Biomanufacture of human platelets for transfusion: Rationale and approaches

Current status of platelet manufacturing in 3D or bioreactors

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

The Immunophenotypic Profile of Healthy Human Bone Marrow

Flow cytometry enables multiparametric characterization of hematopoietic cell immunophenotype. Deviations from normal immunophenotypic patterns comprise a cardinal feature of many hematopoietic neoplasms, underscoring the ongoing essentiality of flow cytometry as a diagnostic tool. However, understanding of aberrant hematopoiesis requires an equal understanding of normal hematopoiesis as a comparator. In this review, we outline key features of healthy adult hematopoiesis and lineage specification as illuminated by flow cytometry and provide diagrams illustrating what a diagnostician may observe in flow cytometric plots. These features provide a profile of baseline hematopoiesis, to which clinical samples with suspected neoplasia may be compared.

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.

Plaquettes sanguines de culture : état de l’art

Les plaquettes sanguines sont des éléments anucléés du sang. D’un diamètre de 2 à 3 μm, ce sont les plus petits éléments figurés du sang. Alors que leur rôle principal est d’arrêter ou prévenir les saignements, elles sont également impliquées dans d’autres fonctions, comme l’immunité, l’inflammation ou la progression tumorale. L’essor des biotechnologies et les connaissances acquises sur les mécanismes qui régulent la biogénèse des plaquettes permettent aujourd’hui d’envisager la production de plaquettes de culture. Dès lors, ce type de produit pourrait avoir sa place pour relever un certain nombre de défis transfusionnels comme l’allo-immunisation ou les états réfractaires. Cependant les rendements de culture restent faibles et de nombreux obstacles doivent encore être franchis avant d’envisager une application en transfusion. Cet article recense les arguments qui motivent la production de plaquettes de culture à visée transfusionnelle et récapitule les principales avancées dans le domaine tout en soulignant ses limites.

Blood platelet formation at a glance

The main function of blood platelets is to ensure hemostasis and prevent hemorrhages. The 1011 platelets needed daily are produced in a well-orchestrated process. However, this process is not yet fully understood and in vitro platelet production is still inefficient. Platelets are produced in the bone marrow by megakaryocytes, highly specialized precursor cells that extend cytoplasmic projections called proplatelets (PPTs) through the endothelial barrier of sinusoid vessels. In this Cell Science at a Glance article and the accompanying poster we discuss the mechanisms and pathways involved in megakaryopoiesis and platelet formation processes. We especially address the – still underestimated – role of the microenvironment of the bone marrow, and present recent findings on how PPT extension in vivo differs from that in vitro and entails different mechanisms. Finally, we recapitulate old but recently revisited evidence that – although bone marrow does produce megakaryocytes and PPTs – remodeling and the release of bona fide platelets, mainly occur in the downstream microcirculation.

[Novel platelet pharming using human induced pluripotent stem cells]

La production in vitro de plaquettes offre une opportunité de résoudre les problèmes liés aux limitations d’approvisionnement et à la sécurité des dons de produits dérivés du sang. Les cellules souches pluripotentes induites – ou iPSC – sont une source idéale pour la production de cellules à des fins de thérapies régénératives. Nous avons précédemment établi avec succès une lignée mégacaryocytaire immortalisée à partir d’iPSC. Celle-ci possède une capacité de prolifération fiable. Par ailleurs, il est possible de les cryoconserver. Elle est donc une source adaptée de cellules primaires pour la production de plaquettes suivant les Bonnes Pratiques de Fabrication (BPF). Dans le même temps, la capacité améliorée des bioréacteurs à reproduire certaines conditions physiologiques, telle que la turbulence, de pair avec la découverte de molécules favorisant la thrombopoïèse, a contribué à l’accomplissement de la production de plaquettes en quantité et qualité suffisantes pour répondre aux besoins cliniques. La production de plaquettes à partir de cellules iPS s’étend aussi aux patients en état de réfraction allo-immune, par la production de plaquettes autologues ou dont on a génétiquement manipulé l’expression des Antigènes des Leucocytes Humains (HLA) et des Antigènes Plaquettaires Humain (HPA). Considérant ces avancées fondamentales, les plaquettes iPSC avec expression des HLA modifiées se présentent comme un potentiel produit de transfusion universel. Dans cette revue, nous souhaitons apporter une vue d’ensemble de la production in vitro de plaquettes à partir de cellules iPS, et de son possible potentiel transformatif, d’importance capitale dans le domaine de la transfusion des produits sanguins.

