Clonal Dominance of Hematopoietic Stem Cells Triggered by Retroviral Gene Marking

Abstract

Gene marking with replication-defective retroviral vectors has been used for more than 20 years to track the in vivo fate of cell clones. We demonstrate that retroviral integrations themselves may trigger nonmalignant clonal expansion in murine long-term hematopoiesis. All 29 insertions recovered from clones dominating in serially transplanted recipients affected loci with an established or potential role in the self-renewal or survival of hematopoietic stem cells. Transcriptional dysregulation occurred in all 12 insertion sites analyzed. These findings have major implications for diagnostic gene marking and the discovery of genes regulating stem cell turnover.

Significant increase of self-renewal in hematopoietic cells after forced expression of EVI1

“…A constellation of intrinsic and extrinsic cellular mechanisms regulates the balance of self-renewal and differentiation in all stem cells and the genetic and molecular mechanisms responsible for the choice of a HSC between these two directions remain to be elucidated. It has recently been reported that retroviral integration in the MDS1/ EVI1 locus leads to the emergence of a dominant hematopoietic clone with enhanced expansion and self-renewal potential [3][4][5]. The MDS1/EVI1 locus encodes 2 major proteins, MDS1/EVI1 and EVI1, but it is not yet known whether one of them is responsible for the emergence of the dominant hematopoietic clone.…”

“…More recently it was reported that there is a significant long-term survival of hematopoietic clones after retroviral integration in the MDS1/EVI1 locus in nonsusceptible mouse strains. However in these animals the retroviral integration does not induce leukemia but it rather leads to the expansion of a nonmalignant clone in long-term hematopoietic progenitors [3]. This effect of retroviral integration in the MDS1/EVI1 locus leading to the emergence of a dominant hematopoietic stem cell clone is not limited to the mouse.…”

Absence of retroviral vector-mediated transformation of gene-modified T cells after long-term engraftment in mice

“…Genomic insertion of marker genes in mouse bone marrow stem cells has resulted in the production of immortalized cell lines in vitro 20 and can produce nonmalignant clonal expansion of hematopoietic stem cells in vivo. 21 Deregulation of cell growth can also proceed further following retroviral transduction, leading to transformation and malignancy following the use of retroviral vectors encoding oncogenes or growth factors, [22][23][24] and the location of viral insertion was thought to play a role in the transforming process. There is also evidence that vectors encoding a marker gene, truncated nerve growth factor receptor, can also lead to leukemia, 25 although other studies have not found this to be the case.…”

Overcoming barriers to the clinical utilization of iPSCs: reprogramming efficiency, safety and quality

“…Methods to overexpress the reprogramming factors that rely on genomic integration within the starting cells have earned much criticism, as the resultant iPSCs also carry the same genomic integrations. The very presence of viral integrations within the genome elicits insertional mutagenesis and reactivation of proximal oncogenes, thus drastically altering cellular properties such as proliferation rate (Kustikova et al, 2005). Furthermore, after such iPSCs are differentiated and the pluripotent state is exited, the silenced integrated reprogramming factors can be reactivated within the subsequent differentiated cells-thus, when such iPSCs are used to form chimeras, the resultant chimeras had a proclivity for tumorigenesis, likely due to spontaneous reactivation of the reprogramming factor c-Myc, which is an oncogene .…”