Genetic engineering has been especially important in the field of pharmaceuticals. For example, the process of viral transfection uses a virus to deliver foreign genetic material to the patient's cells. For example, the human adenovirus, which infects the human respiratory system, has been used to deliver genetic therapies for cystic fibrosis, a lung disorder. Viral transfection takes advantage of viruses' natural life cycle, in which viruses inject their genes into host cells, where those genes are then expressed along with the host's genes.
Beta-carotene is a metabolic precursor to vitamin A, meaning that the human body converts beta-carotene to vitamin A. Many inhabitants of poorer countries lack enough beta-carotene in their diets to produce sufficient quantities of vitamin A. Scientists have used genetic engineering to produce rice with high levels of beta-carotene. This so-called "golden rice" (because of the golden color imparted to the rice by the beta-carotene) has the potential to virtually eliminate vitamin A deficiency across the globe for very little cost.
Transgenics has also been very important in the field of agriculture, where crop destruction by pests costs farmers billions of dollars in damage each year. The two primary areas of agriculture transgenics are pest resistance & herbicide tolerance. An example of the former category is corn resistant to the European corn borer. The protein Cry1Ab from Bacillus thuringiensis (a species of bacteria) is toxic to the European corn borer and was introduced into the corn's genome so that the corn would produce that protein.
Farmers use herbicides to kill weeds on their farms. However, these herbicides can also be toxic to the crops. Accordingly, it has been very beneficial to produce transgenic crops that are resistant to herbicides. The soil bacterium Agrobacterium tumefaciens has developed resistance to the herbicide glyphosate (commercially known as Roundup). This tolerance stems from the cells' version of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). The bacterial EPSPS has been introduced into soybeans so that the soybeans' EPSPS will no longer be inhibited by the herbicide.