Ultrastructural descriptions of interactions between tumor-infiltrating lymphocytes and tumor cells in an in vitro model of culture in serum-free medium.

The ultrastructural morphological characteristics of tumor-infiltrating lymphocytes (TIL) and their interactions with tumor cells were studied in a model previously described. In fresh surgical specimens taken from cancer patients, TIL are found in different amounts, in physical contact with tumor cells, without evident cytotoxic activity. As the culture ages in vitro, however, changes appear in the morphology of the TIL along with degenerative changes and eventually death of the tumor cells. The attachments of the TIL to the tumor cells undergo changes as well. During these changes, some proteinaceous material seems to be secreted by the TIL and transferred to the tumor cells. It is inferred that these changes are related to acquisition of cytotoxicity of the TIL, and this possibility is addressed in the discussion. The morphology of the TIL is that of elongated mononuclear cells. They display motility in the culture medium when not attached to tumor cells. Some of these cellular extensions may be quite impressive in their length and tortuosity, and they are described in detail. An attempt is made to speculate on their function as well.