Chimeric human papilloma virus-simian/human immunodeficiency virus virus-like-particle vaccines: immunogenicity and protective efficacy in macaques

Production, purification and immunogenicity of Gag virus-like particles carrying SARS-CoV-2 components

The virus-like particle (VLP) platform is a robust inducer of humoral and cellular immune responses; hence, it has been used in vaccine development for several infectious diseases. In the current work, VLPs carrying SARS-CoV-2 Spike (S) protein (Wuhan strain) with an HIV-1 Gag core were produced using suspension HEK 293SF-3F6 cells by transient transfection. The Gag was fused with green fluorescent protein (GFP) for rapid quantification of the VLPs. Five different versions of Gag-Spike VLPs (Gag-S-VLPs) consisting of Gag-S alone or combined with other SARS-CoV-2 components, namely Gag-S-Nucleocapsid (N), Gag-S-Matrix (M), Gag-S-Envelope (E), Gag-S-MEN, along with Gag alone were produced and processed by clarification, nuclease treatment, concentration by tangential flow filtration (TFF) and diafiltration. A pilot mouse study was performed to evaluate the immunogenicity of the Gag-S-VLPs through the measurement of the humoral and/or cellular responses against all the mentioned SARS-CoV-2 components. Antibody response to Spike was observed in all variants. The highest number of Spike-specific IFN-γ + T cells was detected with Gag-S-VLPs. No induction of antigen-specific cellular responses to M, N or E proteins were detected with any of the Gag-S, M, E/or N VLPs tested. Therefore, the Gag-S-VLP, by reason of consistently eliciting strong antigen-specific cellular and antibody responses, was selected for further evaluation. The purification process was improved by replacing the conventional centrifugation by serial microfiltration in the clarification step, followed by Spike-affinity chromatography to get concentrated VLPs with higher purity. Three different doses of Gag-S-VLP in conjunction with two adjuvants (Quil-A or AddaVax) were used to assess the dose-dependent antigen-specific cellular and antibody responses in mice. The Gag-S-VLP adjuvanted with Quil-A resulted in a stronger Spike-specific cellular response compared to that adjuvanted with AddaVax. A strong spike neutralisation activity was observed for all doses, independent of the adjuvant combination.

Protein-based nanocages for vaccine development

Protein nanocages have attracted considerable attention in various fields of nanomedicine due to their intrinsic properties, including biocompatibility, biodegradability, high structural stability, and ease of modification of their surfaces and inner cavities. In vaccine development, these protein nanocages are suited for efficient targeting to and retention in the lymph nodes and can enhance immunogenicity through various mechanisms, including excellent uptake by antigen-presenting cells and crosslinking with multiple B cell receptors. This review highlights the superiority of protein nanocages as antigen delivery carriers based on their physiological and immunological properties such as biodistribution, immunogenicity, stability, and multifunctionality. With a focus on design, we discuss the utilization and efficacy of protein nanocages such as virus-like particles, caged proteins, and artificial caged proteins against cancer and infectious diseases such as coronavirus disease 2019 (COVID-19). In addition, we summarize available knowledge on the protein nanocages that are currently used in clinical trials and provide a general outlook on conventional distribution techniques and hurdles faced, particularly for therapeutic cancer vaccines.

Short Disordered Epitope of CRTAM Ig-Like V Domain as a Potential Target for Blocking Antibodies

Class-I Restricted T Cell-Associated Molecule (CRTAM) is a protein that is expressed after T cell activation. The interaction of CRTAM with its ligand, nectin-like 2 (Necl2), is required for the efficient production of IL-17, IL-22, and IFNγ by murine CD4 T cells, and it plays a role in optimal CD8 T and NK cell cytotoxicity. CRTAM promotes the pro-inflammatory cytokine profile; therefore, it may take part in the immunopathology of autoimmune diseases such as diabetes type 1 or colitis. Thus, antibodies that block the interaction between CRTAM and Necl2 would be useful for controlling the production of these inflammatory cytokines. In this work, using bioinformatics predictions, we identified three short disordered epitopes (sDE1-3) that are located in the Ig-like domains of murine CRTAM and are conserved in mammalian species. We performed a structural analysis by molecular dynamics simulations of sDE1 (QHPALKSSKY, Ig-like V), sDE2 (QRNGEKSVVK, Ig-like C1), and sDE3 (CSTERSKKPPPQI, Ig-like C1). sDE1, which is located within a loop of the contact interface of the heterotypic interaction with Nectl2, undergoes an order–disorder transition. On the contrary, even though sDE2 and sDE3 are flexible and also located within loops, they do not undergo order–disorder transitions. We evaluated the immunogenicity of sDE1 and sDE3 through the expression of these epitopes in chimeric L1 virus-like particles. We confirmed that sDE1 induces polyclonal antibodies that recognize the native folding of CRTAM expressed in activated murine CD4 T cells. In contrast, sDE3 induces polyclonal antibodies that recognize the recombinant protein hCRTAM-Fc, but not the native CRTAM. Thus, in this study, an exposed disordered epitope in the Ig-like V domain of CRTAM was identified as a potential site for therapeutic antibodies.

Mucosal and systemic SIV-specific cytotoxic CD4+ T cell hierarchy in protection following intranasal/intramuscular recombinant pox-viral vaccination of pigtail macaques

A HIV vaccine that provides mucosal immunity is urgently needed. We evaluated an intranasal recombinant Fowlpox virus (rFPV) priming vaccine followed by intramuscular Modified Vaccinia Ankara (rMVA) booster vaccine, both expressing SIV antigens. The vaccination generated mucosal and systemic SIV-specific CD4+ T cell mediated immunity and was associated with partial protection against high-dose intrarectal SIVmac251 challenge in outbred pigtail macaques. Three of 12 vaccinees were completely protected and these animals elicited sustained Gag-specific poly-functional, cytotoxic mucosal CD4+ T cells, complemented by systemic poly-functional CD4+ and CD8+ T cell immunity. Humoral immune responses, albeit absent in completely protected macaques, were associated with partial control of viremia in animals with relatively weaker mucosal/systemic T cell responses. Co-expression of an IL-4R antagonist by the rFPV vaccine further enhanced the breadth and cytotoxicity/poly-functionality of mucosal vaccine-specific CD4+ T cells. Moreover, a single FPV-gag/pol/env prime was able to induce rapid anamnestic gp140 antibody response upon SIV encounter. Collectively, our data indicated that nasal vaccination was effective at inducing robust cervico-vaginal and rectal immunity, although cytotoxic CD4+ T cell mediated mucosal and systemic immunity correlated strongly with 'complete protection', the different degrees of protection observed was multi-factorial.