Spotlight on the current perspectives on applications of human blood cell culture and organoids: Introductory remarks

Culture of blood cells, mainly erythrocytes, at industrial levels complying with cGMP regulations, aim to make them available, at large scale, any time and everywhere, when needed for transfusion, or laboratory applications. Understanding how blood cells differentiate and develop in-vivo, and mechanisms of differentiation and growth factors, has opened newer strategies for in-vitro culture from multipotent stem cells or immortalized lines. This offers interesting perspectives for obtaining such cultured bioproduct cells for medical applications. In addition, many attempts for preparing platelets in-vitro from megakaryocyte culture have been reported. Nevertheless, the quantities of functional viable platelets obtained are still not sufficient to envisage transfusion applications. Other strategic approaches concern culture of organoids, which can synthesize functional blood proteins, but still significant scale-up of yield needs to be addressed. Finally, considerable advances have been made in culturing specific lymphocytes for personalized immunotherapy of some cancer patients with highly promising results in certain applications. This concise mini report focuses on the progress made in these directions, and attempts are made to describe some newer perspectives.

Blood donor-derived buffy coat to produce platelets in vitro

BACKGROUND AND OBJECTIVES

Platelet transfusion is a standard medical therapy used to treat several bleeding disorders. However, a critical drawback is the dependency on donor-derived platelets, which leads to concerns like insufficient availability and immunological complications. In vitro platelet production from hematopoietic progenitor cells (CD34) may represent a reasonable solution.

MATERIALS AND METHODS

CD34+ cells were isolated from either buffy coat or peripheral blood and compared in terms of platelet production in vitro. The number and the quality of magnetically isolated CD34+ cells and their capability to differentiate into mature megakaryocytes were investigated using flow cytometry. Additionally, the functionality of megakaryocytes in term of in vitro platelet production was tested.

RESULTS

Similar purity and quantity of CD34+ cells was found after their isolation from both cell sources. In contrast, after 6 days of culture, enhanced number of CD34+ cells isolated from buffy coat compared with peripheral blood was observed (5·3 x 106 vs. 3·0 x 106, respectively). Interestingly, despite a comparable nuclear maturation phenotype, the yield of platelets released from buffy coat-derived megakaryocytes was significantly higher than from peripheral blood cells (platelet yield pro MK: 7·2 vs. 2·7, respectively). Importantly, platelets produced from buffy coat-derived cells could be activated by agonists.

CONCLUSION

Haematopoietic progenitor cells isolated from buffy coat have increased yield of platelets released from mature megakaryocytes and enhanced in vitro functionality, compared with peripheral blood-derived cells. Our study, suggests that buffy coat, obtained during blood donation processing, might be a promising source of megakaryocytes for in vitro platelet production.

