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Peter W Zandstra

Publications and source records attributed to Peter W Zandstra.

At least 19 recordsLinked to original sources
PubMed2006

Understanding cellular networks to improve hematopoietic stem cell expansion cultures.

Efforts to develop culture technologies capable of eliciting robust human blood stem cell growth have met with limited success. Considering that adult stem cell cultures are complex systems, comprising multiple cell types with dynamically changing intracellular signalling environments and cellular compositions, this is not surprising. Typically treated as single-input single-output systems, adult stem cell cultures are better described as complex, non-linear, multiple-input multiple-output systems wherein the proliferation of subpopulations of cells leads to the formation of intercellular endogenously secreted protein interaction networks. Genomic and proteomic tools need to be applied to generate high-throughput (and ideally high-content) biological measurements of stem cell culture evolution. Datasets describing cellular interaction networks need to be integrated into predictive models of in vitro stem cell development. Ultimately, such models will serve as a starting point for the rational design of blood stem cell expansion bioprocesses utilizing dynamic system perturbations to achieve the preferential expansion of target cell populations.

Cell Culture Techniques↗
PubMed2006

Spatial organization of embryonic stem cell responsiveness to autocrine gp130 ligands reveals an autoregulatory stem cell niche.

Highly ordered aggregates of cells, or niches, regulate stem cell fate. Specific tissue location need not be an obligatory requirement for a stem cell niche, particularly during embryogenesis, where cells exist in a dynamic environment. We investigated autoregulatory fixed-location-independent processes controlling cell fate by analyzing the spatial organization of embryonic stem cells (ESCs) using quantitative single-cell immunocytochemistry and a computational approach involving Delaunay triangulation. ESC colonies demonstrated radial organization of phosphorylated signal transducer and activator of transcription 3, Nanog, and Oct4 (among others) in the presence and absence of exogenous leukemia inhibitory factor (LIF). Endogenous self-renewal signaling resulted from autocrine non-LIF gp130 ligands, which buffered cells against differentiation upon exogenous LIF deprivation. Together with a radial organization of differential responsiveness to gp130 ligands within colonies, autocrine signaling produced a radial organization of self-renewal, generating a fixed-location-independent autoregulatory niche. These findings reveal fundamental properties of niches and elucidate mechanisms colonies of cells use to transition between fates during morphogenesis.

Animals↗
PubMed2006

Clinically relevant expansion of hematopoietic stem cells with conserved function in a single-use, closed-system bioprocess.

The clinical potential of umbilical cord blood-derived stem and progenitor cells has been demonstrated in various animal and human transplantation studies. However, the need for increased numbers of appropriate umbilical cord blood-derived cells continues to limit the development and success of these therapies. Ex vivo expansion has been widely studied as a method to overcome this limitation. We describe the use of a clinically relevant single-use, closed-system bioprocess capable of generating greater numbers of hematopoietic stem and progenitor cells that maintain in vivo and in vitro developmental potential. In addition to expanded numbers of CD34+ cells, CD34(+)CD38(-) cells, colony-forming cells, and long-term culture-initiating cells, the bioprocess generated > or =3.3-fold more long-term nonobese diabetic/severe combined immunodeficient repopulating cells (quantitatively determined using limiting dilution analysis) than present at input. Interestingly, these cells were also capable of multilineage engraftment and were shown to maintain their engraftment potency on a per long-term nonobese diabetic/severe combined immunodeficient repopulating cell basis compared with input noncultured cells. The developmental capacity of bioprocess-generated cells was further demonstrated by their ability to repopulate secondary nonobese diabetic/severe combined immunodeficient recipients. In vitro lineage analysis confirmed that bioprocess-generated cells could differentiate into myeloid and natural killer, B, and T cell lymphoid lineages. This in-depth analysis describes a bioprocess that generates human hematopoietic stem and progenitor cells with conserved hematopoietic activity, establishes analysis criteria for in vitro hematopoietic stem cell expansion studies, and serves as a foundation to test the therapeutic utility of cultured hematopoietic stem cells in large animals and humans.

