Hydrogel-based Culture System Research Articles

In vitro induction of in vivo–relevant stellate astrocytes in 3D brain-derived, decellularized extracellular matrices

In vitro fabrication of 3D cell culture systems that could provide in vivo tissue–like, structural, and biochemical environments to neural cells is essential not only for fundamental studies on brain function and behavior, but also for tissue engineering and regenerative medicine applicable to neural injury and neurodegenerative diseases. In particular, for astrocytes—which actively respond to the surroundings and exhibit varied morphologies based on stimuli (e.g., stiffness and chemicals) in vitro, as well as physiological or pathological conditions in vivo—it is crucial to establish an appropriate milieu in in vitro culture platforms. Herein, we report the induction of in vivo–relevant, stellate-shaped astrocytes derived from cortices of Rattus norvegicus by constructing the 3D cell culture systems of brain-derived, decellularized extracellular matrices (bdECMs). The bdECM hydrogels were mechanically stable and soft, and the bdECM-based 3D scaffolds supplied biochemically active environments that astrocytes could interact with, leading to the development of in vivo–like stellate structures. In addition to the distinct morphology with actively elongated endfeet, the astrocytes, cultured in 3D bdECM scaffolds, would have neurosupportive characteristics, indicated by the accelerated neurite outgrowth in the astrocyte-conditioned media. Furthermore, next-generation sequencing showed that the gene expression profiles of astrocytes cultured in bdECMs were significantly different from those cultured on 2D surfaces. The stellate-shaped astrocytes in the bdECMs were analyzed to have reached a more mature state, for instance, with decreased expression of genes for scaffold ECMs, actin filaments, and cell division. The results suggest that the bdECM-based 3D culture system offers an advanced platform for culturing primary cortical astrocytes and their mixtures with other neural cells, providing a brain–like, structural and biochemical milieu that promotes the maturity and in vivo–like characteristics of astrocytes in both form and gene expression. Statement of significanceDecellularized extracellular matrices (dECMs) have emerged as strong candidates for the construction of three-dimensional (3D) cell cultures in vitro, owing to the potential to provide native biochemical and physical environments. In this study, we fabricated hydrogels of brain-derived dECMs (bdECMs) and cultured primary astrocytes within the bdECM hydrogels in a 3D context. The cultured astrocytes exhibited a stellate morphology distinct from conventional 2D cultures, featuring tridimensionally elongated endfeet. qRT-PCR and NGS-based transcriptomic analyses revealed gene expression patterns indicative of a more mature state, compared with the 2D culture. Moreover, astrocytes cultured in bdECMs showed neurosupportive characteristics, as demonstrated by the accelerated neurite outgrowth in astrocyte-conditioned media. We believe that the bdECM hydrogel-based culture system can serve as an in vitro model system for astrocytes and their coculture with other neural cells, holding significant potential for neural engineering and therapeutic applications.

Therapeutic effect of a hydrogel-based neural stem cell delivery sheet for mild traumatic brain injury

Objective: There are no effective clinically applicable treatments for neuronal dysfunction after mild traumatic brain injury (TBI). Here, we evaluated the therapeutic effect of a new delivery method of mouse neural stem cell (mNSC) spheroids using a hydrogel, in terms of improvement in damaged cortical lesions and cognitive impairment after mild TBI. Methods: mNSCs were isolated from the subventricular zone and subgranular zone by a hydrogel-based culture system. GFP-transduced mNSCs were generated into spheroids and wrapped into a sheet for transplantation. Male C57BL/6J mice were randomly divided into four groups: sham operation, TBI, TBI with mNSC spheroids, and TBI with mNSC spheroid sheet transplantation covering the damaged cortex. Histopathological and immunohistochemical features and cognitive function were evaluated 7, 14, and 28 days after transplantation following TBI. Results: Hydrogel-based culture systems and mNSC isolation were successfully established from the adult mice. Essential transcription factors for NSCs, such as SOX2, PAX6, Olig2, nestin, and doublecortin (DCX), were highly expressed in the mNSCs. A transplanted hydrogel-based mNSC spheroid sheet showed good engraftment and survival ability, differentiated into TUJ1-positive neurons, promoted angiogenesis, and reduced neuronal degeneration. Also, TBI mice treated with mNSC spheroid sheet transplantation exhibited a significantly increased preference for a new object, suggesting improved cognitive function compared to the mNSC spheroids or no treatment groups. Conclusion: Transplantation with a hydrogel-based mNSC spheroid sheet showed engraftment, migration, and stability of delivered cells in a hostile microenvironment after TBI, resulting in improved cognitive function via reconstruction of the damaged cortex. Statement of Significance: This study presents the therapeutic effect of a new delivery method of mouse neural stem cells spheroids using a hydrogel, in terms of improvement in damaged cortical lesions and cognitive impairment after traumatic brain injury. Collagen/fibrin hydrogel allowed long-term survival and migratory ability of NSCs spheroids. Furthermore, transplanted hydrogel-based mNSCs spheroids sheet showed good engraftment, migration, and stability of delivered cells in a hostile microenvironment, resulting in reconstruction of the damaged cortex and improved cognitive function after TBI. Therefore, we suggest that a hydrogel-based mNSCs spheroids sheet could help to improve cognitive impairment after TBI.

