Consensus Env Research Articles

Contemporary HIV-1 consensus Env with AI-assisted redesigned hypervariable loops promote antibody binding

An effective HIV-1 vaccine must elicit broadly neutralizing antibodies (bnAbs) against highly diverse Envelope glycoproteins (Env). Since Env with the longest hypervariable (HV) loops is more resistant to the cognate bnAbs than Env with shorter HV loops, we redesigned hypervariable loops for updated Env consensus sequences of subtypes B and C and CRF01_AE. Using modeling with AlphaFold2, we reduced the length of V1, V2, and V5 HV loops while maintaining the integrity of the Env structure and glycan shield, and modified the V4 HV loop. Spacers are designed to limit strain-specific targeting. All updated Env are infectious as pseudoviruses. Preliminary structural characterization suggests that the modified HV loops have a limited impact on Env’s conformation. Binding assays show improved binding to modified subtype B and CRF01_AE Env but not to subtype C Env. Neutralization assays show increases in sensitivity to bnAbs, although not always consistently across clades. Strikingly, the HV loop modification renders the resistant CRF01_AE Env sensitive to 10-1074 despite the absence of a glycan at N332.

Enhancement of Neutralization Responses through Sequential Immunization of Stable Env Trimers Based on Consensus Sequences from Select Time Points by Mimicking Natural Infection.

HIV-1 vaccines have been challenging to develop, partly due to the high level of genetic variation in its genome. Thus, a vaccine that can induce cross-reactive neutralization activities will be needed. Studies on the co-evolution of antibodies and viruses indicate that mimicking the natural infection is likely to induce broadly neutralizing antibodies (bnAbs). We generated the consensus Env sequence for each time point in subject CH505, who developed broad neutralization activities, and selected five critical time points before broad neutralization was detected. These consensus sequences were designed to express stable Env trimers. Priming with the transmitted/founder Env timer and sequential boosting with these consensus Env trimers from different time points induced broader and more potent neutralizing activities than the BG505 Env trimer in guinea pigs. Analysis of the neutralization profiles showed that sequential immunization of Env trimers favored nAbs with gp120/gp41 interface specificity while the BG505 Env trimer favored nAbs with V2 specificity. The unique features such as consensus sequences, stable Env trimers and the sequential immunization to mimic natural infection likely has allowed the induction of improved neutralization responses.

Fine-mapping the immunodominant antibody epitopes on consensus sequence-based HIV-1 envelope trimer vaccine candidates

The HIV-1 envelope glycoprotein (Env) trimer is the key target for vaccines aimed at inducing neutralizing antibodies (NAbs) against HIV-1. The clinical candidate immunogen ConM SOSIP.v7 is a stabilized native-like HIV-1 Env trimer based on an artificial consensus sequence of all HIV-1 isolates in group M. In preclinical studies ConM SOSIP.v7 trimers induced strong autologous NAb responses in non-human primates (NHPs). To fine-map these responses, we isolated monoclonal antibodies (mAbs) from six cynomolgus macaques that were immunized three times with ConM SOSIP.v7 protein and boosted twice with the closely related ConSOSL.UFO.664 immunogen. A total of 40 ConM and/or ConS-specific mAbs were isolated, of which 18 were retrieved after the three ConM SOSIP.v7 immunizations and 22 after the two immunizations with ConSOSL.UFO.664. 22 mAbs (55%) neutralized the ConM and/or ConS virus. Cross-neutralization of ConS virus by approximately one-third of the mAbs was seen prior to ConSOSL.UFO.664 immunization, albeit with modest potency. Neutralizing antibodies predominantly targeted the V1 and V2 regions of the immunogens, with an apparent extension towards the V3 region. Thus, the V1V2V3 region is immunodominant in the potent NAb response elicited by two consensus sequence native-like HIV-1 Env immunogens. Immunization with these soluble consensus Env proteins also elicited non-neutralizing mAbs targeting the trimer base. These results inform the use and improvement of consensus-based trimer immunogens in combinatorial vaccine strategies.

Stepwise Conformational Stabilization of a HIV-1 Clade C Consensus Envelope Trimer Immunogen Impacts the Profile of Vaccine-Induced Antibody Responses.

