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Hanna Kallionpää
AMERICAN SOCIETY OF GENE THERAPY The third annual meeting of AMERICAN SOCIETY OF GENE THERAPY (ASGT) was this year held in Denver (CO, USA) 31.5. - 4.6.2000. Several interesting sessions and scientific symposia on molecular medicine and gene therapy in addition to hundreds of oral and poster presentations on the basic and implemented cutting edge gene therapy research were included into the 4-day meeting. Especially for young scientists several educational programs, like the ABC’s of viral vectors and system biologics, along with vector production workshops were available.
My contribution to the meeting was a poster presentation on "Adventitial Ex Vivo Gene Transfer to WHHL Rabbits Using Feline Immuno-deficiency Virus Encoding Human apoE3 increases total cholesterol". The poster was approached and studied by many, raised keen interest and aroused several fruitful discussions and some constructive criticism.
Within the other sessions and presentations I found especially interesting and thought-provoking issues to be the development of new viral vectors, especially lentiviral vectors. The latest Feline Immunodeficiency virus (FIV) mediated gene transfer in vitro and in vivo studies together with the FIV packaging cell line development raised new hope for this particular gene delivery tool that I myself have lately implemented. Of special interest was an oral presentation given by Dr. Sybille Sauter from Chiron Corporation, (San Diego, CA, USA) about the FIV vector development and methods for large scale production and purification of the vector preparations.
In the field of Human Immunodeficiency virus (HIV) vector development Luigi Naldini’s group (Torino, Italy) presented a novel self inactivating vector containing a 118 bp sequence of pol gene upstream of an internal expression cassette. Restoring the pol sequence (and the central polypurine tract cPPT within) in cis improved the efficacy of infection increasing the amount of integrated vector. That shown they concluded the nuclear translocation mediated by pol being a rate limiting step in lentivirus infection.
Another thought-provoking aspect of presentations involving lentiviruses were the ones describing pseudotyping of HIV vectors with other extremely hazardous virus, like the Ebola virus, envelope glycoproteins. In these attempts to modify the host range of the lentiviral vectors the results were successful, however, in one study showed some 1-2 log reduction in titer compared to the more traditional Vesicular Stomatits Virus (VSV) G-protein pseudotyped lentivirus.
Presentations of the new gene delivery techniques were of great interest as well. Most interesting were the ones concentrating on non-viral gene delivery methods and gene targeting. With a DNA- based Sleeping Beauty system involving transposons somatic integration and long-term therapeutic transgene expression in vivo was demonstrated.
Michele Calos’s group from Stanford University (Stanford, CA, USA) showed that sequences from human and mouse genomes, however divergent from bacterial loxP, can support Cre-mediated recombination with up to 100% efficiency. With a unidirectional phage integrase system they demonstrated some 50% efficiency in human calls.
In the category of genetic diseases and gene transfer target organs the most fascinating presentations were the ones dealing with liver-directed gene transfer as well as the in-utero gene transfer.
In utero gene transfers using retro-, adeno- or adeno-associated viral vectors into pre-natal sheep, mice or rats were shown to be well tolerated. After intraperitonel AAV injection most of the transgene was found in the liver. Direct injections into liver or muscle resulted in dose-dependent expression around the injection site when injected with AAV vector. These results are quite encouraging for planning in utero studies for genetic diseases in Finland as well.
One quite suspicious presentation was about oral administration of chitosan-DNA nano-spheres embedded in gelatin to mice resulting in transgene expression that over a 2 weeks time gradually declined. This group from Johns Hopkins School of Medicine (Baltimore, MD, USA) claimed oral route to be feasible for efficient gene therapy, however concluded that the work is in progress to evaluate the biological activity of the transgene after oral delivery.
Overall the meeting was extremely interesting and rewarding. Apart from a stylish conference bag and a pale reddish ‘30min-a-day-by-the-pool-without-sunblock’ sun tan, I gained tons of first timer experience in international conferencing as well as the latest insights into the research implemented on the field of gene therapy. In addition to that, I met many old friends from around the world, took pleasure in having delicious lunches and dinners with friends and co-workers, enjoyed the extremely hot weather and sunshine of Denver, and even took the time to go see the new John Woo movie. (...Huge computerized daylight chamber for culturing virus!? What a science fiction movie with great effects!) All that and the relaxed atmosphere of the conference as well as the company of my co-workers, especially Pauliina, made the trip worthwhile. I wish to thank the Society for granting me the opportunity to experience this ASGT meeting. Thank you. Hanna Kallionpää |