Comparative study of differentiating human pluripotent stem cells into vascular smooth muscle cells in hydrogel-based culture methods.

Vascular smooth muscle cells (VSMCs), which provides structural integrity and regulates the diameter of vasculature, are of great potential for modeling vascular-associated diseases and tissue engineering. Here, we presented a detailed comparison of differentiating human pluripotent stem cells (hPSCs) into VSMCs (hPSCs-VSMCs) in four different culture methods, including 2-dimensional (2D) culture, 3-dimensional (3D) PNIPAAm-PEG hydrogel culture, 3-dimensional (3D) alginate hydrogel culture, and transferring 3-dimensional alginate hydrogel culture to 2-dimensional (2D) culture. Both hydrogel-based culture methods could mimic invivo microenvironment to protect cells from shear force, and avoid cells agglomeration, resulting in the extremely high culture efficiency (e.g., high viability, high purity and high yield) compared with 2D culture. We demonstrated hPSC-VSMCs produced from hydrogel-based culture methods had better contractile phenotypes and the potential of vasculature formation. The transcriptome analysis showed the hPSC-VSMCs derived from hydrogel-based culture methods displayed more upregulated genes in vasculature development, angiogenesis and blood vessel development, extracellular matrix compared with 2D culture. Taken together, hPSC-VSMCs produced from hydrogel-based culture system could be applied in various biomedical fields, and further indicated the suitable development of alginate hydrogel for industrial production by taking all aspects into consideration.

In Vitro Model to Predict Response to Daratumumab Therapy in Relapsed/Refractory Multiple Myeloma

