In stem cell therapies, human embryonic stem cells at one point were very attractive because they had the ability to self replicate and become any cell in the human body. This meant that the therapeutic applications were endless. However there were ethical concerns about the use of cells from embryos. The ethical hurdles made these cells a less attractive option. This gave rise to induced pluripotent stem cells (iPSCs), in which researchers reprogrammed adult cells to behave like embryonic stem cells – able to become any type of cell in the human body. By using adult cells, researchers were able to eliminate the ethical challenges of using cells from embryos.
Thus iPSCs have become a very attractive cell line for developing stem cell therapies. However, as stem cell based therapeutic applications have entered the clinic, the need to culture these cells at large scale has become an important issue. It is critical to the success of stem cell therapies that these cells are able to be cultured in a way that is scaleable, efficient and cost-effective. Currently these cells are typically cultured using adherent culture or static tissue culture methods, both of which are time and labor intensive and have significant batch-to-batch inconsistency.
One possible solution may be the use of stirred suspension bioreactors. Researchers at the University of Calgary, Department of Medicine have published two studies on the use of stirred suspension bioreactors for large-scale expansion and long-term culture of iPSCs. The first study titled “Expansion and long-term maintenance of induced pluripotent stem cells in stirred suspension bioreactors,” published in the Journal of Tissue Engineering and Regenerative Medicine outlines a method for the culture and expansion of both murine and human embryonic stem cells using stirred suspension bioreactors. Then more recently the same group published “Derivation of iPSCs in Stirred Suspension Bioreactors” in Nature Methods where they describe how they were able to reprogram iPSCs derived from fibroblasts to grow in stirred suspension bioreactors instead of adherent culture. The publication makes the point that even at small scale, stirred suspension bioreactors can produce billions of cells in just a few days. Authors believe that “suspension reprogramming could address a major bottleneck in iPSC production and enable efficient reproducible and large scale generation of cells for both research and potentially clinical applications.”
More importantly, in both studies, the cells that were generated using the stirred suspension bioreactor method were karyotypically normal, expressed pluripotency markers and could be differentiated into all three germ layers both in vitro and in vivo. This is critically important if stirred suspension bioreactors are going to be a viable method for large scale manufacturing of stem cells for clinical application. It is particularly important that they could differentiate into all three germ layers because this is what iPSCs cells so attractive and allows for their use in many different applications. All of the different types of specialized cells in the human body are derived from one of three embryonic germ layers. The germ layers, endoderm, mesoderm, and ectoderm represent different cell types. The endoderm gives rise to lung tissue and digestive organs including the stomach, colon, liver, and pancreas. The mesoderm becomes bone, muscle, and connective tissue, including the heart. Lastly, the ectoderm becomes skin, nerves, and brain, including the eyes, ears, and pituitary gland. The fact that iPSCs can become any type of these cells makes them invaluable in research and stem cell therapies.
Given this data, the use of stirred suspension bioreactors could be an important step forward in the development of a consistent, reliable and cost-effective way to produce large amounts of iPSCs for therapeutic use. However it is only one piece of the manufacturing puzzle. Of course for clinical applications the need to address animal-free culture still exists. Good manufacturing practices are critical to any drug or medical treatment, and it is important to look at the need for good animal-free manufacturing practices for stem cell therapies. Stem cells are frequently grown using animal components, including fetal bovine serum, and there is always a concern about adventitious infectious agents contaminating the stem cells. As we begin to evaluate the ability to produce these stem cells at large scale we must also consider the other critical elements of clinical manufacturing including animal-free culture. One possible solution is the use of animal-free supplements; please see our previous blog “A Critical Role for Recombinant Albumin in Embryonic Stem Cell and iPSC Cell Culture and Therapeutic Development,” for further reading.