IL-7. A type of biological response modifier (a substance that can improve the body's natural response to infection and disease) that enhances the immune system's ability to fight tumor cells. Interleukin-7 is made by cells in the bone marrow, and can stimulate T cells and B cells to grow. Interleukin-7 can also be made in the laboratory for use in treating cancer and other diseases. Also called IL-7.