Sir

In your News story 'Stem-cell claim gets cold reception' (Nature 452, 132; 2008), you report on an announcement that nanotubes have been used to reprogramme adult human cells. As you say, the result was met with scepticism because it was proclaimed at an investors' meeting, rather than in a peer-reviewed publication. There are also questions about the nanotechnological aspects of the work.

Carbon nanotubes are capable of penetrating cell membranes to facilitate cytoplasmic delivery, but their application in medicine is still in its infancy. Much more basic research is needed before deterministic assertions — such as those contained in the company announcement — can be made about the way carbon nanotubes act biologically and pharmacologically. Furthermore, no preclinical therapeutic efficacy data exist yet for any disease using a carbon nanotube construct.

The announcement was unclear about the exact nature of the studies carried out and the promised capabilities of both the carbon nanotubes and stem cells. For example, what was actually delivered by the carbon nanotubes? Proteins, DNA, small interfering RNA, or all three? Dramatically different delivery-system specifications are necessary for successful intracellular delivery and guaranteed biological activity for each of these, making the notion that 'carbon nanotubes deliver all' too simplistic.

The field of medical applications of carbon nanotubes and nanotechnology in general is particularly prone to hype. Claims that nanomaterials can contribute to new treatments of devastating diseases have led to confusion and misrepresentation, risking discreditation of this exciting area of research. We urge caution and patience, and call for sustained investment in basic research and systematic investigation by multidisciplinary teams, to keep expectations realistic.