Characterization of the mononuclear infiltrate in Bowen's disease (squamous cell carcinoma in situ). Evidence for a T cell-mediated anti-tumour immune response.

We investigated the dermal inflammatory infiltrate and the expression of HLA-DR and beta 2-microglobulin on the tumour cells in 8 Bowen's disease (BD) using a series of monoclonal antibodies. The inflammatory infiltrate was classified as mild, moderate or heavy. The infiltrate in all cases consisted mainly of T cells (55 +/- 21%) and where the T helper (TH) subset predominated over the T suppressor/cytotoxic (TS/C) subset (TH/TS/C ratio of 2.4 +/- 1.0). The mean percentage of HLA-DR positive cells was 58 +/- 18%, Langerhans cells (LC) 4 +/- 1% and Leu-M5 positive cells (monocytes/macrophages) 9 +/- 2%. The mean percentage of B cells and natural killer (NK) cells was 4 +/- 5% and 1 +/- 2% respectively. B cells and NK cells did not invade any of the tumours. In the 5 BD with moderate or heavy infiltrate, TH cells, TS/C cells and Leu-M5 positive cells did invade the tumour. In the tumour area where there was invasion, the number of LC was increased and HLA-DR was expressed on the cells. beta 2-microglobulin was generally expressed on the tumour cells of BD. We concluded that there is evidence for a T cell-mediated anti-tumour immune response which may account for the infrequent invasive growth in BD.