Viruses and Virus-Like Particles in Biotechnology: Fundamentals and Applications

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this chapter, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitoring, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Justification for the inclusion of Gag in HIV vaccine candidates

It is widely accepted that effective human immunodeficiency virus (HIV) vaccines need to elicit a range of responses, including neutralising antibodies and T-cells. In natural HIV infections, immune responses to Gag are associated with lower viral load in infected individuals, and these responses can be measured against infected cells before the replication of HIV. Priming immune responses to Gag with DNA or recombinant Bacillus Calmette-Guérin (BCG) vaccines, and boosting with Gag virus-like particles as subunit vaccines or Gag produced in vivo by other vaccine vectors, elicits high-magnitude, broad polyfunctional responses, with memory T-cell responses appropriate for virus control. This review provides justification for the inclusion of HIV Gag in vaccine regimens, either as a transgene expressing protein that may assemble to form budded particles, or as purified virus-like particles. Possible benefits would include early control via CD8(+) T-cells at the site of infection, control of spread from the entry portal, and control of viraemia if infection is established.

Functional assessment and structural basis of antibody binding to human papillomavirus capsid

Persistent high-risk human papillomavirus (HPV) infection is linked to cervical cancer. Two prophylactic virus-like particle (VLP)-based vaccines have been marketed globally for nearly a decade. Here, we review the HPV pseudovirion (PsV)-based assays for the functional assessment of the HPV neutralizing antibodies and the structural basis for these clinically relevant epitopes. The PsV-based neutralization assay was developed to evaluate the efficacy of neutralization antibodies in sera elicited by vaccination or natural infection or to assess the functional characteristics of monoclonal antibodies. Different antibody binding modes were observed when an antibody was complexed with virions, PsVs or VLPs. The neutralizing epitopes are localized on surface loops of the L1 capsid protein, at various locations on the capsomere. Different neutralization antibodies exert their neutralizing function via different mechanisms. Some antibodies neutralize the virions by inducing conformational changes in the viral capsid, which can result in concealing the binding site for a cellular receptor like 1A1D-2 against dengue virus, or inducing premature genome release like E18 against enterovirus 71. Higher-resolution details on the epitope composition of HPV neutralizing antibodies would shed light on the structural basis of the highly efficacious vaccines and aid the design of next generation vaccines. In-depth understanding of epitope composition would ensure the development of function-indicating assays for the comparability exercise to support process improvement or process scale up. Elucidation of the structural elements of the type-specific epitopes would enable rational design of cross-type neutralization via epitope re-engineering or epitope grafting in hybrid VLPs.

Developments in virus-like particle-based vaccines for infectious diseases and cancer

Virus-like particles hold great promise for the development of effective and affordable vaccines. Indeed, virus-like particles are suitable for presentation and efficient delivery of linear as well as conformational antigens to antigen-presenting cells. This will ultimately result in optimal B-cell activation and cross-presentation with both MHC class I and II molecules to prime CD4(+) T-helper as well as CD8(+) cytotoxic T cells. This article provides an update on the development and use of virus-like particles as vaccine approaches for infectious diseases and cancer.

Delivery strategies for novel vaccine formulations

A major challenge in vaccine design is to identify antigen presentation and delivery systems capable of rapidly stimulating both the humoral and cellular components of the immune system to elicit a strong and sustained immunity against different viral isolates. Approaches to achieve this end involve live attenuated and inactivated virions, viral vectors, DNA, and protein subunits. This review reports the state of current antigen delivery, and focuses on two innovative systems recently established at our labs. These systems are the filamentous bacteriophage fd and an icosahedral scaffold formed by the acyltransferase component (E2 protein) of the pyruvate dehydrogenase complex of Bacillus stearothermophilus.

Screening and confirmatory testing of MHC class I alleles in pig-tailed macaques

Pig-tailed macaques (Macaca nemestrina) are a commonly studied primate model of human AIDS. The Mane-A1*084:01 MHC class I allele (previously named Mane-A*10) is important for the control of SIV infection by CD8+ T cells in this model. Validated methods to detect this allele in large numbers of macaques are lacking. We studied this MHC allele using sequence-specific PCRs in 217 pig-tailed macaques and identified 75 (35%) positive animals. We then performed massively parallel pyrosequencing with a universal 568-bp MHC class I cDNA-PCR amplicon for 50 of these 75 macaques. All 50 animals expressed Mane-A1*084:01 or closely related variants of the Mane-A1*084 lineage. Mane-A1*084 transcripts accounted for an average of 20.9% of all class I sequences identified per animal. SIV infection of a subset of these macaques resulted in the induction of SIV-specific CD8+ T cell responses detected by Mane-A1*084:01 tetramers. An average of 19 distinct class I transcripts were identified per animal by pyrosequencing. This analysis revealed 89 new Mane class I sequences as well as 32 previously described sequences that were extended with the longer amplicons employed in the current study. In addition, multiple Mane class I haplotypes that had been inferred previously based on shared transcript profiles between unrelated animals were confirmed for a subset of animals where pedigree information was available. We conclude that sequence-specific PCR is useful to screen pig-tailed macaques for Mane-A1*084:01, although pyrosequencing permits a much broader identification of the repertoire of MHC class I sequences and haplotypes expressed by individual animals.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

Conformational HIV-1 envelope on particulate structures: a tool for chemokine coreceptor binding studies

The human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 presents conserved binding sites for binding to the primary virus receptor CD4 as well as the major HIV chemokine coreceptors, CCR5 and CXCR4.

Concerted efforts are underway to understand the specific interactions between gp120 and coreceptors as well as their contribution to the subsequent membrane fusion process.

