Adenoviruses as vectors for HIV vaccines.

The tropism of adenoviruses (Ad) for mucosal epithelium makes them ideal vectors for the development of recombinant Ad-HIV vaccines. Currently, several Ad-HIV vaccine candidates are being tested in clinical and preclinical trials. Here, we review the progress on the safety, immunogenicity and efficacy of replication-competent and replication-defective Ad-HIV and Ad-SIV vaccines in animal models, including non-human primates. Replication-defective Ad-SIV gag vaccines have elicited cellular responses that control intravenous infection with an HIV/SIV chimeric immunodeficiency virus (SHIV), while replication-competent Ad-SIV env/rev/gag/nef vaccines have stimulated cellular and humoral responses and protected rhesus monkeys from a mucosal challenge with pathogenic SIV. The composition and advantages of these and other Ad vaccines are described, with particular emphasis on strategies to increase the immunogenicity of the replication-defective vaccines and the safety and efficacy of the replication-competent approach. The overall efficacy of Ad-based vaccines in non-human primates should encourage further evaluation of additional replication-competent and replication-defective Ad-HIV candidates in human trials.

Assessment of HIV-1 patient recruitability in the Republic of Guinea-Bissau using African versus North American hematology and biochemistry reference intervals.

Hematology and biochemistry reference intervals have been derived from healthy, HIV-negative populations to guide clinical trials worldwide. However, it is less clear how such values may be applied to clinical trials involving HIV-infected individuals. We show that contradictory interpretations about patient recruitability are reached when applying African versus North American reference intervals to an HIV-1 cohort in Guinea-Bissau. These observations underscore the need to question non-African guidelines in the context of HIV intervention clinical trials in Africa.

Development of standard operating procedures to obtain longitudinal vaginal specimens from nulliparous rabbits as part of HIV vaccine mucosal immunogenicity studies.

The New Zealand white rabbit model (Oryctolagus cuniculus) is widely used to test whether HIV vaccine candidates elicit systemic antibody responses; however, its use in mucosal immunology has not been fully exploited due to the difficulty in collecting mucosal specimens longitudinally and reproducibly. Here we describe feasible and non-feasible methods to collect vaginal and nasal specimens from nulliparous rabbits. Non-feasible methods were those resulting in poor reproducibility and considerable animal twitching during sampling, whereas feasible methods resulted in no animal twitching and potential for sampling reproducibility. Standard operating procedures (SOPs) were implemented to collect vaginal swabs yielding total IgA titres ranging from 12,500 to 312,500. Intranasal immunisation with a naked DNA vaccine encoding HIV gp140 elicited HIV envelope-specific IgA detectable in nasal but not in vaginal secretions. Our methods provide an alternative to reliably assess pre- and post-vaccination mucosal antibody titres longitudinally in rabbits as part of mucosal HIV vaccine immunogenicity studies.

Neutralizing antibody responses to subtype B and C adjuvanted HIV envelope protein vaccination in rabbits.

Improving the potency, breadth, and durability of neutralizing antibody responses to HIV are major challenges for HIV vaccine development. To address these challenges, the studies described evaluate in rabbits the titers, breadth, and epitope specificities of antibody responses elicited by HIV envelope subunit vaccines adjuvanted with MF59 with or without CpG oligodeoxynucleotide (ODN). Animals were immunized with trimeric o-gp140DeltaV2 derived from subtype B HIV-1(SF162) or subtype C HIV-1(TV1), or proteins from both strains. Immunization with SF162 or TV1 with MF59/CpG elicited higher titers of binding and neutralizing antibodies to SF162 than monovalent immunization with MF59 alone (P<0.01). Bivalent immunization increased binding and neutralizing antibody titers over single envelope immunization in MF59 (P<0.01). Bivalent immunization also improved neutralization breadth. Epitope mapping indicated neutralizing activity in rabbits was directed to V3 and V4. Overall, our data suggests that a multivalent vaccination approach with MF59 and CpG can enhance humoral responses to HIV-1.

