The Molecular Virology and Vaccinology Unit (VMV) is implicated in a variety of research projects ranging from the basic study of the early steps of HIV-1 replication, through lentiviral vectorology, to applied gene therapy and vaccination projects. This apparent diversity is in fact unified by a central property of lentiviruses that distinguishes them from all other retroviruses: their ability to efficiently replicate in non-dividing cell targets.
Molecular Virology: Active nuclear import of the HIV-1 genome into the interphasic nucleus is the key feature that accounts for mitosis independent replication of lentiviruses. We showed earlier that a three-stranded DNA structure, called central DNA Flap, created during HIV-1 reverse transcription at the exact center of the HIV-1 DNA genome, acts as a cis-determinant of HIV-1 DNA nuclear import. HIV-1 mutant viruses, or first-generation lentiviral vectors, which lack the DNA Flap show a strong default of entry into the cell nucleus. An extensive mechanistic study of the role of the DNA Flap in HIV-1 nuclear import has been conducted, combining molecular, cellular and ultrastructural approaches. We found that DNA Flap formation, the very last event in HIV-1 reverse transcription, acts as a viral promoting element for the uncoating of the reverse transcription complex (RTC), including an intact capsid shell, to form the pre-integration complex (PIC), that has a size compatible with translocation through the nuclear pore. Most interestingly, scanning electron microscopy studies revealed that DNA Flap defective viruses accumulate at the nuclear pore trapped within intact capsids. This reveals a direct impact of the DNA Flap in an as-yet unexplored step of HIV-1 replication: the maturation (or uncoating) of the RTC into PIC at the nuclear pore. Ongoing work and research projects include the study of HIV-1 host-cell interactions for nuclear import and ultra-structural analysis of the HIV-1 PIC.
Vectorology/Gene Therapy: Mitosis-independent replication of HIV is exploited by lentiviral vector technology for the efficient transduction of non-mitotic cells. We showed a few years ago that re-insertion of the DNA Flap into lentiviral vectors strongly stimulates gene transfer efficiency, including in human hematopoietic stem cells (HSC), brain or liver cells. DNA Flap is nowadays universally used in lentiviral vectors. Efficient transduction of HSC and our pre-clinical collaborative studies with a murine model of Adrenoleucodystrophy recently lead to a first successful gene therapy human trial. We are now conducting several optimization projects of the vector backbone, for the use of lentiviral vectors as vaccines. We are also pursuing long-standing collaborations in the field of HIV gene therapy and lentiviral vectorology.
Vaccinology: Lentiviral vectors are also able to stably transduce non-dividing antigen presenting cells (APCs) such as dendritc cells (DCs). This allows a prolonged antigen presentation through the endogenous pathway, in contrast to all other viral-derived vaccination vectors such as canary-pox adenoviral vectors, which rely on a transient cross-presentation of the antigen. Endogenous Ag presentation make lentiviral vaccination vectors an unprecedented platform for the induction of strong, diversified and memory cellular immune responses. Using this innovative vaccination strategy, we recently demonstrated a long-term sterilizing immunity induced in mice against Plasmodium yoelii, a murine model of malaria. We also showed in a first pilot study in macaques, a strong protection against a massive SIV challenge. The vaccine prototype was further deeply optimized, both in terms of efficacy and safety. This translated into an impressive protection in the SIVmac251/Macaques model with all animals stably controlling SIV replication to undetectable levels after a low dose, cost effective, vaccination regimen (ongoing work).
Lentiviral vector vaccines are also applied to other major infectious diseases where efficient cellular responses are needed for protection, such as tuberculosis. Lentiviral vectors also represent a promising vaccination platform for the induction of humoral responses. We showed previously a sterilizing humoral immunity against West Nile virus after a minute single dose injection. This work was pursued by the proof of concept of protection of horses against West Nile, and other vaccine developments against zoonotic viruses such as Japanese Encephalitis virus (ongoing).