Figure 4.

The metastatic BM niche contains a specific MSC subtype. Metastatic disease in the BM is defined based on qPCR positivity as BM^pos and qPCR negativity as BM^neg (A) Frequency of MSCs in diagnostic BM aspirates of patients relative to the number of BM-mononuclear cells (BM-MNC) (BM^pos n = 33, BM^neg n = 5). MSCs are detected by flow cytometry using the classical MSC-panel (CD34−, 45−, 90+, 105+) and subtype distribution is analyzed based on CD146 and CD271 expression. Dotted line marks average MSC level in control adult BM (n = 5). (*) p < 0.05. (B) MSC (-subtype) levels in BM samples grouped based on stage and extent of BM infiltration (as determined by qPCR). Patients were diagnosed as ‘localized’ when there was no evidence of metastases by ¹²³I-MIBG scintigraphy and morphological examination of BM smears/biopsies. Based on RT-qPCR results, we classified them as negative (n = 5) or positive. qPCR positive localized BM samples (n = 5) all contain less than 0.01% tumor cells. For stage 4 NB-patients (i.e., with metastases) the extent of BM infiltration is classified as <0.1% (n = 12), 0.1–10% (n = 7), or >10% (n = 9). Number of BM samples positive for CD146+CD271− MSC is indicated in brackets above the bar. (C) Relative contribution of distinct MSC subtypes to the MSC compartment in diagnostic BM of NB-patients compared to fetal and adult BM. Adult MSCs: n = 4, fetal MSCs: n = 6. Data from fetal MSCs is adapted from Maijenburg et al., 2012 [36].