Replicating viral vectors as HIV vaccines: summary report from the IAVI-sponsored satellite symposium at the AIDS vaccine 2009 conference.

In October 2009, The International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Replicating Viral Vectors for use in AIDS Vaccines' at the AIDS Vaccine 2009 Conference in Paris. The purpose of the symposium was to gather together researchers, representatives from regulatory agencies, and vaccine developers to discuss issues related to advancement of replication-competent viral vector- based HIV vaccines into clinical trials. The meeting introduced the rationale for accelerating the development of replicating viral vectors for use as AIDS vaccines. It noted that the EMEA recently published draft guidelines that are an important first step in providing guidance for advancing live viral vectors into clinical development. Presentations included case studies and development challenges for viral vector-based vaccine candidates. These product development challenges included cell substrates used for vaccine manufacturing, the testing needed to assess vaccine safety, conducting clinical trials with live vectors, and assessment of vaccination risk versus benefit. More in depth discussion of risk and benefit highlighted the fact that AIDS vaccine efficacy trials must be conducted in the developing world where HIV incidence is greatest and how inequities in global health dramatically influence the political and social environment in developing countries.

Safety and immunogenicity of a canarypox-vectored human immunodeficiency virus Type 1 vaccine with or without gp120: a phase 2 study in higher- and lower-risk volunteers.

Live attenuated viral vectors that express human immunodeficiency virus (HIV) antigens are being developed as potential vaccines to prevent HIV infection. The first phase 2 trial with a canarypox vector (vCP205, which expresses gp120, p55, and protease) was conducted in 435 volunteers with and without gp120 boosting, to expand the safety database and to compare the immunogenicity of the vector in volunteers who were at higher risk with that in volunteers at lower risk for HIV infection. Neutralizing antibodies to the MN strain were stimulated in 94% of volunteers given vCP205 plus gp120 and in 56% of volunteers given vCP205 alone. CD8(+) cytotoxic T lymphocyte cells developed at some time point in 33% of volunteers given vCP205, with or without gp120. Phase 3 field trials with these or similar vaccines are needed, to determine whether efficacy in preventing HIV infection or in slowing disease progression among vaccinees who become infected is associated with the level and types of immune responses that were induced by the vaccines in this study.

A human immunodeficiency virus prime-boost immunization regimen in humans induces antibodies that show interclade cross-reactivity and neutralize several X4-, R5-, and dualtropic clade B and C primary isolates.

A human immunodeficiency virus (HIV) vaccine that will be useful in diverse geographic regions will need to induce a broad immune response characterized by cross-clade immunity. To test whether a clade B-based HIV candidate vaccine could induce interclade humoral responses, including neutralizing activity against primary HIV-1 isolates, sera were tested from recipients of a vaccine consisting of recombinant canarypox virus vCP205 and recombinant gp120(SF2). Serum antibodies exhibited strong immunochemical cross-reactivity with V3 peptides from clades B, C, and F, with weaker activity for several V3 peptides from clades A, D, G, and H; essentially no reactivity could be demonstrated with V3 peptides from clades E and O. Extensive cross-clade reactivity was also documented by enzyme-linked immunosorbent assay with all nine recombinant HIV envelope glycoproteins tested from clades B, D, and E. In addition, vaccinees' sera displayed significant neutralizing activity against 5 of 14 primary isolates tested, including one X4 virus and two dualtropic viruses (from clade B) and two R5 viruses (from clades B and C). This is the first demonstration of the induction by a candidate HIV vaccine constructed from clade B laboratory strains of HIV of neutralizing activity against R5 and clade C primary isolates. The data suggest that, by virtue of their ability to induce cross-clade immune responses, appropriately formulated HIV vaccines based on a finite number of HIV isolates may ultimately be able to protect against the wide range of HIV isolates affecting the populations of many geographic regions.

Human immunodeficiency virus vaccine development in developing countries: are efficacy trials feasible?

The implementation of human immunodeficiency virus (HIV) vaccine efficacy trials in developing countries represents an unprecedented series of challenges for the medical and scientific communities, health authorities, policy makers, and the populations of diverse countries. Such trials require great attention, dedication, and information at the earliest possible time from many groups in these communities, as well as the clear and full collaboration of all the national and international institutions and agencies involved. This article discusses suggestions and makes recommendations regarding multiple hurdles to trial implementation, including access to appropriate populations, incidence and natural history of HRV type 1 (HIV-1) infection, definition of efficacy endpoints, and logistical, ethical, regulatory, political, and media issues. The conduct of phase I and II trials in developing countries will be a critical step for appropriate vaccine selection and in helping to identify the country- and community-specific issues and the needs for further implementation. Some countries have already established their own national HIV vaccine development plans. Additional operational and action plans with special emphasis on efficacy trial implementation would be strongly recommended after country-specific preparedness workshops and constitution of national or regional task forces.

