In their article entitled "
Commentary: Is totipotency of a human cell a sufficient reason to exclude its patentability under the European law" (Stem Cells 2007;25:3026-3028), K.T. Vrtovec and B. Vrtovec conclude that arguments based on differentiation potential should not be an obstacle to patenting human embryonic stem cells (and related cells referred to as totipotent or pluripotent). While concentrating on formal legal aspects, however, these authors fail to consider a major biological and ethical argument already found in the literature, namely that an obstacle to patenting is to be seen in the potential of cells (e.g., of embryonic stem cell lines), if this potential allows (re)constitution of an embryo when tetraploid complementation is performed.