Gammaretroviral vectors: biology, design and applications

Published on November 4, 2014 Updated on November 6, 2014   44 min

Other Talks in the Series: Gene Transfer and Gene Therapy

0:00
Hello. My name is Axel Schambach, and I'm the acting director of the Institute of Experimental Hematology at Hannover Medical School. Within the next 40 to 45 minutes or so, I would like to give you a broad overview on gammaretroviral vectors, their biology, their design, and their applications in clinical trials.
0:23
I will structure my presentation as follows. I will start with an introduction into the biology of retroviruses, including their genome and particle organization and the retroviral life cycle. From there I will give some insights how retroviruses have developed as evolutionary adapted vehicles to deliver genetic information. As a next step, we will convert a retrovirus into the retroviral vector gene delivery tool and mention how this vector system has been efficiently used in the clinical gene therapy arena. We will also touch the occurred adverse events and how these would potentially be prevented in future gene therapy trials. And mention the development of SIN vectors and how to create the right therapeutic window for gene therapy. Apart from the integrating retroviral vectors, we will also mention retroviral intermediates as delivery tools for genetic information. And also in the end take you a little bit on a time journey into the field of retroviral gene therapy and how it has developed. Finally, I will conclude with a summary and a take-home message.
1:30
So let's go into the details. So what's so special about retroviruses that makes them attractive tools for gene transfer? So first of all, retroviruses are evolutionary optimized gene carriers that have naturally adapted to their host to efficiently deliver genetic information into target cells. And as a hallmark and common to all retroviruses, they have the stage of reverse transcription of their single-stranded RNA genome into double-stranded DNA. And this double-stranded DNA is then stably integrated into the host cell genome. Looking back, they are highly evolved parasites which exploit the host cell machinery for their own replication. And it's maybe a little bit surprising to know that retroviruses are already more than 8 million years old and have been found already back then in the mammalian genome. The first approaches have been put forward using retrovirus-based gene transfer approximately 30 years ago. Back then it has been shown that it's much more efficient than DNA transfection in primary cells and that their use in murine bone marrow transplantation was quite successful and paved the way for gene therapy of the hematopoietic system.
2:45
During the past decades, our understanding of the retroviral biology has greatly increased, so we could learn from the occurrence of the sarcomas in chicken, a lot about the Rous sarcoma virus. Leukemias in mice led to the identification of the murine leukemia virus, and the HIV/AIDS global pandemic led to the identification and the better biological understanding of the human immunodeficiency virus. This general knowledge into the retroviral biology allows the rational design of retroviral vectors for specific applications. And interestingly, several members of the family of retroviruses, the so-called Retroviridae, exist with very similar, but not identical retroviral biology.
3:33
So how do retroviruses manage to overcome the cellular hurdles to efficiently deliver their genetic information? The following diagram from a review by Suzuki and Craigie describes how HIV, the human immunodeficiency virus, and MLV, the murine leukemia virus, enter their target cells. After receptor-mediated endocytosis of fusion and a relatively poorly understood encoding process, the so-called reverse transcription complex, RTC, is formed, whereafter the pre-integration complex is reconstituted and bascically mediates the successful integration of the retroviral vector into the host cell genome. As you can see, there are a lot of similarities but also dissimilarities between HIV and MLV. So HIV has the capability to transfuse non-dividing cell types by finding a way to interact with the nuclear pore complex and to transit through this nuclear pore complex, whereas the pre-integration complex of MLV waits at the microtubule-organizing center and has to wait for the nuclear breakdown of the nuclear membrane to really gain access to the host cell chromatin. However, both settings can be viewed as cellular highways as depicted here and, in a way, also as magic bullets, how Paul Ehrlich would have said, because the incoming RNA, depicted here in the middle in blue, is clearly protected from shRNA-mediated degradation.
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Gammaretroviral vectors: biology, design and applications

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