Perforin protein (pfp) and/or IFN-γ knockout (KO) mice predominately develop B-cell lymphomas, especially after 1 year of age (older animals) with a combination of pfp and IFN-γ KO inducing an early onset of lymphoma, suggesting a synergistic immunosurveillance effect (37). The gene discussed is PRF1; the disease is B-cell non-Hodgkin lymphoma.