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National Research Council (US). Trends in Science and Technology Relevant to the Biological and Toxin Weapons Convention: Summary of an International Workshop. Washington (DC): National Academies Press (US); 2011.

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Trends in Science and Technology Relevant to the Biological and Toxin Weapons Convention: Summary of an International Workshop.

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DEVELOPMENTS IN DESIGN, FABRICATION, AND PRODUCTION, CONTINUED

Bioreactors and Transgenic Animals – Ryszard Słomski, Poznań University of Life Sciences, Poland

Dr. Ryszard Słomski opened the session with a discussion on bioreactors and transgenic animals. He began by highlighting the importance of working with a group of experts in a variety of sub-disciplines in order to achieve success. Dr. Słomski continued by outlining a number of systems for transgenesis, and noted that effective research requires the difficult decision of which specific system will be best for a particular application. Agreement on the most suitable selection of protein for production, the most suitable targeted site of transgenesis, and the most appropriate organism for transgenesis is also necessary. Dr. Słomski identified other considerations that must be taken into account in selecting transgenesis systems, including required production yield, processing, utilization of the recombinant product, and time. He noted that multiple classes of polypeptides may be produced in such bioreactors, including growth factors, hormones, enzymes, immunoglobulins, and others.

Dr. Słomski then proceeded to highlight a number of key examples of animal bioreactors, including silkworms, rabbits and goats. He posited that the silkworm is a particularly useful bioreactor because of the productive capacity of the silkworm’s silk gland, ease of harvesting the product from the cocoon, and relative ease with which transgenesis can be achieved. Rabbits were a second example cited as useful because of their capacity for milk production, which can reach as much as two liters of milk per lactation and which can be manipulated to produce secreted protein (Lipinski et al., 2003). Similarly, goat’s milk can be used to produce a recombinant form of human antithrombin, and indeed Dr. Słomski noted that this was the first transgenically produced protein approved for human use in the world.12 He also described work being done to “humanize” pig tissue to make it available for use for organ and tissue transplants.

Dr. Słomski proposed that there were a number of advantages to the exploitation of animal bioreactors including the fact that such bioreactors exhibited high efficiency of expression, although this is not currently controllable, and required comparatively low maintenance costs. There are also disadvantages, namely the time required for development of the transgenic animal and the chance that the genetic modifications may not pass through to the second or third generation. This latter problem can be countered by introducing cloning of animals, though this does bring with it a new set of challenges.13 With respect to the potential impact of research on transgenic animals and the BWC, Dr. Słomski noted that work in this area is tightly controlled and regulated.

Transgenic Plants and Recombinant Pharmaceuticals – Julian Ma, St. Georges University of London, UK

Dr. Julian Ma began the second presentation by positing that molecular pharming–the use of plants as factories for recombinant pharmaceutical proteins–offered an unprecedented opportunity to produce valuable molecules economically and on a massive scale. It was suggested that following the initial genetic manipulation, the process of growing and harvesting the target pharmaceutical protein was essentially low-tech and amenable to facilities around the world. Moreover, new plant biotechnologies had brought about enormous improvements in terms of speed and once the process was initiated the product could be manufactured within two weeks. A number of advantages to this approach were identified as important:

  • Plants cells are eukaryotic, like human cells, and can produce complex proteins. Although plant and animal glycosylation patterns differ, engineered removal of the non-mammalian sugars can achieve very homogenous glycosylation patterns.
  • Plants are the only feasible production system for some proteins that are required at massive scale.
  • Some plant biotechnologies are unparalleled for speed of production
  • Low cost of initial investment and economy of scale
  • A low-tech “high-tech” solution–readily transferred to under-developed regions
  • The prospect of minimal processing for mucosal delivery

Dr. Ma went on to illustrate the advantages of molecular pharming using the example of monoclonal antibodies, highly valuable proteins that are important in both prophylaxis and treatment of disease. Molecular pharming in plants has already produced a number of important monoclonal antibodies, including antibodies directed against HIV, rabies virus, and Streptococcus mutans, and it was suggested that such antibodies can potentially be mass produced for a low cost (Ma et al., 2003; De Muynck et al., 2010).

