Abstract: A target protein is rendered less immunogenic to a given species by (a) determining at least part of the amino acid sequence of the target protein; (b) identifying in the amino acid sequence one or more potential epitopes for T-cells (“T-cell epitopes”) of the given species; and (c) modifying the amino acid sequence to eliminate at least one of the T-cell epitopes identified in step (b) to reduce the immunogenicity of the protein when exposed to the immune system of the given species.