Mycosis fungoides skin lesions contain CD8+ tumor-infiltrating lymphocytes expressing an activated, MHC-restricted cytotoxic T-lymphocyte phenotype

In prior studies, we showed that most CD8⁺ cells infiltrating skin lesions of CD3⁺CD4⁺ mycosis fungoides were CD3⁺ T-line-age tumor-infiltrating lymphocytes (TIL) whose overall phenotype was suggestive of MHC-restricted cytotoxic T lymphocytes (CTL). However, their lack of cytotoxic-associated granzyme A mRNA suggested that they might be inactivated CTL precursors. In this study, we used single- and double-label immunohistologic techniques to assess the expression of TlA-1-reactive protein and HLA-DR by these CD8⁺TIL. Monoclonal antibody TIA-1 recognises a novel family of proteins expressed preferentially by cytotoxic cells, including some that lack grauzyme A. HLA-DR is a marker of T-cell activation. Single-label studies of 32 cases showed that CD8⁺TIL and TIA-1⁺ cells constituted a variable minority of the total cellular infiltrate and had a similar distribution. Double-label studies of 14 cases showed that in most instances the aggregate phenotype of the majority of CD8⁺TIL was CD3⁺TIA-1⁺HLA-DR⁺CD56⁻CD57⁻. These findings suggest that many of the CD8⁺TIL within skin lesions of CD3⁺CD4⁺ mycosis fungoides are activated, MHC-restricted CTL.