Differential expression of CD3 and CD7 in T-cell malignancies: a quantitative study by flow cytometry

Most T-cell antigens are expressed on normal and neoplastic T lymphocytes and for this reason it is not easy to distinguish between the immunophenotype of normal and malignant T cells. We have addressed this problem by comparing the levels of expression of CD3 and CD7 on T lymphocytes from 18 healthy donors with those of 61 cases of T-cell leukaemia using quantitative flow cytometry with a method that converts fluorescence intensity into number of antigen molecules per cell. Normal T lymphocytes expressed 124 ± 25 CD3 and 20 ± 3 × 10³ CD7 molecules per cell. The mean CD3 values were significantly lower in all types of T-cell leukaemia than in normal T cells ( P < 0.05), with the exception of Sezary syndrome. The lowest CD3 values were found in T-lymphoblastic leukaemia (T-ALL), 30 ± 21 × 10³, and adult T-cell leukaemia/lymphoma (ATLL), 38 ± 31 × 10³, followed by T-prolymphocytic leukaemia (T-PLL), 92 ± 47 × 10³, and granular lymphocyte leukaemia (GLL), 95 ± 21 × 10³. In contrast, the number of CD7 molecules was significantly higher in T-ALL, 35 ± 7 × 10³ ( P < 0.01), and T-PLL, 29 ± 12 × 10³, than the normal controls ( P < 0.01), whereas ATLL and GLL showed a low CD7 expression, 13 ± 3 and 12 ± 3 × 10³, respectively. Our results show that the quantitative analysis of CD3 and CD7 and their combined evaluation may enable a distinction between normal and leukaemic T cells and could facilitate the monitoring of minimal residual disease. This study has also defined the T prolymphocyte as a cell of intermediate maturity between thymic derived and peripheral T lymphocytes.