This invention provides a nucleic acid construct comprising a first nucleic acid sequence encoding a pharmaceutically active agent and a second nucleotide sequence encoding a latency associated peptide, in which a nucleic acid sequence encoding a proteolytic cleavage site is provided between the first and second nucleic acid sequences. The invention further provides a fusion protein comprising a latency associated peptide and a proteolytic cleavage site wherein the fusion protein is associated with a pharmaceutically active agent. Also disclosed are processes for preparing the construct and fusion protein, methods of treatment using the construct and fusion protein and pharmaceutical compositions containing the construct and fusion protein.