The present review summarizes the current knowledge on this biological aspect, which represents one of the key and essential points of the HIV-host cell interplay and HIV life cycle. The relevance of conformational HIV-1 Envelope proteins presented on Virus-like Particles for appropriate assessment of this molecular interaction, is also discussed.

Viruses and Virus-Like Particles in Biotechnology

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this article, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitorization, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Viral nanoparticles and virus-like particles: platforms for contemporary vaccine design

Current vaccines that provide protection against infectious diseases have primarily relied on attenuated or inactivated pathogens. Virus‐like particles (VLPs), comprised of capsid proteins that can initiate an immune response but do not include the genetic material required for replication, promote immunogenicity and have been developed and approved as vaccines in some cases. In addition, many of these VLPs can be used as molecular platforms for genetic fusion or chemical attachment of heterologous antigenic epitopes. This approach has been shown to provide protective immunity against the foreign epitopes in many cases. A variety of VLPs and virus‐based nanoparticles are being developed for use as vaccines and epitope platforms. These particles have the potential to increase efficacy of current vaccines as well as treat diseases for which no effective vaccines are available. WIREs Nanomed Nanobiotechnol 2011 3 174–196 DOI: 10.1002/wnan.119

This article is categorized under: 1

Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease

Influenza virus-like particles as an antigen-carrier platform for the ESAT-6 epitope of Mycobacterium tuberculosis

Various virus-like particles (VLPs) have been shown to induce cytotoxic T-cell immune response as well as B-cell immune response. This makes VLPs promising candidates for antigen-carrier platforms for various epitopes. Influenza A VLPs were produced displaying a 20 amino acid sequence from Mycobacterium tuberculosis early secretory antigenic target 6 protein (ESAT-6). As this sequence is known to comprise a potent T-cell epitope it was chosen as a model for a foreign epitope to be presented on an influenza VLP scaffold. The ESAT-6 epitope was engineered into the antigenic region B of the influenza hemagglutinin (HA) from strain A/New Caledonia/20/99. VLPs were expressed in insect cells and subjected to immunization studies in mice. High serum antibody titers detected against recombinant ESAT-6 demonstrated the feasibility of influenza A VLPs serving as an efficient platform for epitope presentation.

Protection against Mucosal SHIV Challenge by Peptide and Helper-Dependent Adenovirus Vaccines

Groups of rhesus macaques that had previously been immunized with HIV-1 envelope (env) peptides and first generation adenovirus serotype 5 (FG-Ad5) vaccines expressing the same peptides were immunized intramuscularly three times with helper-dependent adenovirus (HD-Ad) vaccines expressing only the HIV-1 envelope from JRFL. No gag, pol, or other SHIV genes were used for vaccination. One group of the FG-Ad5-immune animals was immunized three times with HD-Ad5 expressing env. One group was immunized by serotype-switching with HD-Ad6, HD-Ad1, and HD-Ad2 expressing env. Previous work demonstrated that serum antibody levels against env were significantly higher in the serotype-switched group than in the HD-Ad5 group. In this study, neutralizing antibody and T cell responses were compared between the groups before and after rectal challenge with CCR5-tropic SHIV-SF162P3. When serum samples were assayed for neutralizing antibodies, only weak activity was observed. T cell responses against env epitopes were higher in the serotype-switched group. When these animals were challenged rectally with SHIV-SF162P3, both the Ad5 and serotype-switch groups significantly reduced peak viral loads 2 to 10-fold 2 weeks after infection. Peak viral loads were significantly lower for the serotype-switched group as compared to the HD-Ad5-immunized group. Viral loads declined over 18 weeks after infection with some animals viremia reducing nearly 4 logs from the peak. These data demonstrate significant mucosal vaccine effects after immunization with only env antigens. These data also demonstrate HD-Ad vectors are a robust platform for vaccination.

Complexity of the inoculum determines the rate of reversion of SIV Gag CD8 T cell mutant virus and outcome of infection

Escape mutant (EM) virus that evades CD8+ T cell recognition is frequently observed following infection with HIV-1 or SIV. This EM virus is often less replicatively “fit” compared to wild-type (WT) virus, as demonstrated by reversion to WT upon transmission of HIV to a naïve host and the association of EM virus with lower viral load in vivo in HIV-1 infection. The rate and timing of reversion is, however, highly variable. We quantified reversion to WT of a series of SIV and SHIV viruses containing minor amounts of WT virus in pigtail macaques using a sensitive PCR assay. Infection with mixes of EM and WT virus containing ≥10% WT virus results in immediate and rapid outgrowth of WT virus at SIV Gag CD8 T cell epitopes within 7 days of infection of pigtail macaques with SHIV or SIV. In contrast, infection with biologically passaged SHIV_mn229 viruses with much smaller proportions of WT sequence, or a molecular clone of pure EM SIV_mac239, demonstrated a delayed or slow pattern of reversion. WT virus was not detectable until ≥8 days after inoculation and took ≥8 weeks to become the dominant quasispecies. A delayed pattern of reversion was associated with significantly lower viral loads. The diversity of the infecting inoculum determines the timing of reversion to WT virus, which in turn predicts the outcome of infection. The delay in reversion of fitness-reducing CD8 T cell escape mutations in some scenarios suggests opportunities to reduce the pathogenicity of HIV during very early infection.

Understanding how to contain HIV replication by the immune system is a key goal of vaccine strategies. HIV frequently mutates to avoid immune recognition, but this may come at a “fitness cost”, weakening the virus. When HIV is transmitted to a new host, the mutations often revert back to wild-type, allowing the virus to regain a fitter state. We found that when multiple HIV-like viruses are transmitted to monkeys, containing both mutant and wild-type, reversion to wild-type is very rapid and the fitter virus results in higher viral levels. In contrast, when only escape mutant virus initiates the infection, reversion to wild-type is delayed to later during early infection, and lower levels of virus result. Our results suggest that the composition of the infecting virus plays a role in determining the outcome of HIV infections. Strategies to maintain weakened virus strains during the early HIV infection may help the host control virus replication.

