We also know that there are stem cells that persist in our bodies as we grow and which are able to build new tissue, though for the most part these are only able to form one type of tissue and not a whole body. The 'Holy Grail' is a stem cell that can be stimulated into growing into any tissue type and thus potentially be able to grow into any organ - we could replace whole organs as they become defective for example - so if someone is in need of a new pair of lungs or a new heart we could use their cells to grow them a replacement with no risk of tissue rejection!!
Stem cells have proven very difficult to find. The Nobel Prize was awarded in 2012 to two scientists who were able to generate stem cells from mature cells (i.e. the cells that make up our bodies) by introducing four genes into the cells - a major breakthrough in its day. But there were doubts that that technique could be used to treat people for fear of causing cancer.
However the astonishing possibility that replacement organs could be a reality has just come a step closer. Published tomorrow in the journal Nature is a paper by Charles Vacanti (Harvard University, USA) and Haruko Obokata at the Riken Center for Developmental Biology in Kobe, Japan, and colleagues. In it they describe the conversion of ordinary mature spleen cells into stem cells by the disarmingly simple method of incubating them in slightly acid growth conditions for 30 mins. No genes, no chemicals, no manipulation therefore no risk of causing cancer. These cells can form every type of tissue in a body.
Article in Nature
Article in New Scientist