IgG subclass distribution in serum and various mucosal fluids of HIV type 1-infected subjects.

We measured total IgG1, IgG2, IgG3, and IgG4 concentrations by ELISA in serum (S), total saliva (TS), cervicovaginal secretions (CVS), seminal secretions (SPE), and rectal secretions (RS) from either CDC II/III HIV-1-infected subjects or healthy volunteers. Human serum albumin was measured in parallel to calculate the relative coefficient of excretion (RCE). Levels of IgG1 and IgG3 directed against gp120 MN also were measured by ELISA in all samples, and the specific activity (SA) calculated. HIV-1-specific IgG2 and IgG4 were not compared, as total IgG2 and total IgG4 levels in HIV-1-infected subjects were found to be lower than in the healthy controls. Despite substantial interindividual variability, total IgG1 and IgG3 concentrations in all fluids were greater in the HIV-1-infected subjects than in the healthy controls. Calculations of RCE indicated predominantly a transudative origin for IgG subclasses in the different mucosal fluids, except for CVS, in which IgG1, IgG2, and IgG4 was produced locally. The transduction behavior of IgG3 in secretions appears to be different from that of other IgG subclasses. HIV-1-infected subjects were considered positive for IgG1 and IgG3 antibodies against gp120 MN if their antibody levels exceeded the maximum titer measured in the control group. Positive levels of anti-gp120 MN IgG1 were detected for 100% of HIV-1-infected individuals in S, CVS, and SPE, 97% in TS, and 75% in RS. Fewer subjects had positive levels of IgG3 to gp120 MN in their secretions (maximum 67% in CVS). Despite the low concentrations of total IgG3, mean SA values for IgG3 to gp120 MN were greater in secretions than in serum. No significant difference in the SA values for IgG1 to gp120 MN was observed between the different fluids. Only CVS had a local production of HIV-specific IgG1 Our results highlight the importance of an HIV-specific IgG1 and IgG3 immune response in mucosal fluids from HIV-1-infected subjects.

Comparison of the distribution of IgG and IgA antibodies in serum and various mucosal fluids of HIV type 1-infected subjects.

We compared IgG and IgA distribution in serum, three different salivary samples, two different rectal secretion samples, cervicovaginal secretions, and seminal secretions from asymptomatic CDC stage II/III HIV-1-infected subjects (n = 44) and from HIV-1-seronegative volunteers (n = 52). In-house ELISAs were used to measure total IgG and total IgA levels, as well as HIV-specific anti-gp120 MN and anti-p24 LAI IgG and IgA. Human serum albumin was titrated in parallel to calculate the relative coefficient of excretion (RCE). In spite of substantial interindividual variability, total IgG concentrations in all fluids were found to be significantly greater in the HIV-1-infected group than in the seronegative subjects. Calculation of RCE values revealed three different types of mucosal secretion: secretions with no local Ig production, such as sperm; secretions with local production of IgA and transudative origin of IgG, such as salivary and rectal samples; and secretions with local production of both IgG and IgA, such as in cervicovaginal secretions. For all mucosal specimens from HIV-1-infected subjects, the response to HIV-1 was predominantly IgG, with highest titers observed in cervicovaginal secretions (although these were lower than serum levels). In contrast, the specific IgA response appeared weaker in the mucosa than in serum.

A canarypox vaccine expressing multiple human immunodeficiency virus type 1 genes given alone or with rgp120 elicits broad and durable CD8+ cytotoxic T lymphocyte responses in seronegative volunteers.

Induction of CD8+ cytotoxic T cells is considered one of the important correlates for the protective efficacy of candidate human immunodeficiency virus type 1 (HIV-1) vaccines. To induce CD8+ cytotoxic T lymphocytes (CTLs) along with neutralizing antibody and CD4+ T cell help, a live canarypox virus construct expressing gp120, transmembrane gp41, the gag and protease genes, and sequences containing CTL epitopes in nef and pol was given simultaneously with, or followed by, rgp120 SF2. CD8+ CTLs were detected in 61% of volunteers at some time during the trial. Three to 6 months after the last immunization, the gene-specific responses were gag, 26/81; env, 17/77; nef, 12/77; and pol, 3/16. Simultaneous immunization with the canarypox vector and the subunit, beginning with the initial immunization, resulted in earlier antibody responses. In summary, a strategy of immunization with a canarypox vector expressing multiple genes of HIV-1 given with gp120 results in durable CD8+ CTL responses to a broad range of epitopes.

