Production and nonclinical evaluation of an autologous iPSC-derived platelet product for the iPLAT1 clinical trial.

Donor-derived platelets are used to treat or prevent hemorrhage in patients with thrombocytopenia. However, ∼5% or more of these patients are complicated with alloimmune platelet transfusion refractoriness (allo-PTR) due to alloantibodies against HLA-I or human platelet antigens (HPA). In these cases, platelets from compatible donors are necessary, but it is difficult to find such donors for patients with rare HLA-I or HPA. To produce platelet products for patients with aplastic anemia with allo-PTR due to rare HPA-1 mismatch in Japan, we developed an ex vivo good manufacturing process (GMP)-based production system for an induced pluripotent stem cell-derived platelet product (iPSC-PLTs). Immortalized megakaryocyte progenitor cell lines (imMKCLs) were established from patient iPSCs, and a competent imMKCL clone was selected for the master cell bank (MCB) and confirmed for safety, including negativity of pathogens. From this MCB, iPSC-PLTs were produced using turbulent flow bioreactors and new drugs. In extensive nonclinical studies, iPSC-PLTs were confirmed for quality, safety, and efficacy, including hemostasis in a rabbit model. This report presents a complete system for the GMP-based production of iPSC-PLTs and the required nonclinical studies and thus supports the iPLAT1 study, the first-in-human clinical trial of iPSC-PLTs in a patient with allo-PTR and no compatible donor using the autologous product. It also serves as a comprehensive reference for the development of widely applicable allogeneic iPSC-PLTs and other cell products that use iPSC-derived progenitor cells as MCB.

Hemostatic function of cold-stored platelets in a thrombocytopenic rabbit bleeding model.

BACKGROUND: Transfusion of cold-stored platelet concentrates (CS-PCs) appears effective in massively bleeding patients. However, few studies have evaluated their in vivo hemostatic function in severe thrombocytopenia. STUDY DESIGN AND METHODS: The in vivo function of plasma-depleted human PCs was evaluated in rabbits with a blocked reticuloendothelial system and busulfan-induced thrombocytopenia. On day 1, a human apheresis PC was processed in a platelet additive solution (PAS-PC) and split evenly for cold or room temperature storage (RTS). On days 3, 6, or 9, RTS- or CS-PAS-PCs were transfused (4.0 × 109 platelets/kg) after plasma depletion into two to four rabbits that developed adequate thrombocytopenia (<25 × 109 /L). Ear bleeding time was measured by two incisions in small veins. The hemostatic rate was defined as the percentage of rabbits achieving bleeding cessation within 600 s at either incision. The experiment was repeated using five different PCs on each storage day. RESULTS: The mean pre-transfusion rabbit platelet count was 8.6 ± 5.2 × 109 /L. The hemostatic rates with RTS- and CS-PAS-PCs were both 100% on day 3, 93 ± 15% and 73 ± 15% on day 6 (p = .07), and 65 ± 36% and 73 ± 37% on day 9 (p = .27), respectively, with no statistical differences. Total platelet counts were significantly lower after CS-PAS-PC than RTS-PAS-PC transfusion on all days (e.g., 58.7 ± 5.7 vs. 42.4 ± 14.7 × 109 /L, p = .0007, day 9), and did not reach 50 × 109 /L in several experiments. Platelet count increments correlated significantly with hemostatic efficacy for CS-PAS-PC transfusion only. DISCUSSION: CS-PAS-PCs might achieve similar hemostasis as RTS-PAS-PCs in thrombocytopenic patients with mild bleeding. Hemostatic efficacy could be improved by transfusing more CS-PAS-PCs.

Adoptive cell therapy using tumor-infiltrating lymphocytes for melanoma refractory to immune-checkpoint inhibitors.

To evaluate the feasibility of adoptive cell therapy (ACT) using ex vivo-expanded tumor-infiltrating lymphocytes (TILs) in Japanese patients with melanoma who failed immune-checkpoint inhibitor therapy, an open-label, single-arm, pilot study was conducted. We investigated the immunological and genetic factors of the pretreatment tumor and expanded TILs that may be associated with the clinical response. The treatment protocol comprised preparation of TIL culture, lympho-depleting non-myeloablative preconditioning with cyclophosphamide and fludarabine, TIL infusion, and intravenous administration of low-dose IL-2. Three patients of clinical subtypes mucosal, superficial spreading, and acral melanoma underwent TIL-ACT. Most severe adverse events, including fever and leukopenia, were manageable with the supportive regimen specified in the protocol, suggesting that the TIL-ACT regimen is suitable for Japanese patients with melanoma. One patient showed a short-term partial response, one relatively long-stable disease, and one experienced disease progression. Whole-exome and transcriptional sequencing of isolated tumor cells and immunohistochemical analyses before TIL-ACT revealed various immunostimulatory factors, including a high tumor mutation burden and immune cell-recruiting chemokines, as well as various immunosuppressive factors including TGF-ß, VEGF, Wnt/ß-catenin, and MAPK signaling and epithelial-to-mesenchymal transition, which might influence the efficacy of TIL-ACT. Our results imply mechanisms for the antitumor effect of and resistance to TIL-ACT. Further studies of immune-resistant mechanisms of TIL-ACT are warranted. This study is registered with the UMIN Clinical Trial Registry (UMIN 000011431).

