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CD20 positive cells are undetectable in the majority of multiple myeloma cell lines and are not associated with a cancer stem cell phenotype

ABSTRACT: Although new therapies have doubled the survival of multiple myeloma (MM) patients, this remains an incurable disease. It has been postulated that the so-called MM Cancer Stem Cells (MM-CSC) would be responsible for tumor initiation and relapse but their unequivocal identification remains unclear. Here, we investigated in a panel of MM cell lines the presence of CD20+ cells harboring a MM-CSC phenotype. Among the multiple cell lines investigated, only a small population of CD20dim+ cells (0.3%) in the RPMI-8226 cell line was found. CD20dim+ RPMI-8226 cells expressed the plasma cell markers CD38 and CD138 and were CD19-CD27-. Additionally, CD20dim+ RPMI-8226 cells did not exhibit stem-cell markers as shown by gene expression profiling and the aldehyde dehydrogenase (ALDH) assay. Moreover, we demonstrated that CD20dim+ RPMI-8226 cells are not essential for CB17-SCID mice engraftment and show lower self-renewal potential than the CD20- RPMI-8226 cells. These results do not support CD20+ expression for the identification of MM-CSC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE33020 | GEO | 2012/02/27

SECONDARY ACCESSION(S): PRJNA148017

REPOSITORIES: GEO

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Project description:Although new therapies have doubled the survival of multiple myeloma (MM) patients, this remains an incurable disease. It has been postulated that the so-called MM Cancer Stem Cells (MM-CSC) would be responsible for tumor initiation and relapse but their unequivocal identification remains unclear. Here, we investigated in a panel of MM cell lines the presence of CD20+ cells harboring a MM-CSC phenotype. Among the multiple cell lines investigated, only a small population of CD20dim+ cells (0.3%) in the RPMI-8226 cell line was found. CD20dim+ RPMI-8226 cells expressed the plasma cell markers CD38 and CD138 and were CD19-CD27-. Additionally, CD20dim+ RPMI-8226 cells did not exhibit stem-cell markers as shown by gene expression profiling and the aldehyde dehydrogenase (ALDH) assay. Moreover, we demonstrated that CD20dim+ RPMI-8226 cells are not essential for CB17-SCID mice engraftment and show lower self-renewal potential than the CD20- RPMI-8226 cells. These results do not support CD20+ expression for the identification of MM-CSC. For detailed description of Material and Methods, see supplementary Methods. The human MM cell lines RPMI-8226, U266, MM1S, MM1R, NCI-H929, RPMI-LR5, U266-LR7 and U266-Dox4 were studied. Cells were cultured as previously described [Ocio, 2009, 3781]. MM cell lines were immunophenotyped using a 7-color immunofluorescence technique [Paiva, 2011, 697], with the following combination of monoclonal antibodies (Pacific Blue (PB)/ anemonia majano cyan (AmCyan)/ fluorescein isothiocyanate (FITC)/ peridinin chlorophyll protein-cyanin 5.5 (PerCP-Cy5.5)/ PE-cyanin 7 (PE-Cy7)/ allophycocyanin (APC)/ alexafluor 700 (AF700)): CD19/CD45/CD20/CD138/CD27/CD56/CD38. Data were stored for a minimum of 3x105 events. CD20dim+ and CD20- RPMI-8226 cells were sorted after incubation with CD20-APC/7AAD and acquisition on a FACSAria cytometer (Becton Dickison Biosciences). Sorting was performed only for viable cells (7AAD-) and debris were excluded by scatter properties. The CD20- and CD20dim+ RPMI-8266 sorted cells had a final purity of 98% and 88%, respectively. CD20dim+ and CD20- RPMI-8226 cells were extensively characterized. Morphological characterization was done with May-Grünwald-Giemsa staining. Characterization of VDJH and IGKappa rearrangements was performed as described elsewhere [BIOMED-2, BMH4-CT98-3936]. The expression of aldehyde dehydrogenase (ALDH) was assessed using the Aldefluor Kit (StemCell Technologies) following manufacturer’s instructions with further staining with a CD20-APC antibody. For gene expression profile studies, RNA was isolated, labeled and hybridized to Human Gene 1.0 ST array (Affymetrix) according to Affymetrix protocols [Gutiérrez, 2005, 402]. The arrays were analyzed using the DNA-Chip Analyzer software (DChip). Fold change ≥2 was considered significant.

Project description:Despite recent advances in the treatment of multiple myeloma (MM), it remains an incurable disease potentially due to the presence of resistant myeloma cancer stem cells (MM-CSC). Although the presence of clonogenic cells in MM was described more than 30 years ago, the phenotype of MM-CSC is still a matter of debate, especially with respect to the expression of syndecan- 1 (CD138). Here, we demonstrate the presence of two subpopulations - CD138++ (95-99%) and CD138low (1-5%) - in eight MM cell lines. To find out possible stem-cell-like features, we have phenotypically, genomic and functionally characterized the two subpopulations. Our results show that the minor CD138low subpopulation is morphologically identical to the CD138++ fraction and does not represent a more immature B-cell compartment (with lack of CD19, CD20 and CD27 surface expression). Moreover, both subpopulations have similar gene expression and genomic profiles. Importantly, both CD138++ and CD138low subpopulations have similar sensitivity to bortezomib, melphalan and doxorubicin. Finally, serial engraftment in SCID mice shows that CD138++ as well as CD138low cells have self-renewal potential and they are also phenotypically interconvertible. Overall, our results differ from previously published data which attribute a B-cell phenotype to MM-CSC and urge the need to explore more reliable markers to discriminate true clonogenic myeloma cells. To compare the gene expression profile of the subpopulations CD138++ and CD138low within the MM cell line, RPMI-8226. RNA was isolated from CD138++ (n=3) and CD138low (n=3) RPMI-8226 cells. RNA was hybridized to Human Gene 1.0 ST array (Affymetrix) according to Affymetrix protocols [Gutierrez, 2005, 402]. Microarray data were normalized using the Robust Multichip Analysis (RMA) algorithm implemented in the Affymetrix Expression Console. Data analysis was carried out using DNA-Chip Analyzer software (DChip). The comparison criteria used in DChip analysis were fold change E/BM-bM-^IM-%2 or B/EM-bM-^IM-%2, mean difference E-B>100 or B-E>100 and the lower 90% confidence bound of fold-change was used

