A phase I trial in HIV negative healthy volunteers evaluating the effect of potent adjuvants on immunogenicity of a recombinant gp120W61D derived from dual tropic R5X4 HIV-1ACH320

Recombinant Herpesvirus Vectors: Durable Immune Responses and Durable Protection against Simian Immunodeficiency Virus SIVmac239 Acquisition

A prophylactic vaccine that confers durable protection against human immunodeficiency virus (HIV) would provide a valuable tool to prevent new HIV/AIDS cases. As herpesviruses establish lifelong infections that remain largely subclinical, the use of persistent herpesvirus vectors to deliver HIV antigens may facilitate the induction of long-term anti-HIV immunity. We previously developed recombinant (r) forms of the gamma-herpesvirus rhesus monkey rhadinovirus (rRRV) expressing a replication-incompetent, near-full-length simian immunodeficiency virus (SIVnfl) genome. We recently showed that 8/16 rhesus macaques (RMs) vaccinated with a rDNA/rRRV-SIVnfl regimen were significantly protected against intrarectal (i.r.) challenge with SIVmac239. Here we investigated the longevity of this vaccine-mediated protection. Despite receiving no additional booster immunizations, the protected rDNA/rRRV-SIVnfl vaccinees maintained detectable cellular and humoral anti-SIV immune responses for more than 1.5 years after the rRRV boost. To assess if these responses were still protective, the rDNA/rRRV-SIVnfl vaccinees were subjected to a second round of marginal-dose i.r. SIVmac239 challenges, with eight SIV-naive RMs serving as concurrent controls. After three SIV exposures, 8/8 control animals became infected, compared to 3/8 vaccinees. This difference in SIV acquisition was statistically significant (P = 0.0035). The three vaccinated monkeys that became infected exhibited significantly lower viral loads than those in unvaccinated controls. Collectively, these data illustrate the ability of rDNA/rRRV-SIVnfl vaccination to provide long-term immunity against stringent mucosal challenges with SIVmac239. Future work is needed to identify the critical components of this vaccine-mediated protection and the extent to which it can tolerate sequence mismatches in the challenge virus. IMPORTANCE We report on the long-term follow-up of a group of rhesus macaques (RMs) that received an AIDS vaccine regimen and were subsequently protected against rectal acquisition of simian immunodeficiency virus (SIV) infection. The vaccination regimen employed included a live recombinant herpesvirus vector that establishes persistent infection in RMs. Consistent with the recurrent SIV antigen expression afforded by this herpesvirus vector, vaccinees maintained detectable SIV-specific immune responses for more than 1.5 years after the last vaccination. Importantly, these vaccinated RMs were significantly protected against a second round of rectal SIV exposures performed 1 year after the first SIV challenge phase. These results are relevant for HIV vaccine development because they show the potential of herpesvirus-based vectors to maintain functional antiretroviral immunity without the need for repeated boosting.

Characterization and Implementation of a Diverse Simian Immunodeficiency Virus SIVsm Envelope Panel in the Assessment of Neutralizing Antibody Breadth Elicited in Rhesus Macaques by Multimodal Vaccines Expressing the SIVmac239 Envelope

Antibodies that can neutralize diverse viral strains are likely to be an important component of a protective human immunodeficiency virus type 1 (HIV-1) vaccine. To this end, preclinical simian immunodeficiency virus (SIV)-based nonhuman primate immunization regimens have been designed to evaluate and enhance antibody-mediated protection. However, these trials often rely on a limited selection of SIV strains with extreme neutralization phenotypes to assess vaccine-elicited antibody activity. To mirror the viral panels used to assess HIV-1 antibody breadth, we created and characterized a novel panel of 14 genetically and phenotypically diverse SIVsm envelope (Env) glycoproteins. To assess the utility of this panel, we characterized the neutralizing activity elicited by four SIVmac239 envelope-expressing DNA/modified vaccinia virus Ankara vector- and protein-based vaccination regimens that included the immunomodulatory adjuvants granulocyte-macrophage colony-stimulating factor, Toll-like receptor (TLR) ligands, and CD40 ligand. The SIVsm Env panel exhibited a spectrum of neutralization sensitivity to SIV-infected plasma pools and monoclonal antibodies, allowing categorization into three tiers. Pooled sera from 91 rhesus macaques immunized in the four trials consistently neutralized only the highly sensitive tier 1a SIVsm Envs, regardless of the immunization regimen. The inability of vaccine-mediated antibodies to neutralize the moderately resistant tier 1b and tier 2 SIVsm Envs defined here suggests that those antibodies were directed toward epitopes that are not accessible on most SIVsm Envs. To achieve a broader and more effective neutralization profile in preclinical vaccine studies that is relevant to known features of HIV-1 neutralization, more emphasis should be placed on optimizing the Env immunogen, as the neutralization profile achieved by the addition of adjuvants does not appear to supersede the neutralizing antibody profile determined by the immunogen.

IMPORTANCE

Many in the HIV/AIDS vaccine field believe that the ability to elicit broadly neutralizing antibodies capable of blocking genetically diverse HIV-1 variants is a critical component of a protective vaccine. Various SIV-based nonhuman primate vaccine studies have investigated ways to improve antibody-mediated protection against a heterologous SIV challenge, including administering adjuvants that might stimulate a greater neutralization breadth. Using a novel SIV neutralization panel and samples from four rhesus macaque vaccine trials designed for cross comparison, we show that different regimens expressing the same SIV envelope immunogen consistently elicit antibodies that neutralize only the very sensitive tier 1a SIV variants. The results argue that the neutralizing antibody profile elicited by a vaccine is primarily determined by the envelope immunogen and is not substantially broadened by including adjuvants, resulting in the conclusion that the envelope immunogen itself should be the primary consideration in efforts to elicit antibodies with greater neutralization breadth.

