CD47 and acute myeloid leukemia: hSIRPα.40A showed potent antagonism of the two most prevalent SIRPα alleles (e.g. SIRPαV1 and SIRPαV2), as determined by blockade of CD47 binding to U-937 and THP-1 AML cell lines that express SIRPαV1 (data not shown) and SIRPαV2 [32], respectively (Fig. 2b).