An experimental prime-boost regimen leading to HIV type 1-specific mucosal and systemic immunity in BALB/c mice

Combined Oral and Intravenous Immunization Stimulates Strong IgA Responses in Both Systemic and Mucosal Compartments

To investigate the influence of immunization routes onIgG, IgA and IgM production in systemic and mucosal compartments, we immunized mice with keyhole limpet hemocyanin (KLH) via oral, intranasal (i.n.) or subcutaneous (s.c.) routes alone or combined with the intravenous (i.v.) route. We found that administering antigen intravenously could affect antibody production and formation of antibody secreting cells (ASCs) depending on the immunization route previously used. Combined oral/i.v. immunization but not s.c./i.v. immunization caused a great increase of IgA ASCs in the spleen and enhanced IgA production in the small intestine and serum. Combined i.n./i.v. immunization could also increase IgA ASCs in the spleen and enhance IgA production in serum but had no effect on IgA production in the small intestine. Oral/i.v. immunization caused increase of IgG ASCs in both the spleen and bone marrow. In comparison, combined i.n./i.v. and s.c./i.v. immunization could increase IgG ASCs in the spleen but not in bone marrow. Intravenous administration of KLH in mice that had been immunized via oral, i.n. or s.c. routes caused some increase of IgM ASCs in the spleen but not in bone marrow. In conclusion, combined oral and i.v. administration of an antigen can induce fast and strong immune responses, especially for IgA, in both systemic and mucosal compartments.

Heterologous prime-boost-boost immunisation of Chinese cynomolgus macaques using DNA and recombinant poxvirus vectors expressing HIV-1 virus-like particles

Background

There is renewed interest in the development of poxvirus vector-based HIV vaccines due to the protective effect observed with repeated recombinant canarypox priming with gp120 boosting in the recent Thai placebo-controlled trial. This study sought to investigate whether a heterologous prime-boost-boost vaccine regimen in Chinese cynomolgus macaques with a DNA vaccine and recombinant poxviral vectors expressing HIV virus-like particles bearing envelopes derived from the most prevalent clades circulating in sub-Saharan Africa, focused the antibody response to shared neutralising epitopes.

Methods

Three Chinese cynomolgus macaques were immunised via intramuscular injections using a regimen composed of a prime with two DNA vaccines expressing clade A Env/clade B Gag followed by boosting with recombinant fowlpox virus expressing HIV-1 clade D Gag, Env and cholera toxin B subunit followed by the final boost with recombinant modified vaccinia virus Ankara expressing HIV-1 clade C Env, Gag and human complement protein C3d. We measured the macaque serum antibody responses by ELISA, enumerated T cell responses by IFN-γ ELISpot and assessed seroneutralisation of HIV-1 using the TZM-bl β-galactosidase assay with primary isolates of HIV-1.

Results

This study shows that large and complex synthetic DNA sequences can be successfully cloned in a single step into two poxvirus vectors: MVA and FPV and the recombinant poxviruses could be grown to high titres. The vaccine candidates showed appropriate expression of recombinant proteins with the formation of authentic HIV virus-like particles seen on transmission electron microscopy. In addition the b12 epitope was shown to be held in common by the vaccine candidates using confocal immunofluorescent microscopy. The vaccine candidates were safely administered to Chinese cynomolgus macaques which elicited modest T cell responses at the end of the study but only one out of the three macaques elicited an HIV-specific antibody response. However, the antibodies did not neutralise primary isolates of HIV-1 or the V3-sensitive isolate SF162 using the TZM-bl β-galactosidase assay.

Conclusions

MVA and FP9 are ideal replication-deficient viral vectors for HIV-1 vaccines due to their excellent safety profile for use in humans. This study shows this novel prime-boost-boost regimen was poorly immunogenic in Chinese cynomolgus macaques.

Mucosal immunity and HIV-1 infection: applications for mucosal AIDS vaccine development

Natural transmission of human immunodeficiency virus type 1 (HIV-1) occurs through gastrointestinal and vaginal mucosa. These mucosal tissues are major reservoirs for initial HIV replication and amplification, and the sites of rapid CD4(+) T cell depletion. In both HIV-infected humans and SIV-infected macaques, massive loss of CD4(+) CCR5(+) memory T cells occurs in the gut and vaginal mucosa within the first 10-14 days of infection. Induction of local HIV-specific immune responses by vaccines may facilitate effective control of HIV or SIV replication at these sites. Vaccines that induce mucosal responses, in particular CD8(+) cytotoxic T lymphocytes (CTL), have controlled viral replication at mucosal sites and curtailed systemic dissemination. Thus, there is strong justification for development of next generation vaccines that induce mucosal immune effectors against HIV-1 including CD8(+) CTL, CD4(+) T helper cells and secretory IgA. In addition, further understanding of local innate mechanisms that impact early viral replication will greatly inform future vaccine development. In this review, we examine the current knowledge concerning mucosal AIDS vaccine development. Moreover, we propose immunization strategies that may be able to elicit an effective immune response that can protect against AIDS as well as other mucosal infections.

