Establishment of Thymic Epitherial Cell Lines from a Human Thymoma and Its Immuno-biological Analysis.

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Using isolation culture techniques, we have been able to establish human thymic epitherial cells (Thm-1) from a thymoma of a 56 year-old female patient and have developed several subtype cell lines using cloning culture method. The growth characteristics of the cloning cell lines can be roughly divided into twotypes, polygonal and spindle types. Doubling time in vitro was approximately 1.3 day in polygonal Subline (3D) and 7.4 day in spindle Subline (7A). These cells were demonstrated to be highly tumorigenic when injected into nude mice. Thm-1 tumors, grown in nude mice, are histologically identical to the original tumor without lymphcytes. Immunophenotypic analysis of the cells using flow cytometry showed epitherial tumor cells expressing a surface E-cadherin and CEA antigen. Immunohistologically, the cells were demonstrated to express cytokeratin on the cell surface. Electron microscopy of the cultured cells revealed desmozome, tonofirament and granule particles. Nothern analysis demonstrated that E-cadherin mRNA was revealed in these cells. These data indicate that this cell line represents the epitherial lineage. To measure immunological reactivity, mixed lymphocyte-tumor cell culture reaction (MLTR) was studied using a microplate method. The PBL cells were cocultured with Thm-1 cells, lung cancer cell lines and macrophages in the medium supplemented with 200 mu/ml IL-2 and analyzed at periodic intervals for expanded lymph cell-subsets by flow cytometry.We found increased numbers of CD8 positive cells in 16-and 31-day cultures from the coculturing of Thm-1 cells and macrophages (58.7 after 16 days and 72.1% after 31 days of culture), but were small for CD4 positive cells (9.7% after 16 days and 7.5% after 31 days of culture).Establishment of this human thymoma cell line, Thm1, provides an excellent model to study further the biological behavior of thymic epitherial cells and the in vivo immunological effects of a thymoma.