On the Way to in vitro Platelet Production

The severely decreased platelet counts (10–30. 10³ platelets/μL) frequently observed in patients undergoing chemotherapy, radiation treatment, or organ transplantation are associated with life-threatening increased bleeding risks. To circumvent these risks, platelet transfusion remains the treatment of choice, despite some limitations which include a limited shelf-life, storage-related deterioration, the development of alloantibodies in recipients and the transmission of infectious diseases. A sustained demand has evolved in recent years for controlled blood products, free of infectious, inflammatory, and immune risks. As a consequence, the challenge for blood centers in the near future will be to ensure an adequate supply of blood platelets, which calls for a reassessment of our transfusion models. To meet this challenge, many laboratories are now turning their research efforts toward the in vitro and customized production of blood platelets. In recent years, there has been a major enthusiasm for the cultured platelet production, as illustrated by the number of reviews that have appeared in recent years. The focus of the present review is to critically asses the arguments put forward in support of the culture of platelets for transfusion purposes. In light of this, we will recapitulate the main advances in this quickly evolving field, while noting the technical limitations to overcome to make cultured platelet a transfusional alternative.

On the way to in vitro platelet production

The severely decreased platelet counts (10-30.10³ platelets/μL) frequently observed in patients undergoing chemotherapy, radiation treatment or organ transplantation are associated with life-threatening increased bleeding risks. To circumvent these risks, platelet transfusion remains the treatment of choice, despite some limitations which include a limited shelf-life, storage-related deterioration, the development of alloantibodies in recipients and the transmission of infectious diseases. A sustained demand has evolved in recent years for controlled blood products, free of infectious, inflammatory and immune risks. As a consequence, the challenge for blood centers in the near future will be to ensure an adequate supply of blood platelets, which calls for a reassessment of our transfusion models. To meet this challenge, many laboratories are now turning their research efforts towards the in vitro and customized production of blood platelets.

Platelet production from induced pluripotent stem cells

Ex vivo production of human platelets has been pursued as an alternative measure to resolve limitations in the supply and safety of current platelet transfusion products. To this end, induced pluripotent stem cells (iPSCs) are considered an ideal global source, as they are not only pluripotent and self-renewing, but are also available from basically any person, have relatively few ethical issues, and are easy to manipulate. From human iPSCs, megakaryocyte (MK) lines with robust proliferation capacity have been established by the introduction of specified sets of genes. These expandable MKs are also cryopreservable and thus would be suitable as master cells for good manufacturing practice (GMP)-grade production of platelets, assuring availability on demand and safety against blood-borne infections. Meanwhile, developments in bioreactors that physically mimic the in vivo environment and discovery of substances that promote thrombopoiesis have yielded competent platelets with improved efficiency. The derivation of platelets from iPSCs could further resolve transfusion-related alloimmune complications through the manufacturing of autologous products and human leukocyte antigen (HLA)-compatible platelets from stocked homologous HLA-type iPSC libraries or by manipulation of HLAs and human platelet antigens (HPAs). Considering these key advances in the field, HLA-deleted platelets could become a universal product that is manufactured at industrial level to safely fulfill almost all demands. In this review, we provide an overview of the ex vivo production of iPSC-derived platelets toward clinical applications, a production that would revolutionize the blood transfusion system and lead the field of iPSC-based regenerative medicine.

Identifying and enriching platelet-producing human stem cell-derived megakaryocytes using factor V uptake

Stem cell-derived platelets have the potential to replace donor platelets for transfusion. Defining the platelet-producing megakaryocytes (MKs) within the heterogeneous MK culture may help to optimize the in vitro generation of platelets. Using 2 human stem cell models of megakaryopoiesis, we identified novel MK populations corresponding to distinct maturation stages. An immature, low granular (LG) MK pool (defined by side scatter on flow cytometry) gives rise to a mature high granular (HG) pool, which then becomes damaged by apoptosis and glycoprotein Ib α chain (CD42b) shedding. We define an undamaged HG/CD42b⁺ MK subpopulation, which endocytoses fluorescently labeled coagulation factor V (FV) from the media into α-granules and releases functional FV⁺CD42b⁺ human platelet-like particles in vitro and when infused into immunodeficient mice. Importantly, these FV⁺ particles have the same size distribution as infused human donor platelets and are preferentially incorporated into clots after laser injury. Using drugs to protect HG MKs from apoptosis and CD42b shedding, we also demonstrate that apoptosis precedes CD42b shedding and that apoptosis inhibition enriches the FV⁺ HG/CD42b⁺ MKs, leading to increased platelet yield in vivo, but not in vitro. These studies identify a transition between distinct MK populations in vitro, including one that is primed for platelet release. Technologies to optimize and select these platelet-ready MKs may be important to efficiently generate functional platelets from in vitro-grown MKs.

