Heart attack is a leading cause of death in the developed world, and although stem cell therapies offer hope for treatment, they have so far met with limited success. In preclinical studies, human embryonic stem cells (hESCs) grafted into the damaged hearts of mice led only to partial repair, because the cells do not efficiently differentiate into functional heart cells.
Steve Oh at the A*STAR Bioprocessing Technology Institute and co-workers have now developed a new method for producing heart muscle cells (cardiomyocytes) from hESCs that could eventually lead to an effective cell transplantation therapy for heart failure. The technique involves growing hESCs in ‘microcarrier’ cultures containing microscopic beads to which the cells can adhere, and inducing them to differentiate into cardiomyocytes by treating them with a compound that inhibits an enzyme called MAPK.
The conventional cell culture method involves growing hESCs in two-dimensional dishes and using expensive growth factors to induce cardiomyocyte differentiation. Under these conditions, the cells aggregate into large clusters called embryoid bodies, and only a small proportion of these differentiate into functional cardiomyocytes.
By contrast, hESCs grown in microcarrier cultures form small aggregates of controlled size that do not clump together (Fig. 1), leading to a higher surface-to-volume ratio. As a result, the team achieved a three-fold increase in the number of cells that grew and successfully differentiated. The researchers also showed that the microcarrier culture system can be used for screening drugs and evaluating how toxic they are to cardiomyocytes.
Significantly, the system can be scaled up to produce huge numbers of cardiomyocytes in suspension culture. It is estimated that 1–2 billion of these cells are needed to regenerate the tissue damaged in a heart attack, and according to the researchers’ calculations, a 90-liter bioreactor containing microcarrier cultures could produce the 20 billion cells needed for clinical trials.
“The major advantage of our method is the ability to grow cells without growth factors in suspension cultures,” says Oh. “This allows for large-volume scale-up in controlled bioreactors, instead of production in hundreds of stacks of disposable plastic trays, which is much more labor-intensive and has batch-to-batch variation.”
Furthermore, the serum-free media with MAPK inhibitor is a well-defined system that allows for good manufacturing practice for cell therapies, and there is room to optimize the cardiomyocyte production process. “The method can be improved by supplementing the culture medium with nutrients,” adds Oh, “and integrating hESC expansion with differentiation on the microcarriers to achieve even higher yields of cardiomyocytes.”
The A*STAR-affiliated researchers contributing to this research are from the Bioprocessing Technology Institute.