Comparison of protection afforded by whole virus ISCOM versus MDP adjuvanted formalin-inactivated SIV vaccines from IV cell-free or cell-associated homologous challenge

Nonhuman primate models for cell-associated simian immunodeficiency virus transmission: the need to better understand the complexity of HIV mucosal transmission

Nonhuman primates are extensively used to assess strategies to prevent infection from sexual exposure to human immunodeficiency virus (HIV) and to study mechanisms of mucosal transmission. However, although semen represents one of the most important vehicles for the virus, the vast majority of preclinical challenge studies have used cell-free simian immunodeficiency virus (SIV) or simian/human immunodeficiency virus (SHIV) viral particles inoculated as diluted culture supernatants. Semen is a complex body fluid containing many factors that may facilitate or decrease HIV infectiousness. The virus in semen is present in different forms: as free virus particles or as cell-associated virus (ie, within infected leukocytes). Although cell-to-cell transmission of HIV is highly efficient, the role of cell-associated virus in semen has been surprisingly poorly investigated in nonhuman primate models. Mucosal exposure of macaques to cell-associated SIV by using infected peripheral blood mononuclear cells or spleen cells has been shown to be an efficient means of infection; however, it has yet to be shown that SIV- or SHIV-infected seminal leukocytes can transmit infection in vivo. Improvement of animal models to better recapitulate the complex microenvironment at portals of HIV entry is needed for testing candidate antiretrovirals, microbicides, and vaccines.

Comparison of intranasal with targeted lymph node immunization using PR8-Flu ISCOM adjuvanted HIV antigens in macaques

The rapidly spreading HIV epidemic requires a vaccine that elicits potent mucosal immunity to halt or slow transmission. Induction of these responses will depend on the use of appropriate adjuvants and targeting of the mucosal immune system. Previously, immune stimulating complexes (ISCOM) have shown great potency as adjuvant in the induction of mucosal responses in mice and systemic responses in non-human primates. In this study, HIV formulated in PR8-Flu ISCOM adjuvant was applied to immunize rhesus macaques against HIV; targeting the mucosa either via intranasal (IN) application or via targeted lymph node immunization (TLNI). While, strong systemic, HIV specific, cytokine, lymphoproliferative, and antibody responses were induced via the TLNI route, the IN application generated only low responses. Furthermore, all four animals immunized via TLNI developed vaginal IgA antibodies against gp120. In conclusion, in contrast to what has been demonstrated in mice, the IN application of PR8-Flu ISCOM did not induce strong immune responses in rhesus macaques unlike those immunized by the TLNI route.

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.

ISCOMATRIX adjuvant: a potent inducer of humoral and cellular immune responses

ISCOMATRIX adjuvant is capable of inducing broad and potent humoral and cellular immune responses. The components are well defined and the manufacturing process is simple and robust. Many vaccines containing the ISCOMATRIX adjuvant have been tested in a range of animal models, including human and non-human primates. Strong antibody and T cell responses have been induced in these studies. The antibody response is often achieved with lesser amounts of antigen than other adjuvant systems and the maximal responses have also been reached more quickly. Both CD4+ and CD8+ T cell responses are induced with the cytotoxic T lymphocyte responses being very long lived. Additionally, ISCOMATRIX adjuvant can be used in vaccines for induction of mucosal immune responses. This review provides an overview of the immune responses that can be elicited using ISCOMATRIX vaccines and the current state of knowledge regarding the mechanism of action of this adjuvant.