Animals↗
PubMed2005

Shear-controlled single-step mouse embryonic stem cell expansion and embryoid body-based differentiation.

To facilitate the exploitation of embryonic stem cells (ESCs) and ESC-derived cells, scale-up of cell production and optimization of culture conditions are necessary. Conventional ESC culture methods are impractical for large-scale cell production and lack robust microenvironmental control. We developed two stirred-suspension culture systems for the propagation of undifferentiated ESCs--microcarrier and aggregate cultures--and compared them with tissue-culture flask and Petri dish controls. ESCs cultured on glass microcarriers had population doubling times (approximately 14-17 hours) comparable to tissue-culture flask controls. ESC growth could be elicited in shear-controlled stirred-suspension culture, with population doubling times ranging between 24 and 39 hours at 100 rpm impeller speed. Upon removal of leukemia inhibitory factor, the size-controlled ESC aggregates developed into embryoid bodies (EBs) capable of multilineage differentiation. A comprehensive analysis of ESC developmental potential, including flow cytometry for Oct-4, SSEA-1, and E-cadherinprotein expression, reverse transcription-polymerase chain reaction for Flk-1, HNF3-beta, MHC, and Sox-1 gene expression, and EB differentiation analysis, demonstrated that the suspension-cultured ESCs retained the developmental potential of the starting cell population. Analysis of E-cadherin-/- and E-cadherin+/- cells using both systems provided insight into the mechanisms behind the role of cell aggregation control, which is fundamental to these observations. These cell-culture tools should prove useful for both the production of ESCs and ESC-derived cells and for investigations into adhesion, survival, and differentiation phenomena during ESC propagation and differentiation.

Animals↗
PubMed2005

Soluble factor cross-talk between human bone marrow-derived hematopoietic and mesenchymal cells enhances in vitro CFU-F and CFU-O growth and reveals heterogeneity in the mesenchymal progenitor cell compartment.

The homeostatic adult bone marrow (BM) is a complex tissue wherein physical and biochemical interactions serve to maintain a balance between the hematopoietic and nonhematopoietic compartments. To focus on soluble factor interactions occurring between mesenchymal and hematopoietic cells, a serum-free adhesion-independent culture system was developed that allows manipulation of the growth of both mesenchymal and hematopoietic human BM-derived progenitors and the balance between these compartments. Factorial experiments demonstrated a role for stem cell factor (SCF) and interleukin 3 (IL-3) in the concomitant growth of hematopoietic (CD45+) and nonhematopoietic (CD45-) cells, as well as their derivatives. Kinetic tracking of IL-3alpha receptor (CD123) and SCF receptor (CD117) expression on a sorted CD45- cell population revealed the emergence of CD45-CD123+ cells capable of osteogenesis. Of the total fibroblast colony-forming units (CFU-Fs) and osteoblast colony-forming units (CFU-O), approximately 24% of CFU-Fs and about 22% of CFU-Os were recovered from this population. Cell-sorting experiments demonstrated that the CD45+ cell population secreted soluble factors that positively affect the survival and proliferation of CFU-Fs and CFU-Os generated from the CD45- cells. Together, our results provide insight into the intercellular cytokine network between hematopoietic and mesenchymal cells and provide a strategy to mutually culture both mesenchymal and hematopoietic cells in a defined scalable bioprocess.

Cell Differentiation↗
PubMed2005

Development of a perfusion fed bioreactor for embryonic stem cell-derived cardiomyocyte generation: oxygen-mediated enhancement of cardiomyocyte output.

