Detection of MRD during follow-up of ALL patients. (A) Schematic diagram of relative frequencies of ALL cells in BM during and after treatment. I, induction treatment; C, consolidation treatment; II, reinduction treatment. The detection limit of cytomorphology and the detection limit of immunophenotyping and PCR techniques is indicated. (B) Follow-up of a T-ALL patient with CD5/TdT double immunofluorescence microscopy.⁵⁸  The frequencies of the T-ALL cells in blood and BM are very comparable in this patient. D, diagnosis; CR, complete remission; Re, relapse.