Promoter DNA methylation of CD10 in infant acute lymphoblastic leukemia with MLL/AF4 fusion gene

Abstract

10045 Background: Infant ALL displays distinct biologic and clinical features with a poor prognosis. The CD10-negative immunophenotype of infant ALL is a hallmark and provides a predictable signature of MLL rearrangements. While CD10 negativity reflects an earlier stage of B-cell development, complete IgH gene rearrangements (VDJH) show more mature IgH status. Discordance between immunophenotype and genotype of infant ALL suggests an aberrant process in immunophenotypic steps of differentiation or a secondary down-regulation of CD 10 expression associated with MLL rearrangements. We performed methylation analysis of full promoter regions of the CD10 gene to investigate epigenetic mechanisms responsible for CD10 negativity. Methods: CD10-negative infant ALL with MLL/AF4, CD10-positive infant ALL with germ-line MLL, CD10-positive pre-B ALL cell line, infant AML (M5) with MLL/AF9 and pediatric AML (M2) with AML1/ETO were analyzed for VDJH status and methylation of CD10 gene promoters. Results: Three of 4 cases with infant ALL revealed complete rearrangements of VDJH gene with productive joints. Bisulfite sequencing of CD 10 type 1 and 2 promoters identified more than 84% of methylated CpG dinucleotides in all three CD10-negative infant ALL cases with MLL/AF4. The CpG dinucleotides distributed in the clusters of putative Sp 1 binding sites and functionally active regulatory regions of the promoters were fully methylated. In contrast, none or a few of the CpG dinucleotides were methylated in the CD10-positive ALL, AML (M5) with MLL/AF9 or AML (M2) with AML1/ETO. Conclusions: Structural evidence of dense methylation in the CD 10 gene promoter suggested that methylated transcription factor binding sites contribute to CD10 silencing as an epigenetic mechanism. [Table: see text] No significant financial relationships to disclose.