[Phenotypic analysis of immature T-lineage cells]

The characteristics of very immature T-lineage blasts including co-expression of myeloid properties and the distinctions between the phenotypes of pro-thymic (CD7+ CD5+ CD2+ CD3- CD4- CD8- or more immature) and thymic (CD3- CD4+ CD8+ or more mature) blasts are shown. The lineage-derivation of CD7+ CD5- CD2- and CD7+ CD5+ CD2- lymphoid blasts was investigated based on the gene expression of CD3 epsilon, CD3 delta and myeloperoxidase (MPO). The former group included 4 categories; undifferentiated blasts without commitment to myeloid or T-lineage, T-lineage blasts with mRNA of CD3 epsilon, T/myeloid blasts with mRNA of CD3 epsilon and MPO and blasts with mRNA of MPO. The latter included 2 categories; T-lineage blasts with CD3 epsilon and CD3 delta mRNA and T/myeloid blasts with CD3 epsilon, CD3 delta and MPO mRNA. Thus, CD3 epsilon was expressed at a more immature stage than CD3 delta. The blasts at the pro-thymic stage were different from those at the thymic stage in several respects. The T-cell receptor (TCR) beta-chain gene showed a germ-line configuration in most pro-thymic blasts. The CD13/CD33, CD11b and class II MHC antigens were expressed very frequently in the pro-thymic stage. The CD21 antigen was most selectively expressed at the thymic stage. Pro-thymic blasts were of RA type of CD45 antigen, while thymic blasts were of RO type. Recombination activation gene-1 (RAG-1) was only limitedly expressed at the pro-thymic stage, but was highly expressed at the thymic stage. These findings indicate that there are distinctive differences before and after the initiation of clonal selection which is unique and thymus-specific, and that the neoplastic cells represent each stage of T-lineage differentiation involving the unique thymic function.