CD7- T cells represent a subset of normal human blood lymphocytes

In the peripheral blood of normal adults we identified a subpopulation of mature human T cells that lacks expression of CD7. These CD3+CD7- T cells represent 9% +/- 3.4 SD of PBMC as estimated by analyses of 38 different normal donors. The majority of CD7- T cells express TCR alpha/beta, and are of CD4 helper and CD45RO+CD45RA- "memory" phenotype as determined by three-color fluorescence analysis. We established seven CD4+CD7- T cell clones in vitro from purified CD7- blood T cells and compared these cells to CD4+CD7+ clones. Nonexpression and expression, respectively, of CD7 was a stable feature of all clones during long term culture for more than 6 mo. No CD7 mRNA could be detected by dot blot and Northern blot analysis of purified CD7- T cells and of expanded T cell clones implicating a transcriptional regulation of CD7 Ag expression. Ionomycin/TPA and PHA stimulation were not capable to induce CD7 expression in CD7- cells but up-regulated CD7 expression in CD7+ cells. Whereas CD7- cells of cutaneous T cell lymphoma exhibit a cerebriform nucleus (Sézary cells), no evidence was obtained for cerebriform nuclear morphology in normal CD7- T cells from peripheral blood. We suggest that these CD7- T cells represent a physiologic subset of mature T cells and may be the circulating counterpart of those lymphocytes that are found to be enriched in normal skin and in a variety of benign and malignant skin diseases.