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The contribution of molecules such as perforin, IFN-γ (IFNγ), and particularly Fas ligand (FasL) by transferred CD8 + effector T (T E ) cells to rejection of large, established tumors is incompletely understood. Efficient attack against large tumors carrying a surrogate tumor antigen (mimicking a “passenger” mutation) by T E cells requires action of IFNγ on tumor stroma cells to avoid selection of antigen-loss variants. Because “cancer-driving” antigens (CDAs) are rarely counterselected, IFNγ may be expected to be dispensable in elimination of cancers by targeting a CDA. Here, initial regression of large, established tumors required neither IFNγ, FasL, nor perforin by transferred CD8 + T E cells targeting Simian Virus (SV) 40 large T as CDA. However, cytotoxic T E cells lacking IFNγ or FasL could not prevent relapse despite retention of the rejection antigen by the cancer cells. Complete tumor rejection required IFNγ-regulated Fas by the tumor stroma. Therefore, T E cells lacking IFNγ or FasL cannot prevent progression of antigenic cancer because the tumor stroma escapes destruction if its Fas expression is down-regulated.

Blankenstein and colleagues describe a novel strategy to avoid tumor escape from adoptive T cell therapy.