The aging process is main reason for unavoidable death. Adwaita, an Aldabra giant tortoise that died in 2006 in the Alipore Zoological Gardens of Kolkata, India, is believed to have lived to the age of 255 years but this has not been confirmed. You may think that if genes are modified properly, human can live at least 200 years by understanding longevity of tortoise. How about immortality?
http://en.wikipedia.org/wiki/Jonathan_(tortoise)