Monoclonal antibody OKT17 recognizes most cases of T-cell malignancy

Membrane phenotype analysis with monoclonal antibodies (McAb) has demonstrated great heterogeneity within the T-cell malignancies. We describe here the reactivity with an anti-T cell McAb, OKT17, in 80 leukaemia samples. Cells from all types of T-cell leukaemia (48 cases), except from the small group of pre-T-ALL, strongly expressed the antigen identified by OKT17 whereas none of the 32 non-T leukaemias were OKT17 positive. When the reactivity of OKT17 was compared with that of other pan-T markers, OKT17 was positive in a larger number of T-cell leukaemias: 87% of cases compared with 74% with E-rosettes and 73% with the McAb 3A1. In the mature or post-thymic proliferations OKT17 was positive in 96% of cases, compared with 77% with E-rosettes and 61% with 3A1. The latter reagent, on the other hand, was better than OKT17 for detecting leukaemias with a thymic phenotype, 100% and 68% of positive cases respectively. The combined use of OKT17, 3A1 and terminal transferase permits a more precise classification of all the T-cell leukaemias according to the main stages of T-cell differentiation.