Turbulence Activates Platelet Biogenesis to Enable Clinical Scale Ex Vivo Production.

The ex vivo generation of platelets from human-induced pluripotent cells (hiPSCs) is expected to compensate donor-dependent transfusion systems. However, manufacturing the clinically required number of platelets remains unachieved due to the low platelet release from hiPSC-derived megakaryocytes (hiPSC-MKs). Here, we report turbulence as a physical regulator in thrombopoiesis in vivo and its application to turbulence-controllable bioreactors. The identification of turbulent energy as a determinant parameter allowed scale-up to 8 L for the generation of 100 billion-order platelets from hiPSC-MKs, which satisfies clinical requirements. Turbulent flow promoted the release from megakaryocytes of IGFBP2, MIF, and Nardilysin to facilitate platelet shedding. hiPSC-platelets showed properties of bona fide human platelets, including circulation and hemostasis capacities upon transfusion in two animal models. This study provides a concept in which a coordinated physico-chemical mechanism promotes platelet biogenesis and an innovative strategy for ex vivo platelet manufacturing.

Refined methods to evaluate the in vivo hemostatic function and viability of transfused human platelets in rabbit models.

BACKGROUND: To bridge the gap between in vitro function and clinical efficacy of platelet (PLT) transfusion products, reliable in vivo PLT functional assays for hemostasis and survival in animal models are required. However, there are no standardized methods for assessing the in vivo quality of transfused human PLTs. STUDY DESIGN AND METHODS: Plasma-depleted human PLT concentrates (PCs; Day 3, Day 5, Day 7, Day 10, and damaged) were transfused into busulfan-induced rabbits with thrombocytopenia with prolonged bleeding times 1 day after treatment with ethyl palmitate (EP) to block their reticuloendothelial systems. The hemostatic effect of PC transfusion was evaluated by the ear fine vein bleeding time. For the in vivo survival assay, splenectomized EP-treated rabbits were transfused with human PCs, and viability of the human PLTs in the rabbits was determined by flow cytometry using human PLT-specific antibodies and Trucount tubes. RESULTS: The hemostatic effect of PCs was slightly reduced with increasing storage periods for early time points, but more dramatically reduced for later time points. PLT survival was similar after 3 and 7 days of storage, but PLTs stored for 10 days showed significantly poorer survival than those stored only 3 days. CONCLUSION: Our new and improved protocol for in vivo assessment of transfused PLTs is sufficiently sensitive to detect subtle changes in hemostatic function and viability of human PLTs transfused into rabbit models. This protocol could contribute to preclinical in vivo functional assessment and clinical quality assurance of emerging novel PLT products such as cultured cell-derived human PLTs.

Ability of fibrinogen γ-derived dodecapeptides with different sequences to bind to rat platelets.

A dodecapeptide (γ400-411) derived from a fibrinogen γ-chain carboxyl-terminal sequence recognizes specifically the active form of GPIIb/IIIa on the surface of activated platelets. For the purpose of efficient hemostasis, we previously developed ADP-encapsulated liposomes modified with human-dodecapeptide (HHLGGAKQAGDV, human-H12). On the other hand, the amino-acid sequence of H12 from rats is HHMGGSKQVGDM, having only 67% homology to that from humans. Here, we investigated the ability of rat-H12 in comparison with human-H12 to bind to platelets. Firstly, rat platelets were activated with phorbol-12-myristate-13-acetate (PMA), and the activation was confirmed by flow cytometry. Next, we evaluated the dissociation constant (K(d)) of human-H12 and rat-H12 for dissociation from rat platelets by using FACS. As a result, the K(d) of human-H12 and rat-H12 with respect to rat platelets was 2.78 ± 0.21 and 2.91 ± 0.22 µM, respectively. Furthermore, H12 from both species inhibited quite similarly the aggregation of rat platelets in platelet-rich plasma (PRP). These results suggest that H12 from different species with different amino acid sequences interacts similarly with GPIIb/IIIa on platelets.

