Residual T lymphocytes as assessed by CD45 and CD3 staining. (A) Flow cytometric identification of weak cytoplasmic CD3 (cCD3) PE expression in APL blasts, identified by weak CD45 expression relative to the minor mature T-lymphocyte population (brighter CD45 and cCD3 expression). Cytoplasmic CD3 expression by APL was also weaker than (shaded) MPO expression (which uses a different isotype control to cCD3). Columns from left to right show the morphologic and CD45 gates and expression of cCD3 and MPO relative to isotype controls. (B) Absence of TdT expression is shown for both cCD3⁺ APLs.