Cell transplantation is emerging as a promising new approach to replace scarred, nonfunctional myocardium in a diseased heart. At present, however, generating the numbers of donor cardiomyocytes required to develop and test animal models is a major limitation. Embryonic stem (ES) cells may be a promising source for therapeutic applications, potentially providing sufficient numbers of functionally relevant cells for transplantation into a variety of organs. We developed a single-step bioprocess for ES cell-derived cardiomyocyte production that enables both medium perfusion and direct monitoring and control of dissolved oxygen. Implementation of the bioprocess required combining methods to prevent ES cell aggregation (hydrogel encapsulation) and to purify for cardiomyocytes from the heterogeneous cell populations (genetic selection), with medium perfusion in a controlled bioreactor environment. We used this bioprocess to investigate the effects of oxygen on cardiomyocyte generation. Parallel vessels (250 mL culture volume) were run under normoxic (20% oxygen tension) or hypoxic (4% oxygen tension) conditions. After 14 days of differentiation (including 5 days of selection), the cardiomyocyte yield per input ES cell achieved in hypoxic vessels was 3.77 +/- 0.13, higher than has previously been reported. We have developed a bioprocess that improves the efficiency of ES cell-derived cardiomyocyte production, and allows the investigation of bioprocess parameters on ES cell-derived cardiomyogenesis. Using this system we have demonstrated that medium oxygen tension is a culture parameter that can be manipulated to improve cardiomyocyte yield.

Animals↗
PubMed2005

Dynamic changes in cellular and microenvironmental composition can be controlled to elicit in vitro human hematopoietic stem cell expansion.

OBJECTIVE: The absence of effective strategies for the ex vivo expansion of human hematopoietic stem cells (HSCs) limits the development of many cell-based therapies. Prior attempts to stimulate HSC expansion have focused on media supplementation using cytokines and growth factors. In these cultures, cellular and microenvironmental compositions change with time. In this study, the impact of controlling these dynamic changes on HSC output is determined. MATERIALS AND METHODS: Cord blood-derived lin(-) cells were cultured for 8 days in serum-free medium supplemented with stem cell factor, Flt3 ligand, and thrombopoietin. Functional, phenotypic, and molecular (gene and protein) analyses were used to characterize dynamic changes in cellular and microenvironmental composition. The effects of these changes and the mechanism behind their effects on HSC expansion were assessed using a selection/media exchange-based global culture manipulation (GCM) technique. RESULTS: We show that the direct secretion of negative regulators by culture-generated lin(+) cells, and the indirect stimulation of cells to secrete negative regulators by culture-conditioned media, limits in vitro HSC generation. The GCM strategy was able to abrogate these effects to produce elevated numbers of LTC-ICs (14.6-fold relative to input), migrating rapid NOD/SCID repopulating cells (12.1-fold), and long-term NOD/SCID repopulating cells (5.2-fold). CONCLUSIONS: Cellular and microenvironmental changes that occur during all in vitro HSC cultures can significantly affect HSC output through the direct or indirect secretion of negative regulators. This study provides insight into the mechanisms regulating HSC fate in vitro and describes a novel methodology to regulate overall in vitro microenvironmental dynamics to enable the generation of clinically relevant numbers of HSCs.

Animals↗
PubMed2005

Clonal evolution of stem and differentiated cells can be predicted by integrating cell-intrinsic and -extrinsic parameters.

Stem cells and their derivatives represent a renewable source of cells for therapeutic applications. However, the inability to quantitatively integrate and exploit the effects of multiple parameters on the fate of stem cells limits their use in clinical applications. To address this, we developed a computational model that combines probabilistic, individual-cell and deterministic cell-population parameters to simultaneously calculate the specific effects of exogenous and endogenous factors on the overall population-dynamics behaviour. The model tracks the progeny trajectory of individual cells over several generations as a threshold function of ligand-receptor signalling interactions. Simulations in silico were validated against an Oct 4-promoter-driven green-fluorescent-protein-expressing murine embryonic stem cell line, and used to understand the effects of key parameters on the clonal evolution of stem versus differentiated cells in this system. Our approach demonstrated the ability to distinguish between individual-cell and population-averaged parameters with respect to their effects on governing dynamic behaviour. Moreover, we could discriminate between digital versus graded regulation of the Oct 4 transcription factor in accounting for experimental observations. Finally, we showed that our approach could be generalized to other stem-cell systems, in particular the previously characterized intestinal crypt system, in elucidating relative contributions of stem and progenitor cells to population output. On the basis of all these results, we believe that our iterative experimental and computational approach has been found to be useful for the study of various stem-cell systems.

