Elizabeth Csaszar

Pyrimidoindole derivatives are agonists of human hematopoietic stem cell self-renewal

Human adult stem cell expansion Transfused blood saves lives. Despite the widespread use of this critical resource, it is difficult to increase blood cell numbers outside of the body. By screening thousands of small compounds, Fares et al. identify a molecule that expands human stem cell numbers in cord blood. The researchers generate many variations of that molecule and show that one such compound provides even greater human blood cell expansion. If researchers can provide increased numbers of stem cells and progenitor cells, cord blood should find even greater use in the clinic. Science, this issue p. 1509 The self-renewal of human hematopoietic stem cells in vitrois enhanced by the pyrimidoindole derivative UM171. The small number of hematopoietic stem and progenitor cells in cord blood units limits their widespread use in human transplant protocols. We identified a family of chemically related small molecules that stimulates the expansion ex vivo of human cord blood cells capable of reconstituting human hematopoiesis for at least 6 months in immunocompromised mice. The potent activity of these newly identified compounds, UM171 being the prototype, is independent of suppression of the aryl hydrocarbon receptor, which targets cells with more-limited regenerative potential. The properties of UM171 make it a potential candidate for hematopoietic stem cell transplantation and gene therapy.

Rapid Expansion of Human Hematopoietic Stem Cells by Automated Control of Inhibitory Feedback Signaling

Clinical hematopoietic transplantation outcomes are strongly correlated with the numbers of cells infused. Anticipated novel therapeutic implementations of hematopoietic stem cells (HSCs) and their derivatives further increase interest in strategies to expand HSCs ex vivo. A fundamental limitation in all HSC-driven culture systems is the rapid generation of differentiating cells and their secreted inhibitory feedback signals. Herein we describe an integrated computational and experimental strategy that enables a tunable reduction in the global levels and impact of paracrine signaling factors in an automated closed-system process by employing a controlled fed-batch media dilution approach. Application of this system to human cord blood cells yielded a rapid (12-day) 11-fold increase of HSCs with self-renewing, multilineage repopulating ability. These results highlight the marked improvements that control of feedback signaling can offer primary stem cell culture and demonstrate a clinically relevant rapid and relatively low culture volume strategy for ex vivo HSC expansion.

High-throughput combinatorial cell co-culture using microfluidics

Co-culture strategies are foundational in cell biology. These systems, which serve as mimics of in vivo tissue niches, are typically poorly defined in terms of cell ratios, local cues and supportive cell-cell interactions. In the stem cell niche, the ability to screen cell-cell interactions and identify local supportive microenvironments has a broad range of applications in transplantation, tissue engineering and wound healing. We present a microfluidic platform for the high-throughput generation of hydrogel microbeads for cell co-culture. Encapsulation of different cell populations in microgels was achieved by introducing in a microfluidic device two streams of distinct cell suspensions, emulsifying the mixed suspension, and gelling the precursor droplets. The cellular composition in the microgels was controlled by varying the volumetric flow rates of the corresponding streams. We demonstrate one of the applications of the microfluidic method by co-encapsulating factor-dependent and responsive blood progenitor cell lines (MBA2 and M07e cells, respectively) at varying ratios, and show that in-bead paracrine secretion can modulate the viability of the factor dependent cells. Furthermore, we show the application of the method as a tool to screen the impact of specific growth factors on a primary human heterogeneous cell population. Co-encapsulation of IL-3 secreting MBA2 cells with umbilical cord blood cells revealed differential sub-population responsiveness to paracrine signals (CD14+ cells were particularly responsive to locally delivered IL-3). This microfluidic co-culture platform should enable high throughput screening of cell co-culture conditions, leading to new strategies to manipulate cell fate.

Dynamic interaction networks in a hierarchically organized tissue

Intercellular (between cell) communication networks maintain homeostasis and coordinate regenerative and developmental cues in multicellular organisms. Despite the importance of intercellular networks in stem cell biology, their rules, structure and molecular components are poorly understood. Herein, we describe the structure and dynamics of intercellular and intracellular networks in a stem cell derived, hierarchically organized tissue using experimental and theoretical analyses of cultured human umbilical cord blood progenitors. By integrating high‐throughput molecular profiling, database and literature mining, mechanistic modeling, and cell culture experiments, we show that secreted factor‐mediated intercellular communication networks regulate blood stem cell fate decisions. In particular, self‐renewal is modulated by a coupled positive–negative intercellular feedback circuit composed of megakaryocyte‐derived stimulatory growth factors (VEGF, PDGF, EGF, and serotonin) versus monocyte‐derived inhibitory factors (CCL3, CCL4, CXCL10, TGFB2, and TNFSF9). We reconstruct a stem cell intracellular network, and identify PI3K, Raf, Akt, and PLC as functionally distinct signal integration nodes, linking extracellular, and intracellular signaling. This represents the first systematic characterization of how stem cell fate decisions are regulated non‐autonomously through lineage‐specific interactions with differentiated progeny.

