Scalable generation of universal platelets from human induced pluripotent stem cells

Immunological platelet transfusion refractoriness: current insights from mechanisms to therapeutics

Although there have been tremendous improvements in the production and storage of platelets, platelet transfusion refractoriness (PTR) remains a serious clinical issue that may lead to various severe adverse events. The burden of supplying platelets is worsened by rising market demand and limited donor pools of compatible platelets. Antibodies against platelet antigens are known to activate platelets through FcγR-dependent or complement-activated channels, thereby rapidly eliminating foreign platelets. Recently, other mechanisms of platelet clearance have been reported. The current treatment strategy for PTR is to select appropriate and compatible platelets; however, this necessitates a sizable donor pool and technical assistance for costly testing. Consolidation of these mechanisms should be of critical significance in providing insight to establish novel therapeutics to target immunological platelet refractoriness. Therefore, the purposes of this review were to explore the modulation of the immune system over the activation and elimination of allogeneic platelets and to summarize the development of alternative approaches for treating and avoiding alloimmunization to human leukocyte antigen or human platelet antigen in PTR.

Platelet Storage-Problems, Improvements, and New Perspectives

Platelet transfusions are routine procedures in clinical treatment aimed at preventing bleeding in critically ill patients, including those with cancer, undergoing surgery, or experiencing trauma. However, platelets are susceptible blood cells that require specific storage conditions. The availability of platelet concentrates is limited to five days due to various factors, including the risk of bacterial contamination and the occurrence of physical and functional changes known as platelet storage lesions. In this article, the problems related to platelet storage lesions are categorized into four groups depending on research areas: storage conditions, additive solutions, new testing methods for platelets (proteomic and metabolomic analysis), and extensive data modeling of platelet production (mathematical modeling, statistical analysis, and artificial intelligence). This article provides extensive information on the challenges, potential improvements, and novel perspectives regarding platelet storage.

Generating human bone marrow organoids for disease modeling and drug discovery

The bone marrow supports and regulates hematopoiesis, responding to physiological requirements for blood cell production over ontogeny and during pathological challenges. Interactions between hematopoietic cells and niche components are challenging to study mechanistically in the human context, but are important to delineate in order to explore the pathobiology of blood and bone marrow disorders. Organoids are proving transformative in many research settings, but an accurate human bone marrow model incorporating multiple hematopoietic and stromal elements has been lacking. This protocol describes a method to generate three-dimensional, multilineage bone marrow organoids from human induced pluripotent stem cells (hiPSCs), detailing the steps for the directed differentiation of hiPSCs using a series of cytokine cocktails and hydrogel embedding. Over 18 days of differentiation, hiPSCs yield the key lineages that are present in central myelopoietic bone marrow, organized in a well-vascularized architecture that resembles native hematopoietic tissues. This presents a robust, in vitro system that can model healthy and perturbed hematopoiesis in a scalable three-dimensional microenvironment. Bone marrow organoids also support the growth of immortalized cell lines and primary cells from healthy donors and patients with myeloid and lymphoid cancers, including cell types that are poorly viable in standard culture systems. Moreover, we discuss assays for the characterization of organoids, including interrogation of pathogenic remodeling using recombinant TGF-ß treatment, and methods for organoid engraftment with exogenous cells. This protocol can be readily adapted to specific experimental requirements, can be easily implemented by users with tissue culture experience and does not require access to specialist equipment.

Studies of infused megakaryocytes into mice support a "catch-and-release" model of pulmonary-centric thrombopoiesis

Many aspects of thrombopoiesis, the release of platelets from megakaryocytes (Mks), remain under debate, including where this process occurs. Murine lung in situ -microscopy studies suggested that a significant fraction of circulating platelets were released from lung-entrapped, marrow-derived Mks. We now confirm these in situ studies that endogenous mMks are entrapped in the lungs and show that intravenously infused in vitro -differentiated, mature murine (m) and human (h) Mks are similarly entrapped followed by shedding of their cytoplasm over ∼30 minutes with a peak number of released platelets occurring 1.5-4 hours later. However, while infused Mks from both species shed large intrapulmonary cytoplasmic fragments that underwent further processing into platelet-sized fragments, the two differed: many mMks escaped from and then recycled back to the lungs, while most hMks were enucleated upon first intrapulmonary passage. Infused immature hMks, inflammatory hMks, umbilical cord-blood-derived hMks and immortalized Mk progenitor cell (imMKCL)-derived hMks were also entrapped in the lung of recipient mice, and released their cytoplasm, but did so to different degrees. Intraarterial infused hMks resulted in few Mks being entrapped in tissues other than the lungs and was accompanied by a blunted and delayed rise in circulating human platelets. These studies demonstrate that the lung entraps and processes both circulating Mks and released large cytoplasmic fragments consistent with a recent lung/heart murine study and support a pulmonary-centric "catch-and-release" model of thrombopoiesis. Thus, thrombopoiesis is a drawn-out process with the majority of cytoplasmic processing derived from Mks occurring in the pulmonary bed.

Key Points

Infused in vitro -differentiated megakaryocytes synchronously release cytoplasmic fragments highly selectively in the pulmonary bed. Large, released megakaryocyte fragments recycle to the lungs, undergo further fission, terminally form platelets.

Mass production of iPSC-derived platelets toward the clinical application

The ex vivo production of platelets from induced pluripotent cells (iPSCs) may offer a safer and sustainable alternative for transfusions and drug delivery systems (DDS). However, the mass production of the clinically required number of iPSC-derived platelets (iPSC-PLTs) is challenging. Here, we introduce recent technologies for mass production and the first-in-human clinical trial using ex vivo iPSC-PLTs. To this end, we established immortalized megakaryocyte progenitor cell lines (imMKCLs) as an expandable master cell bank (MCB) through the overexpression of c-MYC, BMI1 and BCL-XL, which modulated megakaryopoiesis and thrombopoiesis. We also optimized a culture cocktail for maturation of the imMKCLs by mixing an aryl hydrocarbon receptor (AhR) antagonist, SR1/GNF-316; a Rho-associated protein kinase (ROCK) inhibitor, Y-27632/Y-39983; and a small-molecule compound replacing recombinant thrombopoietin (TPO), TA-316. Finally, we discovered the importance of turbulence on the manufacturing of intact iPSC-PLTs, allowing us to develop a turbulence-based bioreactor, VerMES. Combination of the MCB and VerMES enabled us to produce more than 100 billion iPSC-PLTs, leading to the first-in-human clinical trial. Despite these advancements, many challenges remain before expanding the clinical implementation of this strategy.

Reprogramming Megakaryocytes for Controlled Release of Platelet-like Particles Carrying a Single-Chain Thromboxane A2 Receptor-G-Protein Complex with Therapeutic Potential

In this study, we reported that novel single-chain fusion proteins linking thromboxane A2 (TXA2) receptor (TP) to a selected G-protein α-subunit q (SC-TP-Gαq) or to α-subunit s (SC-TP-Gαs) could be stably expressed in megakaryocytes (MKs). We tested the MK-released platelet-linked particles (PLPs) to be used as a vehicle to deliver the overexpressed SC-TP-Gαq or the SC-TP-Gαs to regulate human platelet function. To understand how the single-chain TP-Gα fusion proteins could regulate opposite platelet activities by an identical ligand TXA2, we tested their dual functions-binding to ligands and directly linking to different signaling pathways within a single polypeptide chain-using a 3D structural model. The immature MKs were cultured and transfected with cDNAs constructed from structural models of the individual SC-TP-Gαq and SC-TP-Gαs, respectively. After transient expression was identified, the immature MKs stably expressing SC-TP-Gαq or SC-TP-Gαs (stable cell lines) were selected. The stable cell lines were induced into mature MKs which released PLPs. Western blot analysis confirmed that the released PLPs were carrying the recombinant SC-TP-Gαq or SC-TP-Gαs. Flow cytometry analysis showed that the PLPs carrying SC-TP-Gαq were able to perform the activity by promoting platelet aggregation. In contrast, PLPs carrying SC-TP-Gαs reversed Gq to Gs signaling to inhibit platelet aggregation. This is the first time demonstrating that SC-TP-Gαq and SC-TP-Gαs were successfully overexpressed in MK cells and released as PLPs with proper folding and programmed biological activities. This bio-engineering led to the formation of two sets of biologically active PLP forms mediating calcium and cAMP signaling, respectively. As a result, these PLPs are able to bind to identical endogenous TXA2 with opposite activities, inhibiting and promoting platelet aggregation as reprogrammed for therapeutic process. Results also demonstrated that the nucleus-free PLPs could be used to deliver recombinant membrane-bound GPCRs to regulate cellular activity in general.