Modulation of HIV-1 immunity by adjuvants

Purpose of review

To summarize the role of adjuvants in eliciting desirable antibody responses against HIV-1 with particular emphasis on both historical context and recent developments.

Recent findings

Increased understanding of the role of pattern recognition receptors such as Toll-like receptors in recruiting and directing the immune system has increased the variety of adjuvant formulations being tested in animal models and humans. Across all vaccine platforms, adjuvant formulations have been shown to enhance desirable immune responses such as higher antibody titers and increased functional activity. Although no vaccine formulation has yet succeeded in eliciting broad neutralizing antibodies against HIV-1, the ability of adjuvants to direct the immune response to immunogens suggests they will be critically important in any successful HIV-1 vaccine.

Summary

The parallel development of adjuvants along with better HIV-1 immunogens will be needed for a successful AIDS vaccine. Additional comparative testing will be required to determine the optimal adjuvant and immunogen regimen that can elicit antibody responses capable of blocking HIV-1 transmission.

Antibody persistence and T-cell balance: two key factors confronting HIV vaccine development

The quest for a prophylactic AIDS vaccine is ongoing, but it is now clear that the successful vaccine must elicit protective antibody responses. Accordingly, intense efforts are underway to identify immunogens that elicit these responses. Regardless of the mechanism of antibody-mediated protection, be it neutralization, Fc-mediated effector function, or both, antibody persistence and appropriate T-cell help are significant problems confronting the development of a successful AIDS vaccine. Here, we discuss the evidence illustrating the poor persistence of antibody responses to Env, the envelope glycoprotein of HIV-1, and the related problem of CD4(+) T-cell responses that compromise vaccine efficacy by creating excess cellular targets of HIV-1 infection. Finally, we propose solutions to both problems that are applicable to all Env-based AIDS vaccines regardless of the mechanism of antibody-mediated protection.

Heterologous protection elicited by candidate monomeric recombinant HIV-1 gp120 vaccine in the absence of cross neutralising antibodies in a macaque model

BACKGROUND

Current data suggest that an efficacious human immunodeficiency virus type 1 (HIV-1) vaccine should elicit both adaptive humoral and cell mediated immune responses. Such a vaccine will also need to protect against infection from a range of heterologous viral variants. Here we have developed a simian-human immunodeficiency virus (SHIV) based model in cynomolgus macaques to investigate the breadth of protection conferred by HIV-1W61D recombinant gp120 vaccination against SHIVsbg and SHIVSF33 challenge, and to identify correlates of protection.

RESULTS

High titres of anti-envelope antibodies were detected in all vaccinees. The antibodies reacted with both the homologous HIV-1W61D and heterologous HIV-1IIIB envelope rgp120 which has an identical sequence to the SHIVsbg challenge virus. Significant titres of virus neutralising antibodies were detected against SHIVW61D expressing an envelope homologous with the vaccine, but only limited cross neutralisation against SHIVsbg, SHIV-4 and SHIVSF33 was observed. Protection against SHIVsbg infection was observed in vaccinated animals but none was observed against SHIVSF33 challenge. Transfer of immune sera from vaccinated macaques to naive recipients did not confer protection against SHIVsbg challenge. In a follow-up study, T cell proliferative responses detected after immunisation with the same vaccine against a single peptide present in the second conserved region 2 of HIV-1 W61D and HIV-1 IIIB gp120, but not SF33 gp120.

CONCLUSIONS

Following extended vaccination with a HIV-1 rgp120 vaccine, protection was observed against heterologous virus challenge with SHIVsbg, but not SHIVSF33. Protection did not correlate with serological responses generated by vaccination, but might be associated with T cell proliferative responses against an epitope in the second constant region of HIV-1 gp120. Broader protection may be obtained with recombinant HIV-1 envelope based vaccines formulated with adjuvants that generate proliferative T cell responses in addition to broadly neutralising antibodies.

Towards tailored vaccine delivery: needs, challenges and perspectives

The ideal vaccine is a simple and stable formulation which can be conveniently administered and provides life-long immunity against a given pathogen. The development of such a vaccine, which should trigger broad and strong B-cell and T-cell responses against antigens of the pathogen in question, is highly dependent on tailored vaccine delivery approaches. This review addresses vaccine delivery in its broadest scope. We discuss the needs and challenges in the area of vaccine delivery, including restrictions posed by specific target populations, potentials of dedicated stable formulations and devices, and the use of adjuvants. Moreover, we address the current status and perspectives of vaccine delivery via several routes of administration, including non- or minimally invasive routes. Finally we suggest possible directions for future vaccine delivery research and development.

