Multi-envelope HIV-1 vaccine devoid of SIV components controls disease in macaques challenged with heterologous pathogenic SHIV

Harnessing Natural Mosaics: Antibody-Instructed, Multi-Envelope HIV-1 Vaccine Design

The year 2021 marks the 40th anniversary since physicians recognized symptoms of the acquired immunodeficiency syndrome (AIDS), a disease that has since caused more than 30 million deaths worldwide. Despite the passing of four decades, there remains no licensed vaccine for the human immunodeficiency virus type 1 (HIV-1), the etiologic agent of AIDS. Despite the development of outstanding anti-retroviral drugs, there are currently more than one-half million deaths each year due to AIDS. Here, we revisit a conventional vaccine strategy used for protection against variable pathogens like HIV-1, which combines an array of diverse surface antigens. The strategy uses antibody recognition patterns to categorize viruses and their surface antigens into groups. Then a leader is assigned for each group and group leaders are formulated into vaccine cocktails. The group leaders are ‘natural mosaics’, because they share one or more epitope(s) with each of the other group members. We encourage the application of this conventional approach to HIV-1 vaccine design. We suggest that the partnering of an antibody-instructed envelope cocktail with new vaccine vectors will yield a successful vaccine in the HIV-1 field.

How Basic Immunological Principles May Instruct the Design of a Successful HIV-Type 1 Vaccine

This article is dedicated to Dr. Peter Doherty. While Peter continues to make groundbreaking discoveries in the field of immunology, he also provides outstanding scientific mentorship to his trainees. Here we contemplate our past training with Peter, Peter's teachings of basic immunological principles, and how basic principles may instruct the design of a successful human immunodeficiency virus-type 1 vaccine.

Vaccine Design Informed by Virus-Induced Immunity

When an individual is exposed to a viral pathogen for the first time, the adaptive immune system is naive and cannot prevent virus replication. The consequence may be severe disease. At the same time, the host may rapidly generate a pathogen-specific immune response that will prevent disease if the virus is encountered again. Parvovirus B19 provides one such example. Children with sickle cell disease can experience life-threatening transient aplastic crisis when first exposed to parvovirus B19, but an effective immune response confers lifelong protection. We briefly examine the induction and benefits of virus-induced immunity. We focus on three human viruses for which there are no licensed vaccines (respiratory syncytial virus, human immunodeficiency virus type 1, and parvovirus B19) and consider how virus-induced immunity may inform successful vaccine design.

Multi-Envelope HIV-1 Vaccine Development: Two Targeted Immune Pathways, One Desired Protective Outcome

In 2016, there were more than 30 million individuals living with HIV-1, ∼1.8 million new HIV-1 infections, and ∼1 million HIV-1-related deaths according to UNAIDS ( unaids.org ). Hence, a preventive HIV-1 vaccine remains a global priority. The variant envelopes of HIV-1 present a significant obstacle to vaccine development and the vaccine field has realized that immunization with a single HIV-1 envelope protein will not be sufficient to generate broadly neutralizing antibodies. Here we describe two nonmutually exclusive, targeted pathways with which a multi-envelope HIV-1 vaccine may generate protective immune responses against variant HIV-1. Pathways include (i) the induction of a polyclonal immune response, comprising a plethora of antibodies with subset-reactive and cross-reactive specificities, together able to neutralize diverse HIV-1 (termed Poly-nAb in this report) and (ii) the induction of one or a few monoclonal antibodies, each with a broadly neutralizing specificity (bnAb). With each pathway in mind, we describe challenges and strategies that may ultimately support HIV-1 vaccine success.

