Conference summary: novel HIV therapies--from discovery to clinical proof of concept

Inhibition of HIV-1 by an anti-integrase single-chain variable fragment (SFv): delivery by SV40 provides durable protection against HIV-1 and does not require selection

Human immunodeficiency virus type 1 (HIV-1) encodes several proteins that are packaged into virus particles. Integrase (IN) is an essential retroviral enzyme, which has been a target for developing agents to inhibit virus replication. In previous studies, we showed that intracellular expression of single-chain variable antibody fragments (SFvs) that bind IN, delivered via retroviral expression vectors, provided resistance to productive HIV-1 infection in T-lymphocytic cells. In the current studies, we evaluated simian-virus 40 (SV40) as a delivery vehicle for anti-IN therapy of HIV-1 infection. Prior work suggested that delivery using SV40 might provide a high enough level of transduction that selection of transduced cells might be unnecessary. In these studies, an SV40 expression vector was developed to deliver SFv-IN (SV(Aw)). Expression of the SFv-IN was confirmed by Western blotting and immunofluorescence staining, which showed that > 90% of SupT1 T-lymphocytic cells treated with SV(Aw) expressed the SFv-IN protein without selection. When challenged, HIV-1 replication, as measured by HIV-1 p24 antigen expression and syncytium formation, was potently inhibited in cells expressing SV40-delivered SFv-IN. Levels of inhibition of HIV-1 infection achieved using this approach were comparable to those achieved using murine leukemia virus (MLV) as a transduction vector, the major difference being that transduction using SV40 did not require selection in culture whereas transduction with MLV did require selection. Therefore, the SV40 vector as gene delivery system represents a novel therapeutic strategy for gene therapy to target HIV-1 proteins and interfere with HIV-1 replication.

Diversity of HIV-1 Vpr interactions involves usage of the WXXF motif of host cell proteins

Targeting protein or RNA moieties to specific cellular compartments may enhance their desired functions and specificities. Human immunodeficiency virus type I (HIV-1) encodes proteins in addition to Gag, Pol, and Env that are packaged into virus particles. One such retroviral-incorporated protein is Vpr, which is present in all primate lentiviruses. Vpr has been implicated in different roles within the HIV-1 life cycle. In testing a new hypothesis in which viral proteins are utilized as docking sites to incorporate protein moieties into virions, we used the peptide phage display approach to search for Vpr-specific binding peptides. In the present studies, we demonstrate that most of the peptides that bind to Vpr have a common motif, WXXF. More importantly, we demonstrate that the WXXF motif of uracil DNA glycosylase is implicated in the interaction of uracil DNA glycosylase with Vpr intracellularly. Finally, a dimer of the WXXF motif was fused to the chloramphenicol acetyl transferase (CAT) gene, and it was demonstrated that the WXXF dimer-CAT fusion protein construct produces CAT activity within virions in the presence of Vpr as a docking protein. This study provides a novel potential strategy in the targeting of anti-viral agents to interfere with HIV-1 replication.

Development of a novel anti-HIV-1 agent from within: effect of chimeric Vpr-containing protease cleavage site residues on virus replication

Effective antiviral agents will be of great value in controlling virus replication and delaying the onset of HIV-1-related disease symptoms. Current therapy involves the use of antiviral agents that target the enzymatic functions of the virus, resulting in the emergence of resistant viruses to these agents, thus lowering their effectiveness. To overcome this problem, we have considered the idea of developing novel agents from within HIV-1 as inhibitors of virus replication. The specificity of the Vpr protein for the HIV-1 virus particle makes it an attractive molecule for the development of antiviral agents targeting the events associated with virus maturation. We have generated chimeric Vpr proteins containing HIV-1-specific sequences added to the C terminus of Vpr. These sequences correspond to nine cleavage sites of the Gag and Gag-Pol precursors of HIV-1. The chimeric Vpr constructs were introduced into HIV-1 proviral DNA to assess their effect on virus infectivity using single- and multiple-round replication assays. The virus particles generated exhibited a variable replication pattern depending on the protease cleavage site used as a fusion partner. Interestingly, the chimeric Vpr containing the cleavage sequences from the junction of p24 and p2, 24/2, completely abolished virus infectivity. These results show that chimeric proteins generated from within HIV-1 have the ability to suppress HIV-1 replication and make ideal agents for gene therapy or intracellular immunization to treat HIV-1 infection.