Stabilization of the HIV-1 Envelope glycoprotein trimer (Env) in its native pre-fusion closed conformation is regarded as one of several requirements for the induction of neutralizing antibody (nAb) responses, which, in turn, will most likely be a prerequisite for the development of an efficacious preventive vaccine. Here, we systematically analyzed how the stepwise stabilization of a clade C consensus (ConC) Env immunogen impacts biochemical and biophysical protein traits such as antigenicity, thermal stability, structural integrity, and particle size distribution. The increasing degree of conformational rigidification positively correlates with favorable protein characteristics, leading to optimized homogeneity of the protein preparations, increased thermal stability, and an overall favorable binding profile of structure-dependent broadly neutralizing antibodies (bnAbs) and non-neutralizing antibodies (non-nAbs). We confirmed that increasing the structural integrity and stability of the Env trimers positively correlates with the quality of induced antibody responses by the immunogens. These and other data contribute to the selection of ConCv5 KIKO as novel Env immunogens for use within the European Union’s H2020 Research Consortium EHVA (European HIV Alliance) for further preclinical analysis and phase 1 clinical development.

Common antibody dependent cell mediated cytotoxicity (ADCC) antibody epitopes of HIV-1 CRF01_AE Env and Gag in early HIV-1 infected individuals

There have been a few studies aimed at identifying epitopes of ADCC-inducing antibodies when compared to those of neutralizing antibodies and cytotoxic T lymphocytes against a variety of HIV-1 clades. To map the common ADCC epitopes of HIV-1 CRF01_AE. We screened 65 sera of confirmed early HIV-1 CRF01_AE infected individuals for ADCC antibody against gp120 utilizing an EGFP-CEM-NKr flow cytometric assay. Sera with high ADCC antibody were then examined against ADCC epitopes using the complete HIV-1 CRF01_AE gp160- and subtype A Gag-overlapping peptide sets which were divided into 7 pools:E1-E7 and 5 pools:G1-G5, respectively. Each positive peptide pool was further investigated for fine ADCC epitope mapping using matrix formats. Twenty, 25 and 20 sera demonstrated the high-, medium- and low-ADCC antibody activities against gp120, respectively. Interestingly, 11 Env- and 6 Gag-peptides of pools E3, E4, E7 and pools G1, G2, G4 with high ADCC responses were also responded by at least 20%, 12% and 5%, 10% of medium- and low-ADCC antibody sera, respectively. These eleven common Env ADCC epitopes were localized at C2-V3-C3-V4 regions of gp120 and cytoplasmic tail of gp41 while six common Gag ADCC epitopes were localized at p17-p24-p2 regions. Although the degree of ADCC antibody responses to the gp120 protein varied from high to low, there were certain consensus Env and Gag peptides that could induce the ADCC antibody responses of 21.54-58.46% and 23.08-41.54%, respectively of the early infected individuals. This epitope information should be useful as the new antibody-based vaccine immunogens.

HIV-1 Consensus Envelope-Induced Broadly Binding Antibodies.

Antibodies that cross-react with multiple HIV-1 envelopes (Envs) are useful reagents for characterizing Env proteins and for soluble Env capture and purification assays. We previously reported 10 murine monoclonal antibodies induced by group M consensus Env, CON-6 immunization. Each demonstrated broad cross-reactivity to recombinant Envs. Here we characterized the Env epitopes to which they bind. Seven mapped to linear epitopes in gp120, five at the Env N-terminus, and two at the Env C-terminus. One antibody, 13D7, bound at the gp120 N-terminus (aa 30-42), reacted with HIV-1-infected CD4+ T cells, and when expressed in a human IgG1 backbone, mediated antibody-dependent cellular cytotoxicity. Antibody 18F11 bound at the gp120 C-terminus (aa 445-459) and reactivity was glycan dependent. Antibodies 13D7, 3B3, and 16H3 bound to 100 percent of HIV-1 Envs tested in ELISA and sodium dodecyl sulfate/polyacrylamide gel electrophoresis/western blot analysis. These data define the epitopes of monoclonal antibody reagents for characterization of recombinant Envs, one epitope of which is also expressed on the surface of HIV-1-infected CD4+ T cells.

