Variable CD7 expression on T cells in the leukemic phase of cutaneous T cell lymphoma (Sezary syndrome)

CD7, a molecule normally expressed on 90% of normal CD4(+) T cells, is ofte n deficient on the malignant T cells of cutaneous T cell lymphoma. To inves tigate the clinical and biologic implications of CD7 expression, blood lymp hocytes from 42 patients with the leukemic phase of cutaneous T cell lympho ma (CD4/CD8 ratio of 10 or more with evidence of a T cell clone in the bloo d) were analyzed for level of expression of CD7 by flow cytometry. CD7 expr ession by cells did not clearly segregate into two distinct subgroups that are either CD7 positive or CD7 negative as generally thought; however, nine of 17 patients with a predominantly CD4(+)CD7(+) tumor population on early studies became CD4(+)CD7(-) over time whereas the converse situation was n ot observed. In addition, of three patients with evidence of large tumor ce lls in the blood coexisting with smaller cells, discordant CD7 expression w as observed in one instance. In lymph node specimens, the percentage of cel ls expressing CD7 and other T cell markers did not correlate with histologi c evidence of involvement. CD7 expression on blood lymphocytes also did not correlate with patients' survival nor to serum IgE levels or blood eosinop hil counts, a finding suggesting that this marker does not identify functio nal cell subsets that produce serum interleukin-4 or -5, respectively. We s peculate that the level of CD7 expression on malignant T cells may be the e ffect of sustained antigen stimulation in vivo analogous to what has been p roposed to occur with normal T cells during aging.