Immunological classification of chronic myeloid leukemia distinguishes chronic phase, imminent blastic transformation, and acute lymphoblastic leukemia.

The clinical course of chronic myeloid leukemia (CML) is highly variable and therefore it is difficult to predict the duration of the chronic phase. We studied the immunological expression of maturation patterns in 62 cases of CML (30 cases in clinical/cytological blast crisis (BC), 32 cases in clinical/cytological chronic phase (CP) by means of a double marker enzyme immuno assay (DM-EIA). Immunological findings were supplemented by Southern blots using Ig-JH-, TCRbeta- and bcr-probes. Patients in BC (n = 30) expressed high proportions of CD10, CD20, CD33, CD34 and low degrees of a mature myeloid marker (CD15). Myeloid BC bone marrow (BM) cells showed a high degree of coexpression of unusual, lineage restricted markers: 25% of CD15-positive cells also expressed markers like CD10, CD20 or CD34. In contrast, BM cells in lymphoid BC did not show this coexpression. In CP two groups were distinguished immunologically: concordant cases which were immunologically normal (n = 14) and discordant cases (n = 18) which showed increased proportions of unusual, lineage restricted markers and double labelled cells (e.g. CD15/CD34). The latter group developed clinical BC earlier during further follow up (p = 0.009). Cases of lymphoid BC (n = 11)--in contrast to acute lymphoblastic leukemia (ALL) patients (n = 21)--did not show coexpression of CD15/CD10, CD20, CD34. These data show that blast clones can be detected in CML-CP by characteristic immunological maturation defects several months before the clinical onset of BC. Moreover, the lymphoid "blasts" of CML-BC represent a relatively differentiated lymphoid population of cells which can be distinguished from ALL by their lack of coexpression of unusual, lineage restricted markers.