Generating hematopoietic cells from human pluripotent stem cells: approaches, progress and challenges

Human pluripotent stem cells (hPSCs) have been suggested as a potential source for the production of blood cells for clinical application. In two decades, almost all types of blood cells can be successfully generated from hPSCs through various differentiated strategies. Meanwhile, with a deeper understanding of hematopoiesis, higher efficiency of generating progenitors and precursors of blood cells from hPSCs is achieved. However, how to generate large-scale mature functional cells from hPSCs for clinical use is still difficult. In this review, we summarized recent approaches that generated both hematopoietic stem cells and mature lineage cells from hPSCs, and remarked their efficiency and mechanisms in producing mature functional cells. We also discussed the major challenges in hPSC-derived products of blood cells and provided some potential solutions. Our review summarized efficient, simple, and defined methodologies for developing good manufacturing practice standards for hPSC-derived blood cells, which will facilitate the translation of these products into the clinic.

Research Progress of Neutrophil-Mediated Drug Delivery Strategies for Inflammation-Related Disease

As the most abundant white blood cells in humans, neutrophils play a key role in acute and chronic inflammation, suggesting that these cells are a key component of targeted therapies for various inflammation-related diseases. Specific enzyme-responsive or specific ligand-modified polymer nanoparticles are beneficial for improving drug efficacy, reducing toxicity, and enhancing focal site retention. However, there remain significant challenges in biomedical applications of these synthetic polymer nanoparticles, mainly due to their rapid clearance by the reticuloendothelial system. In recent years, biomimetic drug delivery systems such as neutrophils acting directly as drug carriers or neutrophil-membrane-coated nanoparticles have received increasing attention due to the natural advantages of neutrophils. Thus, neutrophil-targeted, neutrophil-assisted, or neutrophil-coated nanoparticles exhibit a prolonged blood circulation time and improved accumulation at the site of inflammation. Despite recent advancements, further clinical research must be performed to evaluate neutrophil-based delivery systems for future biomedical application in the diagnosis and treatment of related inflammatory diseases. In this review, we have summarized new exciting developments and challenges in neutrophil-mediated drug delivery strategies for treating inflammation-related diseases.

Universal and hypoimmunogenic pluripotent stem cells for clinical usage

It is urgent to prepare and store large numbers of clinical trial grade human pluripotent stem (hPS) cells for off-the-shelf use in stem cell therapies. However, stem cell banks, which store off-the-shelf stem cells, need financial support and large amounts of technicians for daily cell maintenance. Therefore, it is valuable to create "universal" or "hypoimmunogenic" hPS cells with genome editing engineering by knocking in or out immune-related genes. Only a small number of universal or hypoimmunogenic hPS cell lines should be needed to store for off-the-shelf usage and reduce the large amounts of instruments, consumables and technicians. In this article, we consider how to create hypoimmunogenic or universal hPS cells as well as the demerits of the technology. β2-Microglobulin-knockout hPS cells did not harbor human leukocyte antigen (HLA)-expressing class I cells but led to the activation of natural killer cells. To escape the activities of macrophages and natural killer cells, homozygous hPS cells having a single allele of an HLA class I gene, such as HLA-C, were proposed. Major HLA class Ia molecules were knocked out, and CD47, HLA-G and PD-L1 were knocked in hPS cells utilizing CRISPR/Cas9 genome editing. Finally, some researchers are trying to generate universal hPS cells without genome editing. The cells evaded the activation of not only T cells but also macrophages and natural killer cells. These universal hPS cells have high potential for application in cell therapy.

Human Bone Marrow Organoids for Disease Modeling, Discovery, and Validation of Therapeutic Targets in Hematologic Malignancies

A lack of models that recapitulate the complexity of human bone marrow has hampered mechanistic studies of normal and malignant hematopoiesis and the validation of novel therapies. Here, we describe a step-wise, directed-differentiation protocol in which organoids are generated from induced pluripotent stem cells committed to mesenchymal, endothelial, and hematopoietic lineages. These 3D structures capture key features of human bone marrow-stroma, lumen-forming sinusoids, and myeloid cells including proplatelet-forming megakaryocytes. The organoids supported the engraftment and survival of cells from patients with blood malignancies, including cancer types notoriously difficult to maintain ex vivo. Fibrosis of the organoid occurred following TGFβ stimulation and engraftment with myelofibrosis but not healthy donor-derived cells, validating this platform as a powerful tool for studies of malignant cells and their interactions within a human bone marrow-like milieu. This enabling technology is likely to accelerate the discovery and prioritization of novel targets for bone marrow disorders and blood cancers.

SIGNIFICANCE

We present a human bone marrow organoid that supports the growth of primary cells from patients with myeloid and lymphoid blood cancers. This model allows for mechanistic studies of blood cancers in the context of their microenvironment and provides a much-needed ex vivo tool for the prioritization of new therapeutics. See related commentary by Derecka and Crispino, p. 263. This article is highlighted in the In This Issue feature, p. 247.

Hypoimmunogenic human pluripotent stem cells are valid cell sources for cell therapeutics with normal self-renewal and multilineage differentiation capacity

Hypoimmunogenic human pluripotent stem cells (hPSCs) are expected to serve as an unlimited cell source for generating universally compatible "off-the-shelf" cell grafts. However, whether the engineered hypoimmunogenic hPSCs still preserve their advantages of unlimited self-renewal and multilineage differentiation to yield functional tissue cells remains unclear. Here, we systematically studied the self-renewal and differentiation potency of three types of hypoimmunogenic hPSCs, established through the biallelic lesion of B2M gene to remove all surface expression of classical and nonclassical HLA class I molecules (B2Mnull), biallelic homologous recombination of nonclassical HLA-G1 to the B2M loci to knockout B2M while expressing membrane-bound β2m-HLA-G1 fusion proteins (B2MmHLAG), and ectopic expression of soluble and secreted β2m-HLA-G5 fusion proteins in B2MmHLAG hPSCs (B2Mm/sHLAG) in the most widely used WA09 human embryonic stem cells. Our results showed that hypoimmunogenic hPSCs with variable expression patterns of HLA molecules and immune compromising spectrums retained their normal self-renewal capacity and three-germ-layer differentiation potency. More importantly, as exemplified by neurons, cardiomyocytes and hepatocytes, hypoimmunogenic hPSC-derived tissue cells were fully functional as of their morphology, electrophysiological properties, macromolecule transportation and metabolic regulation. Our findings thus indicate that engineered hypoimmunogenic hPSCs hold great promise of serving as an unlimited universal cell source for cell therapeutics.

Adoptive Immunotherapy: A Human Pluripotent Stem Cell Perspective

The past decade has witnessed significant advances in cancer immunotherapy, particularly through the adoptive transfer of engineered T cells in treating advanced leukemias and lymphomas. Despite these excitements, challenges remain with scale, cost, and ensuring quality control of engineered immune cells, including chimeric antigen receptor T, natural killer cells, and macrophages. The advent of human pluripotent stem cells (hPSCs), including human embryonic stem cells and induced pluripotent stem cells, has transformed immunotherapy by providing a scalable, off-the-shelf source of any desired immune cells for basic research, translational studies, and clinical interventions. The tractability of hPSCs for gene editing could also generate homogenous, universal cellular products with custom functionality for individual or combinatory therapeutic applications. This review will explore various immune cell types whose directed differentiation from hPSCs has been achieved and recently adapted for translational immunotherapy and feature forward-looking bioengineering techniques shaping the future of the stem cell field.

Ex vivo manufacturing of platelets: beyond the first-in-human clinical trial using autologous iPSC-platelets

Platelet transfusion is a common clinical approach to providing platelets to patients suffering from thrombocytopenia or other ailments that require an additional platelet source. However, a stable supply of platelet products is challenged by aging societies, pandemics, and other factors. Many groups have made extensive efforts toward the in vitro generation of platelets for clinical application. We established immortalized megakaryocyte progenitor cell lines (imMKCLs) from human induced pluripotent stem cells (iPSCs) and achieved clinical-scale manufacturing of iPSC-derived platelets (iPSC-PLTs) from them by identifying turbulent flow as a key physical condition. We later completed the iPLAT1 study, the first-in-human clinical trial using autologous iPSC-PLTs. This review summarizes current findings on the ex vivo generation of iPSC-PLTs that led to the iPLAT1 study and beyond. We also discuss new insights regarding the heterogeneity of megakaryocytes and the implications for the ex vivo generation of iPSC-PLTs.