Murine Monoclonal Antibodies for Antigenic Discrimination of HIV-1 Envelope Proteins

In the influenza virus field, antibody reagents from research animals have been instrumental in the characterization of antigenically distinct hemagglutinin and neuraminidase membrane molecules. These small animal reagents continue to support the selection of components for inclusion in human influenza virus vaccines. Other cocktail vaccines against variant pathogens (e.g., polio virus, pneumococcus) are similarly designed to represent variant antigens, as defined by antibody reactivity patterns. However, a vaccine cocktail comprising diverse viral membrane antigens defined in this way has not yet been advanced to a clinical efficacy study in the HIV-1 field. In this study, we describe the preparation of mouse antibodies specific for HIV-1 gp140 or gp120 envelope molecules. Our experiments generated renewable reagents able to discriminate HIV-1 envelopes from one another. Monoclonals yielded more precise discriminatory capacity against their respective immunogens than did a small panel of polyclonal human sera derived from recently HIV-1-infected patients. Perhaps these and other antibody reagents will ultimately support high-throughput cartography studies with which antigenically-distinct envelope immunogens may be formulated into a successful HIV-1 envelope cocktail vaccine.

A Multi-Vector, Multi-Envelope HIV-1 Vaccine

The St. Jude Children's Research Hospital (St. Jude) HIV-1 vaccine program is based on the observation that multiple antigenically distinct HIV-1 envelope protein structures are capable of mediating HIV-1 infection. A cocktail vaccine comprising representatives of these diverse structures (immunotypes) is therefore considered necessary to elicit lymphocyte populations that prevent HIV-1 infection. This strategy is reminiscent of that used to design a currently licensed and successful 23-valent pneumococcus vaccine. Three recombinant vector systems are used for the delivery of envelope cocktails (DNA, vaccinia virus, and purified protein), and each of these has been tested individually in phase I safety trials. A fourth FDA-approved clinical trial, in which diverse envelopes and vectors are combined in a prime-boost vaccination regimen, has recently begun. This trial will continue to test the hypothesis that a multi-vector, multi-envelope vaccine can elicit diverse B- and T-cell populations that can prevent HIV-1 infections in humans.

UV-inactivated vaccinia virus (VV) in a multi-envelope DNA-VV-protein (DVP) HIV-1 vaccine protects macaques from lethal challenge with heterologous SHIV

The pandemic of HIV-1 has continued for decades, yet there remains no licensed vaccine. Previous research has demonstrated the effectiveness of a multi-envelope, multi-vectored HIV-1 vaccine in a macaque-SHIV model, illustrating a potential means of combating HIV-1. Specifically, recombinant DNA, vaccinia virus (VV) and purified protein (DVP) delivery systems were used to vaccinate animals with dozens of antigenically distinct HIV-1 envelopes for induction of immune breadth. The vaccinated animals controlled disease following challenge with a heterologous SHIV. This demonstration suggested that the antigenic cocktail vaccine strategy, which has succeeded in several other vaccine fields (e.g. pneumococcus), might also succeed against HIV-1. The strategy remains untested in an advanced clinical study, in part due to safety concerns associated with the use of replication-competent VV. To address this concern, we designed a macaque study in which psoralen/ultraviolet light-inactivated VV (UV VV) was substituted for replication-competent VV in the multi-envelope DVP protocol. Control animals received a vaccine encompassing no VV, or no vaccine. All VV vaccinated animals generated an immune response toward VV, and all vaccinated animals generated an immune response toward HIV-1 envelope. After challenge with heterologous SHIV 89.6P, animals that received replication-competent VV or UV VV experienced similar outcomes. They exhibited reduced peak viral loads, maintenance of CD4+ T cell counts and improved survival compared to control animals that received no VV or no vaccine; there were 0/15 deaths among all animals that received VV and 5/9 deaths among controls. Results define a practical means of improving VV safety, and encourage advancement of a promising multi-envelope DVP HIV-1 vaccine candidate.

