Our long-term objective is to develop sufficient understanding of the critical differences between CML and normal hematopoietic progenitor cells to enable one to develop more selective treatment. Our studies will focus on comparative differences between early normal and CML progenitors because, based on evidence already obtained in our laboratory, differences in the early progenitors appear to be most revealing in identifying possible therapeutically exploitable differences. We have developed the necessary methods and expertise to highly concentrate subpopulations of early progenitors and to carry out a wide variety of biological, molecular and protein analyses using relatively few cells. An important concept which has come from our recent research in CML is that the major biological abnormality in the initial phase of the disease is one discordant maturation and that the dominance of the leukemic population is not due to unregulated proliferation, but rather to abnormal maturation and expansion in the later maturational compartments which are not under strict regulatory control. The altered tyrosine kinase activity of the p210bcr/abl fusion protein in CML cells presumably changes the normal pattern of phosphorylation of key regulatory proteins in the signal transduction pathways so that the genes which normally direct the orderly sequence of proliferation and maturation of the myeloid progenitors are not properly regulated. The results of this 'disregulation' are that there is asynchronous development of the nucleus and cytoplasm, and the leukemic cells go through one or more additional divisions during passage through the maturation compartments than do comparable normal precursors. We have constructed a mathematical model of granulocytopoiesis which illustrates the close linkage between the proliferative and maturational abnormalities in CML, and are now developing a more elaborate time- dependent model. A critical but as yet unanswered question is what is the primary event brought about by the increased tyrosine kinase activity of the bcr/abl gene product which leads to the initiation of slightly earlier cytoplasmic maturational event(s)? To address this question, we are currently focusing on studies aimed at identifying differences in proteins constitutively phosphorylated on tyrosine in whole cell lysates of comparable primary early blast subpopulations derived from normal and chronic phase CML marrows as well as the blastic phase of CML. In preliminary studies, we have consistently observed a pp62 protein constitutively tyrosine phosphorylated in purified CML blasts that is not detectable in comparable normal blasts, and we are now trying to characterize, purify, and sequence this protein. The presence of a unique protein containing tumor specific amino acid sequences at the fusion point may also allow the development of an immunological approach (T cell mediated) to therapy.