Arabidopsis metacaspase 2d is a positive mediator of cell death induced during biotic and abiotic stresses.

Cysteine proteases such as caspases play important roles in programmed cell death (PCD) of metazoans. Plant metacaspases (MCPs), a family of cysteine proteases structurally related to caspases, have been hypothesized to be ancestors of metazoan caspases, despite their different substrate specificity. Arabidopsis thaliana contains six type II MCP genes (AtMCP2a-f). Whether and how these individual members are involved in controlling PCD in plants remains largely unknown. Here we investigated the function and regulation of AtMCP2d, the predominant and constitutively expressed member of type II MCPs, in stress-inducible PCD. Two AtMCP2d mutants (mcp2d-1 and mcp2d-3) exhibited reduced sensitivity to PCD-inducing mycotoxin fumonisin B1 as well as oxidative stress inducers, whereas AtMCP2d over-expressors were more sensitive to these agents, and exhibited accelerated cell-death progression. We found that AtMCP2d exclusively localizes to the cytosol, and its accumulation and self-processing patterns were age-dependent in leaves. Importantly, active proteolytic processing of AtMCP2d proteins dependent on its catalytic activity was observed in mature leaves during mycotoxin-induced cell death. We also found that mcp2d-1 leaves exhibited reduced cell death in response to Pseudomonas syringae carrying avirulent gene avrRpt2, and that self-processing of AtMCP2d was also detected in wild-type leaves in response to this pathogen. Furthermore, increases in processed AtMCP2d proteins were found to correlate with conditional cell-death induction in two lesion-mimic mutants (cpr22 and ssi4) that exhibit spontaneous cell-death phenotypes. Taken together, our data strongly suggest that AtMCP2d plays a positive regulatory role in biotic and abiotic stress-induced PCD.

Decoration of fibrinogen γ-chain peptide on adenosine diphosphate-encapsulated liposomes enhances binding of the liposomes to activated platelets.

For the purpose of efficient hemostasis, we previously developed ADP-encapsulated liposomes modified with a dodecapeptide (HHLGGAKQAGDV, H12), H12-(ADP)Lipo. This liposome actually enhanced platelet aggregation in vitro, and showed significant hemostatic effect in vivo. Since fibrinogen (Fbg) is abundant in the bloodstream, it is unclear why this liposome binds platelets so efficiently, overcoming the competition with Fbg. Therefore, we investigated the relationship between H12 density on the liposome and the binding ability to platelets, and evaluated the inhibitory effect of Fbg on the binding of H12-(ADP)Lipo to platelets. As a result, the binding ability to platelets steeply increased depending on H12 density until it reached about 3×10(15) H12 molecules/m(2). The 50% inhibition concentration of Fbg on the binding of H12-(ADP)Lipo to platelets was about 25-fold over the concentration of H12 molecules on the liposome. Moreover, almost no inhibition by Fbg was observed at the physiological concentration of it. This result suggests that the ability of H12 to bind to GPIIb/IIIa increased overwhelmingly by the anchoring to the liposome that enabled the cooperative binding of H12 peptides to the platelets.

Calcium-dependent activation and autolysis of Arabidopsis metacaspase 2d.

Metacaspases (MCPs) are members of a new family of cysteine proteases found in plants, fungi, and protozoa that are structurally related to metazoan caspases. Recent studies showed that plant MCPs are arginine/lysine-specific cysteine proteases with caspase-like processing activities in vitro and in vivo, and some of the plant type II MCPs exhibit Ca(2+) dependence for their endopeptidase activity in vitro. However, the mechanisms and biological relevance of Ca(2+) dependence and self-processing of plant MCPs remains unclear. Here we show that recombinant AtMCP2d, the most abundantly expressed member of Arabidopsis type II MCPs at the transcriptional level, exhibits a strict Ca(2+) dependence for its catalytic activation that is apparently mediated by intramolecular self-cleavage mechanism. However, rapid inactivation of AtMCP2d activity concomitant with Ca(2+)-induced self-processing at multiple internal sites was observed. Because active AtMCP2d can cleave its inactive form, intermolecular cleavage (autolysis) of AtMCP2d could also occur under our assay conditions. Ca(2+)-induced self-processing of recombinant AtMCP2d was found to correlate with the sequential appearance of at least six intermediates, including self-cleaved forms, during the proenzyme purification process. Six of these peptides were characterized, and the cleavage sites were mapped through N-terminal protein sequencing. Mutation analysis of AtMCP2d revealed that cleavage after Lys-225, which is a highly conserved residue among the six Arabidopsis type II MCPs, is critical for the catalytic activation by Ca(2+), and we demonstrate that this residue is essential for AtMCP2d activation of H(2)O(2)-induced cell death in yeast. Together, our results provide clues to understand the mode of regulation for this class of proteases.

