Figure 1. Ewing sarcoma cells transition between CXCR4 negative and positive states in vivo.

A. FACS-sorting of TC-32 cells on the basis of cell surface CXCR4 prior to injection into tail veins of NOD-SCID mice. B. FACS-sorting generated cell populations with differential expression of CXCR4 transcript as determined by qRT-PCR. C. Tumors were excised at necropsy and volumes determined. Nine tumors were analyzed in each group (from 5 CXCR4 negative and 8 CXCR4 positive recipient mice). D. A direct correlation was observed between CXCR4 expression, as determined by qRT-PCR, and tumor volume in excised tumors. E. CXCR4 expression in tumors at the time of necropsy as determined by qRT-PCR. Expression of CXCR4 was highly variable. Mean expression was equivalent between the two groups.