Safety and immunogenicity of a live recombinant canarypox virus expressing HIV type 1 gp120 MN MN tm/gag/protease LAI (ALVAC-HIV, vCP205) followed by a p24E-V3 MN synthetic peptide (CLTB-36) administered in healthy volunteers at low risk for HIV infection. AGIS Group and L'Agence Nationale de Recherches sur Le Sida.

A live recombinant canarypox vector expressing HIV-1 gpl20 MN tm/gag/protease LAI (ALVAC-HIV, vCP205) alone or boosted by a p24E-V3 MN synthetic peptide (CLTB-36) was tested in healthy volunteers at low risk for HIV infection for their safety and immunogenicity. Both antigens were well tolerated. ALVAC-HIV (vCP205) induced low levels of neutralizing antibodies against HIV-1 MN in 33% of the volunteers. None of them had detectable neutralizing antibodies against a nonsyncytium-inducing HIV-1 clade B primary isolate (Bx08). After the fourth injection of vCP205, CTL activity was detected in 33% of the volunteers and was directed against Env, Gag, and Pol. This activity was mediated by both CD4+ and CD8+ lymphocytes. On the other hand, the CLTB-36 peptide was poorly immunogenic and induced no neutralizing antibodies or CTLs. Although the ALVAC-HIV (vCP205) and CLTB-36 prime-boost regimen was not optimal, further studies with ALVAC-HIV (vCP205) are warranted because of its clear induction of a cellular immune response and utility as a priming agent for other subunit antigens such as envelope glycoproteins, pseudoparticles, or new peptides.

Development and standardization of methods to evaluate the antibody response to an HIV-1 candidate vaccine in secretions and sera of seronegative vaccine recipients.

Enzyme-linked immunosorbent assays (ELISA) were developed to test, in serum and mucosal samples, total IgG, total IgA, serum albumin, and anti-gp120 MN and anti-p24 LAI IgG and IgA levels. These ELISAs were optimized according to reagents and experimental conditions. Inter- and intra-assay coefficients of variation ranged from 3.3% to 18.6%. The ELISA results were linear and precise, and for anti-HIV-1 IgG and IgA, the analytical recovery was close to 100%. For IgG and IgA titration against gp120 MN and p24 LAI, standards were made using pooled sera or gammaglobulins with assigned titres in ELISA units per ml (EU/ml). These standards were used to obtain a linear regression curve that could then be used to obtain the titres of experimental samples. The cut-offs for positivity were determined for sera and mucosal fluid using healthy controls. Validation conditions were defined for ELISAs, and samples that did not satisfy these conditions were retested. Measurement of total IgG and IgA allowed normalization and comparison of the results of specific immunoglobulin levels between different samples. Serum albumin was tested as a marker of transudation from serum to mucosal fluid, allowing calculation of the relative coefficient of excretion, which is one element required to determine the origin of the immunoglobulin detected in mucosal samples. These ELISAs were developed with samples from HIV-1-infected and healthy subjects. We now have the tools to study and understand mucosal immunity in seronegative subjects vaccinated with an HIV-1 candidate vaccine.

Neutralization of syncytium-inducing primary isolates by sera from human immunodeficiency virus (HIV)-uninfected recipients of candidate HIV vaccines.

Most candidate human immunodeficiency virus (HIV)-1 vaccines induce antibodies that neutralize T cell line-adapted HIV-1 strains. Until recently, however, no neutralizing activity against primary HIV-1 isolates had been demonstrated in sera from human vaccinees. Since most candidate HIV-1 vaccines have been constructed from T cell line-adapted syncytium-inducing (SI) strains, experiments were done to test whether sera from recipients of SI-based vaccines could preferentially neutralize SI primary HIV-1 isolates. Various neutralization assays were performed with sera from volunteers receiving ALVACgp160MN and/or rgp120SF2. Neutralizing activity was detected against 4 of 8 SI primary isolates but against none of 5 non-SI primary isolates. The data suggest that, for the induction of neutralizing antibodies to a broad array of HIV-1 primary isolates, a polyvalent vaccine will be needed containing representatives of more than a single category of viruses.

Potentials and limitations of protein vaccines in infants.