TLR, NLR Agonists, and Other Immune Modulators as Infectious Disease Vaccine Adjuvants

Vaccines based on attenuated or killed viruses and bacteria are highly effective in preventing infection with a range of pathogens, but can have safety issues. Therefore, a move is underway toward the development of subunit vaccines based on recombinant proteins or naked DNA. However, protein subunit vaccines are typically poorly immunogenic when administered alone and therefore require coadministration with adjuvants to boost the immune response. For many decades, very little progress was made in understanding the mechanism of action of adjuvants, but recently several significant breakthroughs have occurred in this area. The binding of pathogen-derived molecules to different immune sensors, including Toll-like receptors (TLR), nucleotide-binding oligomerization domain-like receptors (NLR), and retinoic acid-inducible gene (RIG)-1-like receptors (RLR), activates important innate immune pathways and provides not only an understanding of how current vaccines and adjuvants work, but also potential targets for novel adjuvant development.

Cationic lipid/DNA complex-adjuvanted influenza A virus vaccination induces robust cross-protective immunity

Influenza A virus is a negative-strand segmented RNA virus in which antigenically distinct viral subtypes are defined by the hemagglutinin (HA) and neuraminidase (NA) major viral surface proteins. An ideal inactivated vaccine for influenza A virus would induce not only highly robust strain-specific humoral and T-cell immune responses but also cross-protective immunity in which an immune response to antigens from a particular viral subtype (e.g., H3N2) would protect against other viral subtypes (e.g., H1N1). Cross-protective immunity would help limit outbreaks from newly emerging antigenically novel strains. Here, we show in mice that the addition of cationic lipid/noncoding DNA complexes (CLDC) as adjuvant to whole inactivated influenza A virus vaccine induces significantly more robust adaptive immune responses both in quantity and quality than aluminum hydroxide (alum), which is currently the most widely used adjuvant in clinical human vaccination. CLDC-adjuvanted vaccine induced higher total influenza virus-specific IgG, particularly for the IgG2a/c subclass. Higher levels of multicytokine-producing influenza virus-specific CD4 and CD8 T cells were induced by CLDC-adjuvanted vaccine than with alum-adjuvanted vaccine. Importantly, CLDC-adjuvanted vaccine provided significant cross-protection from either a sublethal or lethal influenza A viral challenge with a different subtype than that used for vaccination. This superior cross-protection afforded by the CLDC adjuvant required CD8 T-cell recognition of viral peptides presented by classical major histocompatibility complex class I proteins. Together, these results suggest that CLDC has particular promise for vaccine strategies in which T cells play an important role and may offer new opportunities for more effective control of human influenza epidemics and pandemics by inactivated influenza virus vaccine.

Optimized subunit vaccine protects against experimental leishmaniasis

Development of a protective subunit vaccine against Leishmania spp. depends on antigens and adjuvants that induce appropriate immune responses. We evaluated a second generation polyprotein antigen (Leish-110f) in different adjuvant formulations for immunogenicity and protective efficacy against Leishmania spp. challenges. Vaccine-induced protection was associated with antibody and T cell responses to Leish-110f. CD4 T cells were the source of IFN-gamma, TNF, and IL-2 double- and triple-positive populations. This study establishes the immunogenicity and protective efficacy of the improved Leish-110f subunit vaccine antigen adjuvanted with natural (MPL-SE) or synthetic (EM005) Toll-like receptor 4 agonists.

New horizons in adjuvants for vaccine development

Over the last decade, there has been a flurry of research on adjuvants for vaccines, and several novel adjuvants are now in licensed products or in late stage clinical development. The success of adjuvants in enhancing the immune response to recombinant antigens has led many researchers to re-focus their vaccine development programs. Successful vaccine development requires knowing which adjuvants to use and knowing how to formulate adjuvants and antigens to achieve stable, safe and immunogenic vaccines. For the majority of vaccine researchers this information is not readily available, nor is access to well-characterized adjuvants. In this review, we outline the current state of adjuvant research and development and how formulation parameters can influence the effectiveness of adjuvants.

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.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.

The challenges of eliciting neutralizing antibodies to HIV-1 and to influenza virus

The ability to elicit broadly neutralizing antibody responses against HIV-1 is a crucial goal for a prophylactic HIV-1 vaccine. Here, we discuss the difficulties of achieving broad HIV-1 neutralization in the context of both the effective annual human influenza virus vaccine and the need to develop a pandemic influenza vaccine. Immunogen-design strategies are underway to target functionally conserved regions of the HIV-1 envelope glycoproteins, and similar strategies might be applicable to pandemic influenza virus vaccine development. Efforts to develop broadly neutralizing vaccines against either HIV-1 or influenza virus might establish a paradigm for future vaccines against highly variable pathogens.

Bacterial ghosts as adjuvant particles

The development of more advanced and effective vaccines is of great interest in modern medicine. These new-generation vaccines, based on recombinant proteins or DNA, are often less reactogenic and immunogenic than traditional vaccines. Thus, there is an urgent need for the development of new and improved adjuvants. Besides many other immunostimulatory components, the bacterial ghost (BG) system is currently under investigation as a potent vaccine delivery system with intrinsic adjuvant properties. BGs are nonliving cell envelope preparations from Gram-negative cells, devoid of cytoplasmic contents, while their cellular morphology and native surface antigenic structures remain preserved. Owing to the particulate nature of BGs and the fact that they contain many well known immune-stimulating compounds, BGs have the potential to enhance immune responses against ghost-delivered target antigens.

