SCIENCE: N.I.H. May Fund Human-Animal Stem Cell Research. “The purpose is to try to grow human tissues or organs in animals to better understand human diseases and develop therapies to treat them. Researchers have long been putting human cells into animals — like pieces of human tumors in mice to test drugs that might destroy the tumors — but stem cell research is fundamentally different. The stem cells are put into developing embryos where they can become any cells, like those in organs, blood and bone.”