Andy McMahon: Leigh Turner and Paul Knoepfler present a disturbing report in Cell Stem Cell on the growth of businesses marketing stem cell interventions in the US. Los Angeles is one “stem cell treatment” hotspot. Through their examination of these unproven, potentially unethical and even dangerous treatments, Turner and Knoepfler raise serious concerns about practices that currently avoid rigorous regulatory scrutiny. Science-grounded stem cell therapies need to be distinguished in the public’s mind from treatments based on little else than wishful thinking (and the dollar).

Gage Crump: In the latest issue of Science Translational Medicine, Katja M. Heinemeier and coauthors use “bomb pulse” labeling to provide new insights into cell turnover in our joints. This technique takes advantage of the temporary high radiation levels in the atmosphere during the 1950s and 1960s period of above-ground nuclear bomb testing, which labeled the cells of exposed adults. Analysis of their radioactive signatures 50 years later showed no new joint cartilage formation—the post-adolescent joint cartilage lasts for life, or as long as it can. Our poor capacity to regenerate joint cartilage may explain the high occurrence of arthritis as we age.