A recombinant therapeutic agent which is chemically identical to or similar to the endogenous cytokine interleukin-4 (IL-4). Produced primarily by activated T-cells, IL-4 binds to and activates its cell-surface receptor, stimulating the proliferation and differentiation of activated B-cells and enhancing their ability to present antigens to T-cells. As a potential immunotherapeutic agent, recombinant IL-4 also augments the effects of other cytokines on dendritic cells (DC), cytotoxic T lymphocytes (CTL), and tumor-infiltrating lymphocytes (TIL).