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ATC Workshop
Papers
From Cell to
Production
Technical Challenges
of Cloning Pigs for BioMedical Research
Somatic Cell
Nuclear Transfer in Mammals
SATACs and Transgenesis
Concerns About
Gene Transfer and Nuclear Transfer in Domestic Animals
Prospects and
Hurdles in Optimizing the Vascular Support of Engineered Tissues
ES Cells Make
Neurons in a Dish
Nuclear Transfer
and Gene Targeting in Domestic Animals: Bioreactors of the Future
Application
of Nuclear Transfer Technology in the Generation of Pigs for Xenetransplantation
Nuclear Transfer
Technology
Gene Targeting
in Domestic Species: Challenges and Opportunities
Homologous Recombination
and Genetic Engineering of Transgenic Recombinant Animals
Nuclear Transplantation
in the Cow: Future Challenges
Enhancing Transgenics
through Cloning
ES Cells Offer
is a Power Tool for Understanding the Genetic Control of Tissue
Development and for Screening Potential Therapeutic Drugs
Human Germline
Engineering -- The Prospects for Commercial Development
Mammalian Artificial
Chromosomes for Animal Transgenesis
Understanding
Developmental Abnormalities in Offspring Produced by Nuclear Transplantation
Role of Cell
Cycle
Cloning and
Other Reproductive Technologies for Application in Transgenics
Cell Culturing
Technology as a Major Hurdle in the Commercialization of Genetically
Altered Animals
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| ADVANCED TRANSGENESIS AND
CLONING: Genetic Manipulation in Animals
Electronic Workshop Presentation: Paper
No. 10
GENOMICS: DELIVERING CELL CULTURE
SYSTEMS FOR TISSUE THERAPY
Participant:
Peter Mountford
CellBio, Inc.
Introduction
The undeniable and dramatic trend in population
growth and aging is accelerating the need for new and cost effective
treatments for human disease. While there is no doubt that the current
genomics-lead explosion in biological understanding will identify
many new opportunities for drug-based intervention, it is also evident
that genomics will provide important information needed for the development
of cell-based gene and tissue therapies. In particular, genomics offers
a powerful route to establish stem cell culture systems for tissue-based
therapies through the identification of key stem cell regulatory genes.
Two fundamental challenges must be
addressed for any tissue-based therapy to have a meaningful impact
on human medicine: tissue supply and transplant bio-compatibility.
While each tissue therapy regime will face different technical hurdles,
each must address both challenges. For example, the supply of animal
tissues for transplantation will be less of a challenge than bio-compatibility
issues of transplant efficacy and tolerance. Conversely, transplanted
human tissues are more bio-compatible but limited in supply.
With tissue supply the major limitation
to tissue-based therapies, new technologies that expand the source
of donor tissue are of fundamental importance. One approach, which
relies heavily upon the use of advanced cell culture and genetic
engineering strategies, is to generate genetically modified animals
which provide bio-compatible tissues for human transplantation.
Another approach, also reliant upon advanced cell culture, is to
grow cells and tissues for transplantation in vitro.
The common requirement for developing
animal- and in vitro-derived tissues for human transplantation is
cell culture.
Cell Culture
The Origin of Genetically Engineered
Animals
The development of transgenic animals
as tissue donors for human transplantation requires advanced genetic
engineering of cultured cells. Embryonic stem (ES) cell-mediated transgenesis
offers a robust and reliable system for generating transgenic mice,
while somatic cell culture/genetic engineering combined with nuclear
transfer technology offers a powerful alternate strategy in a number
of species. In both instances, a single, genetically modified, cultured
cell is the origin for a significantly larger resource of genetically
engineered animal tissues for human transplantation. Genetic modification
provides a powerful route to meeting the challenge of bio-compatibility
while animal breeding addresses the challenge of tissue supply.
The Alternative to Genetically Engineered
Animals
A fundamental difference between ES cells
and somatic cells is their capacity for growth in culture. As pluripotential
stem cells capable of growth and multi-lineage differentiation in
vitro, ES cells provide not only a route to generating transgenic
animals, but more importantly, an in vitro resource from which to
derive a wide range of cell types for tissue transplantation. Indeed,
ES-derived somatic cells have successfully generated functional blood,
neurones and cardiac tissue in mouse and rat transplantation models
(1-3).
While in vitro cell culture is unlikely
to replace the need for transgenic animals to supply entire organs,
a wide range of alternate cell therapies an be envisaged through
in vitro cell culture. For example, cell-based therapies for neural
dysfunction or damage are likely to require neural stem cells which
can only be obtained in limited supply from foetal tissue. While
large numbers of animal foetuses could be generated a more plentiful
and accessible source of neural cells would be derived from ES cell
cultures.
The Challenge
The challenge before us now is to accelerate
our understanding of ES cell growth and establish universal ES cell
culture systems through the direct and focused application of a genomics-lead
ES cell research. A molecular understanding of ES cell regulation
will be pivotal to the development of robust stem cell culture systems
necessary for the supply of bio-compatible animal-derived and in vitro-derived
tissues for human transplantation.
What's Needed?
The key components required for the genomics-lead
establishment of universal ES cell culture systems are:
(i) an inventory of genes expressed
by ES cells of different species (molecular profiling), (ii) analysis
of ES cell gene sequence and expression data for candidate regulatory
gene selection (bioinformatics), (iii) comprehensive functional
analysis of candidate ES cell regulatory genes by gene expression,
deletion and mutation analysis in ES cells (functional genomics),
and (iv) development of conditional expression systems for cDNA
library screening in ES cell-based functional assays.
What's available?
The technologies, materials and analytical
systems required to establish molecular profiles and identify candidate
ES cell regulatory genes for functional investigation are available.
More importantly, the expression systems required for functional investigation
of candidate ES cell regulatory genes have recently been reported
(4).
Endnotes
- Hole, N, Graham, GJ, Menzel, U
& Ansell, JD: A limited temporal window for the derivation of
multilineage hematopoietic progenitors during embryonal stem cell
differentiation in vitro. Blood 1996, 88:1266-1276.
- Deacon, T, Dinsmore, J, Costantini,
LC, Ratliff, J & Isacson, O: Blastula-stage stem cells can differentiate
into dopaminergic and serotonergic neurons after transplantation.
Exp. Neurol. 1998, 149:28-41.
- Klug, MG, Soonpaa, MH, Koh, GY
& Field, LJ: Genetically selected cardiomyocytes from differentiating
embryonic stem cells form stable intracardiac grafts. J. Clin.
Invest. 1996, 98:216-224.
- Niwa, H. Burdon, T. Chambers, I.
and Smith, A. Self-renewal of pluripotential embryonic stem cells
is mediated via activation of STAT3. Genes & Dev. 12: 2048-2060.
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