Current progress in the development of a prophylactic vaccine for HIV-1

Since its discovery and characterization in the early 1980s as a virus that attacks the immune system, there has been some success for the treatment of human immunodeficiency virus-1 (HIV-1) infection. However, due to the overwhelming public health impact of this virus, a vaccine is needed urgently. Despite the tireless efforts of scientist and clinicians, there is still no safe and effective vaccine that provides sterilizing immunity. A vaccine that provides sterilizing immunity against HIV infection remains elusive in part due to the following reasons: 1) degree of diversity of the virus, 2) ability of the virus to evade the hosts' immunity, and 3) lack of appropriate animal models in which to test vaccine candidates. There have been several attempts to stimulate the immune system to provide protection against HIV-infection. Here, we will discuss attempts that have been made to induce sterilizing immunity, including traditional vaccination attempts, induction of broadly neutralizing antibody production, DNA vaccines, and use of viral vectors. Some of these attempts show promise pending continued research efforts.

Generation of recombinant vaccinia viruses via green fluorescent protein selection

We developed a rapid method to generate recombinant vaccinia viruses (rVVs) based upon a bicistronic cassette encoding the gene for green fluorescent protein (GFP) and a foreign gene of interest separated by an internal ribosome entry site (IRES). As proof-of-concept, we inserted a mutant env gene of human immunodeficiency virus (HIV) into the cassette, which was cloned into the vaccinia virus (VV) insertion vector pSC59 under the control of the early-late VV synthetic promoter and flanked by disrupted tk gene sequences. To generate rVVs, 293T cells were inoculated with wild-type (wt) VV, followed by transfection of the modified pSC59 vector containing the bicistronic cassette, which allows expression of GFP and the protein of interest. Next, GFP-positive cells were isolated by flow cytometry or by picking under a fluorescent microscope. Thymidine kinase-deficient (Tk(-)) 143B cells were then exposed to lysates of GFP-positive 293T cells and cultured in the presence of bromodeoxyuridine. This selection allows only Tk(-) rVV to remain viable. We demonstrated the success of this GFP selection strategy by expressing high levels of mutant HIV Env. Our approach shortens the time needed to generate rVVs and represents a practical approach to generate recombinant proteins.

Heterologous Prime-Boost HIV-1 Vaccination Regimens in Pre-Clinical and Clinical Trials

Currently, there are more than 30 million people infected with HIV-1 and thousands more are infected each day. Vaccination is the single most effective mechanism for prevention of viral disease, and after more than 25 years of research, one vaccine has shown somewhat encouraging results in an advanced clinical efficacy trial. A modified intent-to-treat analysis of trial results showed that infection was approximately 30% lower in the vaccine group compared to the placebo group. The vaccine was administered using a heterologous prime-boost regimen in which both target antigens and delivery vehicles were changed during the course of inoculations. Here we examine the complexity of heterologous prime-boost immunizations. We show that the use of different delivery vehicles in prime and boost inoculations can help to avert the inhibitory effects caused by vector-specific immune responses. We also show that the introduction of new antigens into boost inoculations can be advantageous, demonstrating that the effect of `original antigenic sin' is not absolute. Pre-clinical and clinical studies are reviewed, including our own work with a three-vector vaccination regimen using recombinant DNA, virus (Sendai virus or vaccinia virus) and protein. Promising preliminary results suggest that the heterologous prime-boost strategy may possibly provide a foundation for the future prevention of HIV-1 infections in humans.

SHIV infection protects against heterologous pathogenic SHIV challenge in macaques: a gold-standard for HIV-1 vaccine development?