A pilot study of the feasibility and potential effectiveness of using smartphones to provide recovery support

The low number of envelope (Env) spikes presented on native HIV-1 particles is a major impediment for HIV-1 prophylactic vaccine development. We designed virus-like particle encoding adenoviral vectors utilizing SIVmac239 Gag as an anchor for full length and truncated HIV-1 M consensus Env. Truncated Env overexpressed VRC01 and 17b binding antigen on the surface of transduced cells while the full length Env vaccine presented more and similar amounts of antigen binding to the trimer conformation sensitive antibodies PGT151 and PGT145, respectively. The adenoviral vectors were used to prime Balb/c mice followed by sequential boosting with chimpanzee type 63, and chimpanzee type 3 adenoviral vectors encoding SIVmac239 Gag and full length consensus Env. Both vaccine regimens induced increasing titers of binding antibody responses after each immunization, and significant differences in immune responses between the two groups were observed after the final immunization. Full length Env priming skewed antibody responses towards gp41, while truncated Env priming induced responses primarily targeting gp120 containing and derived antigens. Importantly, no differences in neutralizing antibody responses were found between the different priming regimens as both induced high titered tier 1 neutralizing antibodies, but no tier 2 antibodies, possibly reflecting the similar presentation of trimer specific antibody epitopes. The described vaccine regimens provide insight into the effects of the HIV-1 Env cytoplasmic tail on epitope presentation and subsequent immune responses, which is relevant for the interpretation of current clinical trials that are using truncated Env as an immunogen. The regimens described here provide similar neutralization titers, and thus are useful for investigating the importance of specificity in non-neutralizing antibody mediated protection against viral challenge.

Effect of HIV-1 envelope cytoplasmic tail on adenovirus primed virus encoded virus-like particle immunizations

The low number of envelope (Env) spikes presented on native HIV-1 particles is a major impediment for HIV-1 prophylactic vaccine development. We designed virus-like particle encoding adenoviral vectors utilizing SIVmac239 Gag as an anchor for full length and truncated HIV-1 M consensus Env. Truncated Env overexpressed VRC01 and 17b binding antigen on the surface of transduced cells while the full length Env vaccine presented more and similar amounts of antigen binding to the trimer conformation sensitive antibodies PGT151 and PGT145, respectively. The adenoviral vectors were used to prime Balb/c mice followed by sequential boosting with chimpanzee type 63, and chimpanzee type 3 adenoviral vectors encoding SIVmac239 Gag and full length consensus Env. Both vaccine regimens induced increasing titers of binding antibody responses after each immunization, and significant differences in immune responses between the two groups were observed after the final immunization. Full length Env priming skewed antibody responses towards gp41, while truncated Env priming induced responses primarily targeting gp120 containing and derived antigens. Importantly, no differences in neutralizing antibody responses were found between the different priming regimens as both induced high titered tier 1 neutralizing antibodies, but no tier 2 antibodies, possibly reflecting the similar presentation of trimer specific antibody epitopes. The described vaccine regimens provide insight into the effects of the HIV-1 Env cytoplasmic tail on epitope presentation and subsequent immune responses, which is relevant for the interpretation of current clinical trials that are using truncated Env as an immunogen. The regimens described here provide similar neutralization titers, and thus are useful for investigating the importance of specificity in non-neutralizing antibody mediated protection against viral challenge.

Protective efficacy of centralized and polyvalent envelope immunogens in an attenuated equine lentivirus vaccine.

Lentiviral Envelope (Env) antigenic variation and related immune evasion present major hurdles to effective vaccine development. Centralized Env immunogens that minimize the genetic distance between vaccine proteins and circulating viral isolates are an area of increasing study in HIV vaccinology. To date, the efficacy of centralized immunogens has not been evaluated in the context of an animal model that could provide both immunogenicity and protective efficacy data. We previously reported on a live-attenuated (attenuated) equine infectious anemia (EIAV) virus vaccine, which provides 100% protection from disease after virulent, homologous, virus challenge. Further, protective efficacy demonstrated a significant, inverse, linear relationship between EIAV Env divergence and protection from disease when vaccinates were challenged with viral strains of increasing Env divergence from the vaccine strain Env. Here, we sought to comprehensively examine the protective efficacy of centralized immunogens in our attenuated vaccine platform. We developed, constructed, and extensively tested a consensus Env, which in a virulent proviral backbone generated a fully replication-competent pathogenic virus, and compared this consensus Env to an ancestral Env in our attenuated proviral backbone. A polyvalent attenuated vaccine was established for comparison to the centralized vaccines. Additionally, an engineered quasispecies challenge model was created for rigorous assessment of protective efficacy. Twenty-four EIAV-naïve animals were vaccinated and challenged along with six-control animals six months post-second inoculation. Pre-challenge data indicated the consensus Env was more broadly immunogenic than the Env of the other attenuated vaccines. However, challenge data demonstrated a significant increase in protective efficacy of the polyvalent vaccine. These findings reveal, for the first time, a consensus Env immunogen that generated a fully-functional, replication-competent lentivirus, which when experimentally evaluated, demonstrated broader immunogenicity that does not equate to higher protective efficacy.

