WT1 and cancer: RT-PCR using 4a-forward and Ex6-reverse primer pair (Fig 4A) that amplified only the Ex4a(+)WT1 isoform was performed in six WT1-expressing cancer cell lines (AZ-521, HT-1080, LU99B, K562, Kasumi-1, and HL60) and one WT1-expressing normal kidney cell line 293 (Fig 4B).