Shear-dependent suppression of platelet thrombus formation by phosphodiesterase 3 inhibition requires low levels of concomitant Gs-coupled receptor stimulation.

Phosphodiesterase (PDE)3 inhibitors exert potent antiplatelet effects through maintaining elevated intracellular cyclic adenosine monophosphate levels, but do not prolong bleeding time. To resolve this discrepancy, we hypothesised that PDE3 inhibitors effectively suppress shear-induced platelet thrombus formation initiated by the interaction of the platelet receptor GPIb/V/IX with its ligand, von Willebrand factor (VWF), since arterial thrombosis is more dependent on shear stress as compared with haemostatic plug formation. To test the hypothesis, we compared the in vitro effects of K-134 (a PDE3 inhibitor), tirofiban (a GPIIb/IIIa inhibitor) and acetylsalicylic acid (ASA) on ristocetin-induced platelet aggregation and platelet thrombus formation on VWF or collagen surfaces under flow conditions. K-134 inhibited GPIIb/IIIa-dependent platelet aggregation to the same extent as tirofiban and more potently than ASA. Likewise, K-134 and tirofiban effectively inhibited stable platelet thrombus formation (platelet firm adhesion and subsequent aggregation) on the VWF or collagen surface under high shear, but ASA only inhibited aggregation. Notably, inhibition by K-134 became evident only when a low concentration of PGE1 was present. These inhibitors did not block shear-induced initial platelet contact with VWF via GPIb/V/IX. In contrast, under low shear, the inhibitory effects of K-134 on platelet aggregation on the collagen surface were lower than tirofiban or ASA. The observed shear-dependent suppression of platelet thrombus formation by PDE3 inhibitor in the presence of low levels of adenylate cyclase stimulator may contribute to high therapeutic benefit with low risk of bleeding.

Defining the functional network of epigenetic regulators in Arabidopsis thaliana.

Development of ChIP-chip and ChIP-seq technologies has allowed genome-wide high-resolution profiling of chromatin-associated marks and binding sites for epigenetic regulators. However, signals for directing epigenetic modifiers to their target sites are not understood. In this paper, we tested the hypothesis that genome location can affect the involvement of epigenetic regulators using Chromatin Charting (CC) Lines, which have an identical transgene construct inserted at different locations in the Arabidopsis genome. Four CC lines that showed evidence for epigenetic silencing of the luciferase reporter gene were transformed with RNAi vectors individually targeting epigenetic regulators LHP1, MOM1, CMT3, DRD1, DRM2, SUVH2, CLF, and HD1. Involvement of a particular epigenetic regulator in silencing the transgene locus in a CC line was determined by significant alterations in luciferase expression after suppression of the regulator's expression. Our results suggest that the targeting of epigenetic regulators can be influenced by genome location as well as sequence context. In addition, the relative importance of an epigenetic regulator can be influenced by tissue identity. We also report a novel approach to predict interactions between epigenetic regulators through clustering analysis of the regulators using alterations in gene expression of putative downstream targets, including endogenous loci and transgenes, in epigenetic mutants or RNAi lines. Our data support the existence of a complex and dynamic network of epigenetic regulators that serves to coordinate and control global gene expression in higher plants.

Bax Inhibitor-1, a conserved cell death suppressor, is a key molecular switch downstream from a variety of biotic and abiotic stress signals in plants.

In Nature plants are constantly challenged by a variety of environmental stresses that could lead to disruptions in cellular homeostasis. Programmed cell death (PCD) is a fundamental cellular process that is often associated with defense responses to pathogens, during development and in response to abiotic stresses in fungi, animals and plants. Although there are many characteristics shared between different types of PCD events, it remains unknown whether a common mechanism drives various types of PCD in eukaryotes. One candidate regulator for such a mechanism is Bax Inhibitor-1 (BI-1), an evolutionary conserved, endoplasmic reticulum (ER)-resident protein that represents an ancient cell death regulator that potentially regulates PCD in all eukaryotes. Recent findings strongly suggested that BI-1 plays an important role in the conserved ER stress response pathway to modulate cell death induction in response to multiple types of cell death signals. As ER stress signaling pathways has been suggested to play important roles not only in the control of ER homeostasis but also in other biological processes such as the response to pathogens and abiotic stress in plants, BI-1 might function to control the convergence point that modulates the level of the "pro-survival and pro-death" signals under multiple stress conditions.

