In vitro reconstruction of a three-dimensional mouse hematopoietic microenvironment in the pore of polyurethane foam

Influential factors for optimizing and strengthening mesenchymal stem cells and hematopoietic stem cells co-culture

Mesenchymal stem cells (MSCs) and Hematopoietic stem cells (HSCs) are two types of bone marrow stem cells that can proliferate and differentiate into different cell lineages. HSCs interact with MSCs under protective conditions, called niche. Numerous studies have indicated supportive effects of MSCs on HSCs proliferation and differentiation. Furthermore, HSCs have many clinical applications and could treat different hematologic and non-hematologic diseases. For this purpose, there is a need to perform in vitro studies to optimize their expansion. Therefore, various methods including co-culture with MSCs are used to address the limitations of HSCs culture. Some parameters that might be effective for improving the MSC/ HSC co-culture systems. Manipulating culture condition to enhance MSC paracrine activity, scaffolds, hypoxia, culture medium additives, and the use of various MSC sources, have been examined in different studies. In this article, we investigated the potential factors for optimizing HSCs/ MSCs co-culture. It might be helpful to apply a suitable approach for providing high-quality HSCs and improving their therapeutic applications.

Exosomes in the Healthy and Malignant Bone Marrow Microenvironment

The bone marrow (BM) is a complex organ that sustains hematopoiesis via mechanisms involving the microenvironment. The microenvironment includes several cell types, neurotransmitters from innervated fibers, growth factors, extracellular matrix proteins, and extracellular vesicles. The main function of the BM is to regulate hematopoietic function to sustain the production of blood and immune cells. However, the BM microenvironment can also accommodate the survival of malignant cells. A major mechanism by which the cancer cells communicate with cells of the BM microenvironment is through the exchange of exosomes, a subset of extracellular vesicles that deliver molecular signals bidirectionally between malignant and healthy cells. The field of exosomes is an active area of investigation since an understanding of how the exosomal packaging, cargo, and production can be leveraged therapeutically to deter cancer progression and sensitize malignant cells to other therapies. Altogether, this chapter discusses the crucial role of exosomes in the development and progression of BM-associated cancers, such as hematologic malignancies and marrow-metastatic breast cancer. Exosome-based therapeutic strategies and their limitations are also considered.

Differentiation of human induced pluripotent stem cells into erythroid cells

During the last years, several strategies have been made to obtain mature erythrocytes or red blood cells (RBC) from the bone marrow or umbilical cord blood (UCB). However, UCB-derived hematopoietic stem cells (HSC) are a limited source and in vitro large-scale expansion of RBC from HSC remains problematic. One promising alternative can be human pluripotent stem cells (PSCs) that provide an unlimited source of cells. Human PSCs, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), are self-renewing progenitors that can be differentiated to lineages of ectoderm, mesoderm, and endoderm. Several previous studies have revealed that human ESCs can differentiate into functional oxygen-carrying erythrocytes; however, the ex vivo expansion of human ESC-derived RBC is subjected to ethical concerns. Human iPSCs can be a suitable therapeutic choice for the in vitro/ex vivo manufacture of RBCs. Reprogramming of human somatic cells through the ectopic expression of the transcription factors (OCT4, SOX2, KLF4, c-MYC, LIN28, and NANOG) has provided a new avenue for disease modeling and regenerative medicine. Various techniques have been developed to generate enucleated RBCs from human iPSCs. The in vitro production of human iPSC-derived RBCs can be an alternative treatment option for patients with blood disorders. In this review, we focused on the generation of human iPSC-derived erythrocytes to present an overview of the current status and applications of this field.

Ex vivo culture of adult CD34+ stem cells using functional highly porous polymer scaffolds to establish biomimicry of the bone marrow niche

Haematopoiesis, the process of blood production, occurs from a tiny contingent of haematopoietic stem cells (HSC) in highly specialised three-dimensional niches located within the bone marrow. When haematopoiesis is replicated using in vitro two-dimensional culture, HSCs rapidly differentiate, limiting self-renewal. Emulsion-templated highly porous polyHIPE foam scaffolds were chosen to mimic the honeycomb architecture of human bone. The unmodified polyHIPE material supports haematopoietic stem and progenitor cell (HSPC) culture, with successful culture of erythroid progenitors and neutrophils within the scaffolds. Using erythroid culture methodology, the CD34⁺ population was maintained for 28 days with continual release of erythroid progenitors. These cells are shown to spontaneously repopulate the scaffolds, and the accumulated egress can be expanded and grown at large scale to reticulocytes. We next show that the polyHIPE scaffolds can be successfully functionalised using activated BM(PEG)₂ (1,8-bismaleimido-diethyleneglycol) and then a Jagged-1 peptide attached in an attempt to facilitate notch signalling. Although Jagged-1 peptide had no detectable effect, the BM(PEG)₂ alone significantly increased cell egress when compared to controls, without depleting the scaffold population. This work highlights polyHIPE as a novel functionalisable material for mimicking the bone marrow, and also that PEG can influence HSPC behaviour within scaffolds.

Polyurethane scaffolds seeded with CD34(+) cells maintain early stem cells whilst also facilitating prolonged egress of haematopoietic progenitors

We describe a 3D erythroid culture system that utilises a porous polyurethane (PU) scaffold to mimic the compartmentalisation found in the bone marrow. PU scaffolds seeded with peripheral blood CD34⁺ cells exhibit a remarkable reproducibility of egress, with an increased output when directly compared to human bone scaffolds over 28 days. Immunofluorescence demonstrated the persistence of CD34⁺ cells within the scaffolds for the entirety of the culture. To characterise scaffold outputs, we designed a flow cytometry panel that utilises surface marker expression observed in standard 2D erythroid and megakaryocyte cultures. This showed that the egress population is comprised of haematopoietic progenitor cells (CD36⁺GPA^−/low). Control cultures conducted in parallel but in the absence of a scaffold were also generally maintained for the longevity of the culture albeit with a higher level of cell death. The harvested scaffold egress can also be expanded and differentiated to the reticulocyte stage. In summary, PU scaffolds can behave as a subtractive compartmentalised culture system retaining and allowing maintenance of the seeded “CD34⁺ cell” population despite this population decreasing in amount as the culture progresses, whilst also facilitating egress of increasingly differentiated cells.

Bone, microenvironment and hematopoiesis

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) mature to form all blood cells and the study into how HSC fate decisions are made has exploded in recent years. In an effort to fully understand the function and organization of HSCs and hematopoietic progenitor cells (HPCs), many groups have identified the microenvironment in which they reside as playing a key role. This review highlights the findings within the last 18 months on the cells and molecules shown to be important within the bone marrow HSC niche for HSC regulation.

RECENT FINDINGS

Previous research has heavily concentrated on the role of osteoblasts, mesenchymal stem cells (MSCs), reticular stromal cells, endothelial cells and nerve cells. More recently, research has not only expanded on the role of these cells, but has also shown that mature hematopoietic cells such as macrophages and megakaryocytes are also important in the maintenance of hematopoiesis within the HSC niche.

SUMMARY

Identifying and understanding the roles of all cells comprising the HSC niche coupled with the development of better 3D imaging and 3D in-vitro mimicking of the HSC niche will increase our understanding of where HSCs reside and how they are regulated. Research will lead to better manipulation of HSCs for mobilization, homing and hematopoietic reconstitution following injury or disease.