The present invention relates to agents that modulate interleυkin-15 ('IL-15') signal transduction or function ('Therapeutic Agents') and the use ol' those agents to modulate immune function. The Therapeutic Agents target the interaction between IL-15 and its receptor and modulate IL-15-induced signal transduction. The Therapeutic Agents may be formulated with polymers, such as poly-β- 1- ♦4-N-acetylglucosamine. for administration to a human subject to modulate IL-15-mediated immune function.