Inactivated simian immunodeficiency virus-pulsed autologous fresh blood cells as an immunotherapy strategy

Practical immunotherapies for human immunodeficiency virus infection are needed. We evaluated inactivated simian immunodeficiency virus (SIV) pulsed onto fresh peripheral blood mononuclear cells in 12 pigtail macaques with chronic SIV(mac251) infection for T-cell immunogenicity in a randomized cross-over design study. The immunotherapy was safe and convincingly induced high levels of SIV-specific CD4(+) T-cell responses (mean, 5.9% +/- 1.3% of all CD4(+) T cells) and to a lesser extent SIV-specific CD8(+) T-cell responses (mean, 0.7% +/- 0.4%). Responses were primarily directed toward Gag and less frequently toward Env but not Pol or regulatory/accessory SIV proteins. T-cell responses against Gag were generally broad and polyfunctional, with a mean of 2.7 CD4(+) T-cell epitopes mapped per animal and more than half of the SIV Gag-specific CD4(+) T cells expressing three or more effector molecules. The immunogenicity was comparable to that found in previous studies of peptide-pulsed blood cells. Despite the high-level immunogenicity, no reduction in viral load was observed in the chronically viremic macaques. This contrasts with our studies of immunization with peptide-pulsed blood cells during early SIV infection in macaques. Future studies of inactivated virus-pulsed blood cell immunotherapy during early infection of patients receiving antiretroviral therapy are warranted.

Delivery of immunotherapy with peptide-pulsed blood in macaques

Simple and effective delivery methods for cellular immunotherapies are needed. We assessed ex vivo pulsing of overlapping SIV Gag 15mer peptides onto either whole blood or PBMC in 15 randomly assigned SIV-infected macaques. Both delivery methods were safe and immunogenic, stimulating high levels of broad and polyfunctional Gag-specific CD4 and CD8 T cells. Delivery of overlapping Gag peptides via either whole blood or PBMC is suitable for clinical evaluation.

Control of viremia and prevention of AIDS following immunotherapy of SIV-infected macaques with peptide-pulsed blood

Effective immunotherapies for HIV are needed. Drug therapies are life-long with significant toxicities. Dendritic-cell based immunotherapy approaches are promising but impractical for widespread use. A simple immunotherapy, reinfusing fresh autologous blood cells exposed to overlapping SIV peptides for 1 hour ex vivo, was assessed for the control of SIV_mac251 replication in 36 pigtail macaques. An initial set of four immunizations was administered under antiretroviral cover and a booster set of three immunizations administered 6 months later. Vaccinated animals were randomized to receive Gag peptides alone or peptides spanning all nine SIV proteins. High-level, SIV-specific CD4 and CD8 T-cell immunity was induced following immunization, both during antiretroviral cover and without. Virus levels were durably ∼10-fold lower for 1 year in immunized animals compared to controls, and a significant delay in AIDS-related mortality resulted. Broader immunity resulted following immunizations with peptides spanning all nine SIV proteins, but the responses to Gag were weaker in comparison to animals only immunized with Gag. No difference in viral outcome occurred in animals immunized with all SIV proteins compared to animals immunized against Gag alone. Peptide-pulsed blood cells are an immunogenic and effective immunotherapy in SIV-infected macaques. Our results suggest Gag alone is an effective antigen for T-cell immunotherapy. Fresh blood cells pulsed with overlapping Gag peptides is proceeding into trials in HIV-infected humans.

Effective immunotherapies for HIV are needed. We assessed a simple technique, reinfusion of fresh blood cells incubating with overlapping SIV peptides (Overlapping Peptide-pulsed Autologous ceLls, OPAL), in 36 randomly allocated SIV-infected monkeys. We analyzed this therapy for the stimulation of immunity, control of virus levels, and prevention of AIDS. The OPAL immunotherapy was safe and stimulated remarkable levels of T-cell immunity. Levels of virus in vaccinated monkeys were 10-fold lower than in controls, and this was durable for over 1 year after the initial vaccinations. The immunotherapy resulted in fewer deaths from AIDS. We conclude this is a promising immunotherapy technique. Trials in HIV-infected humans of OPAL therapy are planned.

The testis and epididymis are productively infected by SIV and SHIV in juvenile macaques during the post-acute stage of infection

Background

Little is known about the progression and pathogenesis of HIV-1 infection within the male genital tract (MGT), particularly during the early stages of infection.

Results

To study HIV pathogenesis in the testis and epididymis, 12 juvenile monkeys (Macacca nemestrina, 4–4.5 years old) were infected with Simian Immunodeficiency Virus mac 251 (SIV_mac251) (n = 6) or Simian/Human Immunodeficiency Virus (SHIV_mn229) (n = 6). Testes and epididymides were collected and examined by light microscopy and electron microscopy, at weeks 11–13 (SHIV) and 23 (SIV) following infection. Differences were found in the maturation status of the MGT of the monkeys, ranging from prepubertal (lacking post-meiotic germ cells) to post-pubertal (having mature sperm in the epididymal duct). Variable levels of viral RNA were identified in the lymph node, epididymis and testis following infection with both SHIV_mn229 and SIV_mac251. Viral protein was detected via immunofluorescence histochemistry using specific antibodies to SIV (anti-gp41) and HIV-1 (capsid/p24) protein. SIV and SHIV infected macrophages, potentially dendritic cells and T cells in the testicular interstitial tissue were identified by co-localisation studies using antibodies to CD68, DC-SIGN, αβTCR. Infection of spermatogonia, but not more mature spermatogenic cells, was also observed. Leukocytic infiltrates were observed within the epididymal stroma of the infected animals.

Conclusion

These data show that the testis and epididymis of juvenile macaques are a target for SIV and SHIV during the post-acute stage of infection and represent a potential model for studying HIV-1 pathogenesis and its effect on spermatogenesis and the MGT in general.

Vaccine-induced T cells control reversion of AIDS virus immune escape mutants

Many current-generation human immunodeficiency virus (HIV) vaccines induce specific T cells to control acute viremia, but their utility following infection with escape mutant virus is unclear. We studied reversion to wild type of an escape mutant simian-HIV in major histocompatibility complex-matched vaccinated pigtail macaques. High levels of vaccine-induced CD8+ T cells strongly correlated with maintenance of escape mutant virus during acute infection. Interestingly, in animals with lower CD8+ T-cell levels, transient reversion to wild-type virus resulted in better postacute control of viremia. Killing of wild-type virus facilitated by transient reversion outweighs the benefit of a larger CD8+ T-cell response that only maintains the less fit escape mutant virus. These findings have important implications for the further development of T-cell-based HIV vaccines where exposure to escape mutant viruses is common.