Animals↗
PubMed2005

Scalable production of embryonic stem cell-derived cells.

Embryonic stem (ES) cells have the ability to self-renew as well as differentiate into any cell type in the body. These traits make ES cells an attractive "raw material" for a variety of cell-based technologies. However, uncontrolled cell aggregation in ES cell differentiation culture inhibits cell proliferation and differentiation and thwarts the use of stirred suspension bioreactors. Encapsulation of ES cells in agarose microdrops prevents physical interaction between developing embryoid bodies (EBs) that, in turn, prevents EB agglomeration. This enables use of stirred suspension bioreactors that can generate large numbers of ES-derived cells under controlled conditions.

Animals↗
PubMed2004

Quantitative screening of embryonic stem cell differentiation: endoderm formation as a model.

Embryonic stem (ES) cells have attracted much attention as a possible source of functional cells for regenerative medicine. Therapeutic use of ES cells requires control over the types and frequencies of cells generated during their in vitro differentiation. Due to the complexity of factors that impact upon ES cell differentiation, novel approaches for the optimization of tissue-specific development are required. This motivates our use of factorial and composite design methods to make empirical investigations more efficient, and to reveal unexpected interactions missed by conventional dose-response analysis. Factorial experiments would benefit from the high content evaluation of a large number of test conditions, necessitating the development of a quantitative screening technology (QST) capable of reporting the absolute number and frequency of target cells. We have developed and validated such a technology for ES cell differentiation analysis using automated fluorescence microscopy, employing endoderm differentiation as a model system. To test this platform, a two-level factorial experiment was carried out to identify major and interactive effects of glucose, insulin, retinoic acid (RA), basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF) on endoderm formation. RA was found to have inhibitory effects on endoderm formation, while low glucose proved beneficial. QST was demonstrated to be a powerful tool to study factors impacting endoderm-specific ES cell differentiation, and should be applicable to the analysis of a range of ES cell-derived tissues.

Algorithms↗
PubMed2004

Signal processing underlying extrinsic control of stem cell fate.

PURPOSE OF REVIEW: Strategies to manipulate stem cells for therapeutic applications are limited by our inability to control or predict stem cell fate decisions in response to exogenous stimuli. This review focuses on the mechanisms by which exogenous stimuli influence cell fate. RECENT FINDINGS: Limitations in our ability to control cell fate arises from our primarily qualitative understanding of stem cell regulation, which proposes straightforward cue-fate relationships that appear to be the exception rather than the rule. Alternatively, consideration of the underlying quantitative, temporal, and spatial mechanisms governing extrinsic regulation of stem cell fate may enable novel approaches to control stem cell output predictively. SUMMARY: The authors review advances in the understanding of these underlying mechanisms, and discuss experimental and analytic tools necessary to investigate and use these mechanisms to control stem cell fate.

Animals↗
PubMed2004

Sustained in vitro expansion of bone progenitors is cell density dependent.

Osteogenic cells are an integral part of the dynamic tissue-remodeling process in bone and are potential tools for tissue engineering and cell-based therapies. We examined the role of glucocorticoids and cell density in the expansion of primary rat calvaria cell populations and osteoprogenitor subpopulations in adherent cell culture. Osteoprogenitor response to dexamethasone (dex, a synthetic glucocorticoid known to stimulate bone formation in vitro) supplementation and long-term osteoprogenitor cell proliferation and differentiation were quantified using functional (colony forming unit-osteoblast [CFU-O]) and phenotypic analyses. Although osteoprogenitor self-renewal occurred at both standard and high initiating cell densities, progenitor cell expansion (measured by changes in CFU-O number relative to input) was sustained and dramatically increased at high initiating cell densities (30-fold CFU-O expansion for standard-density cultures compared with a greater than 10,000-fold CFU-O expansion in high-density cultures). Cell density was also found to impact upon the potential of dex to recruit additional progenitors towards bone development. These multifaceted effects appeared to be independent of cell proliferation rates or population phenotypic expression. Together, our results emphasize a roll for cell-cell interactions and/or community effects in the control and maintenance of progenitor cells during in vitro culture.