P-E2 Selection of single domain antibody fragments (nanobodies) from dromedaries immunized with HIV-1 subtype C gp140 SOSIPs

Nanobodies (VHH) are single domain antibodies derived from heavy chain only antibodies in camelidae. Due to their small size and long HCDR3 loops they are ideally suited to penetrate into receptor binding cavities thereby mediating neutralizing potential. Here we immunized 4 dromedaries with soluble trimeric gp140 SOSIP constructs derived from different HIV-1 subtype C Envs with the aim to select broadly neutralizing nanobodies against this most prevalent subtype. SOSIPs were constructed from 2 transmitted/founder viruses (C t/f) and a C consensus Env (C cons). After expression in 293T cells, soluble trimeric SOSIPs were purified by lectin chromatography followed by size exclusion and anion exchange chromatography. Two dromedaries were immunized with a mixture of trimeric C t/f SOSIPs and 2 animals animals received trimeric C cons SOSIP. VHH immune libraries were generated from the 4 animals by amplification of VHH sequences from lymphocytes by RT-PCR and cloning into a phagemid vector. Sera from immunized dromedaries showed Env-specific binding and neutralization of autologous pseudoviruses in Tzm-bl assays. Neutralization breadth is currently being further evaluated. The generated VHH libraries were screened on the respective autologous trimeric SOSIPs. Selected clones were tested by ELISA for SOSIP-specific binding. About 80% of the clones selected on C cons were positive by ELISA. Of 25 sequences analyzed so far, only 7 represented individual sequences, whereas others were found up to 6×. Further genetic analysis and crossneutralization studies are ongoing. Trimeric GP140 SOSIPs of epidemiologically relevant HIV-1 strains may represent suited immunogens to induce broadly neutralizing nanobodies for preventive/therapeutic applications.

DNA prime-protein boost using subtype consensus Env was effective in eliciting neutralizing antibody responses against subtype BC HIV-1 viruses circulating in China

Previously, we have shown that DNA prime-protein boost is effective in eliciting neutralizing antibodies (NAb) against randomly selected HIV-1 isolates. Given the genetic diversity of HIV-1 viruses and the unique predominant subtypes in different geographic regions, it is critical to test the DNA prime-protein boost approach against circulating viral isolates in key HIV endemic areas. In the current study, the same DNA prime-protein boost vaccine was used as in previous studies to investigate the induction of NAb responses against HIV-1 clade BC, a major subtype circulating in China. A codon optimized gp120-BC DNA vaccine, based on the consensus envelope (Env) antigen sequence of clade BC, was constructed and a stable CHO cell line expressing the same consensus BC gp120 protein was produced. The immunogenicity of this consensus gp120-BC was examined in New Zealand White rabbits by either DNA prime-protein boost or protein alone vaccination approaches. High levels of Env-specific antibody responses were elicited by both approaches. However, DNA prime-protein boost but not the protein alone immune sera contained significant levels of NAb against pseudotyped viruses expressing HIV-1 BC Env antigens. Furthermore, high frequencies of CD4 binding site-targeted antibodies were found in the DNA prime- protein boost rabbit sera indicating that the positive NAb may be the result of antibodies against conformationally sensitive epitopes on HIV-1 Env. The findings support that DNA prime-protein boost was effective in eliciting NAb against a key HIV-1 virus subtype in China. This result may lead to the development of regional HIV vaccines through this approach.

