To validate our experimental approach, we first analyzed CpG1 island methylation in two cell types: THP-1 (acute monocytic leukemia cell line, hematopoietic origin) and 293TT (human kidney epithelial, non-hematopoietic origin), where the tissue specific expression of SHP-1 is driven by two different and mutually exclusive promoters P2 and P1, respectively. The gene discussed is PTPN6; the disease is acute monocytic leukemia.