Animals↗
PubMed2004

Controlled, scalable embryonic stem cell differentiation culture.

Embryonic stem (ES) cells are of significant interest as a renewable source of therapeutically useful cells. ES cell aggregation is important for both human and mouse embryoid body (EB) formation and the subsequent generation of ES cell derivatives. Aggregation between EBs (agglomeration), however, inhibits cell growth and differentiation in stirred or high-cell-density static cultures. We demonstrate that the agglomeration of two EBs is initiated by E-cadherin-mediated cell attachment and followed by active cell migration. We report the development of a technology capable of controlling cell-cell interactions in scalable culture by the mass encapsulation of ES cells in size-specified agarose capsules. When placed in stirred-suspension bioreactors, encapsulated ES cells can be used to produce scalable quantities of hematopoietic progenitor cells in a controlled environment.

Animals↗
PubMed2003

Supplementation-dependent differences in the rates of embryonic stem cell self-renewal, differentiation, and apoptosis.

Although it is known that leukemia inhibitory factor (LIF) supports the derivation and expansion of murine embryonic stem (ES) cells, it is unclear whether this is due to inhibitory effects of LIF on ES cell differentiation or stimulatory effects on ES cell survival and proliferation. Using an ES cell line transgenic for green fluorescent protein (GFP) expression under control of the Oct4 promoter, we were able to simultaneously track the responses of live Oct4-GFP-positive (ES) and -negative (differentiated) fractions to LIF, serum, and other growth factors. Our findings show that, in addition to inhibiting differentiation of undifferentiated cells, the administration of LIF resulted in a distinct dose-dependent survival and proliferation advantage, thus enabling the long-term propagation of undifferentiated cells. Competitive responses from the differentiated cell fraction could only be elicited upon addition of serum, fibroblast growth factor-4 (FGF-4), or insulin-like growth factor-1 (IGF-1). The growth factors did not induce additional differentiation of ES cells, but rather they significantly improved the proliferation of already differentiated cells. Our analyses show that, by adjusting culture conditions, including the type and amount of growth factors or cytokines present, the frequency of media exchange, and the presence or absence of serum, we could selectively and specifically alter the survival, proliferation, and differentiation dynamics of the two subpopulations, and thus effectively control population outputs. Our findings therefore have important applications in engineering stem cell culture systems to predictably generate desired stem cells or their derivatives for various regenerative therapies.

Apoptosis↗
PubMed2003

Fluorescence activated cell sorting reveals heterogeneous and cell non-autonomous osteoprogenitor differentiation in fetal rat calvaria cell populations.

