IL-15, one of the most promising biological agents for cancer treatment,6 has been used in the in vitro culture (via rIL-15) or modification (via transgene IL-15) of CD8+ T cells, DC or tumor cells for generation of tumor-specific CD8+ T cells and DC- or tumor cell-based vaccines, and administered systemically in vivo by injection of rIL-15 or expression of transgene IL-15 alone or in combination with other agents/approaches (e.g., IL-12, IL-21, IL-7, GM-CSF, anti-CD40, anti-PD-L1, anti-CTLA-4, adoptive CD8+T cell transfer, irradiation).6-12,48-52. Here, IL21 is linked to cancer.