Diminished CD3 expression is useful for detecting and enumerating Sezary cells

We evaluated 44 peripheral blood, bone marrow, and lymph node specimens fro m 23 patients with the clinical diagnosis or suspicion of cutaneous T-cell lymphoma by 4-color flow cytometry for the presence of altered CD3 expressi on and compared the results with light microscopic evidence of involvement by mycosis fungoides (MF) or Sezary syndrome ISS). In 19 specimens (15 peri pheral blood, 3 lymph node, I bone marrow) from 6 patients, we noted reduce d CD3 expression compared with normal T lymphocytes. Diminished CD3 express ion correlated with morphologic evidence of MF/SS cells in all cases, altho ugh the enumeration of MF/SS cells differed Comparison of the enumeration o f MF/SS cells in the peripheral blood by CD3+CD7-phenotyping with CD3dim ph enotyping suggested that CD3dim phenotyping was the most accurate method fo r counting MF/SS cells. Therefore, diminished CD3 expression as shown by fl ow cytometry may be particularly useful for detecting and enumerating MF/SS cells in hematopoietic tissue of patients with cutaneous T-cell lymphoma.