Human iPS Cells for Clinical Applications and Cellular Products

Human induced pluripotent stem cells (iPSCs), since their discovery in 2007, have rapidly become a starting cell type of choice for the differentiation of many mature cell types. Their flexibility, amenability to gene editing and functional equivalence to embryonic stem cells ensured their subsequent adoption by many manufacturing processes for cellular products. In this chapter, we will discuss the process whereby iPSCs are generated, key quality control steps which should be considered during manufacturing, the application of good manufacturing practice to production processes and iPSC-derived cellular products which are already undergoing clinical trials. iPSCs provide a new avenue for the next generation of cellular therapeutics and by combining new differentiation protocols, quality control and reproducible manufacturing, iPSC-derived cellular products could provide treatments for many currently untreatable diseases, allowing the large-scale manufacture of high-quality cell therapies.

Immune Editing: Overcoming Immune Barriers in Stem Cell Transplantation

Purpose of Review

Human pluripotent stem cells have the potential to revolutionize the treatment of inborn and degenerative diseases, including aging and autoimmunity. A major barrier to their wider adoption in cell therapies is immune rejection. Genome editing allows for tinkering of the human genome in stem and progenitor cells and raises the prospect for overcoming the immune barriers to transplantation.

Recent Findings

Initial attempts have focused primarily on the major histocompatibility barrier that is formed by the human leukocyte antigens (HLA). More recently, immune checkpoint inhibitors, such as PD-L1, CD47, or HLA-G, are being explored both, in the presence or absence of HLA, to mitigate immune rejection by the various cellular components of the immune system.

Summary

In this review, we discuss progress in surmounting immune barriers to cell transplantation, with a particular focus on genetic engineering of human pluripotent stem and progenitor cells and the therapeutic cell types derived from them.

Engineered cord blood megakaryocytes evade killing by allogeneic T-cells for refractory thrombocytopenia

The current global platelet supply is often insufficient to meet all the transfusion needs of patients, in particular for those with alloimmune thrombocytopenia. To address this issue, we have developed a strategy employing a combination of approaches to achieve more efficient production of functional megakaryocytes (MKs) and platelets collected from cord blood (CB)-derived CD34+ hematopoietic cells. This strategy is based on ex-vivo expansion and differentiation of MKs in the presence of bone marrow niche-mimicking mesenchymal stem cells (MSCs), together with two other key components: (1) To enhance MK polyploidization, we used the potent pharmacological Rho-associated coiled-coil kinase (ROCK) inhibitor, KD045, resulting in liberation of increased numbers of functional platelets both in-vitro and in-vivo; (2) To evade HLA class I T-cell-driven killing of these expanded MKs, we employed CRISPR-Cas9-mediated β-2 microglobulin (β2M) gene knockout (KO). We found that coculturing with MSCs and MK-lineage-specific cytokines significantly increased MK expansion. This was further increased by ROCK inhibition, which induced MK polyploidization and platelet production. Additionally, ex-vivo treatment of MKs with KD045 resulted in significantly higher levels of engraftment and donor chimerism in a mouse model of thrombocytopenia. Finally, β2M KO allowed MKs to evade killing by allogeneic T-cells. Overall, our approaches offer a novel, readily translatable roadmap for producing adult donor-independent platelet products for a variety of clinical indications.

Repeated intravenous administration of hiPSC-MSCs enhance the efficacy of cell-based therapy in tissue regeneration

We seek to demonstrate whether therapeutic efficacy can be improved by combination of repeated intravenous administration and local transplantation of human induced pluripotential stem cell derived MSCs (hiPSC-MSCs). In this study, mice model of hind-limb ischemia is established by ligation of left femoral artery. hiPSC-MSCs (5 × 10⁵) is intravenously administrated immediately after induction of hind limb ischemia with or without following intravenous administration of hiPSC-MSCs every week or every 3 days. Intramuscular transplantation of hiPSC-MSCs (3 × 10⁶) is performed one week after induction of hind-limb ischemia. We compare the therapeutic efficacy and cell survival of intramuscular transplantation of hiPSC-MSCs with or without a single or repeated intravenous administration of hiPSC-MSCs. Repeated intravenous administration of hiPSC-MSCs can increase splenic regulatory T cells (Tregs) activation, decrease splenic natural killer (NK) cells expression, promote the polarization of M2 macrophages in the ischemic area and improved blood perfusion in the ischemic limbs. The improved therapeutic efficacy of MSC-based therapy is due to both increased engraftment of intramuscular transplanted hiPSC-MSCs and intravenous infused hiPSC-MSCs. In conclusion, our study support a combination of repeated systemic infusion and local transplantation of hiPSC-MSCs for cardiovascular disease.

A combination of repeated systemic infusion and local transplantation of hiPSC-MSCs could enhance regenerative therapies for cardiovascular disease.

The Analysis of the Human Megakaryocyte and Platelet Coding Transcriptome in Healthy and Diseased Subjects

Platelets are generated and released into the bloodstream from their precursor cells, megakaryocytes that reside in the bone marrow. Though platelets have no nucleus or DNA, they contain a full transcriptome that, during platelet formation, is transported from the megakaryocyte to the platelet. It has been described that transcripts in platelets can be translated into proteins that influence platelet response. The platelet transcriptome is highly dynamic and has been extensively studied using microarrays and, more recently, RNA sequencing (RNA-seq) in relation to diverse conditions (inflammation, obesity, cancer, pathogens and others). In this review, we focus on bulk and single-cell RNA-seq studies that have aimed to characterize the coding transcriptome of healthy megakaryocytes and platelets in humans. It has been noted that bulk RNA-seq has limitations when studying in vitro-generated megakaryocyte cultures that are highly heterogeneous, while single-cell RNA-seq has not yet been applied to platelets due to their very limited RNA content. Next, we illustrate how these methods can be applied in the field of inherited platelet disorders for gene discovery and for unraveling novel disease mechanisms using RNA from platelets and megakaryocytes and rare disease bioinformatics. Next, future perspectives are discussed on how this field of coding transcriptomics can be integrated with other next-generation technologies to decipher unexplained inherited platelet disorders in a multiomics approach.

Pluripotent stem cells in clinical setting - new developments and overview of current status

The number of clinical trials using human pluripotent stem cells (hPSC)—both embryonic and induced pluripotent stem cells (hESC/iPSC)—has expanded in the last several years beyond expectations. By the end of 2021, a total of 90 trials had been registered in 13 countries with more than 3000 participants. However, only US, Japan, China, and the UK are conducting both hESC- and hiPSC-based trials. Together US, Japan, and China have registered 78% (70 out of 90) of all trials worldwide. More than half of all trials (51%) are focused on the treatment of degenerative eye diseases and malignancies, enrolling nearly 2/3 of all participants in hPSC-based trials. Although no serious adverse events resulting in death or morbidity due to hPSC-based cellular therapy received have been reported, information about safety and clinical efficacy are still very limited. With the availability of novel technologies for precise genome editing, a new trend in the development of hPSC-based cellular therapies seems to be emerging. Engineering universal donor hPSC lines has become a holy grail in the field. Indeed, because of its effectiveness and simplicity nanomedicine and in vivo delivery of gene therapy could become more advantageous than cellular therapies for the treatment of multiple diseases. In the future, for the best outcome, hPSC-based cellular therapy might be combined with other technological advancements, such as biomimetic epidural electrical stimulation that can restore trunk and leg motor functions after complete spinal injury.

There and Back Again: The Once and Current Developments in Donor-Derived Platelet Products for Products for Hemostatic Therapy

Over 100 years ago, Duke transfused whole blood to a thrombocytopenic patient to raise the platelet count and prevent bleeding. Since then, platelet transfusions have undergone numerous modifications from whole blood-derived platelet-rich plasma to apheresis-derived platelet concentrates. Similarly, the storage time and temperature have changed. The mandate to store platelets for a maximum of 5-7 days at room temperature has been challenged by recent clinical trial data, ongoing difficulties with transfusion-transmitted infections, and recurring periods of shortages, further exacerbated by the COVID-19 pandemic. Alternative platelet storage approaches are as old as the first platelet transfusions. Cold-stored platelets may offer increased storage times (days) and improved hemostatic potential at the expense of reduced circulation time. Frozen (cryopreserved) platelets extend the storage time to years but require storage at -80 °C and thawing before transfusion. Lyophilized platelets can be powder-stored for years at room temperature and reconstituted within minutes in sterile water but are probably the least explored alternative platelet product to date. Finally, whole blood offers the hemostatic spectrum of all blood components but has challenges, such as ABO incompatibility. While we know more than ever before about the in vitro properties of these products, clinical trial data on these products are accumulating. The purpose of this review is to summarize the findings of recent preclinical and clinical studies on alternative, donor-derived platelet products.

