Human B cell lymphomas including multiple myeloma and Hodgkin¿s disease are frequent malignancies and a major clinical problem. Their high incidence is due to special features of normal B cell development that promote chromosomal translocations and other genetic alterations. Another contributing factor is Epstein-Barr-Virus (EBV), a B cell-transforming virus endemic in humans. EBV-infected cells are usually eliminated by the immune system, but in immunosuppressed (post-transplant or AIDS) patients, EBV infection spreads and drives lymphomagenesis.We have generated a novel genetic tool that allows us to introduce combinations of loss- and gain-of-function mutations specifically into B cells in the mouse, to analyze the cooperation of oncogenic factors thought to contribute to B lymphomagenesis in humans. The unique feature of this method is that only a small fraction of cells is mutated (mimicking the sporadic nature of somatic cancerogenesis) and that cells having acquired either single or combined mutations can be observed side-by-side.Using a large set of mutant alleles, we will test whether the interplay of certain combinations of survival, proliferation and differentiation signals determines the development of different classes of human B cell malignancies. A special focus is on Hodgkin¿s disease, where EBV infection and genetic reprogramming play a critical role. We will also investigate the mechanism of immune surveillance of EBV-infected B cells and EBV-driven B cell lymphomas.Ultimately we hope to elucidate key pathways of lymphoma pathogenesis, identify novel contributing mutations, and generate preclinical mouse models to assess therapeutic strategies and mechanisms of tumor immune surveillance.