Project description:Background: Mutant BRAF targeted therapies remain a standard of care for the treatment of metastatic malignant melanoma (MM); however high initial response rates are tempered by the persistence of residual MM cells that eventually lead to disease recurrence and mortality. Since MM recurrence during targeted therapy can present with the simultaneous occurrence of multiple tumour nodules at the original body sites, we hypothesised the presence of an intrinsically resistant MM cell sub-population. Objectives: Identify an MM cell subpopulation that is intrinsically resistant to targeted therapy and so may be responsible for MM recurrence. Methods: Using melanoma cell lines, we define culture conditions for reproducible 3D growth of melanospheres to investigate putative cancer stem cell populations. We undertook RNA sequencing and bioinformatic analysis to characterise cell populations between adherent and non-adherent culture, and cells expressing or not expressing CD20. Furthermore, we define an in vitro assay to evaluate killing of melanoma cancer stem cells as a therapeutic test using combination therapies targeting driver mutation and CD20 marker. Results: We have described culture conditions that promote MM cells to form melanospheres with a reproducible colony forming efficiency of 0.3% to 1.3%. RNA sequencing of melanosphere versus conventional MM cell cultures (n=6), irrespective of the BRAF mutation status, showed that melanosphere formation was associated with growth and differentiation transcriptional signatures resembling MM tumours. Importantly, melanosphere formation also led to the emergence of a CD20+ MM cell subpopulation, similar to that observed in primary human MM tumours. CD20+ MM cells were resistant to BRAF inhibitor therapy, and consistent with this finding demonstrated a Forkhead box protein M1 (FOXM1) transcriptomic profile (n=6). Combining BRAF inhibitor and anti-CD20 antibody treatment led to the additional killing of previously resistant CD20+ BRAF mutant MM cells. Conclusions: In MM patients that harbour a CD20+ sub-population, combined therapy with BRAF inhibitor and anti-CD20 antibody could potentially kill residual MM cells and so prevent disease recurrence.

Project description:Despite recent advances in the treatment of multiple myeloma (MM), it remains an incurable disease potentially due to the presence of resistant myeloma cancer stem cells (MM-CSC). Although the presence of clonogenic cells in MM was described more than 30 years ago, the phenotype of MM-CSC is still a matter of debate, especially with respect to the expression of syndecan- 1 (CD138). Here, we demonstrate the presence of two subpopulations - CD138++ (95-99%) and CD138low (1-5%) - in eight MM cell lines. To find out possible stem-cell-like features, we have phenotypically, genomic and functionally characterized the two subpopulations. Our results show that the minor CD138low subpopulation is morphologically identical to the CD138++ fraction and does not represent a more immature B-cell compartment (with lack of CD19, CD20 and CD27 surface expression). Moreover, both subpopulations have similar gene expression and genomic profiles. Importantly, both CD138++ and CD138low subpopulations have similar sensitivity to bortezomib, melphalan and doxorubicin. Finally, serial engraftment in SCID mice shows that CD138++ as well as CD138low cells have self-renewal potential and they are also phenotypically interconvertible. Overall, our results differ from previously published data which attribute a B-cell phenotype to MM-CSC and urge the need to explore more reliable markers to discriminate true clonogenic myeloma cells. To compare the Copy Number Abnormalities of the subpopulations CD138++ and CD138low within the MM cell line, RPMI-8226. DNA was isolated from CD138++ (n=3) and CD138low (n=3) RPMI-8226 cells. The detection of CNA was investigated using the CytoScan HD array (Affymetrix, Santa Clara, CA, USA) which includes more than 2.6 million copy number markers and 750.000 SNPs. Briefly, genomic DNA was digested with Nsp I restriction endonuclease, ligated to adaptors that recognize the cohesive four base pair overhangs and amplified by PCR. PCR product was purified and fragmented with DNAse I and then end-labeled using terminal deoxynucleotidyl transferase and hybridized to the CytoScan HD array. The arrays were processed using the Fluidics Station 450, GeneChip Scanner 3000 7 G and AGCC (AffymetrixGeneChip Command Console Software). For the analysis we employed the AffymetrixM-BM-. Chromosome Analysis Suite (ChAS) Software v2.0 and Nexus Copy Number Software Version 7.0 (BioDiscovery, El Segundo, CA, USA). The complete data set was analyzed by visual inspection using ChAS software. CNA were reported when the three following criteria were achieved: minimum of 50 markers per segment, 200 Kb minimum genomic sizes and 50% overlap with known copy number variants (Database of Genomic Variants).

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CD20 positive cells are undetectable in the majority of multiple myeloma cell lines and are not associated with a cancer stem cell phenotype

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