Deletion of Specific Immune-Modulatory Genes from Modified Vaccinia Virus Ankara-Based HIV Vaccines Engenders Improved Immunogenicity in Rhesus Macaques

Modified vaccinia virus Ankara (MVA) is a safe, attenuated orthopoxvirus that is being developed as a vaccine vector but has demonstrated limited immunogenicity in several early-phase clinical trials. Our objective was to rationally improve the immunogenicity of MVA-based HIV/AIDS vaccines via the targeted deletion of specific poxvirus immune-modulatory genes. Vaccines expressing codon-optimized HIV subtype C consensus Env and Gag antigens were generated from MVA vector backbones that (i) harbor simultaneous deletions of four viral immune-modulatory genes, encoding an interleukin-18 (IL-18) binding protein, an IL-1β receptor, a dominant negative Toll/IL-1 signaling adapter, and CC-chemokine binding protein (MVAΔ4-HIV); (ii) harbor a deletion of an additional (fifth) viral gene, encoding uracil-DNA glycosylase (MVAΔ5-HIV); or (iii) represent the parental MVA backbone as a control (MVA-HIV). We performed head-to-head comparisons of the cellular and humoral immune responses that were elicited by these vectors during homologous prime-boost immunization regimens utilizing either high-dose (2 × 10(8) PFU) or low-dose (1 × 10(7) PFU) intramuscular immunization of rhesus macaques. At all time points, a majority of the HIV-specific T cell responses, elicited by all vectors, were directed against Env, rather than Gag, determinants, as previously observed with other vector systems. Both modified vectors elicited up to 6-fold-higher frequencies of HIV-specific CD8 and CD4 T cell responses and up to 25-fold-higher titers of Env (gp120)-specific binding (nonneutralizing) antibody responses that were relatively transient in nature. While the correlates of protection against HIV infection remain incompletely defined, our results indicate that the rational deletion of specific genes from MVA vectors can positively alter their cellular and humoral immunogenicity profiles in nonhuman primates.

Comparison of the depth of vaccine-elicited HIV-1 Env epitope-specific CD8+ T lymphocyte responses

Background One of the major challenges in the development of an effective HIV-1 vaccine is the extraordinary genetic diversity of the virus. Immunizations of nonhuman primates using consensus and mosaic immunogens have been shown to elicit cross-reactive CD8+T lymphocyte responses that increase the depth of epitope recognition. However, one of the limitations of vaccine-induced epitope-specific CD8+T lymphocytes includes lack of protection against diverse strains and emergent forms of HIV-1 due to altered T cell receptor (TCR) affinity for variant peptide:MHC class I complexes. Methods In this study, we immunized a cohort of fifteen MamuA*01+ rhesus monkeys with either a 3-valent mosaic Env, group M consensus Env, or single clade B Env vaccine and compared the ability of the CD8+T lymphocyte populations elicited by each immunogen to recognize variants of an HIV-1 envelope epitope sequence p41A (YI9). We identified vaccine-induced CD8+T lymphocytes populations using tetramers constructed with 9 variants of p41A epitope. We assessed the ability of those variant peptides to activate CTL by measuring cytokine production and CD107a expression. We evaluated proliferation using carboxyfluorescein succinimidyl ester. Finally, we investigated the functional avidity of these CD8+T lymphocytes for the variant peptide:Mamu-A*01 complexes using surface plasmon resonance technology. Results Our data show that Env immunizations can generate cross-reactive CD8+T lymphocytes that recognize 2 of 9 (22%) of the variants of p41A epitope, with higher responses induced by the consensus and the 3-valent mosaic immunogens (variant from clade C and variant from clade A/E) compared to the single clade Env immunogen. Tetramer-binding data also show that CD8+ T lymphocytes from monkeys immunized with mosaic immunogen have a trend of higher binding to majority of the variant peptides tested.

Comparison of cellular and humoral immune responses induced by primary, consensus or mosaic HIV-1 Env DNA vaccines

Background The genomic variability of HIV viruses has impeded the development of globally relevant HIV vaccines with ability to induce strong and broad cellular and humoral immune responses. Many strategies, such as codon/ RNA optimization, addition of highly efficient leader sequences, use of consensus or mosaic antigens, and electroporation (EP) have all been applied to enhance the breadth and magnitude of immune responses induced by DNA vaccines.

Immunogenicity of native and CD4 liganded monomeric and trimeric envelope glycoproteins based on HIV-1 Subtype C consensus Founder virus sequences

Background The ability to induce a broadly neutralizing antibody (bNAb) response following vaccination is regarded as a crucial aspect in developing an effective HIV-1 vaccine. This study describes the design and construction of a subtype C founder virus consensus Env immunogen derived from newly transmitted/founder virus sequences, and its immunogenicity testing in the presence or absence of liganded CD4, in small animals.

