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Read the passage and answer the question that follows:
(This passage is adapted from Emily Anthes, Frankenstein's Cat, 2013.)[/passage-header] When scientists first learned how to edit the genomes of animals, they began to imagine all the ways they could use this new power. Creating brightly colored novelty pets was not a high priority. Instead, most researchers envisioned far more consequential applications, hoping to create genetically engineered animals that saved human lives. One enterprise is now delivering on this dream. Welcome to the world of pharming, in which simple genetic tweaks turn animals into living pharmaceutical factories.
53499Many of the proteins that our cells crank out naturally make for good medicine. Our bodies' own enzymes, hormones, clotting factors, and antibodies are commonly used to treat cancer, diabetes, autoimmune diseases, and more
93455.
42998The trouble is that its difficult and expensive to make these compounds on an industrial scale, and as a result, patients can face shortages of the medicines they need. Dairy animals, on the other hand, are
41493expert protein producers, their udders swollen with milk
45597. So the creation of the first transgenic animals---first mice, then other species---in the 1980s gave scientists an idea: What
65143if they put the gene for a human antibody or enzyme into a cow, goat, or sheep? If they put the gene in just the right place, under the control of the right molecular switch, maybe they could engineer animals that produced healing human proteins in their milk
59518. Then doctors could collect medicine by the bucketful.
Throughout the 1980s and '90s, studies provided proof of principle, as scientists created transgenic mice, sheep, goats, pigs, cattle, and rabbits that did, in fact, make therapeutic compounds in their milk.
94444At first, this work was merely gee-whiz, scientific geekery, lab-bound thought experiments come true
34533.
80905That all changed with ATryn, a drug produced by the Massachusetts firm GTC Biotherapeutics. ATryn is antithrombin, an anticoagulant that can be used to prevent life-threatening blood clots
10651. The compound, made by our liver cells, plays a key role in keeping our bodies clot-free.
86900It acts as a molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream
46291.
71054But as many as 1 in 2,000 Americans are born with a genetic mutation that prevents them from making antithrombin
74998. These patients are prone to clots, especially in their legs and lungs, and they are at elevated risk of suffering from fatal complications during surgery and childbirth. Supplemental antithrombin can reduce this risk, and GTC decided to try to manufacture the compound using genetically engineered goats.
To create its special herd of goats, GTC used microinjection, the same technique that produced GloFish and AquAdvantage salmon. The company's scientists took the gene for human antithrombin and injected it directly into fertilized goat eggs. Then they implanted the eggs in the wombs of
68619female goats. When the kids were born, some of them proved to be transgenic, the human gene nestled safely in their cells.
53784The researchers paired the antithrombin gene with a promoter (
94525which is a sequence of DNA that controls gene activity
81896) that is normally active in the goat's mammary glands during milk production
91149.
When the transgenic females lactated, the promoter turned the transgene on and the goats' udders filled with milk containing antithrombin. All that was left to do was to collect the milk, and extract and purify the protein. Et voila--human medicine! And, for GTC, 59156liquid gold. A Tryn hit the market in 2006, becoming the worlds first transgenic animal drug. Over the course of a year, the "milking parlors" on GTC's 300-acre farm in Massachusetts can collect more than a kilogram of medicine from a single animal.