Aryl hydrocarbon receptor-dependent enrichment of a megakaryocytic precursor with a high potential to produce proplatelets

The mechanisms regulating megakaryopoiesis and platelet production (thrombopoiesis) are still incompletely understood. Identification of a progenitor with enhanced thrombopoietic capacity would be useful to decipher these mechanisms and to improve our capacity to produce platelets in vitro. Differentiation of peripheral blood CD34(+) cells in the presence of bone marrow-human mesenchymal stromal cells (MSCs) enhanced the production of proplatelet-bearing megakaryocytes (MKs) and platelet-like elements. This was accompanied by enrichment in a MK precursor population exhibiting an intermediate level of CD41 positivity while maintaining its expression of CD34. Following sorting and subculture with MSCs, this CD34(+)CD41(low) population was able to efficiently generate proplatelet-bearing MKs and platelet-like particles. Similarly, StemRegenin 1 (SR1), an antagonist of the aryl hydrocarbon receptor (AhR) transcription factor known to maintain CD34 expression of progenitor cells, led to an enriched CD34(+)CD41(low) fraction and to an increased capacity to generate proplatelet-producing MKs and platelet-like elements ultrastructurally and functionally similar to circulating platelets. The effect of MSCs, like that of SR1, appeared to be mediated by an AhR-dependent mechanism because both culture conditions resulted in repression of its downstream effector CYP1B1. This newly described isolation of a precursor exhibiting strong MK potential could be exploited to study normal and abnormal thrombopoiesis and for in vitro platelet production.

Understanding platelet generation from megakaryocytes: implications for in vitro-derived platelets

Platelets are anucleate cytoplasmic discs derived from megakaryocytes that circulate in the blood and have major roles in hemostasis, thrombosis, inflammation, and vascular biology. Platelet transfusions are required to prevent the potentially life-threatening complications of severe thrombocytopenia seen in a variety of medical settings including cancer therapy, trauma, and sepsis. Platelets used in the clinic are currently donor-derived which is associated with concerns over sufficient availability, quality, and complications due to immunologic and/or infectious issues. To overcome our dependence on donor-derived platelets for transfusion, efforts have been made to generate in vitro-based platelets. Work in this area has advanced our understanding of the complex processes that megakaryocytes must undergo to generate platelets both in vivo and in vitro. This knowledge has also defined the challenges that must be overcome to bring in vitro-based platelet manufacturing to a clinical reality. This review will focus on our understanding of committed megakaryocytes and platelet release in vivo and in vitro, and how this knowledge can guide the development of in vitro-derived platelets for clinical application.

Manipulating megakaryocytes to manufacture platelets ex vivo

Historically, platelet transfusion has proven a reliable way to treat patients suffering from thrombocytopenia or similar ailments. An undersupply of donors, however, has demanded alternative platelet sources. Scientists have therefore sought to recapitulate the biological events that convert hematopoietic stem cells into platelets in the laboratory. Such platelets have shown good function and potential for treatment. Yet the number manufactured ex vivo falls well short of clinical application. Part of the reason is the remarkable gaps in our understanding of the molecular mechanisms driving platelet formation. Using several stem cell sources, scientists have progressively clarified the chemical signaling and physical microenvironment that optimize ex vivo platelets and reconstituted them in synthetic environments. Key advances in cell reprogramming and the ability to propagate self-renewal have extended the lifetime of megakaryocytes to increase the pool of platelet progenitors.