Evaluation of immunogenicity and efficacy of combined DNA and adjuvanted protein vaccination in a human immunodeficiency virus type 1/murine leukemia virus pseudotype challenge model

A DNA plasmid encoding human immunodeficiency virus type 1 (HIV-1) env, nef and tat genes was used in mice in a prime-boost immunization regimen with the corresponding recombinant proteins. The genetic immunogen was delivered with a gene gun and the proteins were injected intramuscularly together with the adjuvant AS02A. Immunizations were followed by experimental challenge with pseudotyped HIV-1 subtype A or B virus. In an initial experiment in which animals were challenged four weeks after the final immunization, all single modality and prime-boost vaccinations resulted in a significant level of protection as compared to control animals. There was a trend for DNA-alone immunization yielding the highest protection. In a subsequent study, a late challenge was performed 19 weeks after the final immunization. All groups having received the DNA vaccine, either alone or in combination with adjuvanted protein, exhibited strong protection against HIV replication. The subtype-specific protection against the experimental HIV challenge was significantly stronger than the cross-protection. Cellular and humoral immune responses were assessed during immunization and after challenge, but without clear correlation to protection against HIV replication. The data suggest that either DNA or protein antigens alone provide partial protection against an HIV-1/MuLV challenge and that DNA immunization is essential for achieving very high levels of efficacy in this murine HIV-1 challenge model. While prime-boost combinations were more immunogenic than DNA alone, they did not appear to provide any further enhancement over DNA vaccine mediated efficacy. The DNA immunogen might prime low levels of CD8+ T cells responsible for virus clearance or possibly a yet unidentified mechanism of protection.

Durable HIV-1 antibody and T-cell responses elicited by an adjuvanted multi-protein recombinant vaccine in uninfected human volunteers

BACKGROUND

Use of the recombinant proteins NefTat and gp120(W61D) formulated with the AS02A adjuvant system was previously shown to protect against AIDS in a rhesus macaque SHIV animal model system.

METHODS

Eighty-four HIV uninfected human participants were vaccinated intramuscularly at 0, 1, and 3 months and evaluated for safety. Immune responses were analyzed for the presence of vaccine-induced antibody and T lymphocyte responses.

RESULTS

The vaccines were safe and well tolerated at all doses. Nef-, Tat-, and gp120-specific binding antibodies were induced in all individuals that received the respective antigen, lasting up to 9 months after the final immunization. Antibodies able to neutralize the T-cell laboratory-adapted strain of HIV-1(W61D) were detected in the majority of vacinees, but did not neutralize primary isolates. Envelope-specific antibody-dependent cell cytoxicity was detected in most of the individuals receiving gp120. Robust and persistent HIV-specific lymphoproliferative responses were detected against all subunit proteins in the majority of immunized participants. As expected, HIV-specific CD8 T-cell responses were not detected.

CONCLUSIONS

Despite the lack of primary isolate neutralizing antibody induction, the observed high frequency and magnitude of other immune responses warrant further work with this vaccine or vaccine components.

Evaluation of the Mtb72F polyprotein vaccine in a rabbit model of tuberculous meningitis

Using a rabbit model of tuberculous meningitis, we evaluated the protective efficacy of vaccination with the recombinant polyprotein Mtb72F, which is formulated in two alternative adjuvants, AS02A and AS01B, and compared this to vaccination with Mycobacterium bovis bacillus Calmette-Guérin (BCG) alone or as a BCG prime/Mtb72F-boost regimen. Vaccination with Mtb72F formulated in AS02A (Mtb72F+AS02A) or Mtb72F formulated in AS01B (Mtb72F+AS01B) was protective against central nervous system (CNS) challenge with Mycobacterium tuberculosis H37Rv to an extent comparable to that of vaccination with BCG. Similar accelerated clearances of bacilli from the cerebrospinal fluid, reduced leukocytosis, and less pathology of the brain and lungs were noted. Weight loss of infected rabbits was less extensive for Mtb72F+AS02A-vaccinated rabbits. In addition, protection against M. tuberculosis H37Rv CNS infection afforded by BCG/Mtb72F in a prime-boost strategy was similar to that by BCG alone. Interestingly, Mtb72F+AS01B induced better protection against leukocytosis and weight loss, suggesting that the polyprotein in this adjuvant may boost immunity without exacerbating inflammation in previously BCG-vaccinated individuals.

Potent enhancement of cellular and humoral immune responses against recombinant hepatitis B antigens using AS02A adjuvant in healthy adults

Recombinant subunit protein vaccines generally elicit good humoral immune responses, weak helper T cell responses and no cytotoxic T cell responses. Certain adjuvants are known to enhance humoral and cellular immune responses. This study evaluated the humoral, CD4+ T helper and CTL responses induced by the recombinant SL* protein adjuvanted with AS02A in comparison with non-adjuvanted SL* in PBS in two groups of 15 healthy adult volunteers. The AS02A adjuvant contains monophosphoryl lipid A (MPL), QS21 and an oil in water emulsion. The adjuvanted vaccine induced fast and vigorous humoral and helper T cell responses of the Th1 type. Using a pool of overlapping 20mer peptides a cytotoxic response was detected in 6 out of 14 HLA-A2-positive (+) and HLA-A2-negative (-) recipients of the adjuvanted vaccine. All HLA-A2-positive subjects in the adjuvanted group and up to 30% of the subjects in the SL* PBS group displayed a CTL response against selected HLA-A2-restricted CD8+ T cell epitopes. The non-adjuvanted vaccine induced a very weak antibody response and no helper T cell responses. Local and general reactions were more frequently reported by AS02A recipients than in the non-adjuvanted group but the safety profile was considered acceptable. AS02A can be considered as a useful adjuvant that strongly enhances the cellular and humoral responses of subunit protein vaccines.

