Human immunodeficiency virus

Efficiency of recombinant bacille Calmette-Guérin in inducing humoral and cell mediated immunities against human immunodeficiency virus type 1 third variable domain in immunized mice

PURPOSE

The third variable (V3) loop of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein has been intensively studied for AIDS vaccine development. Bacille Calmette-Guérin (BCG) is widely used to immunize against tuberculosis and has many advantages as a vaccine vehicle, such as low toxicity, adjuvant potential, low cost, and long-lasting immune-inducing capacity. This work was initiated to investigate the immunogenicity of recombinant BCG (rBCG-mV3) designed to express trimeric HIV-1 V3 loop (mV3) in rBCG-mV3-immunized animals.

MATERIALS AND METHODS

HIV-1 V3-concatamer was cloned into pMV261, a BCG-expression vector, and then rBCG-mV3 was constructed by introducing the recombinant plasmid (pMV-V3). The recombinant BCG was examined with regard to its expression of V3-concatamer and the genetic stability in vivo and in vitro. The immune responses induced by recombinant BCG were tested in immunized mice and guinea pigs.

RESULTS

The rBCG-mV3 expressed detectable amounts of V3-concatamer when induced by single heat-shock. The recombinant BCG was genetically stable and maintained the introduced mV3 gene for several weeks. V3-specific antibodies were clearly detected 6 weeks after inoculation. The antibody titer rapidly increased after immunization up to 10 weeks, and then maintained for over 4 weeks. IgG2a was prevalent in the V3-specific antiserum. The recombinant BCG was also effective in inducing delayed-type hypersensitivity responses in the immunized guinea pigs. rBCG-immunized mice retained substantial amounts of V3-specific T cells in the spleen, even 5 months after the first immunization.

CONCLUSION

Recombinant BCG-mV3 is very efficient in inducing humoral and long-lasting cell-mediated immunity against HIV-1 V3 in the immunized animals.

In vitro intersubtype recombinants of human immunodeficiency virus type 1: comparison to recent and circulating in vivo recombinant forms

The increased prevalence of human immunodeficiency virus type 1 (HIV-1) intersubtype recombinants (ISRs) is shaping HIV-1 evolution throughout the world and will have an impact on both therapeutic and vaccine strategies. This study was designed to generate and compare in vitro ISRs to those isolated from HIV-infected individuals throughout the world. Human peripheral blood mononuclear cells were dually infected with seven pairs of HIV-1 isolates from different subtypes (i.e., A to F). Recombinant crossover sites were mapped to specific regions in the envelope (env) gene by using a cloning-hybridization technique and subtype-specific probes. In vitro intersubtype recombination was at least twofold more frequent in the V1-to-V3 region than in any other env fragment, i.e., C1 to V1, V3 to V5, or V5 to gp41. Sequence and recombination site analyses suggested the C2 env domain as a "hot region" for recombination and selection of replication-competent ISRs during the 15-day incubation. In addition to these regional preferences for env recombination, homopolymeric nucleotide tracts, i.e., sequences known to pause reverse transcriptase and promote template switching, were found in most in vitro crossover sites. ISRs, originating from recent dual infections and limited transmission events, partly retained this in vitro regional or sequence preference for recombination sites. However, a shift to crossover sites flanking the gp120-coding sequence was evident in the stable circulating recombinant forms of HIV-1. Based on these findings, HIV-1 recombinants generated from these dual infections may be used as a model for in vivo intersubtype recombination and for the design of various diagnostic assays and vaccine constructs.

Variability and immunogenicity of caprine arthritis-encephalitis virus surface glycoprotein

The complete surface glycoprotein (SU) nucleotide sequences of three French isolates of caprine arthritis-encephalitis virus (CAEV) were determined and compared with those of previously described isolates: three American isolates and one French isolate. Phylogenetic analyses revealed the existence of four distinct and roughly equidistant evolutionary CAEV subtypes. Four conserved and five variable domains were identified in the SU. The fine specificities of antibodies produced against these domains during natural infection were examined using a pepscan analysis. Nine immunogenic segments were delineated throughout the conserved and variable domains of SU, two of them corresponding to conserved immunodominant epitopes. Antigenic determinants which may be involved in the immunopathogenic process induced by CAEV were identified. These results also provide sensitive and specific antigen peptides for the serological detection and differentiation of CAEV and visna/maedi virus infections.

Pronounced acute immunosuppression in vivo mediated by HIV Tat challenge

HIV infection is accompanied by an early immune dysfunction limiting host control of virus and likely contributing to difficulties in achieving a successful vaccine against HIV. We report here that the HIV Tat protein is strongly immunosuppressive, both immediately after immunization of mice with soluble protein (sTat), and in seroconverting humans, and propose that Tat-induced suppression cripples immune surveillance to HIV infection. We show that macrophages are sensitive to sTat stimulation at concentrations 1,000-fold lower (500 pM) than T cells, and this stimulation is accompanied by the immunosuppressive induction of Fas ligand on the macrophage. T cell proliferative defects induced by sTat in vitro can be completely (at lower concentrations of sTat) or partially (at higher concentrations) reversed by antagonists to Fas/Fas ligand interaction. We further report a method to preserve immunogenicity while inactivating Tat immunosuppression through oxidation, which advances the use of oxidized Tat as a component of an anti-HIV vaccine. These observations define additional methods to study the immunosuppressive functions of sTat that now may be rapidly applied to primary isolates from individuals with differing clinical courses. Our findings have immediate relevance for vaccine development, by describing and supporting a strategy that includes inactivated sTat in a multicomponent, anti-HIV vaccine.