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 x 10(3) 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)I 30+/-21 x 10(3), and adult T-cell leukaemia/lymphoma (ATLL), 38+/-31 x 10(3), followed by T-prolymphocytic leukaemia (T-PLL), 92+/-47 x 10(3), and granular lymphocyte leukaemia (GLL), 95+/-21 x 10(3). In contrast, the number of CD7 molecules was significantly higher in T-ALL, 35+/-7 x 10(3) (P < 0 . 01), and T-PLL, 29+/-12 x 10(3), than the normal controls (P < 0 . 01), whereas ATLL and GLL showed a low CD7 expression, 13+/-3 and 12+/-3 x 10(3), 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 las also defined the T prolymphocyte as a cell of intermediate maturity between thymic derived and peripheral T lymphocytes.