Criteria for Determining Pluripotency in Human Cells
Pluripotency is defined as the ability of a single stem cell to give rise to all of the various cell types that make up the body. Current scientific understanding of pluripotency is based on extensive study of mouse embryonic stem (ES) cells. In mice, the gold standard test for the ability to form derivatives of all three germ layers (ectoderm, mesoderm, and endoderm) is injection of a single putative pluripotent cell (labeled to permit tracking of daughter cells) into a mouse blastocyst. If the labeled injected cell is truly pluripotent, labeled daughter cells will be seen throughout the embryo, in tissues derived from all germ layers. This practice, however, is neither ethical nor practical in primates, including human cells or blastocysts. Consequently, scientists typically demonstrate formation of all three germ layers in primate stem cells via teratoma formation. As our understanding of pluripotency and its molecular characteristics advances, alternative methods are likely to be developed and accepted.
Criteria for Demonstration of Pluripotency
- Provide evidence that cells from the proposed cell line form a teratoma that contains cells from all 3 embryonic germ layers (endoderm, mesoderm, and ectoderm). This method was chosen because it is currently the gold standard for determining whether a human line is pluripotent. If cells from the line have not demonstrated teratoma formation, the derivers may provide alternative evidence of pluripotentiality for consideration by the NIH.
- Provide evidence that the cell line is capable of unlimited self-renewal.
In addition, derivers should provide information on the expression of the transcription factors and cell surface markers that are widely used to characterize human pluripotent stem cells (see FAQ #5). NIH will update these criteria as additional and/or new standards are developed to establish pluripotency.
Determination of Qualified Cell Lines
The NIH Stem Cell Task Force has established a Pluripotency Standards Working Group that will evaluate submissions of cells and cell lines and assess them with respect to required properties. The Pluripotency Standards Working Group will also advise NIH on updating the criteria for establishing pluripotency as new science emerges. If appropriate, lines listed on the registry will be tested to determine that they meet the new standards.