Modulation of HIV immune responses in natural infection and after genetic immunization

Abstract

Identification and treatment of HIV-1 infection are both urgent, in view of the continued spread of the infection. We developed easy and inexpensive serological methods for the diagnosis and follow-up of children born to HIV-1-infected mothers. A quantitative immunofluorescence method replaced the cumbersome Western blot. The possibility of titrating antibodies made discrimination between HIV-infected and noninfected children feasible. In addition, we showed that an anti-HIV-1 IgA assay is effective for early diagnosis of HIV-1-infected children, with significant and high detection in children over 6 months of age.

Epitope reactivity might discriminate between different HIV-1 infected populations. Specificity of antibodies directed to conserved regions of HIV-1 was compared between patients from Argentina and Sweden. A new immunodominant region of gp41 was identified, against which the majority of Argentinian and Swedish patients showed reactivity. Although the epitope did not appear to be involved in functional reactivity, it may be useful as a diagnostic tool.

Reactivity against peptides representing the immunodominant third variable region of HIV-1 gpl20 was analyzed in sera from Argentinian patients. Some peptides representing the subtype B showed low reactivities, indicating the need to identify and characterize local strains in order to design adequate diagnostic and vaccine strategies.

The efficacy of HIV-DNA, a novel class of vaccines, was evaluated for induction of immune responses in humans. Asymptomatic HIV-1-infected patients were immunized with DNA constructs encoding either HIV-1 nef, rev or tat regulatory proteins. Patients were selected for having no or low antibody reactivities to the antigen encoded by the plasmid DNA used for immunization. The DNA immunization induced HIV-specific cytotoxic and proliferative cellular responses. Increased levels of cytotoxic memory cells were induced in all DNA-immunized patients. Antibody induction was of a low magnitude. This demonstrates for the first time that HIV-DNA vaccination may be capable of inducing or reinducing immune responses in HIV-infected humans.

Intensive chemotherapy is capable of reducing the viral load in HIV-1 infected individuals while infected cells are still present. HIV-specific cellular immune responses were evaluated in patients who started highly active antiretroviral treatment (HAART) during or after DNA immunizations. Significant reductions in viral load and increases in CD4+ counts were observed in those patients. DNA immunization by itself did not reduce viral load. The initiation of HAART therefore appears to contribute to the induction of HIV-specific CTL responses but by itself did not cause obvious re-induction of these activities.

The efficacy of a combination of plasmids encoding the HIV-1 regulatory genes (nef, rev and tat) was evaluated. The most remarkable change observed after immunization with the gene combination was the appearance of memory CTL against autologous targets infected with HIV-1. Autologous cells infected with HIV-1 will present all viral peptides and represent the in vivo situation. The possibility of enhancing HIV-specific immune responses in immunodeficient individuals is promising for continued genetic vaccine development.