Somatic cell nuclear transfer and transcription-factor-based reprogramming revert adult cells to an embryonic state, and yield pluripotent stem cells that can generate all tissues. Through different ...mechanisms and kinetics, these two reprogramming methods reset genomic methylation, an epigenetic modification of DNA that influences gene expression, leading us to hypothesize that the resulting pluripotent stem cells might have different properties. Here we observe that low-passage induced pluripotent stem cells (iPSCs) derived by factor-based reprogramming of adult murine tissues harbour residual DNA methylation signatures characteristic of their somatic tissue of origin, which favours their differentiation along lineages related to the donor cell, while restricting alternative cell fates. Such an 'epigenetic memory' of the donor tissue could be reset by differentiation and serial reprogramming, or by treatment of iPSCs with chromatin-modifying drugs. In contrast, the differentiation and methylation of nuclear-transfer-derived pluripotent stem cells were more similar to classical embryonic stem cells than were iPSCs. Our data indicate that nuclear transfer is more effective at establishing the ground state of pluripotency than factor-based reprogramming, which can leave an epigenetic memory of the tissue of origin that may influence efforts at directed differentiation for applications in disease modelling or treatment.
Multiple myeloma is a plasma cell neoplasm residing in bone marrow. Despite advances in myeloma therapies, novel therapies are required to improve patient outcomes. CD47 is highly expressed on ...myeloma cells and a potential therapeutic candidate for myeloma therapies. Flow cytometric analysis of patient bone marrow cells revealed that myeloma cells overexpress CD47 when compared with non-myeloma cells in 73% of patients (27/37). CD47 expression protects cells from phagocytosis by transmitting an inhibitory signal to macrophages. Here we show that blocking CD47 with an anti-CD47 monoclonal antibody increased phagocytosis of myeloma cells in vitro. In xenotransplantation models, anti-CD47 antibodies inhibited the growth of RPMI 8226 myeloma cells and led to tumor regression (42/57 mice), implicating the eradication of myeloma-initiating cells. Moreover, anti-CD47 antibodies retarded the growth of patient myeloma cells and alleviated bone resorption in human bone-bearing mice. Irradiation of mice before myeloma cell xenotransplantation abolished the therapeutic efficacy of anti-CD47 antibodies delivered 2 weeks after radiation, and coincided with a reduction of myelomonocytic cells in spleen, bone marrow and liver. These results are consistent with the hypothesis that anti-CD47 blocking antibodies inhibit myeloma growth, in part, by increasing phagocytosis of myeloma cells.
Like many epithelial tumors, head and neck squamous cell carcinoma (HNSCC) contains a heterogeneous population of cancer cells. We developed an immunodeficient mouse model to test the tumorigenic ...potential of different populations of cancer cells derived from primary, unmanipulated human HNSCC samples. We show that a minority population of CD44⁺ cancer cells, which typically comprise <10% of the cells in a HNSCC tumor, but not the CD44⁻ cancer cells, gave rise to new tumors in vivo. Immunohistochemistry revealed that the CD44⁺ cancer cells have a primitive cellular morphology and costain with the basal cell marker Cytokeratin 5/14, whereas the CD44⁻ cancer cells resemble differentiated squamous epithelium and express the differentiation marker Involucrin. The tumors that arose from purified CD44⁺ cells reproduced the original tumor heterogeneity and could be serially passaged, thus demonstrating the two defining properties of stem cells: ability to self-renew and to differentiate. Furthermore, the tumorigenic CD44⁺ cells differentially express the BMI1 gene, at both the RNA and protein levels. By immunohistochemical analysis, the CD44⁺ cells in the tumor express high levels of nuclear BMI1, and are arrayed in characteristic tumor microdomains. BMI1 has been demonstrated to play a role in self-renewal in other stem cell types and to be involved in tumorigenesis. Taken together, these data demonstrate that cells within the CD44⁺ population of human HNSCC possess the unique properties of cancer stem cells in functional assays for cancer stem cell self-renewal and differentiation and form unique histological microdomains that may aid in cancer diagnosis.
Haematopoietic stem cells give rise to progeny that progressively lose
self-renewal capacity and become restricted to one lineage.
The points at which haematopoietic stem cell-derived progenitors ...commit to
each of the various lineages remain mostly unknown. We have identified a clonogenic
common lymphoid progenitor that can differentiate into T, B and natural killer
cells but not myeloid cells. Here we report the prospective
identification, purification and characterization, using cell-surface markers
and flow cytometry, of a complementary clonogenic common myeloid progenitor
that gives rise to all myeloid lineages. Common myeloid progenitors give rise
to either megakaryocyte/erythrocyte or granulocyte/macrophage progenitors.
Purified progenitors were used to provide a first-pass expression profile
of various haematopoiesis-related genes. We propose that the common lymphoid
progenitor and common myeloid progenitor populations reflect the earliest
branch points between the lymphoid and myeloid lineages, and that the commitment
of common myeloid progenitors to either the megakaryocyte/erythrocyte or the
granulocyte/macrophage lineages are mutually exclusive events.