Innovative approaches to develop prophylactic and therapeutic vaccines against HIV/AIDS

The acquired immunodeficiency syndrome (AIDS) emerged in the human population in the summer of 1981. According to the latest United Nations estimates, worldwide over 33 million people are infected with human immunodeficiency virus (HIV) and the prevalence rates continue to rise globally. To control the alarming spread of HIV, an urgent need exists for developing a safe and effective vaccine that prevents individuals from becoming infected or progressing to disease. To be effective, an HIV/AIDS vaccine should induce broad and long-lasting humoral and cellular immune responses, at both mucosal and systemic level. However, the nature of protective immune responses remains largely elusive and this represents one of the major roadblocks preventing the development of an effective vaccine. Here we summarize our present understanding of the factors responsible for resistance to infection or control of progression to disease in human and monkey that may be relevant to vaccine development and briefly review recent approaches which are currently being tested in clinical trials. Finally, the rationale and the current status of novel strategies based on nonstructural HIV-1 proteins, such as Tat, Nef and Rev, used alone or in combination with modified structural HIV-1 Env proteins are discussed.

Beta7-integrin-independent enhancement of mucosal and systemic anti-HIV antibody responses following combined mucosal and systemic gene delivery

Vaccination strategies that can block or limit heterosexual human immunodeficiency virus (HIV) transmissions to local and systemic tissues are the goal of much research effort. Herein, in a mouse model, we aimed to determine whether the enhancement of antibody responses through mucosal and systemic immunizations, previously observed with protein-based vaccines, applies to immunizations with DNA- or RNA-based vectors. Intranasal (i.n.) followed by intramuscular (i.m.) immunizations (i.n./i.m.) with polylactide-coglycolide (PLG)-DNA microparticles encoding HIV-gag (PLG-DNA-gag) significantly enhanced serum antibody responses, compared with i.m., i.n. or i.m. followed by i.n. (i.m./i.n.) immunizations. Moreover, while i.n./i.m., i.n. or i.m./i.n. immunizations with PLG-DNA-gag resulted in genital tract antibody responses, i.m. immunizations alone failed to do so. Importantly, beta7-deficient mice developed local and systemic antibody responses following i.n./i.m. immunization, or immunization via any other route, similar to those of wild-type mice. To compare the DNA with an RNA delivery system, immunizations were performed with VEE/SIN-gag replicon particles, composed of Venezuelan equine encephalitis virus (VEE) replicon RNA and Sindbis surface structure (SIN). i.n./i.m., compared with any other immunizations, i.n./i.m. immunization with VEE/SIN-gag resulted in enhanced genital tract but not serum antibody responses. These data show for the first time that mucosal followed by systemic immunizations with gene delivery systems enhance B-cell responses independent of the mucosal homing receptors alpha4beta7 and alphaEbeta7.

Comparison of antibody- and cell-mediated immune responses after intramuscular hepatitis C immunizations of BALB/c mice

Current treatments for hepatitis C infection have limited efficacy, and there is no vaccine available. The goal of this study was to compare the immune response to several immunization combinations against hepatitis C virus (HCV). Six groups of mice were immunized at weeks 0, 4, and 8 with different combinations of a candidate HCV vaccine consisting of 100 microg recombinant HCV core/E1/E2 (rHCV) DNA plasmid and/or 25 microg rHCV polyprotein and 50 microL Montanide ISA- 51. Four weeks after the last injection, all groups of mice were sacrificed and blood samples and spleens were collected for measuring the levels of specific HCV antibodies (total IgG, IgG1, and IgG2a). Cell proliferation and intracellular interferon-gamma were also measured. Among the groups of immunized mice, only the mice immunized with rHCV DNA plasmid, rHCV polyprotein, and montanide (group D) and mice immunized with rHCV polyprotein and montanide (group F) demonstrated a significant increase in the total IgG titer after immunization. IgG1 was the predominant antibody detected in both groups D and F. No IgG2a was detected in any of the groups. Proliferation assays demonstrated that splenocytes from group D and group C (rHCV DNA primed/rHCV polyprotein boost) developed significant anti-HCV proliferative responses. The combination of an rHCV DNA plasmid, rHCV polyprotein, and montanide induced a high antibody titer with a predominance of IgG1 antibodies and recognized the major neutralization epitopes in HVR1. In contrast, group C did not show an increase in anti-HCV antibodies, but did show a proliferative response.