A current debate in the HIV-1 vaccine field concerns the ability of an immunodeficiency virus to elicit a protective response. One argument is that HIV-1 superinfections are frequent in healthy individuals, because virus evades conventional immune surveillance, a serious obstacle to vaccine design. The opposing argument is that protection from superinfection is significant, reflecting a robust immune response that might be harnessed by vaccination to prevent disease. In an experiment designed to address the debate, two macaques received an I.V. inoculation with SHIV KU-1-d (a derivative of SHIV KU-1) and were rested for >10 months. Infection elicited diverse neutralizing antibody activities in both animals. Animals were then exposed to SHIV 89.6P (I.V.), a virus carrying a heterologous envelope protein relative to the vaccine strain. Infection was monitored by viral load and CD4+ T-cell measurements. All control animals were infected and most succumbed to disease. In contrast, protection from superinfection was statistically significant in test monkeys; one animal showed no evidence of superinfection at any time point and the second showed evidence of virus at only one time point over a 6-month observation period. Neither animal showed signs of disease. Perhaps this protective state may serve as a 'gold-standard' for HIV-1 vaccine development, as a similar degree of protection against immunodeficiency virus infections in humans would be much desired.

HIV-1 vaccine design: harnessing diverse lymphocytes to conquer a diverse pathogen

In the fall of 2007, the HIV-1 research field received news that their front-runner vaccine was not protective. In response to this disappointment, scientists are now reviewing the intricacies of the immune response toward HIV-1 to develop new and better strategies for vaccine development. Decades ago, researchers recognized the impressive amino acid and carbohydrate diversity of HIV-1, and the associated obstacles to vaccine development. At first glance, the diversity and other unique features of HIV-1 may seem insurmountable, but attention to vaccine successes in other fields serves to renew optimism. The newly-licensed rotavirus and papillomavirus cocktail vaccines remind scientists that diverse pathogens can be conquered and that the chronic nature of a virus infection need not thwart successful vaccine design. Here we describe current efforts to gain insights from other vaccine fields and to adopt a cocktail vaccine approach for the prevention of HIV-1 infections in humans.

Neutralizing antibody responses to subtype B and C adjuvanted HIV envelope protein vaccination in rabbits

Improving the potency, breadth, and durability of neutralizing antibody responses to HIV are major challenges for HIV vaccine development. To address these challenges, the studies described evaluate in rabbits the titers, breadth, and epitope specificities of antibody responses elicited by HIV envelope subunit vaccines adjuvanted with MF59 with or without CpG oligodeoxynucleotide (ODN). Animals were immunized with trimeric o-gp140DeltaV2 derived from subtype B HIV-1(SF162) or subtype C HIV-1(TV1), or proteins from both strains. Immunization with SF162 or TV1 with MF59/CpG elicited higher titers of binding and neutralizing antibodies to SF162 than monovalent immunization with MF59 alone (P<0.01). Bivalent immunization increased binding and neutralizing antibody titers over single envelope immunization in MF59 (P<0.01). Bivalent immunization also improved neutralization breadth. Epitope mapping indicated neutralizing activity in rabbits was directed to V3 and V4. Overall, our data suggests that a multivalent vaccination approach with MF59 and CpG can enhance humoral responses to HIV-1.

Preclinical and clinical development of a multi-envelope, DNA-virus-protein (D-V-P) HIV-1 vaccine

The human immune system has evolved to recognize antigenic diversity, a strength that has been harnessed by vaccine developers to combat numerous pathogens (e.g., pneumococcus, influenza virus, rotavirus). In each case, vaccine cocktails were formulated to include antigenic variants of the target. To combat HIV-1 diversity, we assembled a cocktail vaccine comprising dozens of envelopes, delivered as recombinant DNA, vaccinia virus, and protein for testing in a clinical trial. One vaccinee has now completed vaccinations with no serious adverse events. Preliminary analyses demonstrate early proof-of-principle that a multi-envelope vaccine can elicit neutralizing antibody responses toward heterologous HIV-1 in humans.

