New hope for an AIDS vaccine

Current State of Microbicide Development

Efforts in developing an effective vaccine for human immunodeficiency virus (HIV) has been challenging as HIV strains are highly variable and exhibit extraordinary mutability. Despite condom usage and pre-exposure prophylaxis as excellent prevention strategies, lack of accessibility in some developing countries and low adherence due to sociocultural factors continue to act as barriers in reducing the HIV epidemic. Microbicides are topical therapies developed to prevent HIV and other sexually transmitted infections during intercourse. Microbicides applied vaginally or rectally are intended to prevent HIV infection at the site of transmission by either inhibiting its entry into immune cells or prevent viral replication. This review will summarize some of the current state-of-the-art microbicide formulations that are in preclinical and clinical stages of development and discuss some of the challenges associated with microbicide development.

Intranasal Vaccination against HIV-1 with Adenoviral Vector-Based Nanocomplex Using Synthetic TLR-4 Agonist Peptide as Adjuvant

Recombinant type 5 adenovirus (rAd5) vaccines hold the promise to prevent HIV-1 infections. Intranasal vaccination not only stimulates systemic immunity but also elicits mucosal immunity that provides first defense for mucosally transmitted diseases like HIV-1. Adjuvants such as TLR agonists are usually codelivered with antigens to enhance the immunogenicity of vaccines. Here, we present a rAd5 vaccine delivery system using DEG-PEI as the carrier. Adenovirus encoding HIV gag was used as antigen, and was complexed with DEG-PEI polymer via electrostatic interaction. A novel synthetic TLR-4 agonist, RS09, was either chemically linked with DEG-PEI (DP-RS09) or physically mixed with it(DP/RS09) to enhance the immunogenticity of rAd5 vaccine. After intranasal immunization, the systemic antigen-specific immune responses and cytotoxicity T lymphocytes responses induced by DP-RS09-rAd5 and DP/RS09-rAd5 were analyzed. The mucosal secretory IgA level was detected in both nasal and vaginal washes to determine the mucosal immunity. Furthermore, cytokine productions on RAW264.7 cells were tested after preincubation with TLR-4 pathway inhibitors. The results indicated that DEG-PEI could facilitate the intranasal delivery of rAd5 vaccine. Both chemically linked (DP-RS09) and physically mixed RS09 (DP/RS09) could further enhance the mucosal immunity of rAd5 vaccine via TLR-4 pathway. This RS09 adjuvanted DEG-PEI polymer represents a potential intranasal vaccine delivery system and may have a wider application for other viral vectors.

New therapeutic vaccination strategies for the treatment of chronic hepatitis B

Chronic hepatitis B virus (CHB) is currently treated with either interferon-based or nucleot(s)ide-based antiviral therapies. However, treatment with pegylated interferon alpha results in a durable antiviral response in only about 30% patients and is associated with side effects. Most patients receiving nucleot(s)ide analogue treatment do not establish long-term, durable control of infection and have rebounding viremia after cessation of therapy. Thus, novel therapy strategies are necessary to achieve the induction of potent and durable antiviral immune responses of the patients which can maintain long-term control of viral replication. Therapeutic vaccination of HBV carriers is a promising strategy for the control of hepatitis B. Here the authors review new therapeutic vaccination strategies to treat chronic hepatitis B which may be introduced for patient treatment in the future.

Human immunodeficiency virus (HIV) immunopathogenesis and vaccine development: a review

The development of a safe, effective and globally affordable HIV vaccine offers the best hope for the future control of the HIV-1 pandemic. Since 1987, scores of candidate HIV-1 vaccines have been developed which elicited varying degrees of protective responses in nonhuman primate models, including DNA vaccines, subunit vaccines, live vectored recombinant vaccines and various prime-boost combinations. Four of these candidate vaccines have been tested for efficacy in human volunteers, but, to the exception of the recent RV144 Phase III trial in Thailand, which elicited a modest but statistically significant level of protection against infection, none has shown efficacy in preventing HIV-1 infection or in controlling virus replication and delaying progression of disease in humans. Protection against infection was observed in the RV144 trial, but intensive research is needed to try to understand the protective immune mechanisms at stake. Building-up on the results of the RV144 trial and deciphering what possibly are the immune correlates of protection are the top research priorities of the moment, which will certainly accelerate the development of an highly effective vaccine that could be used in conjunction with other HIV prevention and treatment strategies. This article reviews the state of the art of HIV vaccine development and discusses the formidable scientific challenges met in this endeavor, in the context of a better understanding of the immunopathogenesis of the disease.

Human immunodeficiency virus-1 vaccine design: where do we go now?

Numerous human immunodeficiency virus (HIV)-1 vaccines have been developed over the last three decades, but to date an effective HIV-1 vaccine that can be used for prophylactic or therapeutic purposes in humans has not been identified. The failures and limited successes of HIV-1 vaccines have highlighted the gaps in our knowledge with regard to fundamental immunity against HIV-1 and have provided insights for vaccine strategies that may be implemented for designing more effective HIV-1 vaccines in the future. Recent studies have shown that robust mucosal immunity, high avidity and polyfunctional T cells, and broadly neutralizing antibodies are important factors governing the induction of protective immunity against HIV-1. Furthermore, optimization of vaccine delivery methods for DNA or live viral vector-based vaccines, elucidating the immune responses of individuals who remain resistant to HIV-1 infections and also understanding the core immune responses mediating protection against simian immunodeficiency viruses (SIV) and HIV-1 in animal models following vaccination, are key aspects to be regarded for designing more effective HIV-1 vaccines in the future.

Recruiting London gay men into an HIV vaccine trial: Is it feasible?