BackgroundSince its approval in 2015, daratumumab has become incorporated in standard-of-care regimens of antimyeloma therapy. However, response to daratumumab in patients with relapsed/refractory multiple myeloma (RRMM) is heterogeneous, and a reliable biomarker of response is lacking. Expression of CD38 was shown to be associated with response to daratumumab, but failed to predict responses consistently and is therefore not used in clinical practice.Aim of our study was to develop an in vitro method that accurately identifies patients with RRMM that will respond to daratumumab treatment.MethodsWe obtained CD38 mean fluorescent intensity (MFI) of plasma cells from patients with RRMM just before starting daratumumab therapy, as well as best clinical response to treatment and duration of response to daratumumab in weeks. When possible, extra material was obtained at the bone marrow biopsy performed before the start of daratumumab treatment and frozen in liquid nitrogen in our local biobank facility. All included patients provided written informed consent.Bone marrow mononuclear cells from patients with RRMM were thawed and cultured for a week in a hydrogel-based culture system, supplemented with pro-survival cytokines IL-6 and APRIL. To examine the in vitro response to daratumumab, we added 0.1 μg/ml daratumumab or 0.1 μg/ml IgG1κ isotype to the culture wells. We measured complement-dependent cytotoxicity (CDC) by adding 10% pooled human serum and antibody-dependent cellular cytotoxicity (ADCC) by adding healthy-donor peripheral blood mononuclear cells (PBMC) in a 10:1 effector-to-target ratio. After overnight incubation, hydrogel cultures were broken down mechanically and specific lysis was determined with flow cytometry, using CD138 and CD38 multi-epitope antibodies to select plasma cells, and using ToPro3 live/dead stain and Flow-Count Fluorospheres to obtain absolute numbers of surviving plasma cells.ResultsFirst, we analyzed CD38 MFI of plasma cells from 35 patients with RRMM just before starting daratumumab treatment, both as monotherapy or as part of a regimen. As was previously reported by others 1,2, we found a significant association between expression of CD38 and response (p = 0.01) (Figure 1A). However, we also observed considerable overlap between CD38 MFI values of responders and non-responders, with AUC ROC = 0.75. Therefore the discriminatory value of CD38 expression to predict response is weak.Next, we tested daratumumab in vitro on plasma cells obtained from 10 patients with RRMM. Daratumumab ADCC was associated with clinical response by the corresponding patients (p = 0.008), with a median specific lysis of 54.3% for patients who obtained a PR and 26.0% for patients who did not obtain a PR (Figure 1B). Median CDC for patients who did not obtain a PR was 3.16% versus 45.3% for patients who did obtain a PR, without a significant difference between the two groups (p = 0.18). Further evaluation of these results revealed AUC ROC of 1.00 and 0.81 for ADCC and CDC, respectively, outperforming CD38 expression. For ADCC, a threshold value of 39.6% lysis translated to a diagnostic accuracy of 100%, while for CDC a threshold value of 29.4% resulted in a diagnostic accuracy of 87.5%. Ultimately, we compared these results to CD38 expression. With an optimal CD38 MFI threshold value of 10989, diagnostic accuracy of CD38 expression was 71.4%. In addition, we examined ability of the test methods to predict the clinically experienced duration of response to daratumumab treatment. We observed no difference in duration of response when using the optimal threshold values of CD38 MFI (p = 0.13) and CDC lysis (p = 0.12), but duration of response was significantly different for patients with an ADCC lysis above and below the threshold value of 39.6% (p = 0.002) (Figure 1C).ConclusionIn summary, we developed an straightforward and consistent in vitro method to predict response to daratumumab treatment in vivo. Measuring ADCC in patient-derived plasma cells using healthy-donor PBMC within our hydrogel-based culture system corresponds with the overall clinical response and duration of response to daratumumab. Our results support further clinical validation of the in vitro use of primary plasma cells to identify patients most likely to benefit from treatment.

Comparative Study of Human Pluripotent Stem Cell-Derived Endothelial Cells in Hydrogel-Based Culture Systems

Human pluripotent stem cell (hPSC)-derived endothelial cells (ECs) are promising cell sources for drug discovery, tissue engineering, and studying or treating vascular diseases. However, hPSC-ECs derived from different culture methods display different phenotypes. Herein, we made a detailed comparative study of hPSC-ECs from three different culture systems (e.g., 2D, 3D PNIPAAm-PEG hydrogel, and 3D alginate hydrogel cultures) based on our previous reports. We expanded hPSCs and differentiated them into ECs in three culture systems. Both 3D hydrogel systems could mimic an in vivo physiologically relevant microenvironment to protect cells from shear force and prevent cell agglomeration, leading to a high culture efficiency and a high volumetric yield. We demonstrated that hPSC-ECs produced from both hydrogel systems had similar results as 2D-ECs. The transcriptome analysis showed that PEG-ECs and alginate-ECs displayed a functional phenotype due to their higher gene expressions in vasculature development, extracellular matrix, angiogenesis, and glycolysis, while 2D-ECs showed a proliferative phenotype due to their higher gene expressions in cell proliferation. Taken together, both PEG- and alginate-hydrogel systems will significantly advance the applications of hPSC-ECs in various biomedical fields.

Development of a Dual Hydrogel Model System for Vascularization

Numerous hydrogel-based culture systems are used to create in vitro model for prevascularization. Hydrogels used to induce a microenvironment conducive to microvessel formation are typically soft and fast degradable, but often suffer from maintaining a lasting perfusable channel in vitro. Here, a dual hydrogel system that consists of photo-crosslinkable gelatin methacrylate (GelMA) and polyethylene glycol dimethacrylate (PEGDMA) is reported. GelMA hydrogels present soft and rapidly degradable properties and show microporous structures while PEGDMA is relatively stiff, almost nondegradable in vitro, and less porous. The dual hydrogel system is sequentially photo-crosslinked to construct an endothelial cell (EC)-lined perfusable PEGDMA channel and surrounding GelMA for endothelial vascular networks. Such dual hydrogel system exhibits seamless integration of the stiff PEGDMA channel and the surrounding soft GelMA, and facilitates rapid EC sprouting and extensive microvessel formation from a stable endothelium on the PEGDMA channel into the GelMA. Furthermore, diffusivity of biomolecules in the perfusable dual hydrogel system is affected by both the structural and physicochemical properties of the hydrogel system and the microvascular networks formed in the system. The establishment of the dual hydrogel system for vascularization holds great promise as an in vitro angiogenesis model and prevascularization strategy of large tissue constructs.

