Targeted delivery of siRNA to human T cells in vivo: Potential therapy for HIV infectionsTargeted delivery of siRNA to human T cells in vivo: Potential therapy for HIV infectionsTargeted delivery of siRNA to human T cells in vivo: Potential therapy for HIV infectionsTargeted delivery of siRNA to human T cells in vivo: Potential therapy for HIV infections

Abstract

RNA interference (RNAi) has a huge potential as a therapeutic method against the highly mutable HIV virus (1). However, a major obstacle for the clinical application of RNAi is the effective and efficient delivery of siRNAs specifically to T cells and macrophages, the major cell types infected by HIV. This problem is intensified by the fact that T cells are particularly resistant to transfection with nucleic acids. We are exploring a new strategy for the delivery of siRNA to human T cells using a single chain fragment antibody to CD7 (scFvCD7), a pan T cell marker. We conjugated scFvCD7 (2) to a positively charged oligo-9-arginine peptide (scFvCD7-9R) to enable siRNA binding and hence have achieve specific delivery of functionally siRNA into T cells and silenced target gene expression in vitro. For testing in vivo efficacy, we have generated Hu-PBL mice by reconstituting the novel NOD/SCID IL2gamma null mouse strain with human PBMC mouse and administered scFvCD79R/siRNA complexes through tail vein injections. scFvCD7-9R/siCD4 complexes specifically reduced surface expression of CD4 on T cells and these T cells were resistant to HIV infection ex vivo. Moreover, when Hu-PBL mice were treated with scFvCD7-9R complexed to a mixture of siRNAs targeting multiple viral genes and the viral coreceptor CCR5, they successfully resisted subsequent challenge with HIV-BaL. While control mice displayed massive CD4 T cell loss and high levels of p24 antigen in sera, treated mice maintained CD4 T cell numbers similar to uninfected mice and had almost negligible p24 levels in their sera. More importantly, this treatment was also able to preserve CD4 T cell numbers in Hu-PBL mice reconstituted with PBMC from HIV-seropositive individuals. These results indicate that scFvCD7-9R may offer a viable strategy for siRNA-mediated therapy in established HIV infections.