1. ¹Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
2. ²Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
3. ³Aderans Research Institute, Inc., Philadelphia, Pennsylvania, USA

Correspondence: Dr Cheng-Ming Chuong, Department of Pathology, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, HMR 313, Los Angeles, California 9003. E-mail: cheng-ming.chuong@keck.usc.edu

Abstract

One challenge faced by stem cell biologists is the bioengineering of an organ. Ehama et al. (2007, this issue) used cells derived from human and rodent epidermis and dermal papilla to reconstitute hair-follicle mini-organs. Some result in hair follicles; others are hair follicle–like. The challenge calls for the development of a set of criteria to define a hair follicle so that bioengineered products in the future can be evaluated.