Virus-like particles: passport to immune recognition

Virus-like particles (VLPs) are formed by the self-assembly of envelope and/or capsid proteins from many viruses. In many cases such VLPs have structural characteristics and antigenicity similar to the parental virus, and some have already proven successful as vaccines against the cognate virus infection. The structural components of some VLPs have also proven amenable to the insertion or fusion of foreign antigenic sequences, allowing the production of chimeric VLPs exposing the foreign antigen on their surface. Other VLPs have been used as carriers for foreign antigens, including non-protein antigens, via chemical conjugation. This review outlines some of the advantages, disadvantages, and technical considerations for the use of a wide range of VLP systems in vaccine development.

New recombinant vaccines based on the use of prokaryotic antigen-display systems

A major challenge in vaccine design has been to identify antigen presentation systems that elicit strong T- and B-cell responses. In the authors' laboratory, two new delivery vehicles derived from nonpathogenic prokaryotic organisms were recently designed and investigated. Conserved antigenic determinants were inserted into the N-terminal region of the major pVIII coat protein of bacteriophage fd virions or on the surface of an icosahedral scaffold formed by the acyltransferase component (E2 protein) of the pyruvate dehydrogenase complex of Bacillus stearothermophilus. The data indicate that the antigenic determinant displayed by either fd virions or on the surface of the E2 lattice are accessible to the immune system, and are able to trigger a humoral response as well as a potent helper and cytolytic response in vitro and in vivo. These systems offer the potential for safe and inexpensive vaccines to elicit full-spectrum immune responses.

Comparative efficacy of subtype AE simian-human immunodeficiency virus priming and boosting vaccines in pigtail macaques

Vaccination against AIDS is hampered by great diversity between human immunodeficiency virus (HIV) strains. Heterologous B-subtype-based simian-human immunodeficiency virus (SHIV) DNA prime and poxvirus boost vaccine regimens can induce partial, T-cell-mediated, protective immunity in macaques. We analyzed a set of DNA, recombinant fowlpox viruses (FPV), and vaccinia viruses (VV) expressing subtype AE HIV type 1 (HIV-1) Tat, Rev, and Env proteins and SIV Gag/Pol in 30 pigtail macaques. SIV Gag-specific CD4 and CD8 T-cell responses were induced by sequential DNA/FPV vaccination, although lower FPV doses, VV/FPV vaccination, and DNA vaccines alone were not as consistently immunogenic. The SHIV AE DNA prime, FPV boost regimens were significantly less immunogenic than comparable B-subtype SHIV vaccination. Peak viral load was modestly (0.4 log10 copies/ml) lower among the AE subtype SHIV-immunized animals compared to controls following the virulent B subtype SHIV challenge. Protection from persistent high levels of viremia and CD4 T-cell depletion was less in AE subtype compared to B subtype SHIV-vaccinated macaques. Gag was highly immunodominant over the other AE subtype SHIV vaccine proteins after vaccination, and this immunodominance was exacerbated after challenge. Interestingly, the lower level of priming of immune responses did not blunt postchallenge Gag-specific recall responses, despite more modest protection. These studies suggest priming of T-cell immunity to prevent AIDS in humans is possible, but differences in the immunogenicity of various subtype vaccines and broad cross-subtype protection are substantial hurdles.

GP120: target for neutralizing HIV-1 antibodies

The glycoprotein (gp) 120 subunit is an important part of the envelope spikes that decorate the surface of HIV-1 and a major target for neutralizing antibodies. However, immunization with recombinant gp120 does not elicit neutralizing antibodies against multiple HIV-1 isolates (broadly neutralizing antibodies), and gp120 failed to demonstrate vaccine efficacy in recent clinical trials. Ongoing crystallographic studies of gp120 molecules from HIV-1 and SIV increasingly reveal how conserved regions, which are the targets of broadly neutralizing antibodies, are concealed from immune recognition. Based on this structural insight and that from studies of antibody structures, a number of strategies are being pursued to design immunogens that can elicit broadly neutralizing antibodies to gp120. These include (a) the construction of mimics of the viral envelope spike and (b) the design of antigens specifically tailored to induce broadly neutralizing antibodies.

Comparative evaluation of simian, simian-human, and human immunodeficiency virus infections in the pigtail macaque (Macaca nemestrina) model

The global impact of HIV/AIDS intensifies the need for a preventive vaccine and nonhuman primate models can help provide critical insights into effective immunity. Pigtail macaques (Macaca nemestrina) are increasingly studied as a nonhuman primate model for AIDS. We compared the virologic and immunologic characteristics of HIV-1, SIV, and SHIV infection of naive pigtail macaques across a series of preclinical HIV vaccine studies. SIVmac251 and SIVmac239 infection of naive pigtail macaques resulted in a gradual decline in peripheral CD4+ T cells in the setting of high levels of viremia, approximating most closely human infection of HIV-1. In contrast, the CXCR4-utilizing SHIVmn229 virus resulted in rapid depletion of CD4+ T cells and minimal generation of humoral or cellular immune responses, similar to that observed with SHIV89.6P infection of rhesus macaques. Infection with the CCR5-utilizing, rhesus macaque passaged, SHIVSF162P3 resulted in some overall CD4+ T cell decline, however, three of eight macaques naturally control SHIVSF162P3 viremia to very low levels in the setting of robust adaptive immunity. Despite attempts at infecting pigtail macaques with HIV-1 strains passaged in juvenile pigtail macaques in vivo or in PBMC isolated from pigtail macaques in vitro, only lower nonsustained levels of viral replication were observed. Our results provide a series of virologic models with which to evaluate potential AIDS vaccines in pigtail macaques.