This paper describes a study among HIV-negative gay men in London to examine willingness to volunteer for an HIV vaccine trial. HIV-negative gay men (n=506) were surveyed in central London gyms in February-March 2002. Information was collected on willingness to volunteer for an HIV vaccine trial, attitudes toward HIV vaccines and sexual risk behaviour. Men reporting unprotected anal intercourse (UAI) in the previous three months with a man of unknown or discordant HIV status were classified as being at high risk of exposure to HIV (n=94, 18.6%). The remainder, who reported no UAI or UAI only with another HIV-negative man, were considered to be at low risk (n=412, 81.4%). Just under a quarter of the HIV-negative men in the study (23.4%) said they were either quite likely or very likely to volunteer for an HIV vaccine trial. High-risk men were more likely to say they would volunteer for a trial than low-risk men (37.2% versus 20.2%, p<0.001). Of the 506 HIV-negative men surveyed, eight (1.6%) were both high risk and very likely to volunteer for an HIV vaccine trial, while a further 27 (5.3%) were both high risk and quite likely to volunteer. Based on these figures, we estimated that to recruit 1,000 high-risk HIV-negative men into a vaccine trial between 15,000 and 62,000 HIV-negative men would need to be approached in the community. Compared with those at low risk, a greater proportion of high-risk men said that if they were in an HIV vaccine trial they would be more likely to have unprotected sex (23.4% versus 7.8%, p<0.001); that an effective vaccine will make safe sex less important (45.7% versus 31.3%, p=0.01); and that they would participate in an HIV vaccine trial even if they thought the vaccine might not work (46.8% versus 29.9%, p<0.01). This study suggests that, in London, to recruit high-risk HIV-negative gay men for an HIV vaccine trial many thousands of gay men may need to be approached in the community. Some HIV-negative men said that they would be more likely to have unprotected sex if they took part in a trial.

Impact of ETIF deletion on safety and immunogenicity of equine herpesvirus type 1-vectored vaccines

Heterologous gene transfer by viral vector systems is often limited by factors such as preexisting immunity, toxicity, low packaging capacity, or weak immunogenic potential. A novel viral vector system derived from equine herpesvirus type 1 (EHV-1) not only overcomes some of these obstacles but also promotes the robust expression of a delivered transgene and the induction of antigen-specific immune responses. Regarding an enhanced safety profile, we assessed the impact of the gene encoding the sole essential tegument protein, ETIF, on the replication and immunogenicity of recombinant EHVs. The deletion of ETIF severely attenuates replication in permissive RK13 cells and a human lung epithelial cell line but without influencing transgene expression. Whereas the intranasal administration of a recombinant luciferase EHV in BALB/c mice resulted in transgene expression in nasal cavities and lungs for 5 to 6 days, the ETIF deletion limited expression to 2 days and resulted in 30-fold-less luminescence. Attenuated replication was accompanied by a decreased capacity to induce CD8(+) T cells against a delivered HIV Gag transgene in BALB/c mice following repeated intranasal application. However, a single subcutaneous immunization with a gag DNA vaccine primed specific T cells for substantial expansion by two subsequent intranasal booster immunizations with either the gag recombinant ETIF mutant or the parental virus. In addition to inducing Gag-specific serum antibodies, this prime-boost strategy clearly outperformed three sequential immunizations with the parental or EHV-ΔETIF virus or repeated DNA vaccination by inducing substantial specific secretory IgA (sIgA) titers.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck

Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to a satisfactory result. Induction of HBV-specific T cells by therapeutic vaccination or immunotherapies may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients did not result in effective control of HBV infection, suggesting that new formulations of therapeutic vaccines are needed. The woodchuck (Marmota monax) is a useful preclinical model for developing the new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments with nucleos(t)ide analogues, DNA vaccines, and protein vaccines were tested in the woodchuck model. In this paper we summarize the available data concerning therapeutic immunization and gene therapy using recombinant viral vectors approaches in woodchucks, which show encouraging results. In addition, we present potential innovations in immunomodulatory strategies to be evaluated in this animal model.

Exploring peptide mimics for the production of antibodies against discontinuous protein epitopes

Peptide "mimics" (mimotopes) of linear protein epitopes and carbohydrate epitopes have been successfully used as immunogens to elicit cross-reactive antibodies against their cognate epitopes; however, immunogenic mimicry has been difficult to achieve for discontinuous protein epitopes. To explore this, we developed from phage-displayed peptide libraries optimized peptide mimics for three well-characterized discontinuous epitopes on hen egg lysozyme and horse cytochrome c. The peptides competed with their cognate antigens for antibody binding, displayed affinities in the nM range, and shared critical binding residues with their native epitopes. Yet, while immunogenic, none of the peptides elicited antibodies that cross-reacted with their cognate antigens. We analyzed the 3-D structure of the site within each discontinuous epitope that shared critical binding residues with its peptide mimic, and observed that in each case it formed a ridge-like patch on the epitope; in no case did it cover most or all of the epitope. Thus, the peptides' lack of immunogenic mimicry could be attributed to their inability to recapitulate the topological features of their cognate epitopes. Our results suggest that direct peptide immunizations are not a practical strategy for generating targeted antibody responses against discontinuous epitopes.

Probing the possibilities for T-cell-based AIDS vaccines

PURPOSE OF REVIEW

This review will discuss the current challenges facing the development of a successful AIDS vaccine and approaches being pursued to overcome them, with an emphasis on vaccines designed to elicit primarily cellular, rather than humoral, antiviral immune responses.

RECENT FINDINGS

Recent insights into the biology of mucosal virus transmission, CD4 T-cell depletion dynamics, the character of virus-specific CD8 T-cell responses, and the dynamic effects that CD8 T cells exert on virus evolution and genetic diversity manifest during lentivirus infections have engendered an improved understanding of the anatomical, physiological, and immunological aspects of HIV infection. These advances help frame the key scientific hurdles to development of a safe and effective AIDS vaccine that an expanding number and diversity of experimental approaches in vaccine design, administration, and evaluation are now seeking to overcome.

SUMMARY

The development of an effective AIDS vaccine remains elusive. Our increasing knowledge regarding the biology of HIV infection, mechanisms of AIDS pathogenesis, and correlates of protective immunity, however, suggest new hypotheses which, when critically evaluated, should bring us closer to the realization of an AIDS vaccine - or at least an improved understanding of the true nature and magnitude of the obstacles ahead.

Novel Adenovirus type 5 vaccine platform induces cellular immunity against HIV-1 Gag, Pol, Nef despite the presence of Ad5 immunity

Recombinant Adenovirus serotype 5 (Ad5) vectors have been used as vaccine platforms in numerous animal and human clinical studies. The immune response induced by Ad5 vaccines can be mitigated due to pre-existing Ad5 immunity. We previously reported the use of a novel Ad5 platform to induce cellular immune responses (CMI) against HIV-1 Gag in Ad5 hyper immune mice. Here, the effectiveness of the Ad5 [E1-, E2b-] vaccine platform was evaluated using a triad mixture of HIV-1 Gag, Pol, and Nef as antigenic transgenes. Broad CMI was induced following vaccination with the HIV-1 expressing vectors in Ad5 naïve and Ad5 immunized mice. A mixture of the three vaccines induced CMI against each transgene product even in the presence of hyper Ad5 immunity. These studies revealed that CMI responses to immunization with Ad5 [E1-, E2b-]-gag, Ad5 [E1-, E2b-]-pol or Ad5 [E1-, E2b-]-nef vectors were transgene specific and did not induce CMI responses against irrelevant antigens such as carcinoembryonic antigen (CEA), herpes simplex virus glycoprotein B (HSV), cytomegalovirus (CMV) or influenza virus antigens. We are evaluating this recombinant triad viral vector as an HIV-1 vaccine in a non-human primate model and the data indicate that the vaccine is worthy of clinical evaluation.

