The basal layer of the cornea is populated by meroclones and paraclones at the periphery, and only paraclones in the central cornea, reflecting the above process of cell division and differentiation. Holoclones are identified by high expression of the marker p63 and are also known as p63 bright cells. Society and culture
In February 2015, the European Commission approved autologous CLET using the stem cell therapy Holoclar for people with severe LSCD due to corneal burns. This is the first time that a stem cell therapy (other than the use of umbilical cord stem cells) has been approved by any regulatory agency in the world. It was created by Graziella Pellegrini and Michele de Luca. Holoclar is a tissue-engineered product that comprises ex vivo expanded autologous human corneal epithelial cells including stem cells, which replace limbal stem cells in patients where the limbus has been destroyed by ocular burns. The use of p63 transcription factor as a biomarker of potency ensures specified amount of stem cells needed for clinical success. Clinically relevant long-term beneficial results have been documented in the treatment of patients with LSCD due to physical or chemical ocular burns. See also
List of human cell types derived from the germ layers

Figures
References
Further reading
Pellegrini G, Ardigò D, Milazzo G, Iotti G, Guatelli P, Pelosi D, De Luca M (January 2018). "Navigating Market Authorization: The Path Holoclar Took to Become the First Stem Cell Product Approved in the European Union". Stem Cells Transl Med. 7 (1): 146–154. doi:10.1002/sctm.17-0003. PMC 5746151. PMID 29280318.
Kerato-limbal allograft (KLAL) involves transplantation from someone who has died and donated their organs. KLAL can be used for cases of bilateral LSCD when a living related donor is not available, or for patients with unilateral LSCD, who dont want to jeopardise their healthy eye. However, most of these types of transplant fail within five years. KLAL has a number of limitations: the graft is usually up to 24 hours old before retrieval and a further period of time is often required to screen the cadavers blood before the tissue can be used; often the limbus is found to be damaged as the tissue is not immunocompatible, there is a high risk of rejection between the recipient and the donor cadaver and studies report only a temporary success in term of transplant effectiveness, with most failing after 5 years. A recent procedure, less invasive than CLAU, which so far has been tested only in unilateral cases, is simple limbal epithelial transplantation (SLET). In this procedure, healthy limbal tissue from the patients good eye is cut into a number of pieces and transferred directly to human amniotic membrane covering the cornea in the damaged eye. Studies published so far have only investigated the procedure in unilaterally affected patients, and the long-term effectiveness of the technique is yet to be proven. Another recent innovation is cultivated limbal epithelial transplant (CLET), either autologous (where donor and recipient are the same patient) or allogenic (where donor and recipient are different patients).