Blood stem cell fate regulation by Delta-1–mediated rewiring of IL-6 paracrine signaling

Increasing evidence supports the importance of cell extrinsic regulation in stem cell fate control. Hematopoietic stem cells (HSC) are responsive to local signals from their niche and to systemic feedback from progenitors and mature cells. The Notch ligand Delta-1 (DL1), a key component of the stem cell niche, regulates human hematopoietic lineage development in a dose-dependent manner and has been used clinically for primitive progenitor expansion. How DL1 acts to regulate HSC fate and whether these actions are related to its lineage skewing effects are poorly understood. Here we demonstrate that, although DL1 activates signal transducer and activator of transcription 3 signaling similarly to the gp130-activating cytokine interleukin-6 (IL-6), it has opposite effects on myeloid cell production. Mechanistically, these different outcomes are attributable to a DL1-mediated reduction in membrane (m)-bound IL-6 receptor (R) expression, converting progenitor cells from being directly IL-6 responsive to requiring both IL-6 and soluble (s) IL-6R for activation. Concomitant reduction of both mIL-6R (by DL1 supplementation) and sIL-6R (using dynamically fed cultures) reduced myeloid cell production and led to enhanced outputs of human HSCs. This work describes a new mode of cytokine action in which DL1 changes cytokine receptor distributions on hematopoietic cells, altering feedback networks and their impact on stem cell fate.

Real-Time Monitoring and Control of Soluble Signaling Factors Enables Enhanced Progenitor Cell Outputs from Human Cord Blood Stem Cell Cultures

Monitoring and control of primary cell cultures is challenging as they are heterogenous and dynamically complex systems. Feedback signaling proteins produced from off-target cell populations can accumulate, inhibiting the production of the desired cell populations. Although culture strategies have been developed to reduce feedback inhibition, they are typically optimized for a narrow range of process parameters and do not allow for a dynamically regulated response. Here we describe the development of a microbead-based process control system for the monitoring and control of endogenously produced signaling factors. This system uses quantum dot barcoded microbeads to assay endogenously produced signaling proteins in the culture media, allowing for the dynamic manipulation of protein concentrations. This monitoring system was incorporated into a fed-batch bioreactor to regulate the accumulation of TGF-β1 in an umbilical cord blood cell expansion system. By maintaining the concentration of TGF-β1 below an upper threshold throughout the culture, we demonstrate enhanced ex vivo expansion of hematopoietic progenitor cells at higher input cell densities and over longer culture periods. This study demonstrates the potential of a fully automated and integrated real-time control strategy in stem cell culture systems, and provides a powerful strategy to achieve highly regulated and intensified in vitro cell manufacturing systems. Biotechnol. Bioeng. 2014;111: 1258–1264.

An automated system for delivery of an unstable transcription factor to hematopoietic stem cell cultures

An automated delivery system for cell culture applications would permit studying more complex culture strategies and simplify measures taken to expose cells to unstable molecules. We are interested in understanding how intracellular TAT‐HOXB4 protein concentration affects hematopoietic stem cell (HSC) fate; however, current manual dosing strategies of this unstable protein are labor intensive and produce wide concentration ranges which may not promote optimal growth. In this study we describe a programmable automated delivery system that was designed to integrate into a clinically relevant, single‐use, closed‐system bioprocess and facilitate transcription factor delivery studies. The development of a reporter cell assay allowed for kinetic studies to determine the intracellular (1.4 ± 0.2 h) and extracellular (3.7 ± 1.8 h and 78 ± 27 h at 37°C and 4°C, respectively) half‐lives of TAT‐HOXB4 activity. These kinetic parameters were incorporated into a mathematical model, which was used to predict the dynamic intracellular concentration of TAT‐HOXB4 and optimize the delivery of the protein. The automated system was validated for primary cell culture using human peripheral blood patient samples. Significant expansion of human primitive progenitor cells was obtained upon addition of TAT‐HOXB4 without user intervention. The delivery system is thus capable of being used as a clinically relevant tool for the exploration and optimization of temporally sensitive stem cell culture systems. Biotechnol. Bioeng. 2009;103: 402–412.

Blood stem cell products: Toward sustainable benchmarks for clinical translation

Robust ex vivo expansion of umbilical cord blood (UCB) derived hematopoietic stem and progenitor cells (HSPCs) should enable the widespread use of UCB as a source of cells to treat hematologic and immune diseases. Novel approaches for HSPC expansion have recently been developed, setting the stage for the production of blood stem cell derived products that fulfill our current best known criteria of clinical relevance. Translating these technologies into clinical use requires bioengineering strategies to overcome challenges of scale-up, reproducibility, and product quality assurance. Clinical-scale implementation should also define criteria and targets for cost-effective cell manufacturing. As production strategies become more effective, new opportunities in the therapeutic use of ex vivo expanded hematopoietic cell products will emerge. Herein we examine key technological milestones that need to be met in order to move ex vivo expanded HSPC therapies from the bench-top to the bedside in a robust and reliable manner.