Mucosal and systemic anti-HIV responses in rhesus macaques following combinations of intranasal and parenteral immunizations

There is an urgent need to develop vaccines that can elicit immunological memory responses against HIV. Using the rhesus macaque model and a combination of intranasal (IN) and parenteral immunizations with DNA or protein adsorbed to microparticles or mixed with mucosal adjuvants we sought to induce anti-HIV memory-type immune responses in both the mucosal and systemic compartments. Prime/boost immunizations were performed through five IN immunizations alone with HIV-env oligomeric gp140 (Ogp140) or HIV-gag-p24 mixed with Escherichia coli heat labile-derived mutant adjuvants or two parenteral immunizations with DNA encoding HIV-env or -gag adsorbed to microparticles followed by three IN immunizations with p24 gag protein and the mutant adjuvants. Both modes of immunizations induced anti-gp140 plasma and vaginal IgG and IgA as well as interferon (IFN)-gamma secreting peripheral blood mononuclear cells (PBMC) after HIV-env and -gag peptide restimulation. After a resting period of 4 months, when the levels of humoral and cellular responses had decreased, intramuscular (IM) booster immunizations with p55-gag protein adsorbed to microparticles and Ogp140 in MF59 oil in water emulsion significantly enhanced anti-HIV plasma and vaginal antibody, as well as peripheral blood IFN-gamma responses in all groups of vaccinated macaques. Importantly, plasma neutralization activity against both homologous and heterologous HIV strains was observed in all groups following the IM booster immunizations with protein. These findings show that IN priming alone or combinations of parenteral and IN immunizations followed by IM booster immunizations hold promise to significantly enhance mucosal and systemic memory-type immune responses against HIV-1 antigens.

Enhanced sensitivity of detection of cytotoxic T lymphocyte responses to HIV type 1 proteins using an extended in vitro stimulation period for measuring effector function in volunteers enrolled in an ALVAC-HIV phase I/II prime boost vaccine trial in Thailand

A phase I/II prime-boost vaccine trial in HIV-1-seronegative adults was conducted in Thailand using ALVAC-HIV (vCP1521) as a prime, boosting with either oligomeric gp160 TH023/LAI or Chiron HIV Thai subtype E (CM235) plus U. S. subtype B (SF2) gp120. Cytotoxic T lymphocyte (CTL) assays were conducted at one of the vaccine trial sites (Siriraj Hospital) at a single time point following the completion of immunization demonstrated that 8 of 50 (16%) vaccine recipients showed HIV-specific CTL by standard chromium release assay (CRA) after in vitro stimulation (IVS) for 2 weeks. Five additional vaccinees (13/50 = 26%) showed CTL responses after IVS for up to 4 weeks. Moreover, one volunteer with a positive CTL response to a single HIV antigen at Day 14 demonstrated a response to an additional HIV-1 antigen(s) after the longer IVS period. CTL activity was CD8+ restricted. Despite extension of the IVS up to 4 weeks, no CTL responses were detected in placebo recipients. These results imply that extension of the IVS period may increase the sensitivity of the CRA when measuring HIV-specific CTL in ALVAC-HIV prime-boost recipients without compromising specificity.

Mucosal AIDS vaccines

Debates are still being waged over what is the best strategy for developing a potent AIDS vaccine. All the obvious approaches to making AIDS vaccines have been tried in the past two decades without much success. It is clear that new thinking and a revision of prevailing dogmas needs to be in place if we really want a vaccine. Conventional envelope-based antibody-inducing vaccines do not appear to hold promise, and broadly-neutralizing antibodies are now being searched as an alternative to the failed approach with subunit vaccines. The current consensus is that cellular immune responses, especially those mediated by CD8 cytotoxic/suppressor (CTL) and CD4 helper T lymphocytes, are needed to control HIV. Vaccines capable of inducing cell-mediated responses are, therefore, considered critical for controlling the spread of HIV. DNA-based vaccines triggering CTL reaction are currently thought to be an answer, but will they fulfill the promise? In the following paragraphs, a critical assessment of the state of the art will be provided in an attempt to analyze what we know and still don't know. The focus of this review is primarily on mucosal vaccines-a relatively new area in AIDS research. The update on V-1 Immunitor, the first mucosal AIDS vaccine available commercially, is provided within this context. Some of the reviewed concepts may be disputable, but without departure from the uninspiring consensus no substantial progress in the AIDS vaccine field can be envisioned.