Viral linkage in HIV-1 seroconverters and their partners in an HIV-1 prevention clinical trial.

BackgroundCharacterization of viruses in HIV-1 transmission pairs will help identify biological determinants of infectiousness and evaluate candidate interventions to reduce transmission. Although HIV-1 sequencing is frequently used to substantiate linkage between newly HIV-1 infected individuals and their sexual partners in epidemiologic and forensic studies, viral sequencing is seldom applied in HIV-1 prevention trials. The Partners in Prevention HSV/HIV Transmission Study (ClinicalTrials.gov #NCT00194519) was a prospective randomized placebo-controlled trial that enrolled serodiscordant heterosexual couples to determine the efficacy of genital herpes suppression in reducing HIV-1 transmission; as part of the study analysis, HIV-1 sequences were examined for genetic linkage between seroconverters and their enrolled partners.Methodology/Principal FindingsWe obtained partial consensus HIV-1 env and gag sequences from blood plasma for 151 transmission pairs and performed deep sequencing of env in some cases. We analyzed sequences with phylogenetic techniques and developed a Bayesian algorithm to evaluate the probability of linkage. For linkage, we required monophyletic clustering between enrolled partners' sequences and a Bayesian posterior probability of ≥50%. Adjudicators classified each seroconversion, finding 108 (71.5%) linked, 40 (26.5%) unlinked, and 3 (2.0%) indeterminate transmissions, with linkage determined by consensus env sequencing in 91 (84%). Male seroconverters had a higher frequency of unlinked transmissions than female seroconverters. The likelihood of transmission from the enrolled partner was related to time on study, with increasing numbers of unlinked transmissions occurring after longer observation periods. Finally, baseline viral load was found to be significantly higher among linked transmitters.Conclusions/SignificanceIn this first use of HIV-1 sequencing to establish endpoints in a large clinical trial, more than one-fourth of transmissions were unlinked to the enrolled partner, illustrating the relevance of these methods in the design of future HIV-1 prevention trials in serodiscordant couples. A hierarchy of sequencing techniques, analysis methods, and expert adjudication contributed to the linkage determination process.

Similar T-Cell Immune Responses Induced by Group M Consensus Env Immunogens with Wild-Type or Minimum Consensus Variable Regions

Consensus HIV-1 genes can decrease the genetic distances between candidate immunogens and field virus strains. To ensure the functionality and optimal presentation of immunologic epitopes, we generated two group-M consensus env genes that contain variable regions either from a wild-type B/C recombinant virus isolate (CON6) or minimal consensus elements (CON-S) in the V1, V2, V4, and V5 regions. C57BL/6 and BALB/c mice were primed twice with CON6, CON-S, and subtype control (92UG37_A and HXB2/Bal_B) DNA and boosted with recombinant vaccinia virus (rVV). Mean antibody titers against 92UG37_A, 89.6_B, 96ZM651_C, CON6, and CON-S Env protein were determined. Both CON6 and CON-S induced higher mean antibody titers against several of the proteins, as compared with the subtype controls. However, no significant differences were found in mean antibody titers in animals immunized with CON6 or CON-S. Cellular immune responses were measured by using five complete Env overlapping peptide sets: subtype A (92UG37_A), subtype B (MN_B, 89.6_B and SF162_B), and subtype C (Chn19_C). The intensity of the induced cellular responses was measured by using pooled Env peptides; T-cell epitopes were identified by using matrix peptide pools and individual peptides. No significant differences in T-cell immune-response intensities were noted between CON6 and CON-S immunized BALB/c and C57BL/6 mice. In BALB/c mice, 10 and eight nonoverlapping T-cell epitopes were identified in CON6 and CON-S, whereas eight epitopes were identified in 92UG37_A and HXB2/BAL_B. In C57BL/6 mice, nine and six nonoverlapping T-cell epitopes were identified after immunization with CON6 and CON-S, respectively, whereas only four and three were identified in 92UG37_A and HXB2/BAL_B, respectively. When combined together from both mouse strains, 18 epitopes were identified. The group M artificial consensus env genes, CON6 and CON-S, were equally immunogenic in breadth and intensity for inducing humoral and cellular immune responses.

