The present invention relates to genetically engineered cell populations derived from an immortalised/ cancerous cell that do not express MHC class I molecules but that are modified to express membrane-bound IL-15, membrane-bound 4-1 BBL ligand, and at least one other membrane bound molecule, such as an interleukin or anti-CD3 antibody. The co-culture of said cells with a population of immune cells results in the activation and expansion of at least one subpopulation of immune cells. Expanded populations of NK cells derived from the co-culture of a mixed cell culture with the stimulatory cell lines may be used in methods of treating cancer or an infectious disease. In a separate embodiment, a plurality of nucleic acids for use in preparing the engineered cell population are provided.Varias modalidades descritas en el presente documento se refieren a lineas celulares estimuladoras disenadas para expandir preferentemente celulas asesinas naturales (NK) en un cultivo celular mixto que comprende celulas NK y celulas T. En varias modalidades, tambien se proporcionan poblaciones de celulas NK derivadas del cultivo conjunto de un cultivo celular mixto con lineas celulares estimuladoras. Los usos de las lineas celulares estimuladoras para expandir preferentemente las celulas NK en un cultivo celular mixto tambien se proporcionan en varias modalidades.