Toward in Vitro Production of Platelet from Induced Pluripotent Stem Cells

Platelets (PLTs) are small anucleate blood cells that release from polyploidy megakaryocytes(MKs). PLT transfusion is standard therapy to prevent hemorrhage. PLT transfusion is donor-dependent way which have limitations including the inadequate donor blood supply, poor quality, and issues related to infection and immunity. Overcoming these obstacles is possible with in vitro production of human PLTs. Currently several cells have been considered as source to in vitro production of PLTs such as hematopoietic stem cells (HSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). However, HSCs are a limited source for PLT production and large-scale expansion of HSC-derived PLT remains difficult. Alternative sources can be ESCs which have unlimited expansion capacity. But ESCs have ethical issues related to destroying human embryos. iPSCs are considered as an ideal unlimited source for PLT production. They are able to differentiate into any cells and have the capacity of self-renewal. Moreover, iPSCs can be acquired from any donor and easily manipulated. Due to new advances in development of MK cell lines, bioreactors, feeder cell-free production and the ability of large scale generation, iPSC-based PLTs are moving toward clinical applicability and considering the minimal risk of alloimmunization and tumorigenesis of these products, there is great hopefulness they will become the standard source for blood transfusions in the future. This review will focus on how to progress of in vitro generation of PLT from stem cell especially iPSCs and some of the successful strategies that can be easily used in clinic will be described.

Mapping the biogenesis of forward programmed megakaryocytes from induced pluripotent stem cells

Platelet deficiency, known as thrombocytopenia, can cause hemorrhage and is treated with platelet transfusions. We developed a system for the production of platelet precursor cells, megakaryocytes, from pluripotent stem cells. These cultures can be maintained for >100 days, implying culture renewal by megakaryocyte progenitors (MKPs). However, it is unclear whether the MKP state in vitro mirrors the state in vivo, and MKPs cannot be purified using conventional surface markers. We performed single-cell RNA sequencing throughout in vitro differentiation and mapped each state to its equivalent in vivo. This enabled the identification of five surface markers that reproducibly purify MKPs, allowing us insight into their transcriptional and epigenetic profiles. Last, we performed culture optimization, increasing MKP production. Together, this study has mapped parallels between the MKP states in vivo and in vitro and allowed the purification of MKPs, accelerating the progress of in vitro-derived transfusion products toward the clinic.

Sorting nexin 24 is required for α-granule biogenesis and cargo delivery in megakaryocytes

Germline defects affecting the DNA-binding domain of the transcription factor FLI1 are associated with a bleeding disorder that is characterized by the presence of large, fused α-granules in platelets. We investigated whether the genes showing abnormal expression in FLI1-deficient platelets could be involved in platelet α-granule biogenesis by undertaking transcriptome analysis of control platelets and platelets harboring a DNA-binding variant of FLI1. Our analysis identified 2,276 transcripts that were differentially expressed in FLI1-deficient platelets. Functional annotation clustering of the coding transcripts revealed significant enrichment for gene annotations relating to protein transport, and identified Sorting nexin 24 (SNX24) as a candidate for further investigation. Using an induced pluripotent stem cell-derived megakaryocyte model, SNX24 expression was found to be increased during the early stages of megakaryocyte differentiation and downregulated during proplatelet formation, indicating tight regulatory control during megakaryopoiesis. CRISPR-Cas9 mediated knockout (KO) of SNX24 led to decreased expression of immature megakaryocyte markers, CD41 and CD61, and increased expression of the mature megakaryocyte marker CD42b (P=0.0001), without affecting megakaryocyte polyploidisation, or proplatelet formation. Electron microscopic analysis revealed an increase in empty membrane-bound organelles in SNX24 KO megakaryocytes, a reduction in α-granules and an absence of immature and mature multivesicular bodies, consistent with a defect in the intermediate stage of α-granule maturation. Co-localization studies showed that SNX24 associates with each compartment of α-granule maturation. Reduced expression of CD62P and VWF was observed in SNX24 KO megakaryocytes. We conclude that SNX24 is required for α-granule biogenesis and intracellular trafficking of α-granule cargo within megakaryocytes.

Conditional CRISPR-mediated deletion of Lyn kinase enhances differentiation and function of iPSC-derived megakaryocytes

BACKGROUND

Thrombocytopenia leading to life-threatening excessive bleeding can be treated by platelet transfusion. Currently, such treatments are totally dependent on donor-derived platelets. To support future applications in the use of in vitro-derived platelets, we sought to identify genes whose manipulation might improve the efficiency of megakaryocyte production and resulting hemostatic effectiveness. Disruption of Lyn kinase has previously been shown to improve cell survival, megakaryocyte ploidy and TPO-mediated activation in mice, but its role in human megakaryocytes and platelets has not been examined.

METHODS

To analyze the role of Lyn at defined differentiation stages during human megakaryocyte differentiation, conditional Lyn-deficient cells were generated using CRISPR/Cas9 technology in iPS cells. The efficiency of Lyn-deficient megakaryocytes to differentiate and become activated in response to a range of platelet agonists was analyzed in iPSC-derived megakaryocytes.

RESULTS

Temporally controlled deletion of Lyn improved the in vitro differentiation of hematopoietic progenitor cells into mature megakaryocytes, as measured by the rate and extent of appearance of CD41+ CD42+ cells. Lyn-deficient megakaryocytes also demonstrated improved hemostatic effectiveness, as reported by their ability to mediate clot formation in rotational thromboelastometry. Finally, Lyn-deficient megakaryocytes produced increased numbers of platelet-like particles (PLP) in vitro.

CONCLUSIONS

Conditional deletion of Lyn kinase increases the hemostatic effectiveness of megakaryocytes and their progeny as well as improving their yield. Adoption of this system during generation of in vitro-derived platelets may contribute to both their efficiency of production and their ability to support hemostasis.

Isolation of megakaryocytes using magnetic cell separation and adverse effects induced by diclofenac toxicity in an experiment

This study investigates the response of bone marrow (particularly megakaryocytes) in mice under the influence of diclofenac sodium for 10 days using intraperitoneal injection at various doses. A fundamentally new immunomagnetic separation method was applied during the experiment, which helped obtain pure lines of bone marrow cells, particularly megakaryocytes (MC), without admixtures of other cells or their particles. The resulting cells completely retain their structure and can be used in further research. The study determined that different doses of diclofenac sodium have different effects on different groups of diabetes mellitus cells CD34-megakaryocytes. The use of 1.0 mg/ml sharply negatively affects the state of early populations of megakaryocytes (decrease by 80%, p=0.05), a dose of 0.025 mg/ml had the least effect on this population of cells (22.8%, p=0.05). The greatest number of average forms of diabetes mellitus 34 was observed when using a dose of 0.95 mg/ml (22.8%, p=0.05), with a gradual decrease in the dose, the indicator of this group of cells decreased. A dose of 0.03 mg/ml did not affect the quantitative state of megakaryocytes, and a dose of 0.025 mg/ml caused a slight decrease (16.6%, p=0.05). Indicators of mature cells of megakaryocytes CD 34- decreased in all studied groups, however, their maximum value reached a maximum decrease by 0.25 mg/ml (55.2%, p=0.05), the dose of diclofenac sodium 0.03 mg/ml, lower (18.4%, p=0.05). Diclofenac sodium in different doses has different effects on the degree of differentiation of CD 34-. Its introduction positively affects the state of intermediate forms of megakaryocytes, except for minimal doses, while the effect on early and mature forms in all cases turned out to be negative.