Adenovirus vector-induced immune responses in nonhuman primates: responses to prime boost regimens

In the phase IIb STEP trial an HIV-1 vaccine based on adenovirus (Ad) vectors of the human serotype 5 (AdHu5) not only failed to induce protection but also increased susceptibility to HIV-1 infection in individuals with preexisting neutralizing Abs against AdHu5. The mechanisms underlying the increased HIV-1 acquisition rates have not yet been elucidated. Furthermore, it remains unclear if the lack of the vaccine's efficacy reflects a failure of the concept of T cell-mediated protection against HIV-1 or a product failure of the vaccine. Here, we compared two vaccine regimens based on sequential use of AdHu5 vectors or two different chimpanzee-derived Ad vectors in rhesus macaques that were AdHu5 seropositive or seronegative at the onset of vaccination. Our results show that heterologous booster immunizations with the chimpanzee-derived Ad vectors induced higher T and B cell responses than did repeated immunizations with the AdHu5 vector, especially in AdHu5-preexposed macaques.

Long-term vaccine protection from AIDS and clearance of viral DNA following SHIV89.6P challenge

In an earlier study, our group vaccinated rhesus macaques with vesicular stomatitis virus (VSV) vectors expressing Gag, Pol, and Env proteins from a hybrid simian/human immunodeficiency virus (SHIV). This was followed by a single boost with modified vaccinia virus Ankara (MVA) vectors expressing the same proteins. Following challenge with SHIV89.6P, vaccinated animals cleared challenge virus RNA from the blood by day 150 and maintained normal CD4 T cell counts for 8 months. Here we report on the long-term (>5-year post-challenge) status of these animals and the immunological correlates of long-term protection. Using real-time PCR, we found that viral DNA in peripheral blood mononuclear cells (PBMCs) of the vaccinees declined continuously and fell to below detection (<5copies/10(5)cells) by approximately 3 years post-challenge. SHIV DNA was also below the limit of detection in the lymph nodes of two of the four animals at 5 years post-challenge. We detected long-term persistence of multi-functional Gag-specific CD8(+) T cells in both PBMCs and lymph nodes of the two protected animals with the Mamu A01(+) MHC I allele. All animals also maintained SHIV89.6P neutralizing antibody titers for 5 years. Our results show that this vaccine approach generates solid, long-term control of SHIV infection, and suggest that it is mediated by both cytotoxic T lymphocytes and neutralizing antibody.

A preliminary and comparative evaluation of a novel Ad5 [E1-, E2b-] recombinant-based vaccine used to induce cell mediated immune responses

Adenovirus vectors have been shown to be highly effective as vaccine platforms capable of inducing both humoral and cell mediated immune (CMI) responses. An Ad serotype 5 vector containing unique deletions in the E2b region (Ad5 [E1-, E2b-]) has been reported to have several advantages over conventional Adenovirus serotype 5 (Ad5) vectors deleted in only the E1 region (Ad5 [E1-]), including increased carrying capacity and diminished viral late gene expression. Here, we evaluated a novel Ad5 [E1-, E2b-] vector utilizing the E.C7 cell line for viral packaging. Its' effectiveness as a potential vaccine platform as compared to the currently utilized Ad5 [E1-]-based platform was assessed in both Ad5 naïve and Ad5 immune mice. We employed the HIV-1 Gag gene as the antigenic transgene expressed by the novel vector. Cellular expression of the Gag was confirmed by Western Blot analysis. Dose response studies using three intradermal immunizations of 10(7) to 10(10) virus particles (VP) of each construct revealed that immunization with 10(10)VP resulted in the maximum immunological response. Multiple immunizations of Ad naïve BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in higher ELISpot CMI responses as compared to mice immunized with an Ad5 [E1-]-gag vaccine. More importantly, multiple immunizations of Ad5 immune BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in significant increases in ELISpot CMI responses when compared to Ad5 immune mice vaccinated with an Ad5 [E1-]-gag vector. Preliminary studies in three Ad5 immune non-human primates (NHP) demonstrated that vaccination with Ad5 [E1-, E2b-]-gag-induced elevated levels of interferon-gamma and IL-2 secreting lymphocytes as assessed by ELISpot assays. These studies indicate that the novel Ad5 [E1-, E2b-] viral vector can be utilized as a potential vaccine platform to induce elevated CMI responses as compared to current generation Ad5 [E1-] viral vectors even in the presence of pre-existing Ad5 immunity.

The safety and tolerability of an HIV-1 DNA prime-protein boost vaccine (DP6-001) in healthy adult volunteers

This report describes the safety observations following administration of a polyvalent DNA prime-protein boost HIV-1 vaccine formulated with adjuvant QS21. Local injection site reactions were the most common (65% of subjects), and included type IV delayed-type hypersensitivity (DTH) reactions at prior DNA inoculation sites in 12 of 28 (43%) subjects following protein vaccination. Systemic reactions revealed two cases of vasculitis temporally related to inoculation with recombinant Env protein+QS21 adjuvant. Questions remain regarding the cause of the vasculitis, but the unique DTH observation may have contributed to the high level of immune responses previously reported for this vaccine.

