Human peripheral blood mononuclear cells (PBM) cultured in serum-free medium. III. Morphological study of an in vitro microcytotoxicity model.

An in vitro tumor immunity model is suggested. Interactions between lymphocytes and macrophages in serum-free medium are being studied as well as the effect induced upon these interactions by the addition of heterologous and homologous tumor cells. In our model, the tumor cells seem to be approached by the lymphocytes before any contact with the macrophages and then presented to the latter. The macrophages may then acquire an "activated" structure and display cytotoxic properties. A pattern of in vitro cellular immunity is obtained. This description may serve as a model for further study and understanding of the process of tumor immunity. It is suggested that in contrast to generally accepted models of cellular immunology, lymphocytes can interact directly with antigen complexes and present them to macrophages. The latter would in turn be activated, become cytotoxic and produce or accumulate immune globulins. These cells seem to be an in vitro analog of the recently described tumor infiltrating lymphocytes (TIL) which reside in vivo within spontaneous tumors.