Human immunodeficiency virus-like particles with consensus envelopes elicited broader cell-mediated peripheral and mucosal immune responses than polyvalent and monovalent Env vaccines

Envelope (Env) sequences from human immunodeficiency virus (HIV) strains can vary by 15–20% within a single clade and as much as 35% between clades. Previous AIDS vaccines based upon a single isolate often could not elicit protective immune responses against heterologous viral challenges. In order to address the vast sequence diversity in Env sequences, consensus sequences were constructed for clade B and clade C envelopes and delivered to the mouse lung mucosa on the surface of virus-like particles (VLP). Consensus sequences decrease the genetic difference between the vaccine strain and any given viral isolate. The elicited immune responses were compared to a mixture of VLPs with Envs from primary viral isolates. This polyvalent vaccine approach contains multiple, diverse Envs to increase the breadth of epitopes recognized by the immune response and thereby increase the potential number of primary isolates recognized. Both consensus and polyvalent clade B Env VLP vaccines elicited cell-mediated immune responses that recognized a broader number of clade B Env peptides than a control monovalent Env VLP vaccine in both the systemic and the mucosal immune compartments. All three clade C Env vaccine strategies elicited similar responses to clade C peptides. However, both the consensus B and C Env VLP vaccines were more effective at eliciting cross-reactive cellular immune responses to epitopes in other clades. This is the first study to directly compare the breadth of cell-mediated immune responses elicited by consensus and polyvalent Env vaccines.

Recombinant Mycobacterium bovis Bacillus Calmette-Guérin Elicits Human Immunodeficiency Virus Type 1 Envelope-Specific T Lymphocytes at Mucosal Sites

A successful vaccine vector for human immunodeficiency virus type 1 (HIV-1) should induce anti-HIV-1 T-cell immune responses at mucosal sites. We have constructed recombinant Mycobacterium bovis bacillus Calmette-Guérin (rBCG) expressing an HIV-1 group M consensus envelope (Env) either as a surface, intracellular, or secreted protein as an immunogen. rBCG containing HIV-1 env plasmids engineered for secretion induced optimal Env-specific T-cell gamma interferon enzyme-linked immunospot responses in murine spleen, female reproductive tract, and lungs. While rBCG-induced T-cell responses to HIV-1 envelope in spleen were lower than those induced by adenovirus prime/recombinant vaccinia virus (rAd-rVV) boost, rBCG induced comparable responses to rAd-rVV immunization in the female reproductive tract and lungs. T-cell responses induced by rBCG were primarily CD4(+), although rBCG alone did not induce anti-HIV-1 antibody. However, rBCG could prime for a protein boost by HIV-1 envelope protein. Thus, rBCG can serve as a vector for induction of anti-HIV-1 consensus Env cellular responses at mucosal sites.

Cross-Subtype T-Cell Immune Responses Induced by a Human Immunodeficiency Virus Type 1 Group M Consensus Env Immunogen

The genetic diversity among globally circulating human immunodeficiency virus type 1 (HIV-1) strains is a serious challenge for HIV-1 vaccine design. We have generated a synthetic group M consensus env gene (CON6) for induction of cross-subtype immune responses and report here a comparative study of T-cell responses to this and natural strain env immunogens in a murine model. Three different strains of mice were immunized with CON6 as well as subtype A, B, or C env immunogens, using a DNA prime-recombinant vaccinia virus boost strategy. T-cell epitopes were mapped by gamma interferon enzyme-linked immunospot analysis using five overlapping Env peptide sets from heterologous subtype A, B, and C viruses. The CON6-derived vaccine was immunogenic and induced a greater number of T-cell epitope responses than any single wild-type subtype A, B, and C env immunogen and similar T-cell responses to a polyvalent vaccine. The responses were comparable to within-clade responses but significantly more than between-clade responses. The magnitude of the T-cell responses induced by CON6 (measured by individual epitope peptides) was also greater than the magnitude of responses induced by individual wild-type env immunogens. Though the limited major histocompatibility complex repertoire in inbred mice does not necessarily predict responses in nonhuman primates and humans, these results suggest that synthetic centralized env immunogens represent a promising approach for HIV-1 vaccine design that merits further characterization.