DNA-MVA vaccine protection after X4 SHIV challenge in macaques correlates with day-of-challenge antiviral CD4+ cell-mediated immunity levels and postchallenge preservation of CD4+ T cell memory

The ability of vaccines to induce immunity both in mucosal and systemic compartments may be required for prevention of HIV infection and AIDS. We compared DNA-MVA vaccination regimens adjuvanted by IL-12 DNA, administered intramuscularly and nasally or only nasally. Most of the vaccinated Rhesus macaques developed mucosal and systemic humoral and cell-mediated SHIV-specific immune responses. Stimulation of mucosal anti-Env IgA responses was limited. After rectal challenge with SHIV 89.6P, all vaccinated and naive animals became infected. However, most of the vaccinated animals showed significant control of viremia and protection from CD4(+) T cell loss and AIDS progression compared to the control animals. The levels of CD4(+) and CD8(+) T cell virus-specific responses measured on the day of challenge correlated with the level of viremia control observed later during the chronic infection. Postchallenge viremia levels inversely correlated with the preservation of SHIV-specific CD4(+)/IL-2(+) and CD8(+)/TNF-alpha(+) T cells but not with CD4(+)/IFN-gamma(+) T cells measured over time after challenge. We also found that during the early chronic infection SHIV vaccination permitted a more significant preservation of both naive and memory CD4(+) T cells compared to controls. In addition, we observed a more significant and prolonged preservation of memory CD4(+) T cells after SHIV vaccination and challenge than that observed after SIV vaccination and challenge. As the antiviral immunity stimulated by vaccination is present in the memory CD4(+) T cell subpopulations, its more limited targeting by SHIV compared to SIV may explain the better control of X4 tropic SHIV than R5 tropic SIVs by vaccination.

HIV/AIDS vaccines: 2007

Development of an HIV/AIDS vaccine has been slow because classical approaches to vaccine development have not yielded a vaccine. Encouragingly, new approaches using recombinant viral vectors, DNA vaccines, and combinations of different vectors in heterologous prime/boost regimens are yielding vaccines capable of controlling virulent immunodeficiency virus challenges in non-human primate models. These new vaccines elicit T cells capable of recognizing and killing virus-infected cells. Brief synopses are given for six vaccines currently advancing in human trials.

Induction of HIV-specific functional immune responses by a multiclade HIV-1 DNA vaccine candidate in healthy Ugandans

A phase I randomized, double blind, placebo-controlled trial to assess the immunogenicity of a multiclade HIV-1 DNA plasmid vaccine was conducted in 31 HIV-1-negative Ugandans. Following immunization with DNA at 0, 1, and 2 months, the frequency of HIV-specific immune responses was assessed up to 10 months using a standard chromium release assay (CRA), lymphoproliferative assay (LPA), and antibody dependent cell-mediated cytotoxicity assay (ADCC). Seven of 15 (47%) vaccinees demonstrated CTL activity using the CRA to HIV-1 Env B with responses observed 1 month following the second vaccination and as late as 7 months following complete immunization. Additionally, lymphoproliferative reponses were observed in 14/15 vaccinees against p24. No CTL or LPA responses were observed at baseline or in the placebo group. ADCC activity was minimally induced by DNA vaccination. This study demonstrates that immunization with DNA alone induces CTL and lymphoproliferative responses in a population that will participate in a phase IIb study evaluating HIV-1 DNA priming followed by boosting with a replication-defective recombinant adenovirus vector.

Use of viral vectors for the development of vaccines

The exceptional discoveries of antigen/gene delivery systems have allowed the development of novel prophylactic and therapeutic vaccine candidates. This review highlights various antigen-delivery systems, particularly viral vectors, and assesses the underlying technologies in light of their use against AIDS and malaria. Although such recombinant vectors may face extensive preclinical testing and will possibly have to meet stringent regulatory requirements, some of these vectors may benefit from the profound industrial and clinical experience of the parent vaccine. Most notably, novel vaccines based on live, recombinant vectors may combine the induction of broad, strong and persistent immune responses with acceptable safety profiles.

Vaccine adjuvants revisited

The development of new adjuvants for human vaccines has become an expanding field of research in the last thirty years, for generating stronger vaccines capable of inducing protective and long-lasting immunity in humans. Instead of such efforts, with several adjuvant strategies approaching to requirements for their clinical application, limitations like adjuvant toxicity remain to be fully surpassed. Here we summarize the current status of adjuvant development, including regulatory recommendations, adjuvant requirements, and adjuvant categories like mineral salts, tensoactive compounds, microorganism-derived adjuvants, emulsions, cytokines, polysaccharides, nucleic acid-based adjuvants, and a section dedicated to particulate antigen delivery systems. The mechanisms of adjuvanticity are also discussed in the light of recent findings on Toll-like receptors' biology and their involvement on immune activation.

Immunological analysis of a Lactococcus lactis-based DNA vaccine expressing HIV gp120

For reasons of efficiency Escherichia coli is used today as the microbial factory for production of plasmid DNA vaccines. To avoid hazardous antibiotic resistance genes and endotoxins from plasmid systems used nowadays, we have developed a system based on the food-grade Lactococcus lactis and a plasmid without antibiotic resistance genes. We compared the L. lactis system to a traditional one in E. coli using identical vaccine constructs encoding the gp120 of HIV-1. Transfection studies showed comparable gp120 expression levels using both vector systems. Intramuscular immunization of mice with L. lactis vectors developed comparable gp120 antibody titers as mice receiving E. coli vectors. In contrast, the induction of the cytolytic response was lower using the L. lactis vector. Inclusion of CpG motifs in the plasmids increased T-cell activation more when the E. coli rather than the L. lactis vector was used. This could be due to the different DNA content of the vector backbones. Interestingly, stimulation of splenocytes showed higher adjuvant effect of the L. lactis plasmid. The study suggests the developed L. lactis plasmid system as new alternative DNA vaccine system with improved safety features. The different immune inducing properties using similar gene expression units, but different vector backbones and production hosts give information of the adjuvant role of the silent plasmid backbone. The results also show that correlation between the in vitro adjuvanticity of plasmid DNA and its capacity to induce cellular and humoral immune responses in mice is not straight forward.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

Identification of a novel HIV type 1 CRF01_AE cytotoxic T lymphocyte (CTL) epitope restricted by an HLA-Cw0602 allele and a novel HLA-A0206/peptide restriction

This report describes specific T cell responses to HIV-1 CRF01_AE Env and A Gag peptides in 20 HIV-1 CRF01_AE-infected Thai individuals using an interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISpot) assay. Twenty-six potentially novel HLA class I-restricted CD8+ T cell epitopes were identified in 14/20 subjects. Fine mapping analysis using the chromium release cytotoxic T lymphocyte (CTL) assay revealed a novel HLA-Cw0602 restricted epitope of HIV-1 CRF01_AE Env (NAKTIIVHL) and a previously identified HIV-1 A Gag epitope (ATLEEMMTA) with a novel HLA-A0206 restriction.

