Developments in the production of platelets from stem cells (Review)

Leucine-Rich Repeat Containing 15-Mediated Cell Adhesion Is Essential for Integrin Signaling in TGF-β1-Induced PDL Fibroblastic Differentiation

Human periodontal ligament cells (hPDLCs) cultured from periodontal ligament (PDL) tissue contain postnatal stem cells that can be differentiated into PDL fibroblasts. We obtained PDL fibroblasts from hPDLCs by treatment with low concentrations of TGF-β1. Since the extracellular matrix and cell surface molecules play an important role in differentiation, we had previously developed a series of monoclonal antibodies against PDL fibroblast-specific cell surface molecules. One of these, the anti-PDL51 antibody, recognized a protein that was significantly upregulated in TGF-β1-induced PDL fibroblasts and highly accumulated in the PDL region of the tooth root. Mass spectrometry revealed that the antigen recognized by the anti-PDL51 antibody was leucine-rich repeat containing 15 (LRRC15), and this antibody specifically recognized the extracellular glycosylated moiety of LRRC15. Experiments presented here show that as fibroblastic differentiation progresses, increased amounts of LRRC15 localized at the cell surface and membrane. Inhibition of LRRC15 by siRNA-mediated depletion and by antibody blocking resulted in downregulation of the representative PDL fibroblastic markers. Moreover, following LRRC15 inhibition, the directed and elongated cell phenotypes disappeared, and the long processes of the end of the cell body were no longer found. Through a specific interaction between integrin β1 and LRRC15, the focal adhesion kinase signaling pathway was activated in PDL fibroblasts. Furthermore, it was shown that increased LRRC15 was important for the activation of the integrin-mediated cell adhesion signal pathway for regulation of cellular functions, including fibroblastic differentiation, proliferation, and cell migration arising from the expression of PDL-related genes in TGF-β1-induced PDL fibroblastic differentiation.

Humanized mouse models for inherited thrombocytopenia studies

Inherited thrombocytopenia (IT) is a group of hereditary disorders characterized by a reduced platelet count as the main clinical manifestation, and often with abnormal platelet function, which can subsequently lead to impaired hemostasis. In the past decades, humanized mouse models (HMMs), that are mice engrafted with human cells or genes, have been widely used in different research areas including immunology, oncology, and virology. With advances of the development of immunodeficient mice, the engraftment, and reconstitution of functional human platelets in HMM permit studies of occurrence and development of platelet disorders including IT and treatment strategies. This article mainly reviews the development of humanized mice models, the construction methods, research status, and problems of using humanized mice for the in vivo study of human thrombopoiesis.

Current status of platelet manufacturing in 3D or bioreactors

Blood shortages for transfusion are global issues of grave concern. As in vitro manufactured platelets are promising substitutes for blood donation, recent research has shown progresses including different cell sources, different bioreactors, and three-dimensional materials. The first-in-human clinical trial of cultured platelets using induced pluripotent stem cell-derived platelets began in Japan and demonstrated its quality, safety, and efficacy. A novel bioreactor with fluid motion for platelet production has been reported. Herein, we discuss various cell sources for blood cell production, recent advances in manufacturing processes, and clinical applications of cultured blood.

Ectopic Expression of FVIII in HPCs and MSCs Derived from hiPSCs with Site-Specific Integration of ITGA2B Promoter-Driven BDDF8 Gene in Hemophilia A

Hemophilia A (HA) is caused by mutations in the coagulation factor VIII (FVIII) gene (F8). Gene therapy is a hopeful cure for HA; however, FVIII inhibitors formation hinders its clinical application. Given that platelets promote coagulation via locally releasing α-granule, FVIII ectopically expressed in platelets has been attempted, with promising results for HA treatment. The B-domain-deleted F8 (BDDF8), driven by a truncated ITGA2B promoter, was targeted at the ribosomal DNA (rDNA) locus of HA patient-specific induced pluripotent stem cells (HA-iPSCs). The F8-modified, human induced pluripotent stem cells (2bF8-iPSCs) were differentiated into induced hematopoietic progenitor cells (iHPCs), induced megakaryocytes (iMKs), and mesenchymal stem cells (iMSCs), and the FVIII expression was detected. The ITGA2B promoter-driven BDDF8 was site-specifically integrated into the rDNA locus of HA-iPSCs. The 2bF8-iPSCs were efficiently differentiated into 2bF8-iHPCs, 2bF8-iMKs, and 2bF8-iMSCs. FVIII was 10.31 ng/10⁶ cells in lysates of 2bF8-iHPCs, compared to 1.56 ng/10⁶ cells in HA-iHPCs, and FVIII was 3.64 ng/10⁶ cells in 2bF8-iMSCs lysates, while 1.31 ng/10⁶ cells in iMSCs with CMV-driven BDDF8. Our results demonstrated a high expression of FVIII in iHPCs and iMSCs derived from hiPSCs with site-specific integration of ITGA2B promoter-driven BDDF8, indicating potential clinical prospects of this platelet-targeted strategy for HA gene therapy.