[Corneal cell therapy-an overview]

Human platelet lysate as a replacement for fetal bovine serum in human corneal stromal keratocyte and fibroblast culture

The isolation and propagation of primary human corneal stromal keratocytes (CSK) are crucial for cellular research and corneal tissue engineering. However, this delicate cell type easily transforms into stromal fibroblasts (SF) and scar inducing myofibroblasts (Myo‐SF). Current protocols mainly rely on xenogeneic fetal bovine serum (FBS). Human platelet lysate (hPL) could be a viable, potentially autologous, alternative. We found high cell survival with both supplements in CSK and SF. Cell numbers and Ki67+ ratios increased with higher fractions of hPL and FBS in CSK and SF. We detected a loss in CSK marker expression (Col8A2, ALDH3A1 and LUM) with increasing fractions of FBS and hPL in CSK and SF. The expression of the Myo‐SF marker SMA increased with higher amounts of FBS but decreased with incremental hPL substitution in both cell types, implying an antifibrotic effect of hPL. Immunohistochemistry confirmed the RT‐PCR findings. bFGF and HGF were only found in hPL and could be responsible for suppressing the Myo‐SF conversion. Considering all findings, we propose 0.5% hPL as a suitable substitution in CSK culture, as this xeno‐free component efficiently preserved CSK characteristics, with non‐inferiority in terms of cell viability, cell number and proliferation in comparison to the established 0.5% FBS protocol.

[Simple limbal epithelial transplantation (SLET) : A simple technique for the treatment of unilateral complete limbal stem cell deficiency. Video article]

OBJECTIVE

The aim of simple limbal epithelial transplantation (SLET) is the regeneration of the corneal surface in unilateral complete limbal stem cell deficiency (LSCD).

INDICATIONS

SLET is indicated for unilateral complete LSCD.

CONTRAINDICATIONS

Contraindications include bilateral LSCD, severe corneal thinning, pronounced keratoconjunctivitis sicca, chronic inflammatory condition of the ocular surface, malposition of the eyelids and pronounced adhesions of the conjunctiva with trichiasis.

SURGICAL TECHNIQUE

A 1‑h biopsy is obtained from the superior limbus of the healthy donor eye. A 360° peritomy is performed on the LSCD eye and pannus tissue covering the cornea is removed. An amniotic membrane (AM) is glued to the corneal surface with fibrin. The donor tissue is then divided into 8-10 small pieces, which are placed on the AM sparing the visual axis and fixed by fibrin glue. A contact lens is placed on the eye. A surgical video, which is available online, shows the surgical technique in detail.

FOLLOW-UP

Examinations are necessary within the first postoperative week and 1 month after SLET, then every 3 months within the first postoperative year. Antibiotic eye drops should be applied 5 times daily until complete epithelialization. Topical steroids should be applied 6 times daily in the early postoperative period and can be tapered thereafter. Artificial tears can improve epithelial healing. Ideally, all eye drops should be preservative-free. The contact lens can be removed after 7-10 days. The AM dissolves within a few weeks. An epithelialization of the corneal surface can be observed by the second postoperative week.

EVIDENCE

A recent systematic review reported a stable epithelialized corneal surface in 78% of SLET cases after 1.5 years. An improvement of visual acuity of at least two lines was found in 69% of SLET cases.

Engineering of Human Corneal Endothelial Cells In Vitro

Human corneal endothelial cells are responsible for controlling corneal transparency, however they are notorious for their limited proliferative capability. Thus, damage to these cells may cause irreversible blindness. Currently, the only way to cure blindness caused by corneal endothelial dysfunction is via corneal transplantation of a cadaver donor cornea with healthy corneal endothelium. Due to severe shortage of donor corneas worldwide, it has become paramount to develop human corneal endothelial grafts in vitro that can subsequently be transplanted in humans. Recently, we have reported effective expansion of human corneal endothelial cells by reprogramming the cells into progenitor status through use of p120-Kaiso siRNA knockdown. This new reprogramming approach circumvents the need of using induced pluripotent stem cells or embryonic stem cells. Successful promotion of this technology will encourage scientists to re-think how "contact inhibition" can safely be perturbed to our benefit, i.e., effective engineering of an in vivo-like tissue while successful maintaining the normal phenotype. In this review, we present current advances in reprogramming corneal endothelial cells in vitro, detail the methods to successful engineer human corneal endothelial grafts, and discuss their future clinical applications to cure corneal blindness.