Long-lasting decrease in viremia in macaques chronically infected with simian immunodeficiency virus SIVmac251 after therapeutic DNA immunization

Rhesus macaques chronically infected with highly pathogenic simian immunodeficiency virus (SIV) SIVmac251 were treated with antiretroviral drugs and vaccinated with combinations of DNA vectors expressing SIV antigens. Vaccination during therapy increased cellular immune responses. After the animals were released from therapy, the virus levels of 12 immunized animals were significantly lower (P = 0.001) compared to those of 11 animals treated with only antiretroviral drugs. Vaccinated animals showed a persistent increase in immune responses, thus indicating both a virological and an immunological benefit following DNA therapeutic vaccination. Several animals show a long-lasting decrease in viremia, suggesting that therapeutic vaccination may provide an additional benefit to antiretroviral therapy.

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.

pH-Responsive Poly(styrene-alt-maleic anhydride) Alkylamide Copolymers for Intracellular Drug Delivery

Many macromolecular therapeutics such as peptides, proteins, antisense oligodeoxynucleotides (ASODN), and short interfering RNA (siRNA) are active only in the cytoplasm or nucleus of targeted cells. Endocytosis is the primary route for cellular uptake of these molecules, which results in their accumulation in the endosomal-lysosomal trafficking pathway and loss of therapeutic activity. In this article, we describe the synthesis and pH-dependent membrane-destabilizing activity of a new "smart" polymer family that can be utilized to enhance the intracellular delivery of therapeutic macromolecules through the endosomal membrane barrier into the cytoplasm of targeted cells. These polymers are propylamine, butylamine, and pentylamine derivatives of poly(styrene-alt-maleic anhydride) (PSMA) copolymers. The PSMA-alkylamide derivatives are hydrophilic and membrane-inactive at physiological pH; however, they become hydrophobic and membrane-disruptive in response to endosomal pH values as measured by their hemolytic activity. Results show that the pH-dependent membrane-destabilizing activity of PSMA derivatives can be controlled by varying the length of the alkylamine group, the degree of modification of the copolymer, and the molecular weight of the PSMA copolymer backbone. Butylamine and pentylamine derivatives of PSMA copolymers exhibited more than 80% hemolysis at endosomal pH values, which suggests their potential as a platform of "smart" polymeric carriers for enhanced cytoplasmic delivery of a variety of therapeutic macromolecules.

Excellent safety and tolerability of the human immunodeficiency virus type 1 pGA2/JS2 plasmid DNA priming vector vaccine in HIV type 1 uninfected adults

A vaccine consisting of DNA priming followed by recombinant modified vaccinia Ankara (rMVA) boosting has achieved long-term control of a pathogenic challenge with a chimera of simian and human immunodeficiency viruses (SHIV-89.6P) in rhesus macaques. Based on these results, clade B HIV-1 DNA and rMVA immunogens have been developed for trials in humans. We conducted a first-time in humans phase I safety trial using the pGA2/JS2 (JS2) HIV-1 DNA priming vector expressing Gag, Pol, Env, Tat, Rev, and Vpu. Thirty HIV-uninfected adults were vaccinated with 0.3 or 3 mg of JS2 DNA, or a saline placebo, by intramuscular injection at months 0 and 2. Both doses of DNA were safe and well-tolerated with no differences between the control, 0.3 mg, or 3 mg groups (n = 6, 12, and 12, respectively) through 12 months of postvaccination follow- up. A chromium-release assay using fresh peripheral blood mononuclear cells (PBMCs) and a validated IFN-gamma ELISpot assay with frozen PBMCs failed to detect CD4(+) or CD8(+) HIV-1-specific T cell responses. HIV-specific neutralizing antibodies were also not detected. The vaccine is being further developed as a priming vector for a combined DNA plus rMVA prime/boost HIV vaccination regimen.

Dose-response studies for the elicitation of CD8 T cells by a DNA vaccine, used alone or as the prime for a modified vaccinia Ankara boost

Here, we conduct dose-response studies in mice for the elicitation of CD8 T cells by a DNA vaccine that expresses HIV Gag. For DNA doses ranging from 1 to 100 microg, the studies revealed greater than 10-fold increases in anti-Gag CD8 T cells following a DNA prime or a DNA prime and a constant modified vaccinia Ankara (MVA) boost. These results are in contrast to dose-response studies for MVA vectors expressing Gag, where only 2-3-fold increases in anti-Gag CD8 T cells were elicited by 100-fold increases in dose.

Studies on GM-CSF DNA as an adjuvant for neutralizing Ab elicited by a DNA/MVA immunodeficiency virus vaccine

Here, we use a vaccine consisting of DNA priming followed by MVA boosting in rhesus macaques to investigate the ability of GM-CSF DNA to serve as an adjuvant for the elicitation of neutralizing Ab against an HIV-1 Env. The trial used Gag, Pol, and Env sequences from SHIV-89.6 in the immunogens and a neutralization escape variant of SHIV-89.6, SHIV-89.6P, for challenge. Co-delivery of GM-CSF and vaccine DNAs enhanced the temporal appearance of neutralizing Ab and broadened the specificity of the neutralizing activity to include SHIV-89.6P. Two long-term SHIV-89.6 infections elicited neutralizing activity for SHIV-89.6 but not SHIV-89.6P. Studies on the avidity of the anti-Env antisera revealed that the GM-CSF-adjuvanted vaccine had elicited higher avidity Ab than the non-adjuvanted vaccine or the infection. The GM-CSF-adjuvanted group showed a trend towards better control of the challenge infection and had better control of re-emergent virus (P < 0.01) than the non-adjuvanted group.

Cellular immunotherapy for cytomegalovirus and HIV-1 infection

Current antiviral drugs do not fully reconstitute the specific antiviral immune control in chronically human immunodeficiency virus (HIV)-1-infected patients or in cytomegalovirus (CMV)-infected patients after hematopoietic stem cell transplantation. Therefore, immunotherapy in which the patient's immune system is manipulated to enhance antiviral immune responses has become a promising area of viral immunology research. In this review, an overview is provided on the cellular immunotherapy strategies that have been developed for HIV infection and CMV reactivation in immunocompromised patients. As an introduction, the mechanisms behind the cellular immune system and their importance for the development of a workable immunotherapy approach are discussed. Next, the focus is shifted to the immunopathogenesis of CMV and HIV-1 infections to correlate these findings with the concepts and ideas behind the viral-specific immunotherapies discussed. Current and future perspectives of active and passive cellular immunotherapy for the treatment of CMV and HIV-1 infections are reviewed. Finally, pitfalls and key issues with regard to the development of immunotherapy protocols that can be applied in a clinical setting are addressed.

