Growing human organs inside animals keeps failing because the host embryo's earliest immune cells eat the donor cells alive. Researchers found three ways to shut that off — and the success rate for growing a rat pancreas inside a mouse jumped from 38% to 73%.

Growing human organs inside animals keeps failing because the host embryo's earliest immune cells eat the donor cells alive. Researchers found three ways to shut that off — and the success rate for growing a rat pancreas inside a mouse jumped from 38% to 73%.