Eight cases each of erythroleukemia (AML-M6) and erythroblastic crisis of chronic granulocytic leukemia (CGLBCE) were lmmunophenotyped with the help of a panel of lineage associated monoclonal antibodies (McAbs). The latter Included those reactive with erythrold progenitor (BFU-E and CFU-E) and erythrold precursors at dmerent stages of maturation.
In six of eight cases of AML-M6, efythroblasts revealed an Immature phenotype, as evident from reactivity of the blast cells with McAbs directed against the earlier stages of erythrold maturation. One case had the phenotype of CFU-E, and In the remaining case of AML-M6 the erythroblasts showed a "mature" surface antigenic profile. This lmmunophenotyplc spectrum was unrelated to the morphologk maturity of the erythroblasts.
In two caws of CGLBCE, an early erythroblastlc phenotype was observed, while In as many cases a "mature" phenotype was present. Four of elght cases, however, revealed a mixed, erythrold plus myeloid phenotype. In one of the four cases, two separate blast populations, which represented erythroblasts and myeloblasts, could be Identtfled. In the remaining three cases the blasts wem morphologically homogeneous and undifferentiated.
High Incidence of HLA-DR positivity In the latter three cases suggests the prlmitlve nature of blasts cells and their C~OS~IKJSS to the putative "bipotent" myelold stem cell. Our study has shown phenotypic heterogeneity of blast cells In AML-M6 and CGLBCE.