The fate of mesenchymal stem cells is greatly influenced by the surface chemistry of silica nanoparticles in 3D hydrogel-based culture systems.

Polymeric hydrogel-based 3D scaffolds are well-known structures, being used for cultivation and differentiation of stem cells. However, scalable systems that provide a native-like microenvironment with suitable biological and physical properties are still needed. Incorporation of nanomaterials into the polymeric systems is expected to influence the physical properties of the structure but also the stem cells fate. Here, alginate/gelatin hydrogel beads incorporated with mesoporous silica nanoparticles (MSNs) (average diameter 80.9 ± 10 nm) and various surface chemistries were prepared. Human adipose-derived mesenchymal stem cells (hASCs) were subsequently encapsulated into the alginate/gelatin/silica hydrogels. Incorporation of amine- and carboxyl-functionalized MSNs (A-MSNs and C-MSNs) significantly enhances the stability of the hydrogel beads. In addition, the expression levels of Nanog and OCT4 imply that the incorporation of A-MSNs into the alginate/gelatin beads significantly improves the proliferation and the stemness of encapsulated hASCs. Importantly, our findings show that the presence of A-MSNs slightly suppresses in vivo inflammation. In contrast, the results of marker gene expression analyses indicate that cultivation of hASCs in alginate beads incorporated with C-MSNs (10% w/w) leads to a heterogeneously differentiated population of the cells, i.e., osteocytes, chondrocytes, and adipocytes, which is not appropriate for both cell culture and differentiation applications.

Synergy of Paracrine Signaling During Early-Stage Mouse Ovarian Follicle Development In Vitro.

Paracrine signals, such as soluble cytokines and extracellular matrix cues, are essential for the survival and development of multicellular ovarian follicles. While it is well established that hydrogel-based culture systems successfully support the growth of late-stage follicles for fertility preservation, growing small, early-stage ovarian follicles still proves to be challenging. We hypothesized that paracrine factors secreted from neighboring follicles may be crucial for improving the survival of early-stage follicles in vitro. To test our hypothesis, we investigated the bi-directional crosstalk of the paracrine signals, such as cell-secreted cytokines, sex hormones and transcription factors (TFs), in follicles encapsulated and cultured for 12days in alginate in groups of five (5×) and ten (10×). The differential profiles of TF activity and secretome during folliculogenesis were analyzed using TRanscriptional Activity CEllular aRray (TRACER) and data-driven multivariate modeling approach. The mechano- and oxygen-responsive TFs, NF-κB and HIF1, exhibited a unique upregulation signature in 10× follicles. Consistently, levels of proangiogenic factors, such as VEGF-A and angiopoietin-2, were significantly higher in 10× follicles than those in 5× follicles, reaching 269.77 and 242.82pg/mL on the last day of culture. The analysis of TRACER and secreted cytokines also revealed critical early interactions between cytokines and TFs, correlating with the observed phenotypical and functional differences between conditions. We identified unique signatures of synergism during successful early-stage ovarian follicle development. These findings bring us closer to understanding of mechanisms underlying the downstream effects of interactions between the extracellular microenvironment and early-stage folliculogenesis in vitro.

Role of Rho-Associated Coiled-Coil Forming Kinase Isoforms in Regulation of Stiffness-Induced Myofibroblast Differentiation in Lung Fibrosis.

