The needs to efficiently deliver genetic cargo and to maintain long-term transgene expression in vivo prompted the development of the HIV-1 based vector system. The novel HIV-1 based vectors, devoid of sequences encoding any of the HIV-1 proteins, proved efficient at transducing various tissues in vivo (brain, liver, muscle, retina, and hematopoietic stem cells) without any detectable pathology. However, it is clear that further improvements in: vector production, transgene expression and regulation, better characterization of the mechanisms involved in vector integration, and the development of immune response against vector delivered transgenes are required before HIV-1 vectors are considered safe and efficacious enough for human clinical trials.
Our lab is focused on the development of HIV-1 vectors for gene therapy of genetic diseases such as hemophilia A and B, as well as well as a means of treating prostate cancer. In addition, we are using the vector system to study HIV-1 biology. Specifically, we characterize the mechanism of vector integration into the host cell genome and the risks of insertional mutagenesis involved in this process. In parallel, we develop non-integrating HIV-1 vectors; to this end, we investigate the effects of DNA repair pathways on the formation of episomal HIV-1 vector forms and the mechanisms, which down regulate transgene expression from non-integrated vectors.
We are also interested in utilizing the HIV-1 vector system for functional genomic applications. Recently, we have developed a novel lentiviral vector, which facilitates high throughput gene-function screening of cDNAs. To facilitate the generation of transgenic animals by retroviral vectors, we investigate the mechanism that renders lentiviral vectors resistant to transcriptional silencing in the early mouse embryo.
The ability of HIV-1 and other lentiviruses to transduce non-dividing cells prompt the development of an HIV-1 based gene delivery system. The novel lentivirus vectors proved efficient at transducing various tissues in vivo (brain, liver, muscle, retina, and hematopoietic stem cells) without any detectable pathology. However we believe that further improvements in: vector production, transgene expression and regulation, and better characterization of the mechanism responsible for the development of immune response against vector delivered transgenes are required before we can consider the use of the lentiviral system in clinical trials.
To improve vector production our laboratory is focused on the development of inducible lentivirus vector packaging cell line which is a prerequisite for human clinical trials. Packaging cell lines facilitate large vector production and provide new safety measurements, which are required for clinical trials.
To improve transgene expression we use MLV/HIV-1 chimera vectors to identify and to remove cis sequences that down-regulate transgene expression from HIV-1 vectors.
Regulation of transgene expression
To allow regulation of transgene expression in vivo we develop tetracycline inducible lentivirus vectors. Our objectives are to reduce non-regulated basal transgene production and to minimize the risk of developing immune response against vector transduced cells.
Using hemophilic mice and canines enables us to test the efficacy and safety of our newly developed lentivirus vectors.
HIV-1 Biology. Non-integrated HIV-1 particles
Our laboratory is focused on characterizing the mechanism involved in down-regulation of gene expression from non-integrated HIV-1 genome.
Virus host interaction
We are currently characterizing the effects of unique point mutations in the HIV-1 gag and pol genes on the efficiency of vector particles at transducing a variety of primary cells.
Cockrell AS, van Praag H, Santistevan N, Ma H, Kafri T (2011). The HIV-1 Rev/RRE system is required for HIV-1 5′ UTR cis elements to augment encapsidation of heterologous RNA into HIV-1 viral particles. Retrovirology. 8:51.
Kantor B, Bayer M, Ma H, Samulski J, Li C, McCown T, Kafri T (2011). Notable reduction in illegitimate integration mediated by a PPT-deleted, nonintegrating lentiviral vector. Mol Ther. 19(3):547-56.
Kantor B, Ma H, Webster-Cyriaque J, Monahan PE, Kafri T (2009). Epigenetic activation of unintegrated HIV-1 genomes by gut-associated short chain fatty acids and its implications for HIV infection. Proc Natl Acad Sci U S A. 106(44):18786-91.
Bayer M, Kantor B, Cockrell A, Ma H, Zeithaml B, Li X, McCown T, Kafri T (2008). A large U3 deletion causes increased in vivo expression from a nonintegrating lentiviral vector. Mol Ther. 16(12):1968-76.
Cockrell AS, Kafri T (2007). Gene delivery by lentivirus vectors. Mol Biotechnol. 36(3):184-204. Review.
Bahi A, Boyer F, Kafri T, Dreyer JL (2006). Silencing urokinase in the ventral tegmental area in vivo induces changes in cocaine-induced hyperlocomotion. J Neurochem. 98(5):1619-31.
Cockrell AS, Ma H, Fu K, McCown TJ, Kafri T (2006). A trans-lentiviral packaging cell line for high-titer conditional self-inactivating HIV-1 vectors. Mol Ther. 14(2):276-84.