Immunization of infants represents a difficult challenge since immune responses in infants differ qualitatively from those of adults (immature immune and bias towards Th2 rather than a Th1 immune responses). While protein vaccines are immunogenic in infants earlier than polysaccharides in the very first months of life, requiring repeated administration. Protein vaccines such as diphtheria and tetanus toxoids and hepatitis B antigens are safe and immunogenic in infants, able to induce long-lasting memory, and effective. HB vaccines are the first vaccines administered at birth against a sexually transmitted disease and that prevent cancer. These success stories must however be tempered by the existence of immunologic interferences that may occur when combining vaccines in a single injection. Moreover, very little is known whether inappropriate protein conformation and glycosylation play roles in the impairment of the functional immunogenicity of protein vaccines in infants. Although much is known about how to produce and purify proteins, we know much less about how protein characteristics are related to functional immunogenicity.

Immune responses to human immunodeficiency virus (HIV) type 1 induced by canarypox expressing HIV-1MN gp120, HIV-1SF2 recombinant gp120, or both vaccines in seronegative adults. NIAID AIDS Vaccine Evaluation Group.

A safety and immunogenicity trial was conducted in vaccinia-immune and vaccinia-naive human immunodeficiency virus (HIV)-uninfected adults who were randomized to receive 10(6) or 10(7) TCID50 of canarypox (ALVAC) vector expressing HIV-1MN gp160 or 10(5.5) TCID50 of ALVAC-rabies virus glycoprotein control at 0 and 1 or 2 months and ALVAC-gp160 or 50 microg of HIV-1SF2 recombinant (r) gp120 in microfluidized emulsion at 9 and 12 months; others received rgp120 at 0, 1, 6, and 12 months. All vaccines were well-tolerated. Neither vaccinia-immune status before vaccination nor ALVAC dose affected HIV immune responses. HIV-1MN and HIV-1SF2 neutralizing antibodies were detected more often (100%) in ALVAC-gp160/rgp120 recipients than in recipients of ALVAC-gp160 (<65%) or rgp120 (89%) alone. ALVAC-gp160/rgp120 also elicited more frequent HIV V3-specific and fusion-inhibition antibodies, antibody-dependent cellular cytotoxicity, lymphoproliferation, and cytotoxic CD8+ T cell activity than did either vaccine alone. Trials with ALVAC expressing additional HIV components and rgp120 are underway.

Induction of immune responses to HIV-1 by canarypox virus (ALVAC) HIV-1 and gp120 SF-2 recombinant vaccines in uninfected volunteers. NIAID AIDS Vaccine Evaluation Group.

OBJECTIVE: To determine the ability of live attenuated canarypox virus expressing HIV antigens to induce CD8+ cytotoxic T-cell responses and to prime for neutralizing antibody responses to boosting with purified recombinant gp120 subunit vaccine. DESIGN: A prospective, double-blind, randomized, immunogenicity and safety study was conducted in healthy adults at low risk for acquiring HIV infection and who were seronegative for HIV. METHODS: CD8+ cytotoxic T-cells directed against Env or Gag expressing target cells were measured after live recombinant canarypox-HIV-1 vaccine priming (vaccine given at days 0, 7, 14 and 21). Neutralizing antibodies were measured after subunit boosting (vaccine given at days 28 and 84). RESULTS: CD8+ CTL were induced in 64% of volunteers by the live recombinant canarypox-HIV-1 vaccine. All volunteers who received two doses of subunit vaccine after live recombinant canarypox priming developed neutralizing antibodies directed against laboratory strains of HIV-1 and seven out of eight volunteers tested developed neutralizing antibodies to the primary isolate, BZ167, but to none of eight other primary isolates. Unprimed controls had low or absent neutralizing antibodies after two doses of subunit vaccine. CONCLUSIONS: The live canarypox vector was safe, stimulated cytotoxic T-cells and primed for a vigorous neutralizing antibody response upon boosting with subunit gp120 vaccine. This vaccine combination should be evaluated further for inducing protection against HIV infection.

Restricted specificity of anti-V3 antibodies induced in humans by HIV candidate vaccines.

We analyzed the fine specificity of anti-V3 antibodies elicited in three different species (human, guinea pig, and macaque) by various HIV candidate vaccines. Following immunization with recombinant canarypox virus expressing gp160MN or with recombinant gp160MN/LAI, this antibody response was shown to be directed against the NH2-terminal region of the V3 loop. Although this response was increased by a prime-boost regimen using immunization with canarypox expressing gp160 followed by an rgp160 boost, its specificity remained restricted mainly to the recognition of this region of the V3 loop. Pepscan analysis of sera confirmed the results obtained by ELISA and allowed the definition of an immunodominant common binding site for these sera located within the sequence NKRKRIHIGPGR. In contrast to these results, a boost with the V3 peptide was shown to broaden the antibody response and pepscan analysis showed that sera from individuals boosted with the V3 synthetic peptide recognize determinants all along the V3 loop. Similar fine specificity of anti-V3 antibodies was obtained in human, guinea pig, and macaque following immunization by a prime-boost regimen using canarypox recombinants expressing gp160 or gp120 and purified rgp160. In contrast, a V3 synthetic peptide boost stimulated the production of antibodies that recognize multiple epitopes within the V3 loop. Because the induction of antibodies that recognize multiple sites in the V3 loop could be of major importance to neutralize different HIV isolates, these results may have implications for the design and selection of HIV candidate vaccines.