Stem cells are the natural units of embryonic generation, and also adult regeneration, of a variety of tissues. Recently, the list of tissues that use the model of differentiation from stem to ...progenitor to mature cell has increased from blood to include a variety of tissues, including both central and peripheral nervous systems and skeletal muscle; it is also possible that all organs and tissues are derived from, and still contain, stem cells. Because the number and activities of stem cells and their progeny are homeostatically regulated, clinical stem cell transplantation could greatly add to the physician's armamentarium against degenerative diseases.
We proposed and demonstrated that myelogenous leukemia has a preleukemic phase. In the premalignant phase, normal hematopoietic stem cells (HSCs) gradually accumulate mutations leading to HSC clonal ...expansion, resulting in the emergence of leukemic stem cells (LSCs). Here, we show that preleukemic HSCs are the basis of clonal hematopoiesis, as well as late-onset blood diseases (chronic-phase chronic myeloid leukemia, myeloproliferative neoplasms, and myelodysplastic disease). The clones at some point each trigger surface expression of "eat me" signals for macrophages, and in the clones and their LSC progeny, this is countered by upregulation of "don't eat me" signals for macrophages such as CD47,opening the possibility of CD47-based therapies. We include evidence that similar processes result in fibroblast expansion in a variety of fibrotic diseases, and arterial smooth muscle clonal expansion is a basis of atherosclerosis, including upregulation of both "eat me" and "don't eat me" molecules on the pathogenic cells.
Stem cells are not only units of biological organization, responsible for the development and the regeneration of tissue and organ systems, but also are units in evolution by natural selection. Stem ...cells are generally defined as clonogenic cells capable of both self-renewal and multilineage differentiation. Stem cells can be divided into a long-term subset, capable of indefinite self-renewal, as well as a short-term subset that self-renews for a defined interval. Stem cells give rise to non-self renewing oligolineage progenitors, which in turn give rise to progeny that are more restricted in their differentiating potential, and finally to functionally mature cells. The earliest stem cells in ontogeny are totipotent, extending from the zygote to the inner cell mass of the blastocyst; soon thereafter, totipotent stem cells give rise to somatic stem/progenitor cells and primitive germline stem cells. Very little is known of the stages somatic stem cells take between the blastocyst stage and the emergence of tissue and organ-specific stem cells at about the neurula stage. At this stage, the best studied stem cells-those that will form blood-emerge. This review begins with a detailed examination of hematopoietic (blood-forming) stem cells.
Multipotent stem cells are clonal cells that self-renew as well as
differentiate to regenerate adult tissues. Whereas stem cells and their fates
are known by unique genetic marker studies, the fate ...and function of these
cells are best studied by their prospective isolation. This review is about the
properties of various highly purified tissue-specific multipotent stem cells
and purified oligolineage progenitors. We contend that unless the stem or
progenitor cells in question have been purified to near homogeneity, one cannot
know whether their generation of expected (or unexpected) progeny is a property
of a known cell type. It is interesting that in the hematopoietic system the
only long-term self-renewing cells in the stem and progenitors pool are the
hematopoietic stem cells. This fact is discussed in the context of normal and
leukemic hematopoiesis.
Hematopoietic stem cells (HSCs) reside predominantly in bone marrow, but low numbers of HSCs are also found in peripheral blood. We examined the fate of blood-borne HSCs using genetically marked ...parabiotic mice, which are surgically conjoined and share a common circulation. Parabionts rapidly established stable, functional cross engraftment of partner-derived HSCs and maintained partner-derived hematopoiesis after surgical separation. Determination of the residence time of injected blood-borne progenitor cells suggests that circulating HSCs/progenitors are cleared quickly from the blood. These data demonstrate that HSCs rapidly and constitutively migrate through the blood and play a physiological role in, at least, the functional reengraftment of unconditioned bone marrow.
CD47 is a “don’t eat me” signal to phagocytes that is overexpressed on many tumor cells as a potential mechanism for immune surveillance evasion. CD47 and its interaction with signal-regulating ...protein alpha (SIRPα) on phagocytes is therefore a promising cancer target. Therapeutic antibodies and fusion proteins that block CD47 or SIRPα have been developed and have shown activity in preclinical models of hematologic and solid tumors. Anemia is a common adverse event associated with anti-CD47 treatment, but mitigation strategies—including use of a low ‘priming’ dose—have substantially reduced this risk in clinical studies. While efficacy in single-agent clinical studies is lacking, findings from studies of CD47–SIRPα blockade in combination with agents that increase ‘eat me’ signals or with antitumor antibodies are promising. Magrolimab, an anti-CD47 antibody, is the furthest along in clinical development among agents in this class. Magrolimab combination therapy in phase Ib/II studies has been well tolerated with encouraging response rates in hematologic and solid malignancies. Similar combination therapy studies with other anti-CD47–SIRPα agents are beginning to report. Based on these early clinical successes, many trials have been initiated in hematologic and solid tumors testing combinations of CD47–SIRPα blockade with standard therapies. The results of these studies will help determine the role of this novel approach in clinical practice and are eagerly awaited.
•CD47 is a “don’t eat me” signal overexpressed on cancer cells.•Blockade of the CD47–SIRPα signaling pathway leads to phagocytosis of tumor cells.•CD47–SIRPα blockade plus standard treatment shows promising clinical efficacy.•Clinically, CD47–SIRPα blockade plus standard treatment is well tolerated.•Clinical trials targeting CD47–SIRPα in hematologic and solid tumors are ongoing.
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