Current status and potential application of ISCOMs in veterinary medicine

The immune stimulating complex (ISCOM) is a 40 nm nanoparticle used as a delivery system for vaccine antigens, targeting the immune system both after parenteral and mucosal administration. The ISCOM is made up of saponin, lipids and antigen usually held together by hydrophobic interaction between these three components. The compulsory elements to form the ISCOM structure are cholesterol and saponin. When the antigen is omitted the ISCOM-MATRIX is formed. There are a number of saponins that can form ISCOMs, and many other substances (including antigens, targeting and immuno-modulating molecules) can be incorporated into the ISCOM provided they are hydrophobic or rendered to be hydrophobic. Thus, it is possible to create ISCOM particles with different properties. After parenteral immunisation of the ISCOM, the T cell response is first detected in the draining lymph node. Subsequently, the T cell response is localised to the spleen, while the B cell response is first found both in the draining lymph nodes and in the spleen. Up to 50 days later, the majority of the antibody producing cells is found in the bone marrow (BM). In contrast, antigens that have been adjuvanted in an oil emulsion, limit the T cell response to the draining lymph nodes while the B cell response is found in the draining lymph nodes and spleen, but not in the BM. The ISCOM efficiently evokes CD8+, MHC class 1 restricted T cell response. The deposit of antigens both to the endosomal vesicles and to the cytosol of antigen presenting cells (APCs) explains why both T helper cells (vesicles) and cytotoxic T lymphocytes (cytosol) are efficiently induced by ISCOMs. The T helper (Th) cell response is balanced in the sense that both Th1 and Th2 cells are induced. Prominent IL-12 production by cells in the innate system is a characteristic reaction induced by ISCOMs, promoting the development of a strong Th1 response. After mucosal administration by the intranasal or the intestinal routes, the ISCOM induces strong specific mucosal IgA responses in local and remote mucosal surfaces. Also T cell responses are evoked by the mucosal administration. A large number of experimental ISCOM vaccines have been tested and protection has been induced against a number of pathogens in various species including chronic and persistent infections exemplified by human immune deficiency virus 1 (HIV-1), and 2 (HIV-2) and simian immune deficiency virus (SIV) in primates, and various herpes virus infections in several species. In contrast to a conventional rabies virus vaccine the ISCOM rabies formulation protected mice after exposure to the virulent virus. Recently, experimental ISCOM vaccines were shown to efficiently induce immune response in newborns of murine and bovine species in the presence of maternal antibodies, while conventional vaccines have failed. ISCOM vaccines are on the market for horses and cattle and several other ISCOM vaccines are under development. Since the ISCOM and the ISCOM-MATRIX can be blended with live attenuated vaccine antigens without hampering the proliferation of the live vaccine antigens, it opens the possibility to use the ISCOM adjuvant system in a mixture of live and killed vaccine antigens.

Evaluation of FIV protein-expressing VEE-replicon vaccine vectors in cats

Venezuelan equine encephalitis (VEE) virus-replicon particles (VRP) were used to generate feline immunodeficiency virus (FIV) Gag- and ENV-expressing vaccine vectors. Serum and mucosal FIV-specific antibody was detected in cats immunized subcutaneously, once monthly for 5 months, with FIV-expressing VRP. Expansion of the CD8+ L-selectin negative phenotype and transient CD8+ noncytolytic suppressor activity were seen in cats immunized with FIV-expressing or control VRP. Despite induction of FIV-specific immune responses and nonspecific suppressor responses, all cats became infected following vaginal challenge with high dose, pathogenic cell-associated FIV-NCSU(1) although relative early maintenance of CD4+ cells was seen in FIV-immunized cats.

Immunomodulation by iscoms, immune stimulating complexes

The iscom is a uniform stable complex consisting of cholesterol, phospholipid, adjuvant-active saponin, and antigen. The iscom matrix is a particulate complex with identical composition, shape, and morphology, but lacking the incorporated antigen. The assembly of the complex is based on hydrophobic interactions, but antigens that are not hydrophobic can be conjugated with a hydrophobic tail or hidden hydrophobic regions can be exposed, e.g., by acid treatment, to facilitate the incorporation into iscoms. The functional aspects of iscoms are described emphasizing immunomodulation in mouse models. Iscoms prominently enhance the antigen targeting, uptake, and activity of antigen presenting cells including dendritic and B cells and macrophages resulting in the production of proinflammatory cytokines, above all interleukin (IL)-1, IL-6, and IL-12. The expression of costimulatory molecules major histocompatibility complex (MHC) class II, B7.1 and B7.2, is also enhanced. The latter partly explains why the iscom is an efficient adjuvant for elderly mice. Iscoms enhance the Th1 type of response with increased production of IL-2 and interferon gamma. However, with some antigens and particularly in monkeys immunized with HIV iscoms, the production of IL-4 was enhanced. IL-4, IL-2, and interferon gamma (IFNgamma) together with the beta chemokines MIP-1alpha and MIP-1beta correlated with protection against challenge infection with a chimeric virus (simian immunodeficiency virus-human immunodeficiency virus). Iscoms were also shown to induce a potent immune response in the newborn and to be an efficient delivery system for mucosal administration. Technical information is given about formulation of iscoms and about handling of antigens to optimize their incorporation into iscoms.