Neutralization of a clade B primary isolate by sera from human immunodeficiency virus-uninfected recipients of candidate AIDS vaccines.

The inability of antibodies induced by experimental human immunodeficiency virus type 1 (HIV-1) vaccines to neutralize HIV-1 primary isolates may be due to a failure to elicit such antibodies, antigenic differences between the vaccine and the strains tested, insensitivity of the assays used, or to a combination of factors. New neutralization assays were used to determine the ability of candidate AIDS vaccines to generate neutralizing antibodies for clade B primary isolate BZ167, which is closely related in portions of its envelope to the immunizing strains. Sera from HIV-uninfected volunteers in vaccine trials were tested, and neutralizing activity was found in recipients of recombinant (r) gp120MN or of rgp160MN-containing canarypox boosted with rgp120SF-2. Detection of antibodies that neutralize primary isolate BZ167 correlated with neutralizing activity for homologous vaccine strains. These data demonstrate that certain candidate AIDS vaccines can elicit antibodies that neutralize a primary isolate of HIV-1.

Clade B-based HIV-1 vaccines elicit cross-clade cytotoxic T lymphocyte reactivities in uninfected volunteers.

A fundamental goal of current strategies to develop an efficacious vaccine for AIDS is the elicitation of broadly reactive cytotoxic T lymphocyte (CTL) reactivities capable of destroying virally infected targets. Recent application of recombinant canarypox ALVAC/HIV-1 vectors as vaccine immunogens in HIV-1,-noninfected volunteers has produced CTL responses in a significant number of vaccinees. Using a newly developed targeting strategy, we examined the capacity of vaccine-induced CTL to lyse autologous targets infected with a diverse group of viral isolates. CTL derived from recipients of a canarypox ALVAC/HIV-1 gp160 (MN) vaccine were found capable of lysing autologous CD4+ lymphoblasts infected with the prototypic LAI strain of HIV-1. When tested against autologous targets infected with primary HIV-1 isolates representing genetically diverse viral clades, CTL from ALVAC/gp160 recipients showed both a broad pattern of cytolysis in which viruses from all clades tested were recognized as well as a highly restricted pattern in which no primary isolates, including clade B, were lysed. Differences in the HLA haplotypes of the volunteers immunized with the envelope vector might be a major determinant of the relative breadth of their CTL response. In contrast to ALVAC/gp160 vaccinees, recipients of the ALVAC/HIV-1 immunogen containing envelope as well as gag and protease genes consistently had CTL reactivities effective against a spectrum of primary isolate-infected targets. These studies demonstrate for the first time that clade B-based canarypox vaccines can elicit broad CTL reactivities capable of recognizing viruses belonging to genetically diverse HIV-1 clades. The results also reinforce the impact of viral core elements in the vaccine as well as the pattern of major histocompatibility complex class I allelic expression by the vaccine recipient in determining the relative breadth of the cellular response.

Memory cytotoxic T lymphocyte responses in human immunodeficiency virus type 1 (HIV-1)-negative volunteers immunized with a recombinant canarypox expressing gp 160 of HIV-1 and boosted with a recombinant gp160.

A vaccine against human immunodeficiency virus (HIV) should induce virus-specific cytotoxic T lymphocyte (CTL) activity. Immunization of uninfected volunteers with a canarypox virus expressing HIV envelope was carried out in a phase I trial. Two injections of canarypox expressing HIV-1MN gp 160 (months 0 and 1) were followed by two boosts of recombinant envelope protein (months 3 and 6). HIV envelope-specific CTL were detected in peripheral blood mononuclear cells stimulated with autologous HIV-1-infected blast cells. T cell lines were obtained from 18 of 20 donors: CTL were detected at least once following immunization in 7 (39%) of these 18. This activity was mediated by major histocompatibility complex class I-restricted CD3+CD8+ T cells. For two subjects, this activity was still present 2 years after the initial immunization. The CTL responses with this prime-boost regimen are the best observed with any HIV vaccine tested in humans.