Vaccination of mice with replication-defective human immunodeficiency virus induces cellular and humoral immunity and protects against vaccinia virus-gag challenge

Here we describe as a potential vaccine candidate a replication-defective HIV that encodes multiple viral genes in addition to a cassette that includes both truncated cyclin T1 and an autofluorescent protein. After confirming functionality of the cyclin T1, we immunized mice intramuscularly once or twice with the replication-defective HIV vector pseudotyped with vesicular stomatitis virus (VSV) G protein (RD HIV), a plasmid encoding CMV-driven gag (gag DNA), or adenovirus gag (Ad5-gag). Capsid-specific antibody titers following RD HIV immunization were >10(6)/ml and approximately equivalent to those induced by gag DNA and Ad5-gag. Antibodies against the autofluorescent protein and VSV G were also detected. After RD HIV immunization ELISpot assays demonstrated Gag-specific interferon-gamma (IFN-gamma) SFU equivalent to that of Ad5-gag and fourfold greater than that of gag DNA. HIV polymerase-specific IFN-gamma SFU values were similar, and boosting increased both antibody titers and the IFN-gamma response. Challenge using vaccinia virus (VV)-gag demonstrated significantly lower recoverable VV for RD HIV-immunized mice compared to controls. No significant differences were observed in vaccinated mice challenged with wild-type VV. This study demonstrates the efficacy of RD HIV in conferring HIV-specific immunity and protection in mice and suggests its potential use in humans as either a prophylactic or a therapeutic vaccine.

HIV-1 Envgp140 trimers elicit neutralizing antibodies without efficient induction of conformational antibodies

Currently, no vaccine for human immunodeficiency virus (HIV-1) provides protection from virus infection. One reason for these disappointing results has been the difficulty of current vaccine candidates to elicit high-titer, broadly reactive immunity to a large number of viral proteins. Recently, our laboratory demonstrated that the coupling of C3d to a soluble trimerized HIV-1 envelope (Env(gp140(FT))) elicited higher titers of neutralizing antibodies than monomers of Env(gp120) coupled to C3d [Bower JF, Yang X, Sodroski J, Ross TM. Elicitation of neutralizing antibodies with DNA vaccines expressing soluble stabilized human immunodeficiency virus type 1 envelope glycoprotein trimers conjugated to C3d. J Virol 2004;78(9):4710-9]. To determine if the induction of conformational antibodies correlated with neutralization, mice (BALB/c) were primed (2x) with DNA plasmids expressing monomeric Env(gp120) or trimeric Env(gp140) alone or fused to mC3d(3) at one of two doses (2.0microg or 0.2microg), followed by a boost of recombinant uncleaved, trimeric Env(gp140). Regardless of the priming dose of DNA, all mice had high-titer anti-Env IgG antibodies. Interestingly, Env(gp140) trimers did not elicit higher titers of antibodies that recognized conformational Env epitopes compared to monomers of Env(gp120). Therefore, additional parameters were examined for correlation with neutralization. For neutralization-resistant HIV-1 isolates, ADA and YU-2, neutralization correlated with high-titer, high avidity antibodies, with Env(gp140) eliciting slightly higher neutralization titers than Env(gp120). In contrast, none of the measured parameters correlated with neutralization for the more neutralization-sensitive isolates, MN or 89.6. Therefore, even though soluble, uncleaved Env(gp140) trimers may be marginally more effective at eliciting neutralizing antibodies than Env(gp120), neutralization does not appear to correlate with the elicitation of conformationally dependent antibodies.

Heat shock proteins in immunity

This chapter focuses on immunological effects of eukaryotic and microbial heat shock proteins (HSPs), with molecular weights of about 60, 70, and 90 kDa. The search for tumor-specific antigens resulted in the identification of HSPs. They have been found to elicit a potent anti-cancer immune response mediated by the adoptive and innate immune system. Following receptor-mediated uptake of HSP (HSP70 and gp96) peptide complexes by antigen-presenting cells and representation of HSP-chaperoned peptides by MHC class I molecules, a CD8-specific T cell response is induced. Apart from chaperoning immunogenic peptides derived from tumors, bacterial and virally infected cells, they by themselves provide activatory signals for antigen-presenting cells and natural killer (NK) cells. After binding of peptide-free HSP70 to Toll-like receptors, the secretion of pro-inflammatory cytokines is initiated by antigen-presenting cells and thus results in a nonspecific stimulation of the immune system. Moreover, soluble as well as cell membrane-bound HSP70 on tumor cells can directly activate the cytolytic and migratory capacity of NK cells. Apart form cancer, HSPs of different origins, with a molecular weight of about 60, 70, and 90 kDa, also play a pivotal role in viral infections, including human and simian immunodeficiency virus (HIV, SIV), measles, and choriomeningitis. Moreover, HSPs have been found to induce tolerance against autoimmune diseases. In summary, depending on their mode of induction, intracellular/extracellular location, cellular origin (eukaryote/prokaryote), peptide loading status, intracellular ADP/ATP content, concentration, and route of application, HSPs either exert immune activation as danger signals in cancer immunity and mediate protection against infectious diseases or exhibit regulatory activities in controlling and preventing autoimmunity.

Reduction of viral loads by multigenic DNA priming and adenovirus boosting in the SIVmac-macaque model

In this study, we investigated the ability of a multigenic SIV DNA prime/replication-defective adenovirus serotype 5 (rAd/SIV) boost regimen to induce SIV-specific immune responses and protection against intrarectal challenge with SIVmac251 in rhesus macaques. Four rhesus macaques were immunized intramuscularly three times at 8-week intervals with SIV DNA vaccine and boosted once with rAd/SIV vaccine Four control macaques received the same amount of mock plasmid DNA and mock adenovirus vector. While the SIV DNA vaccine included plasmids expressing a mutated human IL-12 gene (IL-12N222L) as well as SIVmac239 structural and regulatory genes, the rAd/SIV vaccine contained rAd vectors expressing SIVmac239 genes only. Immunization with SIV DNA vaccine alone induced SIV-specific IFN-gamma ELISPOT responses in only two of four vaccinated macaques, whereas all animals developed SIV-specific T-cell responses and Env- and Tat-specific antibody responses following the rAd/SIV vaccine boost. Upon intrarectal challenge with pathogenic SIVmac251, strong anamnestic Env-specific binding and neutralizing antibody responses were detected in the vaccinated macaques. Overall, the immunized macaques had lower peak and set-point viral loads than control macaques, suggesting that the induced immune responses play a role in the control of viremia. In addition, the loss of CD4+ T cells was delayed in the vaccinated macaques after challenge. These results indicate that the multigenic DNA prime-adenovirus boost immunization may be a promising approach in developing an effective AIDS vaccine.

