Biologists say they are close to finding a cellular elixir of youth: a cocktail of proteins that can convert adult cells into embryonic stem cells that are able to grow replacement tissues, according to two studies published in Nature June 14.

If found, this recipe could leapfrog the intense controversy involved in extracting stem cells from a human embryo, which is destroyed in the process.

Instead, doctors might be able to take a simple biopsy of cells from a patient and reprogram them, using one set of proteins to first transform them into embryonic stem cells, and then another to coax them into growing new blood, pancreas or other tissue.