Road blocks in making platelets for transfusion

The production of laboratory-generated human platelets is necessary to meet present and future transfusion needs. This manuscript will identify and define the major roadblocks that must be overcome to make human platelet production possible for clinical use, and propose solutions necessary to accelerate development of laboratory-generated human platelets to market.

Predictions for optimal mitigation of paracrine inhibitory signalling in haemopoietic stem cell cultures

Introduction

Recent studies in the literature have highlighted the critical role played by cell signalling in determining haemopoietic stem cell (HSC) fate within ex vivo culture systems. Stimulatory signals can enhance proliferation and promote differentiation, whilst inhibitory signals can significantly limit culture output.

Methods

Numerical models of various mitigation strategies are presented and applied to determine effectiveness of these strategies toward mitigation of paracrine inhibitory signalling inherent in these culture systems. The strategies assessed include mixing, media-exchange, fed-batch and perfusion.

Results

The models predict that significant spatial concentration gradients exist in typical cell cultures, with important consequences for subsequent cell expansion. Media exchange is shown to be the most effective mitigation strategy, but remains labour intensive and difficult to scale-up for large culture systems. The fed-batch strategy is only effective at very small Peclet number, and its effect is diminished as the cell culture volume grows. Conversely, mixing is effective at high Peclet number, and ineffective at low Peclet number. The models predict that cell expansion in fed-batch cultures becomes independent of increasing dilution rate, consistent with experimental results previously reported in the literature. In contrast, the models predict that increasing the flow rate in perfused cultures will lead to increased cell expansion, indicating the suitability of perfusion for use as an automated, tunable strategy. The effect of initial cell seeding density is also investigated, with the model showing that perfusion outperforms dilution for all densities considered.

Conclusions

The models predict that the impact of inhibitory signalling in HSC cultures can be mitigated against using media manipulation strategies, with the optimal strategy dependent upon the protein diffusion time-scale relative to the media manipulation time-scale. The key messages from this study can be applied to any complex cell culture scenario where cell-cell interactions and paracrine signalling networks impact upon cell fate and cell expansion.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0048-7) contains supplementary material, which is available to authorized users.

Developing a co-culture system for effective megakaryo/thrombopoiesis from umbilical cord blood hematopoietic stem/progenitor cells

BACKGROUND AIMS

Platelet transfusion can be a life-saving procedure in different medical settings. Thus, there is an increasing demand for platelets, of which shelf-life is only 5 days. The efficient ex vivo biomanufacturing of platelets would allow overcoming the shortages of donated platelets.

METHODS

We exploited a two-stage culture protocol aiming to study the effect of different parameters on the megakaryo/thrombopoiesis ex vivo. In the expansion stage, human umbilical cord blood (UCB)-derived CD34(+)-enriched cells were expanded in co-culture with human bone marrow mesenchymal stromal cells (BM-MSCs). The megakaryocytic commitment and platelet generation were studied, considering the impact of exogenous addition of thrombopoietin (TPO) in the expansion stage and a cytokine cocktail (Cyt) including TPO and interleukin-3 in the differentiation stage, with the use of different culture medium formulations, and in the presence/absence of BM-MSCs (direct versus non-direct cell-cell contact).

RESULTS

Our results suggest that an early megakaryocytic commitment, driven by TPO addition during the expansion stage, further enhanced megakaryopoiesis. Importantly, the results suggest that co-culture with BM-MSCs under serum-free conditions combined with Cyt addition, in the differentiation stage, significantly improved the efficiency yield of megakaryo/thrombopoiesis as well as increasing %CD41, %CD42b and polyploid content; in particular, direct contact of expanded cells with BM-MSCs, in the differentiation stage, enhanced the efficiency yield of megakaryo/thrombopoiesis, despite inhibiting their maturation.

CONCLUSIONS

The present study established an in vitro model for the hematopoietic niche that combines different biological factors, namely, the presence of stromal/accessory cells and biochemical cues, which mimics the BM niche and enhances an efficient megakaryo/thrombopoiesis process ex vivo.