Evaluating the immunogenicity of a disulfide-stabilized, cleaved, trimeric form of the envelope glycoprotein complex of human immunodeficiency virus type 1

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) complex comprises three gp120 exterior glycoproteins each noncovalently linked to a gp41 transmembrane glycoprotein. Monomeric gp120 proteins can elicit antibodies capable of neutralizing atypically sensitive test viruses in vitro, but these antibodies are ineffective against representative primary isolates and the gp120 vaccines failed to provide protection against HIV-1 transmission in vivo. Alternative approaches to raising neutralizing antibodies are therefore being pursued. Here we report on the antibody responses generated in rabbits against a soluble, cleaved, trimeric form of HIV-1(JR-FL) Env. In this construct, the gp120 and gp41 moieties are covalently linked by an intermolecular disulfide bond (SOS gp140), and an I559P substitution has been added to stabilize gp41-gp41 interactions (SOSIP gp140). We investigated the value of DNA priming and compared the use of membrane-bound and soluble priming antigens and of repeat boosting with soluble and particulate protein antigen. Compared to monomeric gp120, SOSIP gp140 trimers elicited approximately threefold lower titers of anti-gp120 antibodies. Priming with DNA encoding a membrane-bound form of the SOS gp140 protein, followed by several immunizations with soluble SOSIP gp140 trimers, resulted in antibodies capable of neutralizing sensitive strains at high titers. A subset of these sera also neutralized, at lower titers, HIV-1(JR-FL) and some other primary isolates in pseudovirus and/or whole-virus assays. Neutralization of these viruses was immunoglobulin mediated and was predominantly caused by antibodies to gp120 epitopes, but not the V3 region.

T cell vaccines for microbial infections

Vaccination, or the deliberate induction of protective immunity by administering nonpathogenic forms of a microbe or its antigens to induce a memory immune response, is the world's most cost-effective medical procedure for preventing morbidity and mortality caused by infectious disease. Historically, most vaccines have worked by eliciting long-lived plasma cells. These cells produce antibodies that limit disease by neutralizing a toxin or blocking the spread of the infectious agent. For these 'B cell vaccines,' the immunological marker, or correlate, for protection is the titer of protective antibodies. With the discovery of HIV/AIDS, vaccine development has been confronted by an agent that is not easily blocked by antibody. To overcome this, researchers who are developing HIV/AIDS vaccines have turned to the elicitation of cellular immunity, or 'T cell vaccines,' which recognize and kill infected cells.

DNA vaccines expressing different forms of simian immunodeficiency virus antigens decrease viremia upon SIVmac251 challenge

We have tested the efficacy of DNA immunization as a single vaccination modality for rhesus macaques followed by highly pathogenic SIVmac251 challenge. To further improve immunogenicity of the native proteins, we generated expression vectors producing fusion of the proteins Gag and Env to the secreted chemokine MCP3, targeting the viral proteins to the secretory pathway and to a beta-catenin (CATE) peptide, targeting the viral proteins to the intracellular degradation pathway. Macaques immunized with vectors expressing the MCP3-tagged fusion proteins developed stronger antibody responses. Following mucosal challenge with pathogenic SIVmac251, the vaccinated animals showed a statistically significant decrease in viral load (P = 0.010). Interestingly, macaques immunized with a combination of vectors expressing three forms of antigens (native protein and MCP3 and CATE fusion proteins) showed the strongest decrease in viral load (P = 0.0059). Postchallenge enzyme-linked immunospot values for Gag and Env as well as gag-specific T-helper responses correlated with control of viremia. Our data show that the combinations of DNA vaccines producing native and modified forms of antigens elicit more balanced immune responses able to significantly reduce viremia for a long period (8 months) following pathogenic challenge with SIVmac251.

Studies on the cross-clade and cross-species conservation of HIV-1 Gag-specific CD8 and CD4 T cell responses elicited by a clade B DNA/MVA vaccine in macaques

Here, we evaluate the T cell responses raised by our HIV-1 clade B DNA/MVA vaccine for recognition of a HIV-1 circulating recombinant form (CRF) AG Gag sequence (CRF-02). The cross-clade activity for the AG sequence was better conserved for CD8 than CD4 T cells. CD8 T cells exhibited 75% conservation for height and 83% conservation for breadth, whereas CD4 responses exhibited 45% conservation for height and 50% conservation for breadth. Five CD8 epitopes and 8 CD4 epitopes were mapped. Three of the 5 CD8 epitopes and 2 of the 8 CD4 epitopes were conserved across multiple HIV-1 clades. Impressively, all of the CD8 epitopes and half of the CD4 epitopes have been reported for human infections. Our results demonstrate that the clade B DNA/MVA HIV vaccine elicits T cell responses against epitopes that are conserved in multiple clades and recognized by humans and macaques.

Signature for long-term vaccine-mediated control of a Simian and human immunodeficiency virus 89.6P challenge: stable low-breadth and low-frequency T-cell response capable of coproducing gamma interferon and interleukin-2

In 2001, we reported 20 weeks of control of challenge with the virulent 89.6P chimera of simian and human immunodeficiency viruses (SHIV-89.6P) by a Gag-Pol-Env vaccine consisting of DNA priming and modified vaccinia virus Ankara boosting. Here we report that 22 out of 23 of these animals successfully controlled their viremia until their time of euthanasia at 200 weeks postchallenge. At euthanasia, all animals had low to undetectable viral loads and normal CD4 counts. During the long period of viral control, gamma interferon (IFN-gamma)-producing antiviral T cells were present at unexpectedly low breadths and frequencies. Most animals recognized two CD8 and one CD4 epitope and had frequencies of IFN-gamma-responding T cells from 0.01 to 0.3% of total CD8 or CD4 T cells. T-cell responses were remarkably stable over time and, unlike responses in most immunodeficiency virus infections, maintained good functional characteristics, as evidenced by coproduction of IFN-gamma and interleukin-2. Overall, high titers of binding and neutralizing antibody persisted throughout the postchallenge period. Encouragingly, long-term control was effective in macaques of diverse histocompatibility types.