Identification of osteoblast progenitors, with defined developmental capacity, would facilitate studies on a variety of parameters of bone development. We used expression of alkaline phosphatase (ALP) and the parathyroid hormone/parathyroid hormone-related protein receptor (PTH1R) as osteoblast markers in dual-color fluorescence activated cell sorting (FACS) to fractionate rat calvaria (RC) cells into ALP(-)PTH1R(-), ALP(+)PTH1R(-), ALP(-)PTH1R(+), and ALP(+)PTH1R(+) populations. These fractionated populations were seeded clonally (n = 96) or over a range of cell densities ( approximately 150-8,500 cell/cm(2); n = 3). Our results indicate that colony forming unit-osteoblast (CFU-O)/bone nodule-forming cells are found in all fractions, but the frequency of CFU-O and total mineralized area is different across fractions. Analysis of these differences suggests that ALP(-)PTH1R(-), ALP(-)PTH1R(+), ALP(+)PTH1R(-), and ALP(+)PTH1R(+) cell populations are separated in order of increasing bone formation capacity. Dexamethasone (dex) differentially increased the CFU-O number in the four fractions, with the largest stimulation in the ALP(-) cell populations. However, there was no significant difference in the number or size distribution of CFU-F (fibroblast) colonies that formed in vehicle versus dex. Finally, both cell autonomous and cell non-autonomous (i.e., inhibitory/stimulatory effects of cell neighbors) differentiation of osteoprogenitors was seen. Only the ALP(-)PTH1R(-) population was capable of forming nodules at the clonal level, at approximately 3- or 12-times the predicted frequency of unfractionated populations in dex or vehicle, respectively. These data suggest that osteoprogenitors can be significantly enriched by fractionation of RC populations, that assay conditions modify the osteoprogenitor frequencies observed and that fractionation of osteogenic populations is useful for interrogation of their developmental status and osteogenic capacity.

Alkaline Phosphatase↗
PubMed2003

Adult human bone marrow-derived mesenchymal progenitor cells are capable of adhesion-independent survival and expansion.

OVERVIEW: We show the existence of adult human mesenchymal progenitor cells (hMPCs) that can proliferate, in a cytokine-dependent manner, as individual cells in stirred suspension cultures (SSC) while maintaining their ability to form functional differentiated mesenchymal cell types. MATERIALS AND METHODS: Ficolled human bone marrow (BM)-derived cells were grown in SSC (and adherent controls) in the presence and absence of exogenously added cytokines. Phenotypic, gene expression, and functional assays for hematopoietic and nonhematopoietic cell populations were used to kinetically track cell production. Limiting-dilution analysis was used to relate culture-produced cells to input cell populations. RESULTS: Cytokine cocktail influenced total and progenitor cell expansion, as well as the types of cells generated upon plating. Flow cytometric analysis of CD117, CD123, and CD45 expression showed that cytokine supplementation influenced SSC output. The concomitant growth of CD45(+) and CD45(-) cells in the cultures that exhibited the greatest hMPC expansions suggests that the growth of these cells may benefit from interactions with hematopoietic cells. Functional assays demonstrated that the SSC-derived cells (input CFU-O number: 1990+/-377) grown in the presence of SCF+IL-3 resulted, after 21 days, in the generation of a significantly greater number (p<0.05) of bone progenitors (33,700+/-8763 CFU-O) than similarly initiated adherent cultures (214+/-75 CFU-O). RT-PCR analysis confirmed that the SSC-derived cells grown in osteogenic conditions express bone-specific genes (Cbfa1/Runx2, bone sialoprotein, and osteocalcin). CONCLUSIONS: Our approach not only provides an alternative strategy to expand adult BM-derived nonhematopoietic progenitor cell numbers in a scalable and controllable bioprocess, but also questions established biological paradigms concerning the properties of connective-tissue stem and progenitor cells.

Adult↗
PubMed2003

Two-color image analysis discriminates between mineralized and unmineralized bone nodules in vitro.

Functional assays of progenitor cell capacity for colony formation in vitro typically depend on the investigator's expertise with quantification. The ability to enumerate and analyze colony types with standardized criteria with no bias would be a useful tool for research and drug development. We report the development of a two-color automated analysis system for colony-forming unit-osteoblasts that is capable of reporting progenitor frequency and bone nodule number size, and type (mineralized or unmineralized). Our image analysis system was validated using the rat calvaria cell model to measure in vitro bone nodule development. With computer-aided image analysis, data on nodules can be rapidly generated with a minimum of user bias and fatigue. This novel tool will distinguish mineralized and unmineralized bone nodules, facilitates quantification, enable large-scale experimental design, allow for long-term data storage and tracking, and lead to the identification of new parameters that impact bone development.

Animals↗