A comparative evaluation of nasal and parenteral vaccine adjuvants to elicit systemic and mucosal HIV-1 peptide-specific humoral immune responses in cynomolgus macaques

Cynomolgus macaques were immunized by either the intramuscular (i.m.) or intranasal (i.n.) route with a HIV-1 peptide-based immunogen (C4-V3 89.6P) alone, or formulated with novel adjuvants to evaluate the ability of the adjuvants to augment peptide-specific systemic and mucosal immune responses. A mutant cholera toxin, CT-E29H, or the combination of recombinant human IL-1alpha (rhIL-1alpha) protein and recombinant human GM-CSF (rhGM-CSF) protein were tested as adjuvants for i.n. immunization, while a stable emulsion of a synthetic monophosphoryl lipid A (MPL) analogue (RC529-SE) plus rhGM-CSF protein was tested as an adjuvant for i.m. immunization. Macaques immunized i.n. with peptide alone failed to elicit an anti-C4-V3 89.6P antibody response in serum. In contrast, all the tested peptide/adjuvant formulations elicited peptide-specific immune responses. RC529-SE/rhGM-CSF elicited the highest peak anti-peptide IgG geometric mean titer in serum (1:32,768 at week 25) followed by rhIL-1alpha/rhGM-CSF (1:1217 at week 10) and CT-E29H (1:256 at week 25). Measurable SHIV neutralizing antibody responses were detectable in only one macaque immunized i.m. with peptide formulated with RC529-SE/rhGM-CSF. Macaques immunized by the i.n. route with peptide in combination with CT-E29H failed to elicit measurable antibody responses at nasal or genital mucosal surfaces. In contrast, antibody responses at the nasal and genital mucosa were detected in macaques immunized by the i.n. route with peptide in combination with rhIL-1alpha/rhGM-CSF. However, antibody responses at the nasal and genital mucosa were highest in macaques immunized parenterally with peptide in combination with the adjuvants RC529-SE/rhGM-CSF. These results suggest that parenteral vaccine administration in combination with the appropriate adjuvant formulation can elicit vaccine-specific humoral immune responses in both systemic and mucosal compartments.

Differential Immune Responses and Protective Efficacy Induced by Components of a Tuberculosis Polyprotein Vaccine, Mtb72F, Delivered as Naked DNA or Recombinant Protein

Key Ags of Mycobacterium tuberculosis initially identified in the context of host responses in healthy purified protein derivative-positive donors and infected C57BL/6 mice were prioritized for the development of a subunit vaccine against tuberculosis. Our lead construct, Mtb72F, codes for a 72-kDa polyprotein genetically linked in tandem in the linear order Mtb32(C)-Mtb39-Mtb32(N). Immunization of C57BL/6 mice with Mtb72F DNA resulted in the generation of IFN-gamma responses directed against the first two components of the polyprotein and a strong CD8(+) T cell response directed exclusively against Mtb32(C). In contrast, immunization of mice with Mtb72F protein formulated in the adjuvant AS02A resulted in the elicitation of a moderate IFN-gamma response and a weak CD8(+) T cell response to Mtb32c. However, immunization with a formulation of Mtb72F protein in AS01B adjuvant generated a comprehensive and robust immune response, resulting in the elicitation of strong IFN-gamma and Ab responses encompassing all three components of the polyprotein vaccine and a strong CD8(+) response directed against the same Mtb32(C) epitope identified by DNA immunization. All three forms of Mtb72F immunization resulted in the protection of C57BL/6 mice against aerosol challenge with a virulent strain of M. tuberculosis. Most importantly, immunization of guinea pigs with Mtb72F, delivered either as DNA or as a rAg-based vaccine, resulted in prolonged survival (>1 year) after aerosol challenge with virulent M. tuberculosis comparable to bacillus Calmette-Guérin immunization. Mtb72F in AS02A formulation is currently in phase I clinical trial, making it the first recombinant tuberculosis vaccine to be tested in humans.

Long-term persistence of HIV-1 vaccine-induced CD4+CD45RA-CD62L-CCR7- memory T-helper cells

OBJECTIVE

To determine in chimpanzees if candidate HIV-1 subunit protein vaccines were capable of eliciting long-lasting T-cell memory responses in the absence of viral infection, and to determine the specific characteristics of these responses.

DESIGN

A longitudinal study of cell-mediated immune responses induced in three chimpanzees following immunization with subunit envelope glycoproteins of either HIV-1 or herpes simplex virus (HSV)-2. Following these pre-clinical observations, four human volunteers who had been immunized 7 years previously with the same HIV-1 vaccine candidate donated blood for assessment of immune responses.

METHODS

Responses were monitored by protein and peptide based ELISpot assays, lymphocyte proliferation, and intracellular cytokine staining. Humoral responses were assessed by enzyme-linked immunosorbent assay and virus neutralization assays.

RESULTS

Although antigen (Ag)-specific CD4 T-cell responses persisted for at least 5 years in chimpanzees, CD8 T-cell responses were discordant and declined within 2 years. Detailed cellular analyses revealed that strong Th1 in addition to Th2 type responses were induced by AS2/gp120 and persisted, whereas CD8 T-cell memory declined in peripheral blood. The specificity of both Th and cytotoxic T-lymphocyte responses revealed that the majority of responses were directed to conserved epitopes. The remarkable persistence of Ag-specific CD4 T-cell memory was characterized as a population of the CD45RA-CD62L-CCR7- "effector phenotype" producing the cytokines IFNgamma, IL-2 and IL-4 upon epitope-specific recognition. Importantly, results in chimpanzees were confirmed in peripheral blood of one of four human volunteers studied more than 7 years after immunization.