Early Endosomal GTPase Rab5 (Ras-Related Protein in Brain 5) Regulates GPIbβ (Glycoprotein Ib Subunit β) Trafficking and Platelet Production In Vitro

OBJECTIVE

Maturation of megakaryocytes culminates with extensive membrane rearrangements necessary for proplatelet formation. Mechanisms required for proplatelet extension and origin of membranes are still poorly understood. GTPase Rab5 (Ras-related protein in brain 5) regulates endocytic uptake and homotypic fusion of early endosomes and regulates phosphatidylinositol 3-monophosphate production important for binding of effector proteins during early-to-late endosomal/lysosomal maturation. Approach and Results: To investigate the role of Rab5 in megakaryocytes, we expressed GFP (green fluorescent protein)-coupled Rab5 wild type and its point mutants Q79L (active) and N133L (inactive) in primary murine fetal liver-derived megakaryocytes. Active Rab5 Q79L induced the formation of enlarged early endosomes, while inactive Rab5 N133L caused endosomal fragmentation. Consistently, an increased amount of transferrin internalization in Rab5 Q79L was impaired in Rab5 N133L expressing megakaryocytes, when compared with GFP or Rab5 wild type. Moreover, trafficking of GPIbβ (glycoprotein Ib subunit beta), a subunit of major megakaryocytes receptor and membrane marker, was found to be mediated by Rab5 activity. While GPIbβ was mostly present along the plasma membrane, and within cytoplasmic vesicles in Rab5 wild type megakaryocytes, it accumulated in the majority of Rab5 Q79L enlarged endosomes. Conversely, Rab5 N133L caused mostly GPIbβ plasma membrane retention. Furthermore, Rab5 Q79L expression increased incorporation of the membrane dye (PKH26), indicating higher membrane content. Finally, while Rab5 Q79L increased proplatelet production, inactive Rab5 N133L strongly inhibited it and was coupled with a decrease in late endosomes/lysosomes. Localization of GPIbβ in enlarged endosomes was phosphatidylinositol 3-monophosphate dependent.

CONCLUSIONS

Taken together, our results demonstrate that Rab5-dependent endocytosis plays an important role in megakaryocytes receptor trafficking, membrane formation, and thrombopoiesis.

Rapid and Highly Efficient Isolation and Purification of Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (iPSCs) hold great promise for biomedical applications. However, establishment of new iPSC lines still presents many challenges. Here we describe a simple yet highly efficient two-step protocol for the isolation and purification of human iPSC lines. The first step adapts iPSCs to single cell culture and passaging, promoting survival and self-renewal; the second step enables the isolation and purification of bona fide iPSCs from a mixed population using column-based positive selection of cells expressing pluripotency markers such as TRA-1-60. Both steps utilize commercially available reagents. Using this protocol, iPSCs can be purified from cell preparations containing differentiated or unreprogrammed cells, or even be isolated directly from reprogramming vessels. The protocol could be adopted for high throughput isolation and expansion of iPSC lines and facilitate the widespread use of iPSCs in future applications.

Oxidized Phospholipids Promote NETosis and Arterial Thrombosis in LNK(SH2B3) Deficiency

Supplemental Digital Content is available in the text.

Background:

LNK/SH2B3 inhibits Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling by hematopoietic cytokine receptors. Genome-wide association studies have shown association of a common single nucleotide polymorphism in LNK (R262W, T allele) with neutrophilia, thrombocytosis, and coronary artery disease. We have shown that LNK(TT) reduces LNK function and that LNK-deficient mice display prominent platelet–neutrophil aggregates, accelerated atherosclerosis, and thrombosis. Platelet–neutrophil interactions can promote neutrophil extracellular trap (NET) formation. The goals of this study were to assess the role of NETs in atherosclerosis and thrombosis in mice with hematopoietic Lnk deficiency.

Methods:

We bred mice with combined deficiency of Lnk and the NETosis-essential enzyme PAD4 (peptidyl arginine deiminase 4) and transplanted their bone marrow into Ldlr^–/– mice. We evaluated the role of LNK in atherothrombosis in humans and mice bearing a gain of function variant in JAK2 (JAK2^V617F).

Results:

Lnk-deficient mice displayed accelerated carotid artery thrombosis with prominent NETosis that was completely reversed by PAD4 deficiency. Thrombin-activated Lnk^–/– platelets promoted increased NETosis when incubated with Lnk^–/– neutrophils compared with wild-type platelets or wild-type neutrophils. This involved increased surface exposure and release of oxidized phospholipids (OxPL) from Lnk^–/– platelets, as well as increased priming and response of Lnk^–/– neutrophils to OxPL. To counteract the effects of OxPL, we introduced a transgene expressing the single-chain variable fragment of E06 (E06-scFv). E06-scFv reversed accelerated NETosis, atherosclerosis, and thrombosis in Lnk^–/– mice. We also showed increased NETosis when human induced pluripotent stem cell–derived LNK(TT) neutrophils were incubated with LNK(TT) platelet/megakaryocytes, but not in isogenic LNK(CC) controls, confirming human relevance. Using data from the UK Biobank, we found that individuals with the JAK2^VF mutation only showed increased risk of coronary artery disease when also carrying the LNK R262W allele. Mice with hematopoietic Lnk^+/– and Jak2^VF clonal hematopoiesis showed accelerated arterial thrombosis but not atherosclerosis compared with Jak2^VFLnk^+/+ controls.

Conclusions:

Hematopoietic Lnk deficiency promotes NETosis and arterial thrombosis in an OxPL-dependent fashion. LNK(R262W) reduces LNK function in human platelets and neutrophils, promoting NETosis, and increases coronary artery disease risk in humans carrying Jak2^VF mutations. Therapies targeting OxPL may be beneficial for coronary artery disease in genetically defined human populations.

Induced Pluripotent Stem Cells as a Tool for Modeling Hematologic Disorders and as a Potential Source for Cell-Based Therapies

The breakthrough in human induced pluripotent stem cells (hiPSCs) has revolutionized the field of biomedical and pharmaceutical research and opened up vast opportunities for drug discovery and regenerative medicine, especially when combined with gene-editing technology. Numerous healthy and patient-derived hiPSCs for human disease modeling have been established, enabling mechanistic studies of pathogenesis, platforms for preclinical drug screening, and the development of novel therapeutic targets/approaches. Additionally, hiPSCs hold great promise for cell-based therapy, serving as an attractive cell source for generating stem/progenitor cells or functional differentiated cells for degenerative diseases, due to their unlimited proliferative capacity, pluripotency, and ethical acceptability. In this review, we provide an overview of hiPSCs and their utility in the study of hematologic disorders through hematopoietic differentiation. We highlight recent hereditary and acquired genetic hematologic disease modeling with patient-specific iPSCs, and discuss their applications as instrumental drug screening tools. The clinical applications of hiPSCs in cell-based therapy, including the next-generation cancer immunotherapy, are provided. Lastly, we discuss the current challenges that need to be addressed to fulfill the validity of hiPSC-based disease modeling and future perspectives of hiPSCs in the field of hematology.

Generation of HLA Universal Megakaryocytes and Platelets by Genetic Engineering

Patelet transfusion refractoriness remains a relevant hurdle in the treatment of severe alloimmunized thrombocytopenic patients. Antibodies specific for the human leukocyte antigens (HLA) class I are considered the major immunological cause for PLT transfusion refractoriness. Due to the insufficient availability of HLA-matched PLTs, the development of new technologies is highly desirable to provide an adequate management of thrombocytopenia in immunized patients. Blood pharming is a promising strategy not only to generate an alternative to donor blood products, but it may offer the possibility to optimize the therapeutic effect of the produced blood cells by genetic modification. Recently, enormous technical advances in the field of in vitro production of megakaryocytes (MKs) and PLTs have been achieved by combining progresses made at different levels including identification of suitable cell sources, cell pharming technologies, bioreactors and application of genetic engineering tools. In particular, use of RNA interference, TALEN and CRISPR/Cas9 nucleases or nickases has allowed for the generation of HLA universal PLTs with the potential to survive under refractoriness conditions. Genetically engineered HLA-silenced MKs and PLTs were shown to be functional and to have the capability to survive cell- and antibody-mediated cytotoxicity using in vitro and in vivo models. This review is focused on the methods to generate in vitro genetically engineered MKs and PLTs with the capacity to evade allogeneic immune responses.

Recent lessons learned for ex-vivo platelet production

PURPOSE OF REVIEW

Platelet transfusion can be life-saving but carries a risk of infection or alloimmunization and is limited by insufficient donor sources and restricted unit shelf life. Generating sufficient platelets in vitro to replace a unit of collected blood remains a challenge. Here, we examine the latest advances in the regulation of megakaryocyte maturation and expansion along with platelet formation and survival. We also discuss alternative therapies investigated to induce platelet production.

