FAQ on rat ES cells
Why are rats so important in medical research and drug discovery?
Rats have been vital to medical research and drug discovery during the last 100 years. The rat has been the animal of choice in medical research because they closely mimic human metabolic functions, and are easy to study, thus being the model of choice routinely used in toxicity and efficacy studies. Many human diseases such as cardiac conditions, autoimmune diseases and neurological diseases are modelled in the rat.
What is so important about rat ES (embryonic stem) cells?
As described above the rat is a valuable model for human disease. Until the recent success by Stem Cell Sciences in this area, no one has been able to produce authentic rat embryonic stem cells. These cells are the ‘tools’ that will allow the development of the world’s first generation of precision engineered gene knock-out and knock-in rats. Rats with targeted modifications such as deleted genes (knock-out), inserted genes (knock-in) or with existing genes replaced by modified variants are extremely useful organisms for improved preclinical models for drug discovery.
Why has it been so difficult to produce rat ES cells to date?
Mouse stem cells and transgenic mice have been easier to generate, as the first laboratory isolation of ES cells by Evans & Kaufman (1981) was achieved with mice. There was thus no major focus on larger rodents. A rat is very different from a mouse and it has proved incredibly difficult to repeat the process with rat embryos, due to lack of comprehension of early rat embryogenesis, inappropriate tissue culture techniques and fallible assumptions made from the mouse ES field.
Transgenic rats, in which foreign genes are expressed after random insertion in the genome, and low efficiency gene knock-outs have been successfully created to date by genetic manipulation of the developing rat embryo prior to implantation. However, sophisticated, precise genetic manipulation of the rat genome has proved impossible. Only now with the generation of rat ES cells are there prospects to achieve pure populations of stable pluripotent ES cells and their use to transmit precision engineered genes through the germ line to obtain viable, genetically modified animals.
How are genetically engineered rats created?
The starting point is a rat embryo at 5.5 days of development. ES cells are isolated and grown in SCS’s proprietary CultiCell™ medium. The CultiCell™ medium maintains the ES cells at a primitive stage, creating a pure population of cells . The ES cells can also be differentiated into multiple cell types of the organism in the petri dish, a utility to support the development of cell based assays.
Next, using genetic engineering techniques, genes of interest are added, deleted or replaced (knock-out and knock-in)
The modified rat ES cells are then injected into pre-implantation stage embryos where they contribute to the other cells and importantly, respond to further embryo development cues and begin to differentiate into all cell types of the developing embryo.
The embryo [a chimera consisting of cells of different origin] is then implanted into a surrogate rat and allowed to go to full term.
Transmission of the genetic characteristics of the rat ES cells grown in the petri dish into the germ-line of subsequent rats is achieved by breeding the chimeric rat with normal mates, and via coat colour analysis confirming that the progeny consist of offspring made by the original rat ES cells in this and subsequent generations.
Why is the media the ES cells are grown in so important?
There are two major reasons why the media is so important. The proprietary CultiCell™ media contains a novel combination of enzyme inhibitors that suppress cell differentiation, and keep the ES cells undifferentiated and able to grow and remain in the pluripotent state. Pure populations of ES cells can be generated because this media is also free from animal-derived serum and unnecessary growth factors, which can negatively affect cell growth and lead to cell population variability.
What might this technology be used to do?
This technology has many applications. Rat ES cells and corresponding genetically engineered animal models are expected to be superior and more relevant for drug discovery and medical research than mouse models. The technology can be used in basic academic research, for the generation of knock-in and knock-out models related to various disease states, preclinical disease and toxicology models. As such the technology may offer the potential for replacing mouse models and becoming the gold standard in the drug discovery process.
What is the market potential for this technology?
The global market for transgenic rats is estimated at around US$300M total, ramping up from $80M per year for the first 3-4 years. It is anticipated that the total market will mature in 8-10 years and will be worth well over US$1B.
Are there any moral/ethical considerations that must be taken into account when working with transgenic animals?
There are always important moral and ethical concerns over the production and use of animals in research and SCS works according to national and regional legislation governing the health and welfare of animals in research. SCS strives, where possible, to minimise the number of animals used and procedures required in their handling.