Fibrosis is a major cause of progressive organ dysfunction in several chronic pulmonary diseases. Rho-associated coiled-coil forming kinase (ROCK) has been shown to be involved in myofibroblast differentiation driven by altered matrix stiffness in a fibrotic state. There are two known ROCK isoforms in humans, ROCK1 and ROCK2, but the specific role of each isoform in myofibroblast differentiation in lung fibrosis remains unknown. To study this, we developed a gelatin methacryloyl hydrogel-based culture system with different stiffness levels relevant to healthy and fibrotic lungs. We have shown that stiff matrix, but not soft matrix, can induce myofibroblast differentiation with high smooth muscle actin isoform (αSMA) expression. Furthermore, our data confirmed that the inhibition of ROCK signaling by a pharmacological inhibitor (i.e., Y27632) attenuates stiffness-induced αSMA expression and fiber assembly in myofibroblasts. To assess the role of ROCK isoforms in this process, we used short interfering RNA to knock down the expression of each isoform. Our data showed that knocking down either ROCK1 or ROCK2 did not result in a reduction in αSMA expression in myofibroblasts on stiff matrix, as opposed to soft matrix, where αSMA expression was reduced significantly. Paradoxically, on stiff matrix, the absence of one isoform (particularly ROCK2) exaggerated αSMA expression and led to thick fiber assembly. Moreover, complete loss of αSMA fiber assembly was seen only in the absence of both ROCK isoforms, suggesting that both isoforms are implicated in this process. Overall, our results indicate the differential role of ROCK isoforms in myofibroblast differentiation on soft and stiff matrices.

Three-dimensional tissues using human pluripotent stem cell spheroids as biofabrication building blocks

A recently emerged approach for tissue engineering is to biofabricate tissues using cellular spheroids as building blocks. Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs), can be cultured to generate large numbers of cells and can presumably be differentiated into all the cell types of the human body in vitro, thus are an ideal cell source for biofabrication. We previously developed a hydrogel-based cell culture system that can economically produce large numbers of hPSC spheroids. With hPSCs and this culture system, there are two potential methods to biofabricate a desired tissue. In Method 1, hPSC spheroids are first utilized to biofabricate an hPSC tissue that is subsequently differentiated into the desired tissue. In Method 2, hPSC spheroids are first converted into tissue spheroids in the hydrogel-based culture system and the tissue spheroids are then utilized to biofabricate the desired tissue. In this paper, we systematically measured the fusion rates of hPSC spheroids without and with differentiation toward cortical and midbrain dopaminergic neurons and found spheroids’ fusion rates dropped sharply as differentiation progressed. We found Method 1 was appropriate for biofabricating neural tissues.

Three-dimensional (3D) culture of bone-derived human 786-O renal cell carcinoma retains relevant clinical characteristics of bone metastases

Bone metastases from renal cell carcinoma (RCC) are typically lytic, destructive, and resistant to treatment regimens. Current in vitro models for studying metastasis introduce artifacts that limit their usefulness. Many features of tumors growing in bone are lost when human RCC cells are cultured in two-dimensional (2D) plastic substrata. In this study, we established that RCC spheroids, consisting of aggregates of cells, can be grown in a three-dimensional (3D) hyaluronate hydrogel-based culture system. The bone-derived human 786-O RCC subline proliferated and survived long term in these hydrogels. Additionally, RCC spheroids in 3D hydrogels demonstrated lower proliferation rates than their counterparts grown in 2D. Overall, gene expression patterns of RCC spheroids in 3D more closely mimicked those observed in vivo than did those of cells grown in 2D. Of particular importance, selected adhesion molecules, angiogenesis factors, and osteolytic factors that have been shown to be involved in RCC bone metastasis were found to be expressed at higher levels in 3D than in 2D cultures. We propose that the 3D culture system provides an improved platform for RCC bone metastasis studies compared with 2D systems.

Hydrogel-Based Engineering of Beige Adipose Tissue.

Brown and beige adipose tissues have a significant capacity for energy expenditure that may be exploited as a treatment for obesity and metabolic disease. However, the limited volumes of these tissues in adults hinders realization of this potential. Engineering beige adipose tissue may provide an alternative source of this tissue. In this paper we describe the preparation of poly(ethylene glycol) (PEGDA) hydrogels with mechanical properties similar to native adipose tissue. Adipose derived stem cells (ASC) were cultured in hydrogels without adhesive sequences or degradable monomers. Cells were able to differentiate, independent of scaffold properties and were maintained as a viable and functioning adipose tissue mass. The cells expressed their own basement membrane proteins consistent with the composition of adipose tissue. The ASCs could be induced to express uncoupling protein-1 (UCP-1) and cIDEA, makers of beige adipocytes with expression level varying with hydrogel stiffness. This hydrogel-based culture system serves as a first step in engineering beige adipose tissue.

