The cellular targets of primary mutations and malignant transformation remain elusive in most cancers. Here, we show that clinically and genetically different subtypes of acute lymphoblastic leukemia ...(ALL) originate and transform at distinct stages of hematopoietic development. Primary ETV6-RUNX1 (also known as TEL-AML1) fusions and subsequent leukemic transformations were targeted to committed B-cell progenitors. Major breakpoint BCR-ABL1 fusions (encoding P210 BCR-ABL1) originated in hematopoietic stem cells (HSCs), whereas minor BCR-ABL1 fusions (encoding P190 BCR-ABL1) had a B-cell progenitor origin, suggesting that P190 and P210 BCR-ABL1 ALLs represent largely distinct tumor biological and clinical entities. The transformed leukemia-initiating stem cells in both P190 and P210 BCR-ABL1 ALLs had, as in ETV6-RUNX1 ALLs, a committed B progenitor phenotype. In all patients, normal and leukemic repopulating stem cells could successfully be separated prospectively, and notably, the size of the normal HSC compartment in ETV6-RUNX1 and P190 BCR-ABL1 ALLs was found to be unaffected by the expansive leukemic stem cell population.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Global gene expression profiling of highly purified 5q-deleted CD34+CD38−Thy1+ cells in 5q− myelodysplastic syndromes (MDSs) supported that they might originate from and outcompete normal ...CD34+CD38−Thy1+ hematopoietic stem cells. Few but distinct differences in gene expression distinguished MDS and normal stem cells. Expression of BMI1, encoding a critical regulator of self-renewal, was up-regulated in 5q− stem cells. Whereas multiple previous MDS genetic screens failed to identify altered expression of the gene encoding the myeloid transcription factor CEBPA, stage-specific and extensive down-regulation of CEBPA was specifically observed in MDS progenitors. These studies establish the importance of molecular characterization of distinct stages of cancer stem and progenitor cells to enhance the resolution of stage-specific dysregulated gene expression.
Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia. Within MDS, 5q− syndrome ...constitutes a distinct clinical entity characterized by an isolated deletion of the long arm of chromosome 5 (5q−), a relatively good prognosis, and infrequent transformation to acute leukemia. The cell of origin in 5q− syndrome as well as in other 5q-deleted MDS patients has not been established, but evidence for involvement of multiple myeloid (but not lymphoid) lineages has suggested that a myeloid-restricted progenitor rather than a pluripotent (lympho-myeloid) stem cell might be the primary target in most patients. Although in 9 patients no evidence of peripheral blood T-cell and only 1 case of B-cell involvement was found, the data herein support that 5q deletions occur in hematopoietic stem cells (HSCs) with a combined lympho-myeloid potential. First, in all investigated patients a minimum of 94% of cells in the minor CD34+CD38− HSC compartment were 5q deleted as determined by fluorescence in situ hybridization. Second, in 3 of 5 patients 5q aberrations were detected in a large fraction (25% to 90%) of purified CD34+CD19+ pro-B cells. Furthermore, extensive functional characterization with regard to responsiveness to early-acting cytokines, long-term culture-initiating cells, and nonobese diabetic/severe combined immunodeficiency repopulating cells supported that MDS HSCs in 5q-deleted patients are CD34+CD38−, but inefficient at reconstituting hematopoiesis.
