Megakaryocytes in the bone marrow
Turbulence promotes large-scale production of functional platelets from human induced pluripotent stem cells (hiPSCs), according to research published in Cell.
Exposure to turbulent energy in a bioreactor stimulated hiPSC-derived megakaryocytes to produce 100 billion platelets.
Transfusion of these platelets in 2 animal models promoted blood clotting and prevented bleeding just as well as platelets from human donors.
“The discovery of turbulent energy provides a new physical mechanism and ex vivo production strategy for the generation of platelets that should impact clinical-scale cell therapies for regenerative medicine,” said study author Koji Eto, MD, PhD, of Kyoto University in Japan.
Previous attempts to generate platelets from hiPSC-derived megakaryocytes failed to achieve a scale suitable for clinical manufacturing.
While searching for a solution to this problem, Dr Eto and his colleagues noticed that hiPSC-derived megakaryocytes produced more platelets when being rotated in a flask than under static conditions in a petri dish.
This observation suggested that physical stress from horizontal shaking under liquid conditions enhances platelet generation.
Following up on this discovery, the researchers tested a rocking-bag-based bioreactor followed by a new microfluidic system with a flow chamber and multiple pillars, but these devices generated fewer than 20 platelets per hiPSC-derived megakaryocyte.
To examine the ideal physical conditions for generating platelets, Dr Eto and his team conducted live-imaging studies of mouse bone marrow.
These experiments revealed that megakaryocytes release platelets only when they are exposed to turbulent blood flow. In support of this idea, simulations confirmed that the bioreactor and microfluidic system the researchers previously tested lacked sufficient turbulent energy.
“The discovery of the crucial role of turbulence in platelet production significantly extends past research showing that shear stress from blood flow is also a key physical factor in this process,” Dr Eto said.
“Our findings also show that iPS cells are not the end-all be-all for producing platelets. Understanding fluid dynamics in addition to iPS cell technology was necessary for our discovery.”
After testing various devices, the researchers discovered that large-scale production of high-quality platelets was possible using a bioreactor called VerMES. This system consists of 2 oval-shaped, horizontally oriented mixing blades that generate relatively high levels of turbulence by moving up and down in a cylinder.
With the optimal level of turbulent energy and shear stress created by the blade motion, the hiPSC-derived megakaryocytes generated 100 billion platelets—enough to satisfy clinical requirements.
Transfusion experiments in 2 animal models of thrombocytopenia showed that these platelets perform similarly to platelets from human donors. Both types of platelets promoted blood clotting and reduced bleeding times to a comparable extent after ear vein incisions in rabbits and tail artery punctures in mice.
Dr Eto and his team are taking this work further by designing automated protocols, lowering manufacturing costs, and optimizing platelet yields. They are also developing universal platelets lacking human leukocyte antigens in order to reduce the risk of immune-mediated transfusion reactions.
“We expect clinical trials to begin within a year or two,” Dr Eto said. “We believe these findings will be a last scientific step to receiving permission for clinical trials using our platelets.”