Genetic engineering allows scientists to pluck genes--segments of DNA--from one type of organism and to combine them with genes of a second organism.
In this way, relatively simple organisms such as bacteria or yeast can be induced to make quantities of human proteins, including interferons and interleukins. They can also manufacture proteins from infectious agents, such as the hepatitis virus or the AIDS virus, for use in vaccines.
![Genetic Engineering](https://webarchive.library.unt.edu/eot2008/20080923083613im_/http://www.nci.nih.gov/images/Documents/02853881-1148-4541-b2b6-e8ecd3e50c6f/cancer37.jpg)
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