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Cultivated Limbal Epithelial Transplantation (CLET)

Cornea

1. Clinical Analogy & Conceptual Framework

Clinical Analogy

Imagine a depleted battery that can no longer hold a charge - this is the limbal stem cell-deficient cornea. The limbal stem cells (LSCs) at the corneoscleral junction are the 'battery cells' of the ocular surface. When they fail, the corneal epithelium - like a discharged device - cannot self-renew. Conjunctival cells invade, blood vessels ingrow, and vision fails. CLET is essentially 'recharging the battery' - but instead of replacing the entire battery, you take a tiny fragment of healthy limbal tissue (even from the other eye), expand it ex vivo in a laboratory into millions of stem cells on a biological scaffold, and transplant that sheet onto the diseased surface. The key insight: you are restoring the SOURCE of epithelial regeneration, not just patching the surface.

Prior to cultivated limbal epithelial transplantation (CLET), the treatment of bilateral limbal stem cell deficiency (LSCD) was limited to: - Keratolimbal allograft (KLAL) - Living-related conjunctival limbal allograft (lr-CLAL) - procedures requiring large donor tissue and lifelong systemic immunosuppression.
The concept of ex vivo expansion of limbal epithelial cells was revolutionary: - Pellegrini et al. (1997) in The Lancet demonstrated that cultured limbal epithelial cells could restore a stable corneal surface. - This opened a new era of cell-based therapy for the ocular surface.

The Central Principle

The Central Principle
Principle	Clinical Implication
• Limbal stem cells (LSCs) reside in the limbal palisades of Vogt.	• Biopsy must be from the limbus - not the central cornea.
• Putative limbal stem-cell markers include p63 and ATP-binding cassette subfamily G member 2 (ABCG2).	• Cultures with >3% p63-bright cells were associated with transplant success.
• Ex vivo expansion amplifies cells from a small limbal biopsy.	• A precise cell-yield estimate for a 1–2 mm² biopsy is not substantiated by the supplied evidence.
• A scaffold provides structural support.	• Amniotic membrane (AM) is a commonly used substrate for cultivated limbal epithelial transplantation.
• Limbal stem-cell transplantation restores a corneal epithelial phenotype.	• Limbal stem-cell deficiency causes conjunctivalization and corneal neovascularization.
• Autologous cultivated limbal epithelial transplantation (CLET) uses fellow-eye tissue.	• Does not require systemic immunosuppression for graft rejection.

The Central Principle
Principle	Clinical Implication
• Limbal stem cells (LSCs) reside in the limbal palisades of Vogt.	• Biopsy must be from the limbus - not the central cornea.
• Putative limbal stem-cell markers include p63 and ATP-binding cassette subfamily G member 2 (ABCG2).	• Cultures with >3% p63-bright cells were associated with transplant success.
• Ex vivo expansion amplifies cells from a small limbal biopsy.	• A precise cell-yield estimate for a 1–2 mm² biopsy is not substantiated by the supplied evidence.
• A scaffold provides structural support.	• Amniotic membrane (AM) is a commonly used substrate for cultivated limbal epithelial transplantation.
• Limbal stem-cell transplantation restores a corneal epithelial phenotype.	• Limbal stem-cell deficiency causes conjunctivalization and corneal neovascularization.
• Autologous cultivated limbal epithelial transplantation (CLET) uses fellow-eye tissue.	• Does not require systemic immunosuppression for graft rejection.

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