Extra‐thymic immature t cells: development in polyoma virus‐induced murine salivary gland tumors

Lymphocyte infiltrates which occur in some polyoma virus‐induced murine salivary epithelial tumors are characterized. The lymphocytic infiltrates within the salivary tumors resemble cortical thymocytes with the phenotype PNA⁺, Thy‐1.2^bright, Ly‐2⁺L3T4⁺, Ly‐1^dim, H‐2K^dim, KJ16‐133⁻. The salivary lymphocytes showed proliferation based on analysis of RNA and DNA content. Because thymocytes lose the immature phenotype before leaving the thymus, we propose that the salivary tumor infiltrates result from the intra‐tumoral differentiation of blood‐derived prothymocytes into “cortical thymocytes”. Histologic examination of the salivary tumors indicates expression of class II major histocompatibility antigen on the tumor epithelium which may be essential in establishing the extra‐thymic T lymphocyte‐inductive microenvironment within the tumor.