The phenotypic plasticity of myeloma plasma cells as expressed by dedifferentiation into an immature, resilient, and apoptosis-resistant phenotype.
OBJECTIVE
We previously showed the ability of osteoclasts to support myeloma plasma cell survival and proliferation in vivo and ex vivo. The aim of the current study was to investigate osteoclast-induced phenotypic changes associated with long-term survival of myeloma cells in coculture.


METHODS
CD138-selected myeloma plasma cells from 16 patients were cocultured with human osteoclasts for up to 20 weeks.


RESULTS
Precultured cells were typically CD45(low/intermediate) CD38(high) CD138(high), CD19(-)CD34(-). After >6 weeks, the phenotype of cocultured myeloma cells consistently shifted to cells expressing CD45(intermediate/high) CD19(low) CD34(low). Expression of CD38 and CD138 were reduced to subpopulations with CD38(intermediate) and CD138(low) levels. Morphologically, cocultured plasma cells became plasmablastic. Blocking interleukin-6 activity did not affect the immature phenotype of myeloma cells. The effect of dexamethasone on myeloma cells cultured alone or in cocultures at baseline and after 6 weeks of coculture was determined. When baseline myeloma cells were cultured alone, dexamethasone significantly increased the percentage of apoptotic cells over the spontaneous rate. Conversely, myeloma cells recovered from cocultures had high survival rates and were resistant to dexamethasone-induced apoptosis. Long-term coculture of normal CD34-expressing hematopoietic stem cells (HSC) resulted in loss of CD34 expression, suggesting a common mechanism for osteoclast-induced myeloma and HSC plasticity.


CONCLUSIONS
This study indicates that myeloma cells have plasticity expressed by their ability to reprogram, dedifferentiate, and acquire autonomous survival properties.
Yaccoby
Shmuel
S
Myeloma Institute for Research and Therapy, University of Arkansas for Medical Sciences, Little Rock, 72205, USA. yaccobyshmuel@uams.edu
D018941:Antigens, CD19 / Q000096:biosynthesis; D018952:Antigens, CD34 / Q000096:biosynthesis; D017209:Apoptosis; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002454:Cell Differentiation; D002470:Cell Survival; D018920:Coculture Techniques; D003907:Dexamethasone / Q000494:pharmacology; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006412:Hematopoietic Stem Cells / Q000166:cytology; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D017493:Leukocyte Common Antigens / Q000096:biosynthesis; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D009101:Multiple Myeloma / Q000473:pathology*; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism; D010641:Phenotype; D010950:Plasma Cells / Q000473:pathology*; D011509:Proteoglycans / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053668:Syndecan-1; D053667:Syndecans; D013997:Time Factors; D015854:Up-Regulation
D018941:Antigens, CD19; D018952:Antigens, CD34; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D011509:Proteoglycans; C508241:SDC1 protein, human; D053668:Syndecan-1; D053667:Syndecans; D003907:Dexamethasone; D017493:Leukocyte Common Antigens; D001973:Bromodeoxyuridine