The genomic sequencing technique has been applied to assess the state of methylation in the
DNA from human leukocyte subpopulations from healthy individuals and in the
DNA from several individuals with myeloid or lymphatic
leukemias or non-Hodgkin
lymphomas. Leukocyte populations were purified by the high-gradient magnetic cell sorting technique. In the human
tumor necrosis factor alpha (
TNF-alpha) gene segment between
nucleotides 300 and 1150, the specific methylation profile in the
DNA from human granulocytes and monocytes is maintained in three cases of
myeloid leukemia. In one such case, all
5-methyl-2'-deoxycytidine residues have been replaced by
cytidine. In a chronic lymphatic
T-cell leukemia, all
5-methyl-2'-deoxycytidine residues have been substituted by
cytidine. In normal B lymphocytes, in two cases of chronic lymphatic
B-cell leukemias and two cases of non-Hodgkin
lymphomas, all 5'-CG-3' sequences in this gene segment are devoid of methylation. In the
TNF-beta gene, DNA methylation is decreased in several examples of acute or
chronic myeloid leukemias in comparison to normal human granulocytes or monocytes, whose
DNA is almost completely methylated between
nucleotides 700 and 900. In human T and B lymphocytes, the main producers of
TNF-beta, in three instances of
chronic lymphatic leukemias and two cases of non-Hodgkin
lymphomas, all 5'-CG-3' sequences are unmethylated in this region. The
DNA from the human HeLa cell line is highly methylated at all 5'-CG-3' sequences in the
TNF-alpha and -beta genes. The
TNF-alpha gene is transcribed in the cells of one case of
acute myeloid leukemia in which the analyzed region of the
TNF-alpha gene is completely unmethylated. The
TNF-beta gene is not transcribed in any of the malignant cells tested.