The presentation moved on to point out that antibodies produced in plants could not only be used to combat diseases, but could also serve as biosensors for detection of microbial toxins. Early progress has been made in this field, and Dr. Ma suggested that the important next step will be to link the plant-expressed antibody to a plant signaling cascade to send a signal when the antibody receptor is bound by its target. In concluding slides, Dr. Ma illustrated how minimally processed plant tissue could serve as a source for the generation of vaccine stockpiles. He presented the example of vaccine antigens for Hepatitis B, which were expressed in potatoes and then delivered through feeding. The process resulted in significantly increased antibody levels in human volunteers, which far exceeded the level required for immunity.14 Such a process, it was suggested, could be applied to a number of other disease examples, and the use, for example, of plants seeds, a natural protein storage structure, would enable stockpiling of unprocessed vaccine in large quantities under standard agricultural conditions.

He concluded that although the field of molecular pharming was still young, excellent progress was being made and the first products were in clinical trials. In the future, it was hoped that further significant improvements in yields and speed of production could be achieved.

Neuroscience Developments – James Eberwine, University of Pennsylvania School of Medicine, USA

Dr. James Eberwine of the University of Pennsylvania began by pointing out that the brain affects a range of characteristics, including emotions and the ability to learn. He outlined how his laboratory was involved in fundamental science, which was the key to exploiting the beneficial use of biology and understanding its potential for misuse. In particular, Dr. Eberwine explained the complexity of neurobiology, indicating that such work required the development of techniques to allow researchers to more precisely understand function at the single cell level (Eberwine and Bartfai, 2011).

Dr. Eberwine noted that high-throughput sequencing has significantly advanced neuroscience, and suggested that next generation sequencing would enable researchers to achieve a level of 45 billion nucleotides per week. Research has revealed significant variability in RNA and gene expression between functionally similar individual neurons, highlighting the importance of multiple cellular data points. He suggested that one of the key realizations was the need to think about phenotypic space differently. He posited that this space is not homogenous and thus cellular identity does not reflect a particular point, but rather a position on a three dimensional phenotype “cloud” (Sul et al., 2009; Kim and Eberwine, 2010). This cellular variation has serious implications for the use of model systems for a given cell type, which may result in errors in conclusions if one does not understand the specific variations between the model and the studied system. For example, mRNAs from mouse and rat hippocampal dendritic cells share only 27 percent similarity to each other, which can have serious implications for the observed responses of these cells.

Dr. Eberwine discussed the origins of this variability by using the way that adjusting proportions of common ingredients (e.g., flour, milk, eggs) results in different baked goods (pancakes, cakes, biscuits) as a conceptual model. He noted that cells use the same fundamental components (DNA, proteins, RNA) in different quantities and fashions to create different cellular environments and responses to stimuli. This does not just occur in different types of cells (e.g., neurons vs. astrocytes), but also in cells that appear to be structurally and functionally similar. In particular, Dr. Eberwine noted that RNA is critical in determining the role that a given cell will play in the body, and modification of the RNA profile of a cell allows one to take even differentiated, mature cells, and modify them to perform a different function, such as to turn a neuron into an astrocyte. Manipulation of this cellular plasticity has the potential to reveal fundamental insights into how cells function, to aid in the development of new screening platforms for drug discovery, and potentially to inform the development of personalized cellular therapeutics.

The idea of changing cellular function by insertion of RNA is not a particularly new idea, but the idea of changing the identity of a cell through insertion of RNA is rather different. Though not of immediate concern, Dr. Eberwine noted that the plasticity of brain cells revealed through his research could become a dual-use concern in the future. As the beneficial effects to manipulating this plasticity becomes more apparent and within reach, the potential for misuse will also become a possibility.

Discussion

The open discussion following the presentations included additional discussion of the limits and advantages of using plant and animal bio-production systems. For example, issues that were noted by participants included the ability of plants to produce vaccine proteins and monoclonal antibodies, or to be engineered to serve as biosensors, which may have implications for issues of relevance to the BWC in areas such as detection and countermeasures development. Participants also noted that the ability to store plant seeds and to grow plants as needed may influence flexible production capabilities. Participants also inquired about changes of gene expression in neuronal cells, such as those discussed by Dr. Eberwine, and it was noted that while this has been accomplished in sliced sections, in vivo application would remain extremely challenging.

Footnotes

12

ATryn®, produced by GTC Biotherapeutics (http://gtc-bio​.com).

13
14

An early example of this application includes Thanavala et al. (1995).

Copyright © 2011, National Academy of Sciences.
Bookshelf ID: NBK56621

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