIV-1 circulates within an infected host as a genetically heterogeneous viral population. Viral intrahost diversity is shaped by substitutional evolution and recombination. Although many studies have speculated that recombination could have a significant impact on viral phenotype, this has never been definitively demonstrated. We report here phylogenetic and subsequent phenotypic analyses of envelope genes obtained from HIV-1 populations present in different anatomical compartments. Assessment of env compartmentalization from immunologically discrete tissues was assessed utilizing a single genome amplification approach, minimizing in vitro-generated artifacts. Genetic compartmentalization of variants was frequently observed. In addition, multiple incidences of intercompartment recombination, presumably facilitated by low-level migration of virus or infected cells between different anatomic sites and coinfection of susceptible cells by genetically divergent strains, were identified. These analyses demonstrate that intercompartment recombination is a fundamental evolutionary mechanism that helps to shape HIV-1 env intrahost diversity in natural infection. Analysis of the phenotypic consequences of these recombination events showed that genetic compartmentalization often correlates with phenotypic compartmentalization and that intercompartment recombination results in phenotype modulation. This represents definitive proof that recombination can generate novel combinations of phenotypic traits which differ subtly from those of parental strains, an important phenomenon that may have an impact on antiviral therapy and contribute to HIV-1 persistence in vivo.

Why we don't have an HIV vaccine, and how we can develop one

Confronted with the recent high-profile failures of several clinical trials of promising candidate vaccines against HIV, many scientists have all but given up hope of producing a human-ready vaccine within the next decade. In this review I contend that although the scientific obstacles remain formidable, the economic challenges are just as real. The groundwork will be laid for a major scientific breakthrough in vaccine development only when there are new contractual structures that enhance private incentives for vaccine development; when we have clearly specified the rights to the profitable North American market; when we have established a system of liability protection for vaccine side effects; and when our clinical trials also test the behavioral consequences of vaccination.

Differential induction of functional IgG using the Plasmodium falciparum placental malaria vaccine candidate VAR2CSA

Background

In Plasmodium falciparum malaria endemic areas placental malaria (PM) is an important complication of malaria. The recurrence of malaria in primigravidae women irrespective of acquired protection during childhood is caused by the interaction between the parasite-expressed VAR2CSA antigen and chondroitin sulfate A (CSA) in the placental intervillous space and lack of protective antibodies. PM impairs fetal development mainly by excessive inflammation processes. After infections during pregnancy women acquire immunity to PM conferred by antibodies against VAR2CSA. Ideally, a vaccine against PM will induce antibody-mediated immune responses that block the adhesion of infected erythrocytes (IE) in the placenta.

Principal Findings

We have previously shown that antibodies raised in rat against individual domains of VAR2CSA can block IE binding to CSA. In this study we have immunized mice, rats and rabbits with each individual domain and the full-length protein corresponding to the FCR3 VAR2CSA variant. We found there is an inherently higher immunogenicity of C-terminal domains compared to N-terminally located domains. This was irrespective of whether antibodies were induced against single domains or the full-length protein. Species-specific antibody responses were also found, these were mainly directed against single domains and not the full-length VAR2CSA protein.

Conclusions/Significance

Binding inhibitory antibodies appeared to be against conformational B-cell epitopes. Non-binding inhibitory antibodies reacted highly against the C-terminal end of the VAR2CSA molecule especially the highly polymorphic DBL6ε domain. Differential species-specific induction of antibody responses may allow for more direct analysis of functional versus non-functional B-cell epitopes.

Interbilayer-crosslinked multilamellar vesicles as synthetic vaccines for potent humoral and cellular immune responses

Vaccines based on recombinant proteins avoid the toxicity and antivector immunity associated with live vaccine (for example, viral) vectors, but their immunogenicity is poor, particularly for CD8(+) T-cell responses. Synthetic particles carrying antigens and adjuvant molecules have been developed to enhance subunit vaccines, but in general these materials have failed to elicit CD8(+) T-cell responses comparable to those for live vectors in preclinical animal models. Here, we describe interbilayer-crosslinked multilamellar vesicles formed by crosslinking headgroups of adjacent lipid bilayers within multilamellar vesicles. Interbilayer-crosslinked vesicles stably entrapped protein antigens in the vesicle core and lipid-based immunostimulatory molecules in the vesicle walls under extracellular conditions, but exhibited rapid release in the presence of endolysosomal lipases. We found that these antigen/adjuvant-carrying vesicles form an extremely potent whole-protein vaccine, eliciting endogenous T-cell and antibody responses comparable to those for the strongest vaccine vectors. These materials should enable a range of subunit vaccines and provide new possibilities for therapeutic protein delivery.

A phase I trial of preventive HIV vaccination with heterologous poxviral-vectors containing matching HIV-1 inserts in healthy HIV-uninfected subjects

We evaluated replication-defective poxvirus vectors (modified vaccinia Ankara [MVA] and fowlpox [FPV]) in a homologous and heterologous vector prime-boost vaccination regimen containing matching HIV inserts (MVA-HIV and FPV-HIV) given at months 0, 1, 3, 5 and 7 in 150 healthy HIV-negative vaccinia-naïve participants. FPV-HIV alone was poorly immunogenic, while the high dose (10(9)pfu/2 ml) of MVA-HIV alone elicited maximal responses after two injections: CD4+ and CD8+ T-cell responses in 26/55 (47.3%) and 5/60 (8.3%) of participants, respectively, and IFN-γ ELISpot responses in 28/62 (45.2%). The infrequent CD8+ T-cell responses following MVA-HIV priming were boosted only by the heterologous (FPV-HIV) construct in 14/27 (51.9%) of participants post 4th vaccination. Alternatively, HIV envelope-specific binding antibodies were demonstrated in approximately two-thirds of recipients of the homologous boosting regimen, but in less than 20% of subjects after the heterologous vector boost. Thus, a heterologous poxvirus vector prime-boost regimen can induce HIV-specific CD8+ T-cell and CD4+ T-cell responses, which may be an important feature of an optimal regimen for preventive HIV vaccination.