Interaction of Tumor Cells with the Hematopoietic Stem and Progenitor Cell Niche

IntroductionThe bone marrow microenvironment regulates the self-renewal and differentiation of hematopoietic stem and progenitor cells (HSPCs), through a network dependent on cell-cell interaction. This interaction is mediated by morphogens, the extracellular matrix and cell adhesion molecules expressed and secreted by various cell types in the HSPC niche. Mesenchymal stromal cells (MSCs), as the major cellular component, maintain the stemness properties of the niche. The microenvironment thus becomes conducive for HSPCs to remain quiescent, thereby enabling long term self-renewal. Therefore, the safe haven in the bone marrow microenvironment and its constituent cell types can be targeted during tumorigenesis, thus making the niche neoplastic. Dissemination of breast cancer cells into the bone marrow has been described even in the early stages of the disease. The present study focuses on the influence of breast carcinomas on the genetic and functional profile of mesenchymal and hematopoietic progenitor cells of the bone marrow niche.MethodsIn vitro coculture models of breast cancer cell lines- MDA-MB231, MCF-7 and primary MSCs derived from the bone marrow of healthy donors were used in the study. Atomic- force microscopy based single-cell force spectroscopy (AFM-SCFS) and fluorescence based assays were used for cell adhesion experiments. Hydrogel based culture systems were used for 3-dimensional cocultures of breast cancer cells and MSCs. Hypoxic and normoxic culture conditions (0.5% and 20% oxygen respectively) were used for the experiments.ResultsThe breast cancer cell lines caused a significant reduction in HSPC adhesion to MSCs (88% by MDA-MB 231 cells; p<0.005 and 73% by MCF-7 cells; p<0.005). AFM-SCFS studies also indicated a higher binding force between breast cancer cells and MSCs, as compared to HSPCs (MDA-MB231 cells-0.13nN, MCF-7 cells-0.074nN and HSPCs-0.05nN). MDA-MB231and MCF-7 cells express Intercellular adhesion molecule-1(ICAM-1), which has been shown to promote breast cancer metastasis (Hanlon et al, 2002; Rosette et al, 2005; Schröder C. et al, 2011). There was a significant difference in reduction of HSPC adhesion towards MSCs by ICAM-1 knockdown (ICAM-1 KD) tumor cells as compared to MDA-MB231 cells (84.83% by MDA-MB231 cells versus 28.11% by ICAM-1KD tumor cells, p<0.001). AFM-SCFS studies also showed a reduced binding force between ICAM-1 KD tumor cells and MSCs as compared to MDA-MB231cells (MDA-MB231 cells-0.14nN versus ICAM-1-KD tumor cells-0.05nN, p value<0.001). ICAM-1 KD studies thus showed that reduction in HSPC adhesion to MSCs by breast cancer cells was mediated through ICAM-1 signaling. A cytokine array was performed to investigate if breast cancer cell lines affect the cytokine profile of MSCs. The array showed altered expression of growth factors- Basic fibroblast growth factor (bFGF) and Platelet derived growth factor–beta (PDGF-BB) (2.2 fold upregulation and 0.5 fold downregulation in breast cancer cells- MSC cocultures respectively). Based on the array, a bFGF-mediated increase in the proliferation of MSCs and breast cancer cells in coculture was observed. The bFGF upregulation also caused an increased migration of MDA-MB231 cells towards MSCs in a transwell migration assay. An upregulation in the phosphorylation status of Akt was observed in breast cancer cells – MSC cocultures, as a downstream effect of upregulated bFGF levels. The bFGF-mediated increase in the proliferation of breast cancer cells and MSCs in coculture was shown to be dependent on the activation of PI3K-Akt pathway. The bFGF- mediated increase in the migration of MDA-MB231 cells towards MSCs was also inhibited upon addition of the PI3K blocker. Interestingly, the breast cancer cells caused a reduction in osteoblastic differentiation of MSCs by downregulation of PDGF-BB. Studies with 3-dimensional cocultures of breast cancer cells and MSCs also showed a reduction in osteoblastic differentiation of MSCs. Furthermore, long-term cocultures of breast cancer cells, HSPCs and MSCs showed reduced support for primitive HSPCs in the neoplastic niche.ConclusionsThese findings indicate a perturbed HSPC niche upon tumor invasion. The possible role of altered cytokine expression, consecutive downstream signaling in niche activation and bone turnover will be further studied using in vitro and in vivo approaches to recapitulate tumor micrometastases to the HSPC niche. DisclosuresNo relevant conflicts of interest to declare.