Vaccination of rhesus macaques with recombinant Mycobacterium bovis bacillus Calmette-Guérin Env V3 elicits neutralizing antibody-mediated protection against simian-human immunodeficiency virus with a homologous but not a heterologous V3 motif

Although the correlates of vaccine-induced protection against human immunodeficiency virus type 1 (HIV-1) are not fully known, it is presumed that neutralizing antibodies (NAb) play a role in controlling virus infection. In this study, we examined immune responses elicited in rhesus macaques following vaccination with recombinant Mycobacterium bovis bacillus Calmette-Guérin expressing an HIV-1 Env V3 antigen (rBCG Env V3). We also determined the effect of vaccination on protection against challenge with either a simian-human immunodeficiency virus (SHIV-MN) or a highly pathogenic SHIV strain (SHIV-89.6PD). Immunization with rBCG Env V3 elicited significant levels of NAb for the 24 weeks tested that were predominantly HIV-1 type specific. Sera from the immunized macaques neutralized primary HIV-1 isolates in vitro, including HIV-1BZ167/X4, HIV-1SF2/X4, HIV-1CI2/X4, and, to a lesser extent, HIV-1MNp/X4, all of which contain a V3 sequence homologous to that of rBCG Env V3. In contrast, neutralization was not observed against HIV-1SF33/X4, which has a heterologous V3 sequence, nor was it found against primary HIV-1 R5 isolates from either clade A or B. Furthermore, the viral load in the vaccinated macaques was significantly reduced following low-dose challenge with SHIV-MN, and early plasma viremia was markedly decreased after high-dose SHIV-MN challenge. In contrast, replication of pathogenic SHIV-89.6PD was not affected by vaccination in any of the macaques. Thus, we have shown that immunization with an rBCG Env V3 vaccine elicits a strong, type-specific V3 NAb response in rhesus macaques. While this response was not sufficient to provide protection against a pathogenic SHIV challenge, it was able to significantly reduce the viral load in macaques following challenge with a nonpathogenic SHIV. These observations suggest that rBCG vectors have the potential to deliver an appropriate virus immunogen for desirable immune elicitations.

Studies in macaques on cross-clade T cell responses elicited by a DNA/MVA AIDS vaccine, better conservation of CD8 than CD4 T cell responses

One of the unknowns faced by an HIV/AIDS vaccine is the ability of a single clade vaccine to protect against the multiple genetic subtypes and recombinant forms of HIV-1 present in the current pandemic. Here, we use a macaque model to investigate the ability of our clade B vaccine that consists of DNA priming and modified vaccinia Ankara (MVA) virus boosting to elicit T cell responses that recognize an A/G recombinant of HIV-1. To test for cross-reactive T cells, intracellular cytokine staining was conducted using five pools of Gag and six pools of Env peptides representing B or A/G sequences. Studies using the peptide pools revealed essentially complete conservation of the CD8 response but only approximately 50% conservation of the CD4 response. Thus, the ability of an HIV vaccine for one clade to protect against other clades may be more limited by the ability to provide CD4 T cell help than the ability to elicit CD8 effector functions.

A call for replicating vector prime-protein boost strategies in HIV vaccine design

A key challenge to HIV vaccine development is the integration of HIV proviral DNA into the host genome upon infection. Therefore, an optimal vaccine should block infection within hours of viral exposure, providing 'sterilizing immunity' at mucosal sites and in blood via potent, broadly reactive antibody to the HIV envelope glycoprotein. This is difficult due to the envelope's conformational complexity and sequence diversity. Antibodies that do not completely prevent infection nevertheless could reduce the viral infectious burden, allowing strong cellular immunity to control viremia, delay disease progression and prevent viral transmission, while also providing help for T- and B-cell responses. Rapidly responsive, potent, persistent immunity might best be achieved using prime-boost strategies incorporating a replicating vector and an optimally designed envelope subunit.

Directed Antigen Presentation Using Polymeric Microparticulate Carriers Degradable at Lysosomal pH for Controlled Immune Responses

The types of the immune responses generated against an antigen are determined by the intracellular fate of the antigen. Endogenous antigens are processed in the cytoplasm and initiate cytotoxic T lymphocyte (CTL) activation. In contrast, exogenous antigens are degraded in the lysosome (or phagolysosome) of antigen presenting cells (APCs), and induce antibody-mediated immune responses and assist CTL activation. Therefore, maximizing a desired response by controlling delivery pathways is indispensable in vaccine development and immunotherapy. New cleavable microparticles have been prepared for use as protein-based vaccine carriers by polymerizing water soluble monomers including a newly developed aliphatic monomer with a pendant primary amine group and a cleavable acetal linkage with a wholly aliphatic cleavable acetal cross-linker. Incorporation of the cleavable amine monomer in the polymerization mixture increased the encapsulation efficiency of a model antigen, ovalbumin. Ex vivo assays showed that the composition of the particles greatly affected the magnitude and the pathway of antigen presentations, which determine the type of immune responses. The degradable particles synthesized with the new cross-linker enhanced MHC I antigen presentation 2-3-fold over nondegradable particles. It was also found that, by adding 10% cationic cleavable monomers to the microparticles, MHC I restricted antigen presentation was enhanced ca. 75 times over that achieved with nondegradable particles. The microparticles introduced in this study can be further used for targeting and gene delivery due to functionalizable and cleavable cationic monomers in addition to degradability.

Results of an ELISPOT proficiency panel conducted in 11 laboratories participating in international human immunodeficiency virus type 1 vaccine trials

We used an external quality assurance (EQA) panel to assess laboratory competency and comparability when performing ELISPOT assays in support of human immunodeficiency virus type 1 (HIV-1) vaccine trials. Cell recovery, viability, and frequency of interferon-gamma (IFN-gamma)-secreting cells after antigen stimulation were obtained from 11 laboratories on a coded panel of 11 peripheral blood mononuclear cell samples. The median recovery and viability before plating for all samples were 35% and 86%, respectively, with notable interlaboratory and intrasample variability. Empirical as well as statistical analysis methods were used to define positive ELISPOT responses. Remarkable concordance between laboratories was obtained in defining a qualitative assessment of responder/nonresponder status to antigens, but the frequency of responding cells varied among the laboratories. This study highlights the need for better standardization of protocols and reagents to obtain reliable and reproducible data that may support immunogenicity studies, vaccine regulatory submissions, and licensure.