Human Emt tyrosine kinase is specifically expressed both in mature T-lymphocytes and T-cell associated hematopoietic malignancies.

The pattern of expression of the human Emt tyrosine kinase was established in healthy individuals and hematological malignancies by RT-PCR from bone marrow and blood samples, fractionated into T-cells, B-cells, monocytes, granulocytes and thrombocytes. Previously studied mostly in murine samples or established human cell lines, the in vivo correlation was here further clarified. In hematopoietic cells, expression of the EMT gene was associated with T-cell fractions, but Emt was not detected in cord blood CD34+ cells. In fetal tissues, Emt mRNA was strongly expressed in thymus, no expression could be detected in non-hematopoietic tissues. The expression pattern of the 48 malignant bone marrow samples (23 ALL, 1 PLL, 9 AML, 7 CLL and 8 CML cases) paralleled the findings from normal hematopoietic cells: 9/11 T cell associated ALLs, as well as one T-PLL sample, but only 1/12 samples of B-ALL expressed Emt markedly. Only minor signs of Emt expression could be shown in the AML samples, while CML and CLL samples were totally devoid of expression. In addition the Emt protein could be detected by Western blotting from T-lymphocytes and T-cell associated ALL, corresponding to mRNA expression. In conclusion, Emt (Itk) is T-cell associated both in normal and leukemic cells, but is not expressed in cord blood CD34+ cells, suggesting that Emt expression is switched on only later in T-cell development. In addition, an association between Emt and CD2 expression remains even in malignancies.