RECENT FINDINGS

Recent studies examined candidate niche cells in the bone marrow microenvironment for promoting platelet formation and developed an explant-based bioreactor to enhance platelet production ex vivo. Chemical inhibitors were examined for their ability to promote megakaryocyte maturation and expansion. Microparticles from megakaryocytes or platelets were found to improve megakaryocyte maturation and platelet formation. Membrane budding was identified as a novel mode of platelet formation. Lastly, a chemical inhibitor to improve cold-stored platelets was identified.

SUMMARY

Recent advances in the regulation of megakaryocyte expansion and platelet production provide exciting promise for the development of improved approaches to generate platelets in vitro. These findings bring the field one step closer to achieving the ultimate goal of creating a unit of platelets without the need for donation.

Human induced pluripotent stem cell-derived platelets loaded with lapatinib effectively target HER2+ breast cancer metastasis to the brain

Prognosis of patients with HER2+ breast-to-brain-metastasis (BBM) is dismal even after current standard-of-care treatments, including surgical resection, whole-brain radiation, and systemic chemotherapy. Radiation and systemic chemotherapies can also induce cytotoxicity, leading to significant side effects. Studies indicate that donor-derived platelets can serve as immune-compatible drug carriers that interact with and deliver drugs to cancer cells with fewer side effects, making them a promising therapeutic option with enhanced antitumor activity. Moreover, human induced pluripotent stem cells (hiPSCs) provide a potentially renewable source of clinical-grade transfusable platelets that can be drug-loaded to complement the supply of donor-derived platelets. Here, we describe methods for ex vivo generation of megakaryocytes (MKs) and functional platelets from hiPSCs (hiPSC-platelets) in a scalable fashion. We then loaded hiPSC-platelets with lapatinib and infused them into BBM tumor-bearing NOD/SCID mouse models. Such treatment significantly increased intracellular lapatinib accumulation in BBMs in vivo, potentially via tumor cell-induced activation/aggregation. Lapatinib-loaded hiPSC-platelets exhibited normal morphology and function and released lapatinib pH-dependently. Importantly, lapatinib delivery to BBM cells via hiPSC-platelets inhibited tumor growth and prolonged survival of tumor-bearing mice. Overall, use of lapatinib-loaded hiPSC-platelets effectively reduced adverse effects of free lapatinib and enhanced its therapeutic efficacy, suggesting that they represent a novel means to deliver chemotherapeutic drugs as treatment for BBM.

The heterogeneity of megakaryocytes and platelets and implications for ex vivo platelet generation

Platelets, the chief effector of hemostasis, are small anucleate blood cells generated from megakaryocytes (MKs), and the defects in platelet production or function lead to a variety of bleeding complications. Emerging evidence indicates that MKs and platelets are much more diverse than previously appreciated and involved in many physiological and pathological processes besides hemostasis, such as innate and adaptive immune responses, angiogenesis, and tumor metastasis, while the ontogenic variations in MK and platelet function have also become a focus in the field. However, whether MKs and platelets fulfill these distinct functions by utilizing distinct subpopulations remains poorly understood. New studies aimed at deciphering the MK transcriptome at the single‐cell level have provided some key insights into the functional heterogeneity of MKs. In this review, we will discuss some of the recent discoveries of functional and developmental heterogeneity of MKs and its potential link to the heterogeneity of platelets. We will also discuss the implications of these findings while focusing on the ex vivo generation of platelets from human pluripotent stem cells. The improved understanding of the heterogeneity underlying human MK development and platelet production should open new avenues for future platelet regeneration and clinical treatment of related diseases.

Lung megakaryocytes are immune modulatory cells

Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting their activation and differentiation, as well as all phases of the immune response. Megakaryocytes (Mks) are the cell source of circulating platelets, and until recently Mks were typically only considered bone marrow-resident (BM-resident) cells. However, platelet-producing Mks also reside in the lung, and lung Mks express greater levels of immune molecules compared with BM Mks. We therefore sought to define the immune functions of lung Mks. Using single-cell RNA sequencing of BM and lung myeloid-enriched cells, we found that lung Mks, which we term MkL, had gene expression patterns that are similar to antigen-presenting cells. This was confirmed using imaging and conventional flow cytometry. The immune phenotype of Mks was plastic and driven by the tissue immune environment, as evidenced by BM Mks having an MkL-like phenotype under the influence of pathogen receptor challenge and lung-associated immune molecules, such as IL-33. Our in vitro and in vivo assays demonstrated that MkL internalized and processed both antigenic proteins and bacterial pathogens. Furthermore, MkL induced CD4+ T cell activation in an MHC II-dependent manner both in vitro and in vivo. These data indicated that MkL had key immune regulatory roles dictated in part by the tissue environment.

Modeling genetic platelet disorders with human pluripotent stem cells: mega-progress but wanting more on our plate(let)

PURPOSE OF REVIEW

Megakaryocytes are rare hematopoietic cells that play an instrumental role in hemostasis, and other important biological processes such as immunity and wound healing. With the advent of cell reprogramming technologies and advances in differentiation protocols, it is now possible to obtain megakaryocytes from any pluripotent stem cell (PSC) via hematopoietic induction. Here, we review recent advances in PSC-derived megakaryocyte (iMK) technology, focusing on platform validation, disease modeling and current limitations.

RECENT FINDINGS

A comprehensive study confirmed that iMK can recapitulate many transcriptional and functional aspects of megakaryocyte and platelet biology, including variables associated with complex genetic traits such as sex and race. These findings were corroborated by several pathological models in which iMKs revealed molecular mechanisms behind inherited platelet disorders and assessed the efficacy of novel pharmacological interventions. However, current differentiation protocols generate primarily embryonic iMK, limiting the clinical and translational potential of this system.

SUMMARY

iMK are strong candidates to model pathologic mutations involved in platelet defects and develop innovative therapeutic strategies. Future efforts on generating definitive hematopoietic progenitors would improve current platelet generation protocols and expand our capacity to model neonatal and adult megakaryocyte disorders.

In vitro Generation of Megakaryocytes and Platelets

Platelets, the tiny anucleate cells responsible for stopping bleeding through thrombosis, are derived from hematopoietic stem cells through a series of differentiation steps. Thrombocytopenia, characterized by abnormally low blood platelet counts, may arise from cancer therapies, trauma, sepsis, as well as blood disorders, and could become a life-threatening problem. Platelet transfusion is the most effective strategy to treat thrombocytopenia, however, the source of platelets is in great shortage. Therefore, in vitro generation of platelets has become an important topic and numerous attempts have been made toward generating platelets from different types of cells, including hematopoietic stem cells, pluripotent stem cells, fibroblast cells, and adipose-derived cells. In this review, we will detail the efforts made to produce, in the in vitro culture, platelets from these different cell types. Importantly, as transfusion medicine requires a huge number of platelets, we will highlight some studies on producing platelets on a large scale. Although new methods of gene manipulation, new culture conditions, new cytokines and chemical compounds have been introduced in platelet generation research since the first study of hematopoietic stem cell-derived platelets nearly 30 years ago, limited success has been achieved in obtaining truly mature and functional platelets in vitro, indicating the studies of platelets fall behind those of other blood cell types. This is possibly because megakaryocytes, which produce platelets, are very rare in blood and marrow. We have previously developed a platform to identify new extrinsic and intronic regulators for megakaryocytic lineage development, and in this review, we will also cover our effort on that. In summary, stem cell-based differentiation is a promising way of generating large-scale platelets to meet clinical needs, and continuous study of the cellular development of platelets will greatly facilitate this.

Specific Blood Cells Derived from Pluripotent Stem Cells: An Emerging Field with Great Potential in Clinical Cell Therapy

Widely known for self-renewal and multilineage differentiation, stem cells can be differentiated into all specialized tissues and cells in the body. In the past few years, a number of researchers have focused on deriving hematopoietic stem cells (HSCs) from pluripotent stem cells (PSCs) as alternative sources for clinic. Existing findings demonstrated that it is feasible to obtain HSCs and certain mature blood lineages from PSCs, except for several issues to be addressed. This short review outlines the technologies used for hematopoietic differentiation in recent years. In addition, the therapeutic value of PSCs as a potential source of various blood cells is also discussed as well as its challenges and directions in future clinical applications.

