To determine the nature of deregulated molecular events during CLL and PTCL development in Dnmt3aΔ/Δ mice we performed global methylation analysis by Whole Genome Bisulfite Sequencing (WGBS) and gene expression profiling by RNA-seq on B220+ CD19+ CD5+ (B-1a cells) and CD8-positive T cells isolated from Dnmt3a+/+ spleens, as these cellular populations are immunophenotypically the closest normal counterparts of CLL and PTCL cells, respectively. This evidence concerns the gene CD5 and B-cell chronic lymphocytic leukemia.