CONCLUSION

These studies demonstrate that epitope-specific Th1 and Th2 cytokine-dependent Th responses can be induced and maintained for longer than 5 years by immunization with subunit proteins of HIV-1.

Parasitic infection and the polarized Th2 immune response can alter a vaccine-induced immune response

The AIDS epidemic in the Developing World represents a major global crisis. It is imperative that we develop an effective vaccine. Vaccines are economically the most efficient means of controlling viral infections. However, the development of a vaccine against HIV-1 has been a formidable task, and in developing countries chronic parasitic infection adds another level of complexity to AIDS vaccine development. Helminthic and protozoan infections, common in developing countries, can result in a constant state of immune activation that is characterized by a dominant Th2 type of cytokine profile, high IgE levels, and eosinophilia. Such an immune profile may have an adverse impact on the efficacy of vaccines, in particular, an HIV-1 vaccine. Indeed, the CD8 cellular immune response and the corresponding Th1 type cytokines that enhance the CD8 cellular immune response are important for clearing many viral infections. It is believed that an antigen specific CD8 cellular immune response will be an important component of an HIV-1 vaccine.

HIV-1 vaccines: the search continues

This article gives an overview about the development of an HIV-1 vaccine. Tremendous numbers of papers have been published on this topic during the last 10 years, and this article can only touch on the different directions taken toward the development of an HIV-1 vaccine, and not give a complete overview of the entire field.

Novel synthetic LPS receptor agonists boost systemic and mucosal antibody responses in mice

Safe and cost-effective adjuvants are a critical requirement for subunit vaccine development. We report here the in vivo activity of a series of fully synthetic LPS receptor agonists that have been shown to activate NF-kappaB signaling through the Toll-like receptor 4 (TLR4). These compounds boost antibody responses to protein antigens when coadministered at microgram doses in mice. At these dosage levels no adverse effects are observed. Antibody responses are largely IgG1, with enhanced IgG2a, and down-regulated IgE as compared to alum adjuvanted immunization. Stimulation of Th1 is confirmed by enhanced gamma-interferon production after in vitro antigen restimulation of spleen cells from mice immunized with the synthetic adjuvants. The adjuvants are active by both subcutaneous and intranasal routes of vaccine administration, and in the latter case can amplify both serum IgG and serum and mucosal IgA responses. The compounds must be administered at the same site with antigen to boost anti-vaccine antibody. These fully synthetic ligands of the innate immune system offer the potential for use as effective, safe, and nonbiologically-derived adjuvants.

Prevention of disease induced by a partially heterologous AIDS virus in rhesus monkeys by using an adjuvanted multicomponent protein vaccine

Recombinant protein subunit AIDS vaccines have been based predominantly on the virus envelope protein. Such vaccines elicit neutralizing antibody responses that can provide type-specific sterilizing immunity, but in most cases do not confer protection against divergent viruses. In this report we demonstrate that a multiantigen subunit protein vaccine was able to prevent the development of disease induced in rhesus monkeys by a partially heterologous AIDS virus. The vaccine was composed of recombinant human immunodeficiency virus type 1 (HIV-1) gp120, NefTat fusion protein, and simian immunodeficiency virus (SIV) Nef formulated in the clinically tested adjuvant AS02A. Upon challenge of genetically unselected rhesus monkeys with the highly pathogenic and partially heterologous SIV/HIV strain SHIV(89.6p) the vaccine was able to reduce virus load and protect the animals from a decline in CD4-positive cells. Furthermore, vaccination prevented the development of AIDS for more than 2.5 years. The combination of the regulatory proteins Nef and Tat together with the structural protein gp120 was required for vaccine efficacy.

Effect of monophosphoryl lipid A (MPL) on T-helper cells when administered as an adjuvant with pneumocococcal-CRM197 conjugate vaccine in healthy toddlers

As new vaccines are developed, novel adjuvants may play an important role in eliciting an effective immune response. We evaluated the safety and adjuvant properties of monophosphoryl lipid A (MPL in 129 healthy toddlers immunized with two doses of nine-valent pneumococcal-CRM(197) protein conjugate vaccine (PCV9) combined with 10, 25, or 50 micro g of MPL with or without alum (AlPO(4)). Vaccine-specific humoral and cell-mediated responses were examined following the second dose of study vaccine. All doses of MPL were well-tolerated and a dose-dependent effect of MPL on specific cellular responses was observed. The 10 micro g MPL dose significantly enhanced CRM(197)-specific T-cell proliferation (P=0.02) and interferon-gamma (INF-gamma) production (P=0.009) compared to responses of controls who received PCV9 with AlPO(4). In contrast, CRM(197)-specific T-cell proliferation and interferon-gamma production of the 50 micro g MPL/AlPO(4) group were decreased when compared to controls although these differences did not reach statistical significance. IL-5 and IL-13 responses after immunization showed a similar pattern with increased production in the 10 micro g MPL group and decreased production in the 50 micro g MPL/AlPO(4) group compared to controls. There were no differences in serum IgG antibody concentrations to the nine vaccine pneumococcal capsular polysaccharides and carrier protein between the MPL-containing and control vaccine groups. These findings demonstrate a dose-dependent effect of MPL on T-helper cell type 1 (TH-1) responses to the carrier protein and also suggest an effect on T-helper cell type 2 (TH-2) responses.