Replicating rather than nonreplicating adenovirus-human immunodeficiency virus recombinant vaccines are better at eliciting potent cellular immunity and priming high-titer antibodies.

A major challenge in combating the human immunodeficiency virus (HIV) epidemic is the development of vaccines capable of inducing potent, persistent cellular immunity and broadly reactive neutralizing antibody responses to HIV type 1 (HIV-1). We report here the results of a preclinical trial using the chimpanzee model to investigate a combination vaccine strategy involving sequential priming immunizations with different serotypes of adenovirus (Ad)/HIV-1(MN)env/rev recombinants and boosting with an HIV envelope subunit protein, oligomeric HIV(SF162) gp140deltaV2. The immunogenicities of replicating and nonreplicating Ad/HIV-1(MN)env/rev recombinants were compared. Replicating Ad/HIV recombinants were better at eliciting HIV-specific cellular immune responses and better at priming humoral immunity against HIV than nonreplicating Ad-HIV recombinants carrying the same gene insert. Enhanced cellular immunity was manifested by a greater frequency of HIV envelope-specific gamma interferon-secreting peripheral blood lymphocytes and better priming of T-cell proliferative responses. Enhanced humoral immunity was seen in higher anti-envelope binding and neutralizing antibody titers and better induction of antibody-dependent cellular cytotoxicity. More animals primed with replicating Ad recombinants mounted neutralizing antibodies against heterologous R5 viruses after one or two booster immunizations with the mismatched oligomeric HIV-1(SF162) gp140deltaV2 protein. These results support continued development of the replicating Ad-HIV recombinant vaccine approach and suggest that the use of replicating vectors for other vaccines may prove fruitful.

Phage-displayed mimotopes recognizing a biologically active anti-HIV-1 gp120 murine monoclonal antibody.

Antibody-dependent cellular cytotoxicity (ADCC) is a host defense mechanism in which Fc receptor-bearing effector cells in combination with antigen-specific antibodies recognize and kill antigen-expressing target cells. The authors previously described a murine monoclonal antibody (MAb-ID6) that mediated ADCC activity against HIV-infected cells. It was demonstrated that the specificity of MAb-ID6 maps to the first 204 amino acids of gp120; however, the exact epitope was not identified. In the present work, by screening phage display libraries with MAb-ID6, the authors have mapped the corresponding epitope to amino acids 86-100 (HIV-1 gp120 sequence). This epitope lies within the C1 region of gp120 and is highly conserved among all subtypes and circulating recombinant forms of HIV-1. Thus, these phage mimotopes of C1 may serve as components of a vaccine for the induction of gp120-specific antibodies mimicking MAb-ID6.

Protection against mucosal simian immunodeficiency virus SIV(mac251) challenge by using replicating adenovirus-SIV multigene vaccine priming and subunit boosting.

Whereas several recent AIDS vaccine strategies have protected rhesus macaques against a pathogenic simian/human immunodeficiency virus (SHIV)(89.6P) challenge, similar approaches have provided only modest, transient reductions in viral burden after challenge with virulent, pathogenic SIV, which is more representative of HIV infection of people. We show here that priming with replicating adenovirus recombinants encoding SIV env/rev, gag, and/or nef genes, followed by boosting with SIV gp120 or an SIV polypeptide mimicking the CD4 binding region of the envelope, protects rhesus macaques from intrarectal infection with the highly pathogenic SIV(mac251). Using trend analysis, significant reductions in acute-phase and set point viremia were correlated with anti-gp120 antibody and cellular immune responses, respectively. Within immunization groups exhibiting significant protection, a subset (39%) of macaques have exhibited either no viremia, cleared viremia, or controlled viremia at the threshold of detection, now more than 40 weeks postchallenge. This combination prime-boost strategy, utilizing replication competent adenovirus, is a promising alternative for HIV vaccine development.