This technology includes irradiated Epstein-Barr virus-transformed lymphoblastoid cell lines (EBV-LCL) as feeder cells for the ex vivo expansion of natural killer (NK) cells. EBV-LCL feeder cells, altered by radiation to prevent uncontrolled growth, provide a supportive environment for NK cells to multiply effectively. This method addresses the challenge of obtaining sufficient quantities of functionally active NK cells, which are crucial components of the immune system known for their ability to target and destroy tumor cells and virally infected cells. The use of EBV-LCL feeder cells permits improved scalability and effectiveness of NK cell-based therapies for cancer and infectious diseases.