Abstract

Bioreactors for Megakaryocyte Studies and Platelet Formation: Where Do We Stand?

Jonathan Thon, Assistant Professor, Brigham and Women's Hospital/Harvard Medical School, Co-Founder -- Platelet BioGenesis

Platelets are responsible for clot formation and blood vessel repair and are produced by megakaryocytes in the bone marrow. Low platelet count is a significant consequence of transplant and surgery, for which platelets are a critical first-line therapy to prevent mortality due to uncontrolled bleeding. While cancers and their treatments have been shown affect normal platelet production affecting the pathogenesis of disease, the causes are largely unknown. The development of microfluidic platforms that accurately model microvascular niches and offer high-resolution live-cell visualization of biological phenomenon and precise control of individual environmental components are needed to elucidate the mechanism(s) regulating platelet production in vivo. Likewise, the production of lab-generated human platelets is necessary to meet present and future transfusion needs. We have shown that it is feasible to generate functional megakaryocytes from human embryonic, cord blood and induced pluripotent stem cell cultures. The most significant obstacle to ex vivo platelet production has been triggering megakaryocytes to produce platelets at yields necessary to make production of a platelet transfusion unit clinically and commercially feasible. Evidence suggests that key physiological characteristics of the bone marrow environment including extracellular matrix composition, bone marrow stiffness, endothelial cell contacts, and vascular shear stresses trigger platelet release. We recently developed a scalable microfluidic platelet bioreactor that recapitulates these major characteristics of human bone marrow. By exposing megakaryocytes to physiological shear stresses of blood we have improved the rate and extent of platelet production, and reduced the time to initiation of platelet release. Morphology, ultrastructure and function of our bioreactor platelets is consistent with blood platelets. We are separately adapting our platelet bioreactor to: (1) more accurately recapitulate b