Murine leukaemia viruses (MLVs) are prototypical gammaretroviruses.
MLVs are further classified based on the species that they can infect: ecotropic viruses infect only cells of mouse or rat origin, xenotropic viruses infect only non-mouse cells; and amphotropic and polytropic viruses, infect both mouse cells and cells of other species. MLVs such as Moloney and Friend MLV (M- and F-MLV) induce T-lymphoid and erythroid/myeloid tumours respectively. They have been extensively studied at the molecular and cellular level, and used as model systems for leukaemogenesis.