Emerging gene therapies for enhancing the hemostatic potential of platelets

Platelet transfusions are an integral component of balanced hemostatic resuscitation protocols used to manage severe hemorrhage following trauma. Enhancing the hemostatic potential of platelets could lead to further increases in the efficacy of transfusions, particularly for non-compressible torso hemorrhage or severe hemorrhage with coagulopathy, by decreasing blood loss and improving overall patient outcomes. Advances in gene therapies, including RNA therapies, are leading to new strategies to enhance platelets for better control of hemorrhage. This review will highlight three approaches for creating modified platelets using gene therapies: (i) direct transfection of transfusable platelets ex vivo, (ii) in vitro production of engineered platelets from platelet-precursor cells, and (iii) modifying the bone marrow for in vivo production of modified platelets. In summary, modifying platelets to enhance their hemostatic potential is an exciting new frontier in transfusion medicine, but more preclinical development as well as studies testing the safety and efficacy of these agents are needed.

Improving Human Induced Pluripotent Stem Cell-Derived Megakaryocyte Differentiation and Platelet Production

Several protocols exist for generating megakaryocytes (MKs) and platelets from human induced pluripotent stem cells (hiPSCs) with limited efficiency. We observed previously that mesoderm induction improved endothelial and stromal differentiation. We, therefore, hypothesized that a protocol modification prior to hemogenic endothelial cell (HEC) differentiation will improve MK progenitor (MKP) production and increase platelet output. We further asked if basic media composition affects MK maturation. In an iterative process, we first compared two HEC induction protocols. We found significantly more HECs using the modified protocol including activin A and CHIR99021, resulting in significantly increased MKs. MKs released comparable platelet amounts irrespective of media conditions. In a final validation phase, we obtained five-fold more platelets per hiPSC with the modified protocol (235 ± 84) compared to standard conditions (51 ± 15; p < 0.0001). The regenerative potency of hiPSC-derived platelets was compared to adult donor-derived platelets by profiling angiogenesis-related protein expression. Nineteen of 24 angiogenesis-related proteins were expressed equally, lower or higher in hiPSC-derived compared to adult platelets. The hiPSC-platelet's coagulation hyporeactivity compared to adult platelets was confirmed by thromboelastometry. Further stepwise improvement of hiPSC-platelet production will, thus, permit better identification of platelet-mediated regenerative mechanisms and facilitate manufacture of sufficient amounts of functional platelets for clinical application.

Differentiated Cells Derived from Hematopoietic Stem Cells and Their Applications in Translational Medicine

Hematopoietic stem cells (HSCs) and their development are one of the most widely studied model systems in mammals. In adults, HSCs are predominantly found in the bone marrow, from where they maintain homeostasis. Besides bone marrow and mobilized peripheral blood, cord blood is also being used as an alternate allogenic source of transplantable HSCs. HSCs from both autologous and allogenic sources are being applied for the treatment of various conditions like blood cancers, anemia, etc. HSCs can further differentiate to mature blood cells. Differentiation process of HSCs is being extensively studied so as to obtain a large number of pure populations of various differentiated cells in vitro so that they can be taken up for clinical trials. The ability to generate sufficient quantity of clinical-grade specialized blood cells in vitro would take the field of hematology a step ahead in translational medicine.

Human Leukocyte Antigen Class I Pseudo-Homozygous Mesenchymal Stem Cells Derived from Human Induced Pluripotent Stem Cells

Mesenchymal stem cells (MSC) are an important type of cell that are highly recognized for their safety and efficacy as a cell therapy agent. In order to obtain MSC, primary tissues (adipose tissue, bone marrow, and umbilical cord blood) must be used; however, these tissues, especially umbilical cord blood, are difficult to obtain due to various reasons, such as the low birth rate trend. In addition, to maximize the safety and efficacy of MSC as allogenic cell therapeutic agents, it is desirable to minimize the possibility of an immune rejection reaction after in vivo transplantation. This study tried to establish a novel method for producing induced pluripotent stem cells (iPSC)-derived MSC in which the human leukocyte antigen (HLA)-class I gene is knocked out. To do so, dermal fibroblast originated iPSC generation using Yamanaka 4-factor, HLA class I gene edited iPSC generation using CRISPR/Cas9, and differentiation from iPSC to MSC using MSC culture medium was utilized. Through this, HLA-A, B, and C pseudo-homozygous iPSC-derived MSC (KO iMSC) were produced by monoallelically knocking out the polymorphic HLA-A, B, and C genes, which are the major causes of immune rejection during allogenic cell transplantation. Produced KO iMSC possesses multipotency and it was safe in vivo to be able to be differentiated to cartilage. In addition, it was not attacked by natural killer cells unlike HLA class I null cells. In conclusion, KO iMSC that do not induce immune rejection during allogenic cell transplantation can be produced. In the future, KO iMSC can be successfully utilized as allogenic cell therapeutic agents for many recipients through HLA screening.

Process analysis of pluripotent stem cell differentiation to megakaryocytes to make platelets applying European GMP

Quality, traceability and reproducibility are crucial factors in the reliable manufacture of cellular therapeutics, as part of the overall framework of Good Manufacturing Practice (GMP). As more and more cellular therapeutics progress towards the clinic and research protocols are adapted to comply with GMP standards, guidelines for safe and efficient adaptation have become increasingly relevant. In this paper, we describe the process analysis of megakaryocyte manufacture from induced pluripotent stem cells with a view to manufacturing in vitro platelets to European GMP for transfusion. This process analysis has allowed us an overview of the entire manufacturing process, enabling us to pinpoint the cause and severity of critical risks. Risk mitigations were then proposed for each risk, designed to be GMP compliant. These mitigations will be key in advancing this iPS-derived therapy towards the clinic and have broad applicability to other iPS-derived cellular therapeutics, many of which are currently advancing towards GMP-compliance. Taking these factors into account during protocol design could potentially save time and money, expediting the advent of safe, novel therapeutics from stem cells.

CRISPR-edited megakaryocytes for rapid screening of platelet gene functions

Human anucleate platelets cannot be directly modified using traditional genetic approaches. Instead, studies of platelet gene function depend on alternative models. Megakaryocytes (the nucleated precursor to platelets) are the nearest cell to platelets in origin, structure, and function. However, achieving consistent genetic modifications in primary megakaryocytes has been challenging, and the functional effects of induced gene deletions on human megakaryocytes for even well-characterized platelet genes (eg, ITGA2B) are unknown. Here we present a rapid and systematic approach to screen genes for platelet functions in CD34+ cell-derived megakaryocytes called CRIMSON (CRISPR-edited megakaryocytes for rapid screening of platelet gene functions). By using CRISPR/Cas9, we achieved efficient nonviral gene editing of a panel of platelet genes in megakaryocytes without compromising megakaryopoiesis. Gene editing induced loss of protein in up to 95% of cells for platelet function genes GP6, RASGRP2, and ITGA2B; for the immune receptor component B2M; and for COMMD7, which was previously associated with cardiovascular disease and platelet function. Gene deletions affected several select responses to platelet agonists in megakaryocytes in a manner largely consistent with those expected for platelets. Deletion of B2M did not significantly affect platelet-like responses, whereas deletion of ITGA2B abolished agonist-induced integrin activation and spreading on fibrinogen without affecting the translocation of P-selectin. Deletion of GP6 abrogated responses to collagen receptor agonists but not thrombin. Deletion of RASGRP2 impaired functional responses to adenosine 5'-diphosphate (ADP), thrombin, and collagen receptor agonists. Deletion of COMMD7 significantly impaired multiple responses to platelet agonists. Together, our data recommend CRIMSON for rapid evaluation of platelet gene phenotype associations.

Bioprinting of Human Cord Blood-Derived CD34+ Cells and Exploration of the Multilineage Differentiation Ability in Vitro

The three-dimensional (3D) marrow microenvironment plays an essential role in regulating human cord blood-derived CD34+ cells (hCB-CD34+) migration, proliferation, and differentiation. Extensive in vitro and in vivo studies have aimed to recapitulate the main components of the bone marrow (BM) niche. Nonetheless, the models are limited by a lack of heterogeneity and compound structure. Here, we fabricated coaxial extruded core-shell tubular scaffolds and extrusion-based bioprinted cell-laden mesh scaffolds to mimic the functional niche in vitro. A multicellular mesh scaffold and two different core-shell tubular scaffolds were developed with human bone marrow-derived mesenchymal stromal cells (BMSCs) in comparison with a conventional 2D coculture system. A clear cell-cell connection was established in all three bioprinted constructs. Cell distribution and morphology were observed in different systems with scanning electron microscopy (SEM). Collected hCB-CD34+ cells were characterized by various stem cell-specific and lineage-specific phenotypic parameters. The results showed that compared with hCB-CD34+ cells cocultured with BMSCs in Petri dishes, the self-renewal potential of hCB-CD34+ cells was stronger in the tubular scaffolds after 14 days. Besides, cells in these core-shell constructs tended to obtain stronger differentiation potential of lymphoid and megakaryocytes, while cells encapsulated in mesh scaffolds obtained stronger differentiation tendency into erythroid cells. Consequently, 3D bioprinting technology could partially simulate the niche of human hematopoietic stem cells. The three models have their potential in stemness maintenance and multilineage differentiation. This study can provide initial effective guidance in the directed differentiation research and related screening of drug models for hematological diseases.

