Testing vaccine on animals. Dr Sima Rafati (right) and an assistant preparing a laboratory mouse to test a vaccine. They are carrying out research on the cpa gene of the protozoan parasite (Leishmania sp.). The cpa gene carries instructions for the production of an enzyme (cysteine proteinase a) that is thought to be specific to the parasite. The mouse will be injected with deoxyribonucleic acid (DNA) plasmids engineered to carry the cpa gene, and another gene named cpb. This results in the production of the enzymes, which then provoke an immune response to protect against Leishmania parasites. Photographed at the Pasteur Institute, Tehran, Iran.