Expression of CD26 and DPP IV in T-acute lymphoblastic leukemia: Comparison of immunocytochemistry with enzyme cytochemistry

The possible identity of dipeptidyl peptidase IV (DPP IV) enzymatic activit y and CD26 antigen expression in phenotypically defined T-acute lymphoblast ic leukemia cells (T-ALL) was examined. For comparative studies, the combin ation of immunocytochemistry and enzyme cytochemistry methods was used. The strong correlation between the CD26 antigen expression and DPP IV positivi ty in the majority of T-lymphoblasts in TALL patients was evident. No CD26 antigen was expressed on DPP IV negative T-cells. The variable CD4 and/or C D8 antigen expression, frequent CD5 and CD7 positivity and absence of surfa ce membrane CD3 antigen were the characteristic immunophenotypic features o f CD26/DPP IV positive T-lymphoblasts. Moreover, the clear CD71 and CD26/DP P IV coexpression suggested the association of CD26/DPP IV positive cells w ith proliferation. The immunophenotype of CD26/DPP IV positive T-lymphoblas ts seems to be characteristic for the relative immature cell population In addition, noteworthy was the slight disassociation between the very high CD 26 antigen expression and moderate DPP IV activity in cells of some TALL pa tients. The possible existence of enzymatically inactive structures of CD26 antigen or inactive precursors of DPP IV detectable only by immunocytochem istry was discussed. Our study indicates that CD26 antigen expression is te nded to identify cells with DPP IV enzymatic activity in T-ALL patients. Th e results provide some more information of CD26 antigen involvement in the pathology of leukemic cells via its DPP IV enzyme activity.