Enhanced mucosal and systemic immune responses to Helicobacter pylori antigens through mucosal priming followed by systemic boosting immunizations

It is estimated that Helicobacter pylori infects the stomachs of over 50% of the world's population and if not treated may cause chronic gastritis, peptic ulcer disease, gastric adenocarcinoma and gastric B-cell lymphoma. The aim of this study was to enhance the mucosal and systemic immune responses against the H. pylori antigens cytotoxin-associated gene A (CagA) and neutrophil-activating protein (NAP), through combinations of mucosal and systemic immunizations in female BALB/c mice. We found that oral or intranasal (i.n.) followed by i.m. immunizations induced significantly higher serum titres against NAP and CagA compared to i.n. alone, oral alone, i.m. alone, i.m. followed by i.n. or i.m. followed by oral immunizations. However, only oral followed by i.m. immunizations induced anti-NAP antibody-secreting cells in the stomach. Moreover, mucosal immunizations alone or in combination with i.m., but not i.m. immunizations alone, induced mucosal immunoglobulin A (IgA) responses in faeces. Any single route or combination of immunization routes with NAP and CagA preferentially induced antigen-specific splenic interleukin-4-secreting cells and far fewer interferon-gamma-secreting cells in the spleen. Moreover, i.n. immunizations alone or in combination with i.m. immunizations induced predominantly serum IgG1 and far less serum IgG2a. Importantly, we found that while both i.n. and i.m. recall immunizations induced similar levels of serum antibody responses, mucosal IgA responses in faeces were only achieved through i.n. recall immunization. Collectively, our data show that mucosal followed by systemic immunization significantly enhanced local and systemic immune responses and that i.n. recall immunization is required to induce both mucosal and systemic memory type responses.

New approaches to mucosal immunization

Every year more than 17 million deaths worldwide are caused by infectious diseases. The great majority of these deaths occur in underdeveloped countries and are attributed to diseases preventable by existing vaccines, or diseases that could potentially be prevented with new vaccines. The fact that most human and veterinary pathogens establish infection in the host by initiating contact at a mucosal surface, provide the rationale for the development of mucosal vaccines. An increasing number of strategies have been proposed to facilitate mucosal immunization. Among the most widely investigated strategies are the use of attenuated microorganisms; the inclusion of immunizing antigens in lipid-based carriers, the genetic creation of transgenic plants and the use of mucosal adjuvants derived from bacterial toxins. This review provides a brief summary of the most recent advances in the field of mucosal immunization with an special emphasis on a promising genetically detoxified mucosal adjuvant, LT(R192G), derived from the heat-labile toxin of enterotoxigenic E. coli. We present evidence regarding the safety, immunogenicity, and efficacy of LT(R192G) for the development of a new generation of mucosal vaccines.

Bm86 antigen induces a protective immune response against Boophilus microplus following DNA and protein vaccination in sheep

Vaccination of sheep with a plasmid bearing the full length gene for the tick antigen Bm86 either alone or co-administered with plasmid carrying the ovine genes for the cytokines, granulocyte and macrophage colony stimulating factor (GM-CSF) or interleukin (IL)-1beta induced a relatively low level of protection against subsequent tick infestation. This tick damage reached statistical significance only for the groups which were vaccinated with plasmid encoding for Bm86, co-administered with plasmid encoding for ovine GM-CSF. Antibody titres measured against Bm86 were also low in all groups injected with the Bm86 DNA vaccine. Antibody production and anti-tick effect were significantly less than that achieved by two vaccinations with recombinant Bm86 protein. In all cases only a low level of antigen-specific stimulation of peripheral blood lymphocytes was recorded, as measured either by the incorporation of tritiated thymidine or the release of IFN-gamma. Injection of DNA encoding for Bm86, either alone or with co-administered cytokine genes, did however prime for a strong subsequent antibody response following a single injection of recombinant Bm86 protein in adjuvant. Antibody production nevertheless appeared to be slightly less effective than following two vaccinations with recombinant protein. The persistence of antibody following vaccination was the same regardless of the method of primary sensitization. In all cases the half-life of the antibody response was approximately 40-50 days indicating that, in contrast to results reported in mice, DNA vaccination in sheep did not result in sustained antibody production.

Induction of Genital Immunity by DNA Priming and Intranasal Booster Immunization with a Replication-Defective Adenoviral Recombinant

Mice immunized through different routes such as i.m., intradermally, or intratracheally with a DNA vaccine to rabies virus developed high titers of serum Ab but only borderline levels of mucosal Abs determined from vaginal secretions. DNA vaccines given by either route enhanced vaginal IgA and IgG2a secretion upon a subsequent intranasal booster immunization with an E1-deleted adenoviral recombinant expressing the same Ag of rabies virus. DNA vaccine priming reduced the Ab response to the adenoviral Ags and counterbalanced the impaired B cell response to the rabies virus Ag expressed by the adenoviral recombinant in mice preimmune to adenovirus. The vaginal B cell response could further be enhanced by using the Th2-type cytokines IL-4 or IL-5 as genetic adjuvants concomitantly with the DNA vaccine before intranasal booster immunization with the recombinant vaccine.