MSCs are multipotent stromal cells that can differentiate into a variety of cell types which are being investigated for tissue engineering and cellular therapies.
Such cells come from bone marrow, adipose tissue and umbilical cord blood but are very rare, according to Ana Fernandes-Platzgummer, a research scientist for the Stem Cell Engineering Research Group at the Instituto Superior Técnico in Lisbon, Portugal.
Totipotent cells can form all the cell types in a body, plus the extraembryonic, or placental, cells. The only totipotent cells are embryonic cells within the first couple of cell divisions after fertilisation.
Pluripotent cells can give rise to all of the cell types that make up the body. While embryonic stem cells are considered pluripotent, this class includes induced pluripotent stem cells (iPSC) derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state.
Multipotent cells are more limited than pluripotent cells but can develop into more than one cell type. This class includes mesenchymal stem cells (MSCs) derived from bone marrow, adipose tissue and umbilical cord blood, and hematopoietic stem cells (HSCs) derived from mesoderm and located in the red bone marrow.
“There are only about 100,000 stem cells in an umbilical cord,” she told delegates at the 1st Stem Cell Community day in Germany this week. “For cellular therapies we need doses of more than one million cells per kg [ideal (IBW) or actual (ABW) body weight] so we need to expand these cells.”
Stem cells can be successfully cultivated using flasks and labscale-volume bioreactors but there are many problems in monitoring and controlling growth, and issues with productivity and cell harvest. Therefore scale-up is a problem, hindered further due to a lack of technologies and processes available to cell therapy makers.
The event in Hamburg – organised by bioprocessing tech firm Eppendorf – looked to address these challenges in stem cell cultivation and scale-up by bringing together industry and academia.
And Fernandes-Platzgummer said that research by the Instituto Superior Técnico together with Thermo Fisher-owned Life Technologies showed positive results in the expansion of human MSCs from different sources using a fully-controlled stirred-tank bioreactor combined with microcarrier technology.
“The advantage of this is its easy scalability, the high surface area [of the microcarrier], the ability to monitor and control cultivation, and the reduced labour costs and risks of contamination,” she said.
After five days cultivation the team produced clinically-relevant cell numbers, she added, using an 800ml spinner flask bioreactor, Thermo Fisher’s serum-free medium StemPro and reagent TrypLE Select CTS, and plastic microcarriers coated with the xeno-free substrate CELLstart (also made by Thermo Fisher).
'10,000 doses per year, each of a billion cells'
In a separate presentation, Steve Oh – principal scientist and associate director at the Bioprocessing Technology Institute (BTI), part of Singapore’s Agency for Science, Technology and Research (A*STAR) – said a similar set-up had shown promise in moving MSC cultivation into scalable technologies and his team is trying to move to a 15L scale.
However, the goal for MSC-based therapies would be producing commercial volumes of “10,000 doses per year, each of a billion cells” from the onset, he added.
“We looked at all the approaches and really the only practical experience I have of a technology that will succeed is microcarrier technology using single-use bioreactors,” he said.
Oh added microcarriers produce higher cell densities with the same amount of media while allowing greater control of the process by providing another metric to configure.
Furthermore, having only thin layers of cells between each carrier offers benefits in the harvesting of stem cells which he said is as problematic as cultivation due to the large aggregates of cell clusters formed which are difficult to break up.