Most bloodsuckers have anti-coagulants in their saliva. In the process of identifying candidate proteins in the saliva, they identified an anticoagulant protein similar (probably in sequence homology) to a protein called Tissue Factor Pathway Inhibitor that was know the have anti-cancer properties.
They (or someone else) cloned the gene for that protein into an expression vector, put the vector into yeast, and purified large quantities of the protein for testing. The article below gives more detail and I am "guessing" about the rest but I believe that is what likely happened.
http://www.google.com/hostednews/afp/article/ALeqM5jWX2Bz06S-5zeg6ss1GIPWgQEiBgClick to expand...