Short communication: characteristics of effective immune control of simian/human immunodeficiency virus in pigtail macaques

Considerable evidence suggests both HIV-specific T cells and neutralizing antibodies (nAb) can, separately, assist control of viremia. T cell and nAb responses were studied in detail in three pigtail macaques protected from chronic simian/human immunodeficiency virus (SHIV) viremia by DNA prime/fowlpoxvirus boost vaccine regimens. Immunity was studied both after an initial intrarectal SHIV challenge, as well as during CD8 T cell depletion and a subsequent intravenous SHIV rechallenge. Remarkably, SHIV-specific CD4 and CD8 T cells were detectable in the absence of viremia following an initial SHIV challenge in one animal, subsequent to recovery from CD8 T cell depletion in all three animals, and following control of heterologous SHIV rechallenge in two animals. Neutralizing antibodies were also enhanced following CD8 depletion without recrudescence of viremia in all three animals. These observations, although in a small subset of animals, suggest the hypothesis that combinations of primed T cell immunity and neutralizing antibodies can maintain control of chronic primate lentiviral infections.

The pigtail macaque MHC class I allele Mane-A*10 presents an immundominant SIV Gag epitope: identification, tetramer development and implications of immune escape and reversion

The pigtail macaque (Macaca nemestrina) is a common model for the study of AIDS. The pigtail major histocompatibility complex class I allele Mane-A*10 restricts an immunodominant simian immunodeficiency virus (SIV) Gag epitope (KP9) which rapidly mutates to escape T cell recognition following acute simian/human immunodeficiency virus infection. Two technologies for the detection of Mane-A*10 in outbred pigtail macaques were developed: reference strand-mediated conformational analysis and sequence-specific primer polymerase chain reaction. A Mane-A*10/KP9 tetramer was then developed to quantify CD8(+) T lymphocytes primed by multigenic DNA vaccination, which have previously been difficult to detect using standard interferon-gamma-based T cell assays. We also demonstrate mutational escape at KP9 following acute SIV infection. Mane-A*10(+) animals have lower set point SIV levels than Mane-A*10(-) animals, suggesting a significant fitness cost of escape. These studies pave the way for a more robust understanding of HIV vaccines in pigtail macaques.

Mucosally-administered human–simian immunodeficiency virus DNA and fowlpoxvirus-based recombinant vaccines reduce acute phase viral replication in macaques following vaginal challenge with CCR5-tropic SHIVSF162P3

Further advances are required in understanding protection from AIDS by T cell immunity across mucosal sites of virus transmission. We analysed a set of multigenic HIV and SHIV DNA and Fowlpoxvirus (FPV) prime and boost vaccines for immunogenicity and protective efficacy in outbred pigtail macaques when delivered via mucosal surfaces (intranasally or intrarectally). Intranasally delivered DNA, even when adjuvanted and given as a fine droplet spray, was neither immunogenic nor protective in macaques. Some protection from acute infection with a pathogenic vaginal SHIVSF162P3 challenge was, however, observed with a regimen involving intramuscular DNA vaccine priming followed by either intranasally or intrarectally delivered rFPV boosting. Interestingly, animals boosted with rFPV vaccine via either of these mucosal routes had poor circulating T cell responses prior to challenge with SHIV compared to those boosted via the intramuscular route. Nevertheless, the mucosally-vaccinated animals generated equivalent anamnestic mucosal and systemic SHIV-specific CD4 and CD8 T cell responses following SHIV administration, with significant reduction in acute plasma viremia against this vaginal challenge. Our data suggest strategies for effective priming of partial immunity to mucosal HIV-1 exposure utilizing systemic prime and mucosal boost vaccination strategies.

Phenotypic and kinetic analysis of effective simian–human immunodeficiency virus-specific T cell responses in DNA- and fowlpox virus-vaccinated macaques

Although T cell immunity is important in the control of HIV-1 infection, the characteristics of effective HIV-specific T cell responses are unclear. We previously observed protection from virulent SHIV challenges in macaques administered priming with DNA vaccines and boosting with recombinant fowlpox viruses expressing shared SIV Gag antigens. We therefore performed a detailed kinetic and phenotypic study of the T cell immunity induced by these vaccines prior to and following SHIV challenge utilizing intracellular cytokine staining. Pigtail macaques vaccinated intramuscularly with DNA/recombinant fowlpox virus exhibited a coordinated induction of first Gag-specific CD4 T cell responses and then a week later Gag-specific CD8 T cell responses following the fowlpox virus boost. Overall, the magnitude and timing of the peak CD8 T cell responses following challenge was significantly associated with reductions in SHIV viremia following pathogenic challenge. After pathogenic lentiviral challenge, virus-specific effector memory T cells derived from animals controlling SHIV infection recognized a broad array of epitopes, expressed multiple effector cytokines and rapidly recognized virus-exposed cells ex vivo. These results shed light on some of the requirements for T cells in the control of pathogenic lentiviral infections.

Rapid viral escape at an immunodominant simian-human immunodeficiency virus cytotoxic T-lymphocyte epitope exacts a dramatic fitness cost

Escape from specific T-cell responses contributes to the progression of human immunodeficiency virus type 1 (HIV-1) infection. T-cell escape viral variants are retained following HIV-1 transmission between major histocompatibility complex (MHC)-matched individuals. However, reversion to wild type can occur following transmission to MHC-mismatched hosts in the absence of cytotoxic T-lymphocyte (CTL) pressure, due to the reduced fitness of the escape mutant virus. We estimated both the strength of immune selection and the fitness cost of escape variants by studying the rates of T-cell escape and reversion in pigtail macaques. Near-complete replacement of wild-type with T-cell escape viral variants at an immunodominant simian immunodeficiency virus Gag epitope KP9 occurred rapidly (over 7 days) following infection of pigtail macaques with SHIVSF162P3. Another challenge virus, SHIVmn229, previously serially passaged through pigtail macaques, contained a KP9 escape mutation in 40/44 clones sequenced from the challenge stock. When six KP9-responding animals were infected with this virus, the escape mutation was maintained. By contrast, in animals not responding to KP9, rapid reversion of the K165R mutation occurred over 2 weeks after infection. The rapidity of reversion to the wild-type sequence suggests a significant fitness cost of the T-cell escape mutant. Quantifying both the selection pressure exerted by CTL and the fitness costs of escape mutation has important implications for the development of CTL-based vaccine strategies.

