Correlation of CXCR-4 expression and SDF-1–induced transendothelial migration of primary AML blasts. A positive correlation (r = 0.97) was found between the expression level (mean fluorescence intensity) of CXCR-4 and the percentage of AML blasts (AML no. 1 through AML no. 12) transmigrating in response to SDF-1 (addition of SDF-1–containing conditioned medium to the lower chamber of the transmigration system).