Immunopotentiation of humoral and cellular responses to inactivated influenza vaccines by two different adjuvants with potential for human use

Two quite different adjuvants, currently under development for use in humans, have been examined for their effects on the magnitude and type of immunity elicited in response to inactivated influenza vaccine. Immunostimulating complexes (ISCOM adjuvant) contain the saponin ISCOPREP 703, and SPT is an oil-in-water emulsion of squalane, non-ionic block copolymer (L121) and Tween 80. Influenza virus vaccines formulated in either adjuvant were far superior to the non-adjuvanted aqueous vaccine in eliciting antibody and T-cell responses in mice, particularly at lower doses of antigen. In addition, the vaccines containing adjuvant were superior in eliciting protective immunity. One of the shortcomings of the unadjuvanted inactivated influenza vaccine was its inability to elicit a primary proliferative T-cell response. However, after one dose of either adjuvanted vaccine, strong proliferative responses were achieved. We also show that subcutaneous vaccination with inactivated vaccines is capable of modulating the isotype profile of antibody secreting cells generated in the lungs of mice in response to intranasal challenge with live virus. In this system, the isotype of antibody elicited after challenge of mice that had received ISCOM vaccine more closely mimicked that of animals vaccinated with live virus.

ISCOMs (immunostimulating complexes): the first decade

A little over a decade ago, novel immunostimulating complexes (ISCOMs) were described. This review examines the position and progress that ISCOM technology has achieved in the fields of vaccine research and medicine over this period. Much of the work on ISCOMs has remained in the area of vaccine research where there is still an urgent need for improved adjuvants to help combat important diseases such as AIDS, malaria and influenza. Currently the only widely licensed adjuvants for human use are the aluminium salts, but with the trend towards highly purified subunit vaccines, which are inherently less immunogenic than some of the older vaccines, potent adjuvants capable of promoting specific immune responses are required. ISCOMs are one such technology that offers many of these requirements and as their use in vaccines enters its second decade clinical trials are commencing that will establish whether these submicron, non-living particles composed of saponin, cholesterol, phospholipid and in many cases protein, are useful components for a range of human vaccines.

An experimental chemically inactivated HIV-1 vaccine induces antibodies that neutralize homologous and heterologous viruses

We have developed a unique multiple step procedure to inactivate human immunodeficiency virus chemically with a very high safety margin while retaining antigenically active structural virion proteins, including gp120, in the final immunogen. The whole virus preparation (1-10 micrograms per dose) was highly immunogenic in a variety of small mammals and induced antibodies that recognized homologous and heterologous strains of HIV-1. Sera from immunized animals bound to peptides representing the entire sequence of the external glycoprotein gp120. Neutralizing antibodies active against the homologous immunizing strain and against heterologous HIV-1 strains were also elicited. Sera with virus neutralizing activity did not bind to MHC class I proteins derived from the human cell line used to grow the virus.

Adjuvants: current status, clinical perspectives and future prospects

Adjuvants represent a key issue for vaccines currently under development. Adjuvanticity is linked to the ability to stimulate the T-cell subsets that control the major features of specific immune responses: CD4+ TH1 and TH2 cells and CD8+ cells involved in cytotoxic T lymphocyte responses. Some well-defined immunomodulatory compounds can achieve this stimulation by inducing selective production of appropriate cytokines. Françoise Audibert and Luc Lise review the development of adjuvants and discuss how their combination with suitable vehicles should allow customization of adjuvant preparations capable of inducing protective immune responses better adapted to each type of pathogenicity.

Adjuvants: current status, clinical perspectives and future prospects

Adjuvants represent a key issue for vaccines currently under development. Adjuvanticity is linked to the ability to stimulate the T-cell subsets that control the major features of specific immune responses: CD4+ TH1 and TH2 cells and CD8+ cells involved in cytotoxic T-lymphocyte responses. Some well-defined immunomodulatory compounds can achieve this stimulation by inducing selective production of appropriate cytokines. Françoise Audibert and Luc Lise review the development of adjuvants and discuss how their combination with suitable vehicles should allow customization of adjuvant preparations capable of inducing protective immune responses better adapted to each type of pathogenicity.