Molecular virology and immunology of HIV infection

Great progress has been made with respect to our understanding of the immunopathogenesis of AIDS and the infectious agent, HIV, that causes the disease. HIV, a human retrovirus with tropism for CD4(+) T cells and monocytes, induces a decrease of T-cell counts, T-cell dysfunction, and, ultimately, immunodeficiency. HIV also causes B-cell dysfunction characterized by polyclonal activation, hypergammaglobulinemia, and lack of specific antibody responses. Chemokine receptors-mainly CCR5 and CXCR4-have been found to be necessary for viral entry into the host cell, a step that can be inhibited by chemokine-related molecules that are ligands for those receptors. After HIV infection, a strong cellular immunity develops and partially controls viral replication. It can take several years for HIV infection to become clinically evident. Studies in long-term nonprogressors have shown the determinant roles of both helper and cytotoxic T cells in the control of HIV disease. Advances in HIV immunology research are currently being applied in the development of prophylactic and therapeutic vaccines.

Recent advances in vaccine adjuvants

New generation vaccines, particularly those based on recombinant proteins and DNA, are likely to be less reactogenic than traditional vaccines but are also less immunogenic. Therefore, there is an urgent need for the development of new and improved vaccine adjuvants. Adjuvants can be broadly separated into two classes based on their principal mechanisms of action: vaccine delivery systems and immunostimulatory adjuvants. Vaccine-delivery systems generally are particulate (e.g., emulsions, microparticles, iscoms, and liposomes) and function mainly to target associated antigens into antigen-resenting cells. In contrast, immunostimulatory adjuvants are derived predominantly from pathogens and often represent pathogen-ssociated molecular patterns (e.g., lipopolysaccaride, monophosphoryl lipid A, CpG DNA). which activate cells of the innate immune system. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants may enhance this process. The discovery of more potent adjuvants may allow the development of prophylactic and therapeutic vaccines against cancers and chronic infectious diseases. In addition, new adjuvants may also allow vaccines to be delivered mucosally.

The development and use of vaccine adjuvants

Interest in vaccine adjuvants is intense and growing, because many of the new subunit vaccine candidates lack sufficient immunogenicity to be clinically useful. In this review, I have emphasized modern vaccine adjuvants injected parenterally, or administered orally, intranasally, or transcutaneously with licensed or experimental vaccines in humans. Every adjuvant has a complex and often multi-factorial immunological mechanism, usually poorly understood in vivo. Many determinants of adjuvanticity exist, and each adjuvanted vaccine is unique. Adjuvant safety is critical and can enhance, retard, or stop development of an adjuvanted vaccine. The choice of an adjuvant often depends upon expensive experimental trial and error, upon cost, and upon commercial availability. Extensive regulatory and administrative support is required to conduct clinical trials of adjuvanted vaccines. Finally, comparative adjuvant trials where one antigen is formulated with different adjuvants and administered by a common protocol to animals and humans can accelerate vaccine development.

Rational development of prophylactic HIV vaccines based on structural and regulatory proteins

The severity of the AIDS epidemic clearly emphasises the urgent need to expedite HIV vaccine candidates into clinical trials. Prophylactic HIV vaccine candidates have been evaluated in non-human primates. Based on specific proof of principle studies the first phase III clinical studies have recently begun in humans. However, a truly effective HIV vaccine is not yet at hand and many problems related to specific properties of the virus remain to be overcome. Previously proven empirical approaches have largely failed and now rational thinking based on an understanding of immunity to lentiviral infections is needed. This review addresses the scientific problems and complications facing the development of an HIV vaccine as well as the possible strategies currently available to overcome these problems. Recent attention has focussed on identifying the immune correlates and mechanisms of protection from either HIV infection or protection from disease progression. Based on these observations, the logic and rational behind the development of multiple component vaccine strategies are highlighted.

Vaccine-induced antibodies to the native, oligomeric envelope glycoproteins of primary HIV-1 isolates

A simple and sensitive method for measuring antibodies to primary human immunodeficiency virus type 1 (HIV-1) isolates has been developed. The flow cytometric immuno-fluorescence assay detects antibodies that bind to the native, oligomeric form of the envelope glycoprotein (gp120) expressed on the surface of PM-1 cells infected with primary isolates of HIV-1. Sera from people infected with HIV-1 or those immunized with recombinant gp120 vaccines were tested. Significant correlation was observed between neutralizing activity and oligomeric gp120 binding activity. Thirteen to 100% of individuals immunized with the subtype B bivalent vaccine AIDSVAX B/B developed oligomeric gp120 binding antibodies against a variety of subtype B primary isolates. For several isolates, AIDSVAX B/B sera reacted better than monovalent AIDSVAX B sera, suggesting that addition of the second immunogen improved the breadth of the antibody response. Cross-subtype binding activities, induced by AIDSVAX B/B, were lower than activities to subtype B isolates, suggesting that additional immunogen(s) may be desirable in vaccine(s) formulated for geographic regions where non-B subtypes are dominant.