Clonality studies of mature cells suggest that the primary transformation event in myelodysplastic syndrome (MDS) most frequently occurs in a myeloid-restricted progenitor, a hypothesis supported by ...recent studies of purified CD34+Thy1+hematopoietic stem cells (HSCs) in cases with trisomy 8 (+8). In contrast, we recently demonstrated that a lymphomyeloid HSC is the target for transformation in MDS cases with del(5q), potentially reflecting heterogeneity within MDS. However, since +8 is known to frequently be a late event in the MDS transformation process, it remained a possibility that CD34+CD38−Thy1+ HSC disomic for chromosome 8 might be part of the MDS clone. In the present studies, although a variable fraction of CD34+CD38−Thy1+ cells were disomic for chromosome 8, they did not possess normal HSC activity in long-term cultures and nonobese diabetic–severe combined immunodeficiency (NOD-SCID) mice. Mixing experiments with normal CD34+CD38− cells suggested that this HSC deficiency was intrinsic and not mediated by indirect mechanisms. Furthermore, investigation of 4 MDS cases with combined del(5q) and +8 demonstrated that the +8 aberration was always secondary to del(5q). Whereas del(5q) invariably occurs in CD34+CD38−Thy-1+ HSCs, the secondary +8 event might frequently arise in progeny of MDS HSCs. Thus, CD34+CD38−Thy1+ HSCs are invariably part of the MDS clone also in +8 patients, and little HSC activity can be recovered from the CD34+ CD38−Thy1+ HSC. Finally, in advanced cases of MDS, the MDS reconstituting activity is exclusively derived from the minor CD34+CD38−HSC population, demonstrating that MDS stem cells have a similar phenotype as normal HSCs, potentially complicating the development of autologous transplantation for MDS.
This study shows that even in patients with del(5q) myelodysplastic syndrome who become transfusion-independent in response to lenalidomide, a myelo-dysplastic syndrome stem cell persists that is ...lenalinomide-resistant, continues to acquire genetic defects, and can cause relapse.
The concept that rare cancer stem cells might be required and sufficient to propagate a cancer is not new and has been supported by experimental evidence, first in leukemia
1
and subsequently in solid tumors.
2
Implicit in the cancer stem-cell model are the hypotheses that cancer stem cells are distinct, rare populations of cancer cells and that they may be particularly resistant to conventional cancer therapies.
More recently, key aspects of the cancer stem-cell concept have been questioned, and studies have indicated that at least in some malignant conditions, cancer stem cells are neither rare
3
,
4
nor phenotypically distinct.
5
,
6
However, . . .
Flt3 has emerged as a potential regulator of hematopoietic stem cells (HSC). Sixty percent of cells in the mouse marrow Lin
−Sca1
+c-kit
+ HSC pool expressed flt3. Although single cell cloning showed ...comparable high proliferative, myeloid, B, and T cell potentials of Lin
−Sca1
+c-kit
+flt3
+ and Lin
−Sca1
+c-kit
+flt3
− cells, only Lin
−Sca1
+c-kit
+flt3
− cells supported sustained multilineage reconstitution. In striking contrast, Lin
−Sca1
+c-kit
+flt3
+ cells rapidly and efficiently reconstituted B and T lymphopoiesis, whereas myeloid reconstitution was exclusively short term. Unlike c-kit, activation of flt3 failed to support survival of HSC, whereas only flt3 mediated survival of Lin
−Sca1
+c-kit
+flt3
+ reconstituting cells. Phenotypic and functional analysis support that Lin
−Sca1
+c-kit
+flt3
+ cells are progenitors for the common lymphoid progenitor. Thus, upregulation of flt3 expression on Lin
−Sca1
+c-kit
+ HSC cells is accompanied by loss of self-renewal capacity but sustained lymphoid-restricted reconstitution potential.