Charting functional and physical properties of chromatin in living cells.

With the vast transcriptome database now available, global patterns of gene expression have been mapped in various species to reveal higher order structures in the genome. Location-dependent control of gene expression has also been studied in human cell cultures and in Arabidopsis plants using well-characterized insertion and transposition cell line collections. With the added genome-wide mapping of chromatin features at a high resolution, via advanced microarray and sequencing technologies, comprehensive analysis of structure-function relationships deduced from chromatin organization and gene expression data is now feasible. This has begun to reveal micro-heterogeneity in the genome with respect to structural and functional segmentations.

Generation of megakaryocytes and platelets from human subcutaneous adipose tissues.

Recent advances in regenerative medicine have created a broad spectrum of stem cell research. Among them, tissue stem cell regulations are important issues to clarify the molecular mechanism of differentiation. Adipose tissues have been shown to contain abundant preadipocytes, which are multipotent to differentiate into cells including adipocytes, chondrocytes, and osteoblasts. In this study, we have first shown that megakaryocytes and platelets can be generated from adipocyte precursor cells. Human adipocyte precursor cells were cultured in conditioned media for 12 days to differentiate adipocytes, followed by 12 days of culture in media containing thrombopoietin. The ultrastructures of adipocyte precursor cell- and bone marrow CD34-positive cell-derived megakaryocytes and platelets were similar. In addition, adipocyte precursor cell-derived platelets exhibited surface expression of P-selectin and bound fibrinogen upon stimulation with platelet agonists, suggesting that these platelets were functional. This is the first demonstration that human subcutaneous adipocyte precursor cells can generate megakaryocyte and functional platelets in an in vitro culture system.

SHD1 is a novel cytokine-inducible, negative feedback regulator of STAT5-dependent transcription.

STAT5 is a critical mediator of a variety of cytokine signaling whose transcriptional activity is regulated by associating with various proteins. During a search for STAT5-interacting proteins, we identified SHD1, a mammalian homologue of yeast gene Sac3, as a potential interacter. SHD1 was localized in the nucleus, and induced by cytokines that activate STAT5, such as erythropoietin, interleukin-2 (IL-2), or IL-3. SHD1 interacted specifically with STAT5A and STAT5B, and interestingly, it specifically repressed STAT5-dependent transcription in vitro without affecting the stability or phosphorylation of STAT5 protein. Gene disruption study revealed that T, B, or bone marrow cells from mice lacking SHD1 were hyperresponsive to T-cell-receptor engagement, or stimulation with various STAT5-activating cytokines. These results suggest that SHD1 is a novel cytokine-inducible negative feedback regulator of STAT5.

Mechanisms and consequences of agonist-induced talin recruitment to platelet integrin alphaIIbbeta3.

Platelet aggregation requires agonist-induced alphaIIbbeta3 activation, a process mediated by Rap1 and talin. To study mechanisms, we engineered alphaIIbbeta3 Chinese hamster ovary (CHO) cells to conditionally express talin and protease-activated receptor (PAR) thrombin receptors. Human PAR1 or murine PAR4 stimulation activates alphaIIbbeta3, which was measured with antibody PAC-1, indicating complete pathway reconstitution. Knockdown of Rap1-guanosine triphosphate-interacting adaptor molecule (RIAM), a Rap1 effector, blocks this response. In living cells, RIAM overexpression stimulates and RIAM knockdown blocks talin recruitment to alphaIIbbeta3, which is monitored by bimolecular fluorescence complementation. Mutations in talin or beta3 that disrupt their mutual interaction block both talin recruitment and alphaIIbbeta3 activation. However, one talin mutant (L325R) is recruited to alphaIIbbeta3 but cannot activate it. In platelets, RIAM localizes to filopodia and lamellipodia, and, in megakaryocytes, RIAM knockdown blocks PAR4-mediated alphaIIbbeta3 activation. The RIAM-related protein lamellipodin promotes talin recruitment and alphaIIbbeta3 activity in CHO cells but is not expressed in megakaryocytes or platelets. Thus, talin recruitment to alphaIIbbeta3 by RIAM mediates agonist-induced alphaIIbbeta3 activation, with implications for hemostasis and thrombosis.