A multi-valent vaccine approach that elicits broad immunity within an influenza subtype

Vaccines directed toward individual strains of highly variable viruses like influenza lose efficacy when the circulating viruses no longer resemble the vaccine isolate. Historically, inclusion of more than one isolate per subtype of influenza has been limited by the need to include large doses of antigen with typical protein-based vaccine approaches and by concerns that an immunodominant response to one antigen will limit the response to closely related antigens. Here we provide proof of principle demonstrating that a multi-valent vaccine directed against multiple influenza A virus hemagglutinins (HAs) can elicit broad, neutralizing immunity against multiple strains within a single influenza subtype (H3). We employed a DNA vaccine to direct immunity toward the HA component alone, and a live attenuated influenza virus (LAIV) to assess immunity against the whole virus. Delivery of either HA-DNA or LAIV yielded broad protective immunity across multiple antigenic clusters, including heterologous strains, that was similar to the combined immunity of each antigen assessed separately. Priming with HA-DNA followed by an LAIV boost strengthened and broadened the antibody response toward all three H3 HAs. This prime:boost multi-valent approach was thus able to elicit immunity against multiple strains within the H3 subtype without evidence of immune interference between closely related antigens. Although the trivalent vaccine described here is not a universal vaccine, since protection was limited to circulating viruses from about a two-decade period, these data suggest that full protection within a subtype is possible using this approach with multiple antigens from current and predicted future influenza strains.

A centralized gene-based HIV-1 vaccine elicits broad cross-clade cellular immune responses in rhesus monkeys

One of the major challenges that must be met in developing an HIV-1 vaccine is devising a strategy to generate cellular immunity with sufficient breadth to deal with the extraordinary genetic diversity of the virus. Amino acids in the envelopes of viruses from the same clade can differ by >15%, and those from different clades can differ by >30%. It has been proposed that creating immunogens using centralized HIV-1 gene sequences might provide a practical solution to this problem. Such centralized genes can be generated by employing a number of different strategies: consensus, ancestral, or center of tree sequences. These computer-generated sequences are a shorter genetic distance from any two contemporary virus sequences than those contemporary sequences are from each other. The present study was initiated to evaluate the breadth of cellular immunity generated through immunization of rhesus monkeys with vaccine constructs expressing either an HIV-1 global consensus envelope sequence (CON-S) or a single patient isolate clade B envelope sequence (clade B). We show that vaccine immunogens expressing the single centralized gene CON-S generated cellular immune responses with significantly increased breadth compared with immunogens expressing a wild-type virus gene. In fact, CON-S immunogens elicited cellular immune responses to 3- to 4-fold more discrete epitopes of the envelope proteins from clades A, C, and G than did clade B immunogens. These findings suggest that immunization with centralized genes is a promising vaccine strategy for developing a global vaccine for HIV-1 as well as vaccines for other genetically diverse viruses.

Analysis of the immune responses in chimpanzees infected with HIV type 1 isolates

The mechanisms of resistance to AIDS development in HIV-1-infected chimpanzees have remained elusive. Unique among chimpanzees naturally or experimentally infected with HIV, several animals of the Yerkes cohort have progressed to clinical AIDS with selection of isolates showing increased pathogenicity for chimpanzees. We compared progressors vs. nonprogressors among the HIV-infected chimpanzees that made up this cohort, eight of which have been infected with HIV-1 for over 14 years. The additional two progressors were infected de novo with chimpanzee-pathogenic HIV, rapidly leading to a progressor status. Nonprogressors were characterized by normal CD4(+) T cell counts and the absence of detectable viremia. In contrast, progressor chimpanzees had relatively high plasma viral loads associated with a dramatic loss of CD4(+) T cells. The analysis of immune responses showed a similar amplitude and breadth of ELISPOT T cell responses in both groups. HIV-specific proliferative responses were, however, absent in the progressor animals, which also exhibited increased levels of immune activation characterized by elevated levels of the circulating chemokines IP-10 and MCP-1. Of interest was the conservation of potent NK cell activity in all animals, potentially contributing to the extended symptom-free survival of progressor animals. Modest anti-HIV antibody titers were detectable in the nonprogressor group, but these antibodies exhibited good neutralizing activity. In progressors, however, two sets of data were noted: in animals that gradually selected for pathogenic isolates, or that were superinfected, very high neutralizing antibody titers were observed, although none to the pathogenic HIV. In contrast, two animals infected de novo with chimpanzee pathogenic HIV failed to mount an extensive humoral response and both failed to develop neutralizing antibodies to the virus. Taken together, pathogenic HIV infection in chimpanzees is associated with rapid loss of CD4(+) T cells and proliferative responses as well as higher levels of immune activation.

