Teratoma formation assays with human embryonic stem cells: a rationale for one type of human-animal chimera.

Despite a long and valuable history, human-animal chimera research has often been questioned. Among the moral issues raised by chimeras is the concept that integration of human cells into anatomical locations such as the brain might endow animals with "human-like" capacities including self-awareness. We present a justification for one type of human-animal chimera experiment: the evaluation of hES cell developmental potency via teratoma formation in immunodeficient mice. We argue that this experiment raises no significant moral concerns and should be the jurisdiction of animal care and use committees and exempt from formal review by the stem cell research oversight process.