Enhanced cellular immunity in macaques following a novel peptide immunotherapy

Advances in treating and preventing AIDS depend on understanding how human immunodeficiency virus (HIV) is eliminated in vivo and on the manipulation of effective immune responses to HIV. During the development of assays quantifying the elimination of fluorescent autologous cells coated with overlapping 15-mer simian immunodeficiency virus (SIV) or HIV-1 peptides, we made a remarkable observation: the reinfusion of macaque peripheral blood mononuclear cells, or even whole blood, pulsed with SIV and/or HIV peptides generated sharply enhanced SIV- and HIV-1-specific T-cell immunity. Strong, broad CD4+- and CD8+-T-cell responses could be enhanced simultaneously against peptide pools spanning 87% of all SIV- and HIV-1-expressed proteins-highly desirable characteristics of HIV-specific immunity. De novo hepatitis C virus-specific CD4+- and CD8+-T-cell responses were generated in macaques by the same method. This simple technique holds promise for the immunotherapy of HIV and other chronic viral infections.

Comparison of whole gene and whole virus scrambled antigen approaches for DNA prime and fowlpox virus boost HIV type 1 vaccine regimens in macaques

T cell immunity plays a critical role in controlling HIV-1 viremia, and encoding a limited set of HIV-1 genes within DNA and poxvirus vectors can, when used sequentially, induce high levels of T cell immunity in primates. However, a limited breadth of T cell immunity exposes the host to potential infection with either genetically diverse HIV-1 strains or T cell escape variants of HIV-1. In an attempt to induce maximally broad immunity, we examined DNA and recombinant fowlpox virus (rFPV) vaccines encoding all HIV-1 genes derived from a global HIV-1 consensus sequence, but expressed as multiple overlapping scrambled 30-amino acid segments (scrambled antigen vaccines, or SAVINEs). Three groups of seven pigtail macaques were immunized with sets of DNA and rFPV expressing Gag/Pol antigens only, the whole genome SAVINE antigens, or no HIV-1 antigens and T cell immunity was monitored by ELISpot and intracellular cytokine staining. High levels of cross-subtype HIV-specific T cell immunity to Gag were consistently induced in the seven macaques primed with DNA and rFPV vaccines expressing Gag/Pol as intact proteins. It was, however, difficult to repeatedly boost immunity with further rFPV immunizations, presumably reflecting high levels of anti- FPV immunity. Unfortunately, this vaccine study did not consistently achieve a broadened level of T cell immunity to multiple HIV genes utilizing the novel whole-virus SAVINE approach, with only one of seven immunized animals generating broad T cell immunity to multiple HIV-1 proteins. Further refinements are planned with alternative vector strategies to evaluate the potential of the SAVINE technology.

Subtype AE HIV-1 DNA and recombinant Fowlpoxvirus vaccines encoding five shared HIV-1 genes: safety and T cell immunogenicity in macaques

To induce broad T cell immunity to HIV-1, we evaluated the safety, immunogenicity and dose-response relationship of DNA and recombinant Fowlpoxvirus (rFPV) vaccines encoding five shared HIV subtype AE genes (Gag, Pol, Env, Tat, Rev) in pigtail macaques. The DNA (three doses of either 1 mg or 4.5 mg) and rFPV (a single boost of either 5 x 10(7) or 2 x 10(8) plaque forming units) vaccines were administered intramuscularly without adjuvants. Broadly reactive HIV-specific T cell immunity was stimulated by all doses of the vaccines administered, without significant differences between the high and low doses studied. The vaccines induced both CD4 and CD8 T cell responses to Gag, Pol, Env and Tat/Rev proteins, with CD4 T cell responses being greater in magnitude than CD8 T cell responses. The vaccine-induced T cell responses had significant cross-recognition of heterologous HIV-1 proteins from non-AE HIV-1 subtypes. In conclusion, these subtype AE HIV-1 DNA and rFPV vaccines were safe, induced broad T-cell immunity in macaques, and are suitable for progression into clinical trials.

Granulocyte contamination dramatically inhibits spot formation in AIDS virus-specific ELISpot assays: analysis and strategies to ameliorate

The interferon-gamma (IFNgamma) ELISpot assay has become the most critical tool for HIV vaccine evaluation. External factors affecting ELISpot results must be minimized for the data to be reliably used in vaccine research and development processes. In pre-clinical pigtail macaque studies analyzing HIV/SIV vaccine studies, we detected a strong correlation between levels of granulocytes contaminating PBMC preparations and reduction in the quality and quantity of spots in the IFNgamma ELISpot assay. Acute SHIV infection of macaques worsened granulocyte contamination of PBMC fractions and made the assay much less reliable in detecting SIV-specific T cell immunity compared to intracellular cytokine staining (ICS). This problem could be ameliorated by using an F(ab)(2) form of the MD-1 IFNgamma capture antibody, presumably reflecting that activation of granulocytes in the well by the Fc portion of the standard capture antibody disrupts spot formation. Improving the standard ELISpot assay by using an F(ab)(2) capture antibody should make it more reliable for use in critical vaccine development studies.

A novel adjuvant for mucosal immunity to HIV-1 gp120 in nonhuman primates

The development of a safe and effective mucosal adjuvant is a crucial step toward a mucosal HIV/AIDS vaccine. This study seeks to determine the promise of a nontoxic mutant of cholera toxin (mCT; E112K) as a mucosal adjuvant in nonhuman primates. HIV-1 gp120 was nasally administered together with mCT E112K or native CT (nCT) as adjuvant on five to six occasions over a 6- to 8-wk period to groups of four rhesus macaques and alone to two monkeys that acted as controls. Macaques given nasal gp120 with either mCT E112K or nCT showed elevated gp120-specific IgG and IgA Ab responses with virus-neutralizing activity in both their plasma and mucosal external secretions, as well as higher numbers of gp120-specific IgA Ab-forming cells in their mucosal and peripheral lymphoid tissues and of IL-4-producing Th2-type CD4-positive (CD4(+)) T cells than did controls. Even though significant mucosal adjuvanticity was seen with both mCT E112K and nCT, neuronal damage was observed only in the nCT-treated, but not in the control or mCT E112K-treated groups. These results clearly show that mCT E112K is an effective and safe mucosal adjuvant for the development of a nasal HIV/AIDS vaccine.

