In vitro chemosensitivity of chronic lymphocytic leukaemia to purine analogues--correlation with clinical course.

Samples from 51 chronic lymphocytic leukaemia (CLL) patients (42 typical, nine atypical) were assessed for in vitro response to fludarabine and cladribine (2-CdA) using the flow cytometric terminal deoxynucleotidyl transferase (TdT) assay. No difference was demonstrated between the in vitro response of typical and atypical CLL and previous treatment did not result in a more apoptosis resistant phenotype. The assay could not distinguish those patients who required subsequent treatment from those whose disease remained stable, and universal cross-resistance/sensitivity to the two purine analogues was demonstrated. The assay's potential for use in the rapid assessment of in vivo response to purine analogue therapy in CLL was limited; correctly predicting the clinical outcome of 10/12 patients to treatment but failing to predict progression in two p53 deficient patients. The level of bcl-2 in the clonal lymphocytes did not influence the in vitro, spontaneous or drug-induced, apoptosis.