Target peptide sequence within infectious human immunodeficiency virus type 1 does not ensure envelope-specific T-helper cell reactivation: influences of cysteine protease and gamma interferon-induced thiol reductase activities

Recent clinical trials have shown that the presence of a robust human immunodeficiency virus type 1 (HIV-1)-specific T-cell response may not be sufficient to prevent or control HIV-1 infection. Studies of antigen processing in the context of infectious HIV-1 are therefore warranted. Envelope-specific, major histocompatibility complex class II-restricted murine T-cell hybridomas were tested for responsiveness to splenic antigen-presenting cells exposed to HIV-1-infected GHOST cells. Interleukin-2 assays showed that the presence of a peptide within HIV-1 did not ensure the reactivation of peptide-specific T cells. Further experiments defined the impact of gamma interferon-induced thiol reductase and cysteine proteases on the processing of HIV-1 peptides. The results highlight potential influences of peptide context on T-cell reactivation by HIV-1 and encourage the continued study of antigen processing as support for improved vaccine design.

First phase I clinical trial of an HIV-1 subtype D gp140 envelope protein vaccine: immune activity induced in all study participants

To combat HIV-1 diversity, we are developing a multienvelope vaccine (comprising DNA, vaccinia virus and protein vectors). Toward this goal, we conducted a phase I clinical trial of EnvPro, a gp140 protein formulated in alum. The vaccine was well tolerated and elicited an immune response in every trial participant.

Standardized assessment of NAb responses elicited in rhesus monkeys immunized with single- or multi-clade HIV-1 envelope immunogens

The genetic diversity of HIV-1 envelope glycoproteins (Env) remains a major obstacle to the development of an antibody-based AIDS vaccine. The present studies examine the breadth and magnitude of neutralizing antibody (NAb) responses in rhesus monkeys after immunization with DNA prime-recombinant adenovirus (rAd) boost vaccines encoding either single or multiple genetically distant Env immunogens, and subsequently challenged with a pathogenic simian-human immunodeficiency virus (SHIV-89.6P). Using a standardized multi-tier panel of reference Env pseudoviruses for NAb assessment, we show that monkeys immunized with a mixture of Env immunogens (clades A, B, and C) exhibited a greater breadth of NAb activity against neutralization-sensitive Tier 1 viruses following both vaccination and challenge compared to monkeys immunized with a single Env immunogen (clade B or C). However, all groups of Env-vaccinated monkeys demonstrated only limited neutralizing activity against Tier 2 pseudoviruses, which are more characteristic of the neutralization sensitivity of circulating HIV-1. Notably, the development of a post-challenge NAb response against SHIV-89.6P was similar in monkeys receiving either clade B, clade C, or clade A+B+C Env immunogens, suggesting cross-clade priming of NAb responses. In addition, vaccines encoding Env immunogens heterologous to SHIV-89.6P primed for a rapid anamnestic NAb response following infection compared to vaccines lacking an Env component. These results show that DNA/rAd immunization with multiple diverse Env immunogens is a viable approach for enhancing the breadth of NAb responses against HIV-1, and suggest that Env immunogens can prime for anamnestic NAb responses against a heterologous challenge virus.

