Abstract: Mammalian cells, normally dependent of IL-2, can be successfully transfected to express IL-2 in amounts sufficient to sustain growth without the external addition of IL-2. One cell line expressing IL-2 solely in the endoplasmatic reticulum without secretion, and one cell line capable of secretion of IL-2 have been developed and tested. Preliminary experiments using primary cells from human donors confirm the feasibility of the invention. The invention makes available gene-modified cells, methods for their production, as well as methods of the treatment of cancer and for immunostimulation.