Could we clone organs that would be exact genetic matches?

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­How would you like a clone of yourself stowed away somewhere in case you need a new heart or liver, like a spare tire in the trunk of a car? That, in a nutshell, was the plot of the 2005 high-dollar, low-attendance sci-fi movie, "The Island." Hollywood heartthrobs Scarlett Johansson and Ewan McGregor play dual roles portraying the rich and famous -- and their genetically identical clones. In an appropriate Orwellian twist, doctors must murder the "spare" clones in order to harvest needed body parts.

Chances are, "The Island" isn't a glimpse into the future. Nevertheless, it brings up a relevant point about the potential uses for human reproductive cloning. Organ transplants are difficult undertakings for two major reasons. First, you have to find a donor, and second, there's no guarantee that your body will accept the new organ. Statistically, organ demand far outweighs current supply. According to the Organ Procurement and Transplantation Network, 28,356 Americans received organ transplants in 2007 -- around 78 percent of those came from deceased people. Yet as of August 2008, more than 99,000 people in the United States were on the national waiting list for organs [source: OPTN].

­What if you could eliminate the wait time and risky odds with traditional organ transplants by creating custom, cloned organs from your own cells that your body would recognize? Cloning advocates have touted this type of science as therapeutic cloning. This is different from reproductive cloning since therapeutic cloning deals with embryos only, not human babies carried to term.

Embryos contain pluripotent embryonic stem cells, meaning that they can differentiate into more than 200 types of cells. Scientists extract these stem cells when embryos are in the blastocyst phase, the stage when an embryo contains around 150 cells. The stem cells come from the interior of the blastocyst. In November 2007, scientists successfully cloned monkey embryos for the pur­pose of removing stem cells -- this is the closest we've ever come to performing the same procedure in humans. But removing the stem cells effectively destroys the embryo. Many people within and beyond the scientific community disagree with this practice of cloning that terminates embryos, sparking a continued debate about the bioethics of embryonic stem cell research.

­Controversy aside, how would cloned organ transplants work? If you wanted to keep living, doctors obviously couldn't remove your heart and clone a new one, presto-chango. Cloning yourself in order to use the clone's organs wouldn't fly either. Here's where stem cells come in, along with recent scientific breakthroughs that sidestep cloning altogether.