Abstract 2609
Human primitive stem cells reside in the CD34+CD38- fraction in cord blood and bone marrow. However, there is a high level of heterogeneity in these cell fractions, and the phenotype of ...the rare primitive stem cells remains poorly defined. We have studied expression of integrin alpha2 chain, a member of a family of beta1 integrin cell adhesion receptors, in CD34+CD38- cells in adult bone marrow and cord blood. >90% of bone marrow CD34+CD38- cells and >95% of CD34+CD38-CD90+ cells, enriched in long-term in vivo reconstituting stem cells (Majeti et al., Cell Stem Cell 1:635, 2007) expressed the integrin alpha2 chain. In contrast, in cord blood CD34+CD38- and the CD34+CD38-CD90+ subpopulation, the integrin alpha2 chain was expressed only in 37.1+/− 5.3% and 32.2+/− 4.9% of the cells (mean+/− SD), respectively. To determine whether integrin alpha2 expression could be used to identify functionally distinct stem and progenitor cell populations in cord blood and bone marrow, we isolated CD34+CD38- integrin alpha2+ and alpha2- cells by flow cytometry and analyzed these by in vivo transplantation into immunodeficient NOD/SCID-IL2Rgammacnull (NSG) mice and by in vitro progenitor cell assays (long-term culture initiating cell, LTC-IC, and colony assays). Transplantation of cord blood CD34+CD38- integrin alpha2+ cells resulted in significantly higher level of human CD45+ (p<0.05), myeloid (p<0.01) and CD34+ (p<0.05) cell engraftment at 16–18 weeks after transplantation than integrin alpha2- cells (reconstitution/300 cells in age and sex matched recipients, Figure 1). In contrast, there were no differences in reconstitution at 12 weeks in mice transplanted with cord blood CD34+CD38- alpha2+ and alpha2- cells. Because of lower engraftment capacity of adult bone marrow cells in immunodeficient mice, bone marrow CD34+CD38- cells were analyzed after intra-bone transplantation. After 12 weeks only few mice transplanted with the CD34+CD38- integrin alpha2+ cells but none transplanted with the corresponding alpha2- cells were reconstituted with human CD45+ or myeloid cells at a level '0.1%. The LTC-IC progenitors within the CD34+CD38- populations, assayed after 6 weeks culture on stroma, in adult bone marrow were highly enriched in the alpha2+ as compared with alpha2- fraction (mean +/− SD 96.7+/− 57.0 and 0.2+/− 0.6 colonies/50 cells, respectively), whereas in cord blood they resided equally in both integrin alpha2+ and alpha2- cell fractions (mean +/− SD 77.4+/− 59.4 and 108.8+/− 96.0 colonies/50 cells, respectively). The lineage committed CFU-GM and BFU-E progenitors in adult bone marrow were within integrin CD34+CD38- alpha2+ and alpha2- fractions (mean +/− SD 8.5+/− 5.3 and 14.9+/− 16.2 colonies/100 cells, respectively), whereas in cord blood they were significantly enriched in the alpha2- fraction (mean +/− SD 9.3+/− 5.5 and 22.0+/− 6.7 colonies/100 cells in alpha2+ and alpha2- fractions, respectively). Taken together, our results show expression of integrin alpha2 receptor in most of the primitive cord blood long-term in vivo reconstituting stem cells, with a gradual loss of the integrin alpha2 receptor during maturation to short term in vivo reconstituting stem cells, LTC-IC and lineage committed progenitors. Furthermore, our findings show distinct ontogeny-related differences in the expression of the integrin alpha2 receptor in the functionally defined primitive and lineage-committed CD34+CD38- progenitors, indicating differences in cellular interactions of cord blood and bone marrow progenitors with the hematopoietic niches.
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Ekblom:Bristol-Myers Squibb: Honoraria.
Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia. Within MDS, 5q− syndrome ...constitutes a distinct clinical entity characterized by an isolated deletion of the long arm of chromosome 5 (5q−), a relatively good prognosis, and infrequent transformation to acute leukemia. The cell of origin in 5q− syndrome as well as in other 5q-deleted MDS patients has not been established, but evidence for involvement of multiple myeloid (but not lymphoid) lineages has suggested that a myeloid-restricted progenitor rather than a pluripotent (lympho-myeloid) stem cell might be the primary target in most patients. Although in 9 patients no evidence of peripheral blood T-cell and only 1 case of B-cell involvement was found, the data herein support that 5q deletions occur in hematopoietic stem cells (HSCs) with a combined lympho-myeloid potential. First, in all investigated patients a minimum of 94% of cells in the minor CD34+CD38− HSC compartment were 5q deleted as determined by fluorescence in situ hybridization. Second, in 3 of 5 patients 5q aberrations were detected in a large fraction (25% to 90%) of purified CD34+CD19+ pro-B cells. Furthermore, extensive functional characterization with regard to responsiveness to early-acting cytokines, long-term culture-initiating cells, and nonobese diabetic/severe combined immunodeficiency repopulating cells supported that MDS HSCs in 5q-deleted patients are CD34+CD38−, but inefficient at reconstituting hematopoiesis.
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