I get worried when humans try to play 'God' and begin messing with DNA, much less anything else that has the potential to mutate into something quite deadly.
Regardless of which side of the embrionic stem cell research discussion, the fact remains that chaos rules and genetic anomalies can and do occur.
The MSM isn't covering this at all so the only site I could find the article on was an anti-stem cell research site (so read with a critical eye).
FDA OKs First Embryonic Stem Cell Research Trial on Humans, Despite Concerns
Washington, DC (LifeNews.com) -- The Obama administration has approved the bid by cloning company Geron to undertake the first trial involving the use of embryonic stem cells in humans. They have never been used before in people because the cells cause tumors and have been plagued by immune system rejection issues when tried in animals.
My worry is someone's body will create a mutation of some previously harmless virus or bacterium and result in something the human body's immune system cannot repel. Though realistically speaking...the human race is due for a population control event (PCE).