The Opportunities and Challenges regarding Induced Platelets from Human Pluripotent Stem Cells

As a standard clinical treatment, platelet transfusion has been employed to prevent hemorrhage in patients with thrombocytopenia or platelet dysfunctions. Platelets also show therapeutic potential for aiding liver regeneration and bone healing and regeneration and for treating dermatological conditions. However, the supply of platelets rarely meets the rising clinical demand. Other issues, including short shelf life, strict storage temperature, and allogeneic immunity caused by frequent platelet transfusions, have become serious challenges that require the development of high-yielding alternative sources of platelets. Human pluripotent stem cells (hPSCs) are an unlimited substitution source for regenerative medicine, and patient-derived iPSCs can provide novel research models to explore the pathogenesis of some diseases. Many studies have focused on establishing and modifying protocols for generating functional induced platelets (iPlatelets) from hPSCs. To reach high efficiency production and eliminate the exogenous antigens, media supplements and matrix have been optimized. In addition, the introduction of some critical transgenes, such as c-MYC, BMI1, and BCL-XL, can also significantly increase hPSC-derived platelet production; however, this may pose some safety concerns. Furthermore, many novel culture systems have been developed to scale up the production of iPlatelets, including 2D flow systems, 3D rotary systems, and vertical reciprocal motion liquid culture bioreactors. The development of new gene-editing techniques, such as CRISPR/Cas9, can be used to solve allogeneic immunity of platelet transfusions by knocking out the expression of B2M. Additionally, the functions of iPlatelets were also evaluated from multiple aspects, including but not limited to morphology, structure, cytoskeletal organization, granule content, DNA content, and gene expression. Although the production and functions of iPlatelets are close to meeting clinical application requirements in both quantity and quality, there is still a long way to go for their large-scale production and clinical application. Here, we summarize the diverse methods of platelet production and update the progresses of iPlatelets. Furthermore, we highlight recent advances in our understanding of key transcription factors or molecules that determine the platelet differentiation direction.

Ex Vivo Manufacture of Megakaryocytes and Platelets from Stem Cells: Recent Advances Toward Transfusion in Humans

The generation of ex vivo functional megakaryocytes (MK) and platelets is an important issue in transfusion medicine as donor dependence implies in limitations, such as shortage of eligible volunteers. Indeed, platelet transfusion is still a procedure that saves the lives of patients with defective platelet production. Recent technological development has enabled the isolation and expansion of stem cells that can be used as a source for the production of functional platelets for transfusion. In this review, we discuss recent approaches of in vitro or ex vivo production of MK and platelets, suggesting that, in the near future, donor-independent sources may become a possibility. The feasibility of using these cells in the clinic may be safer, and in vitro manipulation could generate universally compatible products, solving problems related to platelet refractoriness. However, functionality and survival testing of these products in human beings are scarce; therefore, additional studies are needed to consolidate this purpose.

The chemokine CXCL14 mediates platelet function and migration via direct interaction with CXCR4

AIMS

Beyond classical roles in thrombosis and haemostasis, it becomes increasingly clear that platelets contribute as key players to inflammatory processes. The involvement of platelets in these processes is often mediated through a variety of platelet-derived chemokines which are released upon activation and act as paracrine and autocrine factors. In this study, we investigate CXCL14, a newly described platelet chemokine and its role in thrombus formation as well as monocyte and platelet migration. In addition, we examine the chemokine receptor CXCR4 as a possible receptor for CXCL14 on platelets. Furthermore, with the use of artificially generated platelets derived from induced pluripotent stem cells (iPSC), we investigate the importance of CXCR4 for CXCL14-mediated platelet functions.

METHODS AND RESULTS

In this study, we showed that CXCL14 deficient platelets reveal reduced thrombus formation under flow compared with wild-type platelets using a standardized flow chamber. Addition of recombinant CXCL14 normalized platelet-dependent thrombus formation on collagen. Furthermore, we found that CXCL14 is a chemoattractant for platelets and mediates migration via CXCR4. CXCL14 promotes platelet migration of platelets through the receptor CXCR4 as evidenced by murine CXCR4-deficient platelets and human iPSC-derived cultured platelets deficient in CXCR4. We found that CXCL14 directly interacts with the CXCR4 as verified by immunoprecipitation and confocal microscopy.

CONCLUSIONS

Our results reveal CXCL14 as a novel platelet-derived chemokine that is involved in thrombus formation and platelet migration. Furthermore, we identified CXCR4 as principal receptor for CXCL14, an interaction promoting platelet migration.

Transient characteristics of universal cells on human-induced pluripotent stem cells and their differentiated cells derived from foetal stem cells with mixed donor sources

Introduction

It is important to prepare ‘hypoimmunogenic’ or ‘universal’ human pluripotent stem cells (hPSCs) with gene‐editing technology by knocking out or in immune‐related genes, because only a few hypoimmunogenic or universal hPSC lines would be sufficient to store for their off‐the‐shelf use. However, these hypoimmunogenic or universal hPSCs prepared previously were all genetically edited, which makes laborious processes to check and evaluate no abnormal gene editing of hPSCs.

Methods

Universal human‐induced pluripotent stem cells (hiPSCs) were generated without gene editing, which were reprogrammed from foetal stem cells (human amniotic fluid stem cells) with mixing 2‐5 allogenic donors but not with single donor. We evaluated human leucocyte antigen (HLA)‐expressing class Ia and class II of our hiPSCs and their differentiated cells into embryoid bodies, cardiomyocytes and mesenchymal stem cells. We further evaluated immunogenic response of transient universal hiPSCs with allogenic mononuclear cells from survival rate and cytokine production, which were generated by the cells due to immunogenic reactions.

Results

Our universal hiPSCs during passages 10‐25 did not have immunogenic reaction from allogenic mononuclear cells even after differentiation into cardiomyocytes, embryoid bodies and mesenchymal stem cells. Furthermore, the cells including the differentiated cells did not express HLA class Ia and class II. Cardiomyocytes differentiated from transient universal hiPSCs at passage 21‐22 survived and continued beating even after treatment with allogenic mononuclear cells.

Platelet production using adipose-derived mesenchymal stem cells: Mechanistic studies and clinical application

Megakaryocytes (MKs) are platelet progenitor stem cells found in the bone marrow. Platelets obtained from blood draws can be used for therapeutic applications, especially platelet transfusion. The needs for platelet transfusions for clinical situation is increasing, due in part to the growing number of patients undergoing chemotherapy. Platelets obtained from donors, however, have the disadvantages of a limited storage lifespan and the risk of donor-related infection. Extensive effort has therefore been directed at manufacturing platelets ex vivo. Here, we review ex vivo technologies for MK development, focusing on human adipose tissue-derived mesenchymal stem/stromal cell line (ASCL)-based strategies and their potential clinical application. Bone marrow and adipose tissues contain mesenchymal stem/stromal cells that have an ability to differentiate into MKs, which release platelets. Taking advantage of this mechanism, we developed a donor-independent system for manufacturing platelets for clinical application using ASCL established from adipose-derived mesenchymal stem/stromal cells (ASCs). Culture of ASCs with endogenous thrombopoietin and its receptor c-MPL, and endogenous genes such as p45NF-E2 leads to MK differentiation and subsequent platelet production. ASCs compose heterogeneous cells, however, and are not suitable for clinical application. Thus, we established ASCLs, which expand into a more homogeneous population, and fulfill the criteria for mesenchymal stem cells set by the International Society for Cellular Therapy. Using our ASCL culture system with MK lineage induction medium without recombinant thrombopoietin led to peak production of platelets within 12 days, which may be sufficient for clinical application.