CD4/CD8 double negative mycosis fungoides with PD-1 (CD279) expression--a disease of follicular helper T-cells?

CD4/CD8 double negative mycosis fungoides (MF) is a rare phenotypic variant of this epidermotropic cutaneous T-cell lymphoma. Clinically, this MF form manifests with unusual appearances such as annular lesions confined to one body region as in our patient in whom the lesions were found on the left lower leg. The cellular origin of CD4/CD8 double negative MF is unknown. In our case, the intraepidermal CD4/CD8 double negative clonal T-lymphocytes (CD2+, CD4-, CD8-, CD30-, beta-F1+) expressed programmed death-1 but were negative for CXCL-13 and cytotoxic molecules (TIA-1, granzyme B, perforin). Our observation may give an insight into the histogenesis of this unique MF variant and may also be of therapeutic significance because programmed death-1 may serve as a target for therapeutic intervention.