<p>An interleukin-18 mutant protein is provided which is highly stable and retaining biological activities. An interleukin-18 mutant protein may have cysteine residues substituted with other amino acid residues while retaining biological activies. An interleukin-18 mutant protein may also have one or several amino acid residues deleted, substituted or added, and which is more stable than a wild-type interleukin-18 protein.</p>
