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

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Abstract
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.