HIV type 1 vaccines for worldwide use: predicting in-clade and cross-clade breadth of immune responses

One of the greatest challenges in HIV vaccine development is accommodating the worldwide sequence diversity of the HIV-1 virus. To understand how viral sequence diversity may affect the potential breadth of HIV-1 vaccines designed to elicit antiviral T cell immunity, we have developed novel approaches to assess sequence conservation at the amino acid level, where vaccine effects are exerted. Taking each sequence from the LANL 2004 amino acid alignments as a potential vaccine or as a challenge virus, all pairwise combinations of sequences were evaluated by two methods: first, a traditional comparison of aligned sequences, and second, by a new walking 9-mer algorithm chosen to emphasize the typical length of an MHC-I epitope. The rules for comparing mismatched 9-mer pairs between vaccine and challenge sequences were empirically deduced from an experiment on Nef-specific CD8 epitopes and the viral sequences from naturally HIV-1-infected patients. Results were weighted such that each clade contributed in proportion to its global prevalence. Cross-clade breadth of response is best maintained for vaccines encoding Pol and Gag, while commonly proposed Env- and Tat-based vaccines would be more clade sensitive. We evaluated the additional breadth that could be expected from multiclade vaccines including consensus and ancestral sequences. For more diverse proteins, adding a second strain can add a significant increase in breadth, although for three or more strains the intrinsic diversity of the protein leads to diminishing improvement.

Viral peptide immunogens: current challenges and opportunities

Synthetic peptide vaccines have potential to control viral infections. Successful experimental models using this approach include the protection of mice against the lethal Sendai virus infection by MHC class I binding CTL peptide epitope. The main benefit of vaccination with peptide epitopes is the ability to minimize the amount and complexity of a well-defined antigen. An appropriate peptide immunogen would also decrease the chance of stimulating a response against self-antigens, thereby providing a safer vaccine by avoiding autoimmunity. In general, the peptide vaccine strategy needs to dissect the specificity of antigen processing, the presence of B-and T-cell epitopes and the MHC restriction of the T-cell responses. This article briefly reviews the implications in the design of peptide vaccines and discusses the various approaches that are applied to improve their immunogenicity.

A recombinant Sendai virus is controlled by CD4+ effector T cells responding to a secreted human immunodeficiency virus type 1 envelope glycoprotein

The importance of antigen-specific CD4(+) helper T cells in virus infections is well recognized, but their possible role as direct mediators of virus clearance is less well characterized. Here we describe a recombinant Sendai virus strategy for probing the effector role(s) of CD4(+) T cells. Mice were vaccinated with DNA and vaccinia virus recombinant vectors encoding a secreted human immunodeficiency virus type 1 (HIV-1) envelope protein and then challenged with a Sendai virus carrying a homologous HIV-1 envelope gene. The primed mice showed (i) prompt homing of numerous envelope-primed CD4(+) T cell populations to the virus-infected lung, (ii) substantial production of gamma interferon, and interleukin-2 (IL-2), IL-4, and IL-5 in that site, and (iii) significantly reduced pulmonary viral load. The challenge experiments were repeated with immunoglobulin(-/-) microMT mice in the presence or absence of CD8(+) and/or CD4(+) T cells. These selectively immunodeficient mice were protected by primed CD4(+) T cells in the absence of antibody or CD8(+) T cells. Together, these results highlight the role of CD4(+) T cells as direct effectors in vivo and, because this protocol gives such a potent response, identify an outstanding experimental model for further dissecting CD4(+) T-cell-mediated immunity in the lung.

Single epitope mucosal vaccine delivered via immuno-stimulating complexes induces low level of immunity against simian-HIV

