Stem cells and diversity

Abstract

Modern hematology began with two technology-based revolutions. First, assays were developed for cells earlier in lineages than those recognized morphologically. These opened for study important areas such as regulation and response to injury. Second, the rapid development of molecular biology disclosed complex mechanisms within cells and identified important genetic changes in malignancy. When immediate causative lesions were found, specific treatments directed at them were seen to be highly effective.Recently, several groups have provided evidence of the existence in adult tissues of stem cells that are capable of differentiation into such diverse organ systems as hematopoiesis, muscle, liver and brain. The implications of this stem cell plasticity are just beginning to be realized.The purpose of this paper is to review some of the concepts, advances and problems emerging from colony assays, molecular biology and stem cell plasticity. A hypothesis will be presented that links stem cell plasticity to the clinical entity known as metastases with unknown primary source. Colony assaysClonogenic assays, where a single cell gives rise to a recognizable colony, are selective, since they can measure minority populations; the assays are specific, quantitative, qualitative and provide information about the proliferative and differentiation capacities of the cells of origin. Each of these advantages of colony assays has limitations. The most severe limitation of the method is that analysis of cellular composition to determine progenitor properties shows only what the cell of origin did during clonal expansion, but not what it might do if conditions were improved or the time of observation prolonged.

Engineering Next-Generation BET-Independent MLV Vectors for Safer Gene Therapy

“…Therefore, we evaluated the genotoxic potential of next-generation BinMLV vectors carrying a MLV.SIN-vector genome with an internal SF enhancer/promoter, which is known to trigger insertional transformation events21, 45 (Figure S4A) in the in vitro immortalization assay (IVIM) 46 and the transformational incidence in a murine CFU assay (Figure S4B) 47, 48. To ensure the chance of immortalization, at least 55% of cells were transduced, corresponding to a mean vector copy number (VCN) of > 2 49 .…”

“…The assay provides a stringent method for the detection of the tumorigenic potential of transformed murine HSCs in semi-solid medium 47, 48. In a parallel approach, we sought to assess the serial colony-forming capacity of the transduced lineage marker-negative cells 2 weeks after expansion in the IVIM assay.…”

“…To further address whether detargeted BinMLV vectors may be less genotoxic, we employed serial replating CFU assays of expanded murine HSCs47, 48 to assess vector integration-related genotoxicity. The murine CFU assays demonstrated that MLV.SIN.SF IN_WT and MLV.SIN.SF IN_W390A potently transformed murine HSCs, whereas fusion of the CBX1 chromodomain to MLV IN W390A (MLV.SIN.SF IN_W390A-CBX ) resulted in a significantly reduced transformational incidence (p < 0.05, Figure 5E).…”

Engineering Stem Cells for Therapy

“…For example, hematopoietic stem cells (HSCs), the best characterized adult mammalian SC type of selfrenewing cell produce progenitors that differentiate into all lineages of mature blood cells [44,45]. MSCs differentiate towards mesodermal tissue type cells like chondrocytes, osteoblast and adipocytes under appropriate conditions [46,47].…”

Issues in stem cell plasticity

“…There are ethical concerns about the use of ES cells from human embryos for therapeutic purposes. In contrast, adult or tissue-specific stem cells have been used in clinical setting for hematological disorders for many years [39,40,41].…”