The role of tumor stroma in the interaction between tumor and immune system.

It is often assumed that tumor rejection is mainly the result of cytotoxic T lymphocytes (CTLs) killing the tumor cells. However, recent studies have demonstrated that the rejection process is not as simple as this. In some models, tumors are rejected in the absence of lytic mechanisms (e.g. perforin or Fas ligand), and in others CTLs kill tumor stromal cells that cross-present antigen. T cells with lytic function but IFN-gamma deficiency rarely reject tumors. IFN-gamma and, in some models, other T-cell cytokines such as TNF-alpha, IL-4 or IL-10 contribute to tumor rejection by inhibition of tumor stroma formation. These cytokines inhibit tumor-induced angiogenesis, probably through different cellular targets.