The difficulty in developing an effective vaccine to contain the HIV/AIDS epidemic coupled with the fact that primary HIV-1 infection typically occurs via mucosal sites has increased emphasis on vaccine approaches that protect at mucosal surfaces. In this study we employed HIV and simian-HIV (SHIV)-derived T helper (Th) and cytotoxic T lymphocyte (CTL) single epitopes incorporated into immuno-stimulating complexes (ISCOM) as a candidate immunogens. Immunized rhesus macaques (Macaca mulatta) were challenged with CCR5-tropic SHIV(SF162p4). On the day of challenge, low levels of virus-neutralizing antibodies (Ab) and CTLs were detected in ISCOM-immunized macaques. Greater than 10(5) viral RNA copies per ml of plasma in 2/5 immunized and 3/4 control macaques were detected within 3 weeks post-challenge. Depletion of CD4+ T cells from gut-associated lymphoid tissues (GALT) was observed by post-challenge day (PCD) 14 in all macaques regardless immunization. Nonetheless, lower viral loads and relatively better preservation of peripheral CD4+ T cells following the SHIV infection was observed in ISCOM-immunized macaques. We predict that if coadministered with additional epitopes and/or more efficacious mucosal delivery system or route, HIV/SIV-derived peptide vaccines may have potential to elicit heterologous protection.

Immunogenicity of a polyvalent HIV-1 candidate vaccine based on fourteen wild type gp120 proteins in golden hamsters

Background

One of the major obstacles in the design of an effective vaccine against HIV-1 is the hypervariability of the HIV-1 envelope glycoprotein. Most HIV-1 vaccine candidates have utilized envelope glycoprotein from a single virus isolate, but to date, none of them elicited broadly reactive humoral immunity. Herein, we hypothesised that a cocktail of HIV-1 gp120 proteins containing multiple epitopes may increase the breadth of immune responses against HIV-1. We compared and evaluated the immunogenicity of HIV-1 vaccines containing either gp120 protein alone or in combinations of four or fourteen gp120s from different primary HIV-1 isolates in immunized hamsters.

Results

We amplified and characterized 14 different gp120s from primary subtype B isolates with both syncytium and non-syncytium inducing properties, and expressed the proteins in Chinese Hamster Ovary (CHO) cell lines. Purified proteins were used either alone or in combinations of four or fourteen different gp120s to vaccinate golden hamsters. The polyvalent vaccine showed higher antibody titers to HIV-1 subtype B isolates MN and SF162 compared to the groups that received one or four gp120 proteins. However, the polyvalent vaccine was not able to show higher neutralizing antibody responses against HIV-1 primary isolates. Interestingly, the polyvalent vaccine group had the highest proliferative immune responses and showed a substantial proportion of cross-subtype CD4 reactivity to HIV-1 subtypes B, C, and A/E

Conclusion

Although the polyvalent approach achieved only a modest increase in the breadth of humoral and cellular immunity, the qualitative change in the vaccine (14 vs. 1 gp120) resulted in a quantitative improvement in vaccine-induced immunity.

Aiming to induce broadly reactive neutralizing antibody responses with HIV-1 vaccine candidates

Neutralizing antibody induction is a key feature of many effective vaccines and is the only immune response that has proven to be capable of completely blocking AIDS virus infection in animal models. Unfortunately, the extensive genetic variability and complex immune-evasion strategies of HIV-1 have thwarted all attempts to date at eliciting an effective neutralizing antibody response with candidate HIV-1 vaccine immunogens. Recent advances in our understanding of how these evasion strategies operate, coupled with growing progress in unravelling the structure and immunobiology of the viral envelope glycoproteins, are contributing to novel immunogen designs to overcome the many barriers to inducing protective antibodies against HIV-1.

Aiming to induce broadly reactive neutralizing antibody responses with HIV-1 vaccine candidates

Neutralizing antibody induction is a key feature of many effective vaccines and is the only immune response that has proven to be capable of completely blocking AIDS virus infection in animal models. Unfortunately, the extensive genetic variability and complex immune-evasion strategies of HIV-1 have thwarted all attempts to date at eliciting an effective neutralizing antibody response with candidate HIV-1 vaccine immunogens. Recent advances in our understanding of how these evasion strategies operate, coupled with growing progress in unravelling the structure and immunobiology of the viral envelope glycoproteins, are contributing to novel immunogen designs to overcome the many barriers to inducing protective antibodies against HIV-1.