B Lymphocyte Differentiation in Chronic Myeluid Leukemia is not Hampered by the Acquisiiion of the Philadelphia (Ph) Chromosome.

Chronic myelogenous leukemia (LMC) is a clonal neoplastic disease of the hemopoietic sistem 1 In more t:, an 90% of cases a character, stic chromosomal abnorrnality, the Ph chromosome is present in the myeloid cells 2 . This chromosomal marker derives from a reciprocal unbalanced translocation of genetic material between the long arm of chromosome 9 and of chromosome 22 3 . As a consequence of this translocation the c-abl gene mapped on chromosome 9 move into the middle of a region named breakpoint cluster region ( bcr) located on chromosome 22 4 . The normal ensuing gene complex bcr-abl, produces an 8 Kb mRNA, different from the normal 5. 5 Kb mRNA product of the c-abl gene, and an anomalous P210 protein which, although related to their normal P145 c-abl poroduct displays constitutive tyrosine kinase activity 5 - 6 - 12 .