Embryonic stem cells as sources of donor-independent platelets

Abstract

C o m m e n t a r y Thrombocytopenia and the need for alternative platelet sourcesThe blood system comprises a hierarchy of rare, largely quiescent, self-renewing hematopoietic stem cells (HSCs) and highly proliferative lineage-committed progenitors and precursors in the bone marrow, which yield a continual supply of mature blood cells of diverse lineages (1). The nearly one trillion platelets present in circulation derive from bone marrow-resident, multinucleated megakaryocytes, which in turn derive from bipotential megakaryocyte-erythroid progenitors (MEPs). The master transcription factor GATA1 is required for maturation of MEPs into both megakaryocytic and erythroid lineages (1, 2). It is estimated that each megakaryocyte produces approximately 10 3 to 10 4 platelets, which have half-lives of only about three days in the circulation (3-6). Reduction in the number of circulating platelets, termed thrombocytopenia, is a common clinical condition with a variety of etiologies, including infectious and heritable disease, malignancy, liver failure, chemotherapy, and medication side effects (1, 4, 7-9).Transfusion of donor-derived platelets is employed with increasing frequency to treat patients with thrombocytopenia and places a high demand on platelet donation (10). Over two million platelet units are transfused annually in the United States (8, 10); however, there are multiple factors that hinder platelet transfusion. Donor platelets have only a three-to seven-day shelf life, limiting the ability to store and transport these cells and generating substantial waste through the disposal of aged platelets. Intermittent shortages arise due to a mismatch between supply and demand (11,12). Further, donor-derived platelets carry the inherent risk of viral transmission and bacterial contamination due to extended room temperature storage (8). Together, these limitations have motivated the development of sustainable donor-independent platelet sources to meet the growing need for these cells (7,11).Pluripotent embryonic stem (ES) cells or induced pluripotent stem (iPS) cells have been proposed as a potential donor-independent source of platelets. One vision is that either ES cells or iPS cells could be used to produce a renewable and immortalized progenitor-like cell line that retains the capacity to differentiate into mature megakaryocytes, which in turn would produce functional platelets. To date, attempts to employ this strategy have suffered from a poor output of PS cell-derived megakaryocytes. Moreover, inefficient generation of platelets from megakaryocytes in vitro has been an additional challenge (4,6,11,13,14). The GATA switch and regulation of megakaryopoiesisThe study of the GATA transcription factors GATA1 and GATA2 has provided insight into normal and disease-associated megakaryopoiesis. While GATA2 is highly expressed in early stem and progenitor cells, megakaryopoiesis and erythropoiesis are accompanied by a concurrent downregulation of GATA2 and upregulation of the closely related GATA1, a process referred t...

Generation of HLA Universal Megakaryocytes and Platelets by Genetic Engineering

“…Embryonic stem cells (ESCs) provide inherent pluripotency and capability to virtually unlimited proliferation in vitro, which could have been among the main parameters for the clinically-relevant upscaling of donor-independent MK/PLT production on the basis of this source. Numerous groups developed efficient protocols for differentiation of MKs from ESCs (45)(46)(47)(48)(49)(50)(51). However, globally accepted ethical issues with the consequent adaptation of legislative regulations basically limit application of ESCs to the narrow research field and prohibit the progress towards clinics.…”

Thrombopoietin-independent generation of platelet-like particles from megakaryoblastic cells

“…Platelet transfusion is a standard practice needed for patients who have severe bleeding; however, this process depends on donor availability. Several studies have attempted to produce platelets in vitro from donor-independent sources 5 , 6 . Thus, understanding the mechanism of platelet generation requires an in vitro model.…”