HIV-1 is still a major public health problem and one of the priorities of the World Health Organization. The development of HAART against HIV was a considerable advance for infected individuals, but this life-long treatment does only block virus replication, and no viral eradication is obtained. Furthermore, HAART may exhibit long-term toxicity and may eventually lead to the emergence of drug-resistant viral variants. We explore a new durable therapeutic intervention based on a gene therapy that induces RNA interference (RNAi) against HIV-1. In this pre-clinical research setting, "humanized" experimental mouse models are of interest considering the relative ease of handling and relatively low cost as compared to non-human primates.
We have developed an RNAi gene therapy based on the transduction of human hematopoietic progenitor cells (HPC) with lentiviral vectors encoding short-hairpin RNAs to induce silencing of HIV genes. We have tested the efficacy and safety of such a shRNA-based gene therapy strategy in the "Human Immune System" (HIS) BALB/c Rag2-/-IL-2Rγc-/- mouse model, which are reconstituted with human HPC that were first transduced ex vivo with a lentiviral vector expressing the antiviral shRNAs.
We observed a normal in vivo development of the human immune system with a good recovery of human shRNA+cells for the candidate shPol47, shPol1 and shRT5 inhibitors. However, the in vivo recovery of human shGag5-transduced cells was extremely poor, suggesting a negative impact of this specific shRNA on the development of the human immune system. When these 4 shRNAs were combined in a single lentiviral vector (R4), we observed a similar negative off-target effect due to the shGag5 component. Upon removal of shGag5 as in vector R3, transduction of human HPC results in a normal differentiation of the human immune system, highlighting the in vivo safety of this candidate R3 gene therapy vector for a clinical trial. Moreover, human HPC expressing the antiviral shNef generate human CD4+T cells with the ability to resist HIV-1 replication in a sequence specific manner.
Overall, these results underscore the usefulness of the HIS (BALB-Rag/γ) mouse model for testing the safety and efficacy of durable anti-HIV gene therapy approaches. In this model, human HPC expressing anti-HIV-1 shRNA give rise to multi-lineage reconstitution of the immune system in vivo and generate CD4+ T cells that are not susceptible for HIV-1 replication.