Recent developments in adjuvants for vaccines against infectious diseases

New generation vaccines, particularly those based on recombinant proteins and DNA, are likely to be less reactogenic than traditional vaccines, but are also less immunogenic. Therefore, there is an urgent need for the development of new and improved vaccine adjuvants. Adjuvants can be broadly separated into two classes, based on their principal mechanisms of action; vaccine delivery systems and 'immunostimulatory adjuvants'. Vaccine delivery systems are generally particulate e.g. emulsions, microparticles, iscoms and liposomes, and mainly function to target associated antigens into antigen presenting cells (APC). In contrast, immunostimulatory adjuvants are predominantly derived from pathogens and often represent pathogen associated molecular patterns (PAMP) e.g. LPS, MPL, CpG DNA, which activate cells of the innate immune system. Once activated, cells of innate immunity drive and focus the acquired immune response. In some studies, delivery systems and immunostimulatory agents have been combined to prepare adjuvant delivery systems, which are designed for more effective delivery of the immunostimulatory adjuvant into APC. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants may enhance this process. However, a rational approach to the development of new and more effective vaccine adjuvants will require much further work to better define the mechanisms of action of existing adjuvants. The discovery of more potent adjuvants may allow the development of vaccines against infectious agents such as HIV which do not naturally elicit protective immunity. New adjuvants may also allow vaccines to be delivered mucosally.

Towards the rational design of Th1 adjuvants

Finding adjuvants in order to enhance immune responses against target immunogens has been a major and recurrent issue for the vaccine industry. It is yet to be solved, most particularly in the context of a growing interest in designing new types of vaccines capable of eliciting Th1 immune responses. A review of synthetic adjuvants which have been (or are being) tested in clinical studies is presented. Importantly, recent advances in our understanding of the physiology of immune responses offer new avenues to design and test candidate adjuvants, based on either synthetic or natural molecules, with the aim to mimic and recapitulate pro-inflammatory signals initiating both innate and adaptative immune effector mechanisms. Thus, adjuvants of the future might be a mixture of molecules selected singularly for a capacity to attract, target or activate professional antigen presenting cells. Used as a combination, such molecules should facilitate antigen presentation by professional APCs and lead to a potent induction of T cell-mediated effector and immune memory mechanisms.

Vaccines for the prevention of HIV-1 disease

Clinical investigation in humans and experimental lentivirus infection in nonhuman primates have advanced our understanding of immune responses that control HIV-1 disease. Recently, immunization approaches in macaques have shown that the immune response can control viremia and improve clinical outcome. When such vaccine strategies are formulated to be similarly immunogenic in humans, they could form the basis for the development of candidate AIDS vaccines that would prevent infection, suppress progression to disease or reduce HIV-1 transmission in humans.

Identification and characterization of a peptide that specifically binds the human, broadly neutralizing anti-human immunodeficiency virus type 1 antibody b12

Human monoclonal antibody (MAb) b12 recognizes a conformational epitope that overlaps the CD-4-binding site of the human immunodeficiency virus type 1 (HIV-1) envelope. MAb b12 neutralizes a broad range of HIV-1 primary isolates and protects against primary virus challenge in animal models. We report here the discovery and characterization of B2.1, a peptide that binds specifically to MAb b12. B2.1 was selected from a phage-displayed peptide library by using immunoglobulin G1 b12 as the selecting agent. The peptide is a homodimer whose activity depends on an intact disulfide bridge joining its polypeptide chains. Competition studies with gp120 indicate that B2.1 occupies the b12 antigen-binding site. The affinity of b12 for B2.1 depends on the form in which the peptide is presented; b12 binds best to the homodimer as a recombinant polypeptide fused to the phage coat. Originally, b12 was isolated from a phage-displayed Fab library constructed from the bone marrow of an HIV-1-infected donor. The B2.1 peptide is highly specific for b12 since it selected only phage bearing b12 Fab from this large and diverse antibody library.

Therapeutic potential of protein and adjuvant vaccinations on tumour growth

Over 90% of cervical cancers are associated with HPV infection, the commonest being the HPV-16 subtype. Two early viral genes, E6 and 7, play major roles in the development and maintenance of the malignant phenotype. The vaccine potential of a recombinant HPV16 E7 protein was examined in two murine models of E7-expressing tumours. Formulations including the immunostimulants MPL and QS21 induced therapeutically active immune responses leading to regression of pre-established TC1 tumour lesions, associated with induction of IgG antibodies, lymphoproliferation and CTL. Our data provide a clear incentive to investigate the clinical application of this approach in cancer immunotherapy.

Adverse events and vaccination-the lack of power and predictability of infrequent events in pre-licensure study

The recent setback in the development of a safe and effective rotavirus vaccine illustrates an important problem regarding prelicensure testing and its ability to identify rare vaccine-related adverse effects. It is our contention that the possibility of a rare but serious vaccine adverse effect is difficult to detect in prelicensure testing. In this paper, we review the history regarding the testing and eventual studies that led to the permanent withdrawal of that vaccine. The post-licensure discovery of a serious adverse event associated with the rotavirus vaccine is not unique among vaccines, but represents a recurrent phenomenon that in fact is mathematically predictable. Prelicensure studies examine thousands of subjects and not hundreds of thousands. A sample size of 10,000 subjects may provide excellent estimates of efficacy, but cannot provide an adequate denominator to rule out rare adverse events. It lacks the power. Just as with the rotavirus vaccine, only after hundreds of thousands of doses of vaccines are distributed, will such rare events appear often enough to permit detection. For that reason, we must depend upon the modern post-licensure surveillance programs that we already have in place.