Last December, Advanced Cell Technology (ACT) of Marlborough, Massachusetts, made its initial filing with the US Food and Drug Administration (FDA) for a proposed clinical trial using platelets derived from induced pluripotent stem (iPS) cells. If approved, it could be the first clinical trial involving iPS cells, which are reprogrammed adult cells, typically fibroblasts or hematopoietic precursors. But other groups are not far behind. Researchers at Stanford University in Palo Alto, California, have also met with the FDA about a proposed trial of genetically corrected keratinocytes to treat epidermolysis bullosa, a rare skin disease. And ophthalmologist and stem cell biologist Masayo Takahashi, of the RIKEN Center for Developmental Biology in Kobe, Japan, is awaiting final government approval for a trial of iPS cell-derived retinal pigment epithelium (RPE) to treat the wet form of age-related macular degeneration (AMD).

Each of these efforts faces obstacles and dangers that are particular to the pathology of the chosen disease and the nature of the replacement cells used to treat it. And beyond those perils loom the unknowns that accompany any venture into completely new medical territory. Nevertheless, these groups and others (Table 1) are already seriously bidding to make the leap into humans.