Multiple myeloma (MM) is a B-cell neoplasm characterized by clonal proliferation of malignant plasma cells in the bone marrow (BM). The development of new drugs has increased survival time, but the disease is still incurable. Recently, the BM microenvironment has been reported to play an important role in proliferation and survival of MM cells, suggesting that clarification of the interaction between BM stromal cells and MM cells may provide insights to allow the development of novel treatment strategies for MM.
As the signal between MM cells and the BM microenvironment should be bidirectional, it is possible that MM cells produce signals that alter the BM microenvironment to one appropriate for their survival. To validate this hypothesis, we examined the changes in gene expression profile in human BM-derived mesenchymal stem cells (MSC) by co-culture with MM cell line OPM-2. cDNA array analysis indicated that 2 days of co-culture with OPM-2 induced multiple factors in MSC, which are known to have positive effects on survival of MM cells, such as interleukin-6, insulin-like growth factor-1, stromal cell-derived factor 1, vascular cell adhesion molecule 1 (VCAM1), and intercellular adhesion molecule 1 (ICAM1). Other than known factors, thymic stromal lymphopoietin (TSLP), which is a cytokine involved in progression of pancreatic and breast cancer through induction of T helper 2 cell responses, was found to be upregulated by co-culture (ratio 2.22). To confirm the results of cDNA array analysis, MSC co-cultured with OPM-2 or KMS-34 were tested for expression and secretion of TSLP by real-time PCR and ELISA. Real-time PCR revealed that the expression of TSLP in co-cultured MSC was two to three times higher than that in MSC monocultures. Significantly elevated levels of TSLP secretion from MSC after stimulation with PMA/ionomycin were observed by co-culture with OPM-2 or KMS-34 compared with monoculture (201.3 ± 5.0 pg/ml, 176.1 ± 13.3 pg/ml, and 96.6 ± 5.5 pg/ml, respectively; P < 0.01) as measured by ELISA. TSLP did not exhibit any effect on proliferation or drug resistance of MM cells independent of the level of TSLP receptor expression, therefore we evaluated the immunomodulatory effects of TSLP secreted by MSC. Monocyte-derived dendritic cells (MDDC) were first treated with the supernatant of either MSC or MSC co-cultured with KMS-34. Then, allogeneic naïve CD4+ T cells were co-cultured with pretreated MDDC. MDDC treated with the supernatant of co-cultured MSCs expanded IL-13+ CD4+ T cells to a greater extent than MDDC treated with the supernatant of MSC monocultures (10.3 ± 3.7 %, 5.9 ± 4.2 %, respectively; P = 0.02), and addition of anti-TSLP neutralizing antibodies to the supernatant decreased the expansion of IL-13+ CD4+ T cells (10.3 ± 3.7 %, 7.1 ± 2.6 %, respectively; P = 0.04).
These results suggested that MM cells act to form more advantageous BM microenvironment for their survival through induction of pleiotropic molecules in MSC involved in not only proliferation and survival of MM cells, but also modifying immunological status.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.