Expression of Leu-8 antigen, a majority T-cell marker, is uncommon in mycosis fungoides.

Predominance of mature helper T cells with the Leu-1+, 2-, 3+, 4+, 5+ phenotype was confirmed in 22 biopsy specimens of mycosis fungoides from 15 patients. Dissection of the T helper/inducer cells into phenotypically distinct subsets was performed with the use of a new monoclonal antibody, anti-Leu-8. One might predict a predominance of Leu-8+ in mycosis fungoides, as the known ratio of Leu-8+/Leu-8- cells is approximately 70/30 in the peripheral blood. Unexpectedly, a deficiency of Leu-8 was demonstrated in 18 of the 22 specimens from 13 of 15 patients. This finding could not be attributed to an artifact of the staining method or to therapy, and was present in early- as well as late-stage disease. Whether neoplastic cells in mycosis fungoides derive from Leu-8-subset of T cells at risk for malignant transformation, or whether there is antigen loss with malignant transformation remains to be determined. Implications of our finding with regard to etiopathogenesis of mycosis fungoides are discussed.