Analysis of pigtail macaque major histocompatibility complex class I molecules presenting immunodominant simian immunodeficiency virus epitopes

Successful human immunodeficiency virus (HIV) vaccines will need to induce effective T-cell immunity. We studied immunodominant simian immunodeficiency virus (SIV) Gag-specific T-cell responses and their restricting major histocompatibility complex (MHC) class I alleles in pigtail macaques (Macaca nemestrina), an increasingly common primate model for the study of HIV infection of humans. CD8+ T-cell responses to an SIV epitope, Gag164-172KP9, were present in at least 15 of 36 outbred pigtail macaques. The immunodominant KP9-specific response accounted for the majority (mean, 63%) of the SIV Gag response. Sequencing from six macaques identified 7 new Mane-A and 13 new Mane-B MHC class I alleles. One new allele, Mane-A*10, was common to four macaques that responded to the KP9 epitope. We adapted reference strand-mediated conformational analysis (RSCA) to MHC class I genotype M. nemestrina. Mane-A*10 was detected in macaques presenting KP9 studied by RSCA but was absent from non-KP9-presenting macaques. Expressed on class I-deficient cells, Mane-A*10, but not other pigtail macaque MHC class I molecules, efficiently presented KP9 to responder T cells, confirming that Mane-A*10 restricts the KP9 epitope. Importantly, naive pigtail macaques infected with SIVmac251 that respond to KP9 had significantly reduced plasma SIV viral levels (log10 0.87 copies/ml; P=0.025) compared to those of macaques not responding to KP9. The identification of this common M. nemestrina MHC class I allele restricting a functionally important immunodominant SIV Gag epitope establishes a basis for studying CD8+ T-cell responses against AIDS in an important, widely available nonhuman primate species.

Virus-like particles as HIV-1 vaccines

Traditional successful antiviral vaccines have relied mostly on live-attenuated viruses. Live-attenuated HIV vaccine candidates are not ideal as they pose risks of reversion, recombination or mutations. Other current HIV vaccine candidates have difficulties generating broadly effective neutralising antibodies and cytotoxic T cell immune responses to primary HIV isolates. Virus-like-particles (VLPs) have been demonstrated to be safe to administer to animals and human patients as well as being potent and efficient stimulators of cellular and humoral immune responses. Therefore, VLPs are being considered as possible HIV vaccines. Chimeric HIV-1 VLPs constructed with either HIV or SIV capsid protein plus HIV immune epitopes and immuno-stimulatory molecules have further improved on early VLP designs, leading to enhanced immune stimulation. The administration of VLP vaccines via mucosal surfaces has also emerged as a promising strategy with which to elicit mucosal and systemic humoral and cellular immune responses. Additionally, new information on antigen processing and the presentation of particulate antigens by dendritic cells (DCs) has created new strategies for improved VLP vaccine candidates. This paper reviews the field of HIV-1 VLP vaccine development, focusing on recent studies that will likely uncover promising prospects for new HIV vaccines.

Efficacy of DNA and fowlpox virus priming/boosting vaccines for simian/human immunodeficiency virus

Further advances are required in understanding protection from AIDS by T-cell immunity. We analyzed a set of multigenic simian/human immunodeficiency virus (SHIV) DNA and fowlpox virus priming and boosting vaccines for immunogenicity and protective efficacy in outbred pigtail macaques. The number of vaccinations required, the effect of DNA vaccination alone, and the effect of cytokine (gamma interferon) coexpression by the fowlpox virus boost was also studied. A coordinated induction of high levels of broadly reactive CD4 and CD8 T-cell immune responses was induced by sequential DNA and fowlpox virus vaccination. The immunogenicity of regimens utilizing fowlpox virus coexpressing gamma interferon, a single DNA priming vaccination, or DNA vaccines alone was inferior. Significant control of a virulent SHIV challenge was observed despite a loss of SHIV-specific proliferating T cells. The outcome of challenge with virulent SHIV(mn229) correlated with vaccine immunogenicity except that DNA vaccination alone primed for protection almost as effectively as the DNA/fowlpox virus regimen despite negligible immunogenicity by standard assays. These studies suggest that priming of immunity with DNA and fowlpox virus vaccines could delay AIDS in humans.

Cervical cancer vaccines: recent advances in HPV research

Carcinomas of the anogenital tract, particularly cancer of the cervix, account for almost 12% of all cancers in women, and so represent the second most frequent gynecological malignancy in the world (48). It is well established that chronic infection of cervical epithelium by human papillomaviruses (HPV) is necessary for the development of cervical cancer. In fact, HPV DNA has been demonstrated in more than 99.7% of cervical cancer biopsy specimens, with high-risk HPV16 and HPV18 sequences being most prevalent (45,73). Therefore, an effective vaccine that would mount an immune response against HPV-related proteins might contribute to the prevention or elimination of HPV expressing lesions. This review will concentrate on the most recent advances in vaccine-mediated prevention and immunotherapy of HPV-induced cervical cancer, including presentations from the 20(th) International HPV Conference held in October 2002 in Paris.

Progress in prophylactic and therapeutic vaccines for human papillomavirus infection

Virus-like particle (VLP) subunit vaccines composed of the major capsid protein L1 of the genital human papillomaviruses (HPVs) are now in Phase III clinical trials. The vaccines are immunogenic and safe and early results indicate efficacy. VLPs induce strong cell-mediated as well as humoral immune responses and chimeric VLPs including an HPV early protein may have therapeutic potential. Polynucleotide and recombinant viral vaccines encoding nonstructural viral proteins show therapeutic and prophylactic efficacy in animal models and are candidate immunotherapies for established low-grade benign genital infections. Vaccines designed to elicit cytotoxic T-lymphocytes specific for the HPV oncoproteins E6 and E7 show immunogenicity and efficacy in transplantable tumor models in rodents. In Phase I and II trials these vaccines are immunogenic and safe but show limited efficacy.