Tissue-engineered corneal stromal substitutes transplanted in the living feline model: biocompatibility, ultrastructure and performance

Abstract

Purpose: Tissue engineering of a corneal stroma is a promising alternative to overcome the limitations of lamellar corneal replacement with eye bank human corneas. We have demonstrated the feasibility of engineering all three corneal layers. The aim of this study was to evaluate the in vivo functionality, ultrastructure and biocompatibility of allogeneic and xenogeneic tissue-engineered (TE) stromal grafts in the feline model.

Methods: Human and feline keratocytes were isolated from normal corneas and cultured to tissue engineer a 6 sheet-stromal substitute using a self-assembly approach. Eight healthy animals underwent two intra-stromal grafts in one eye and the controlateral eye was used as a control. Animals were followed during 4 months after surgery, with slit lamp ophthalmic examination, intraocular pressure measurement and in vivo optical coherent tomography (Thorlabs®). Histology and transmission electron microscopy (TEM) were performed on all corneas at 4 months.

Results: 16 grafts were performed. The average graft transparency score (0 (opaque) to 4 (crystal clear) scale) was 3.3±0.4 on Day 1 and 3.9±0.2 on Day 37, which was similar to that of normal controls. The minimal intraocular inflammation (cells and flare) observed in all eyes on Day 1 entirely resolved on Day 10. The mean graft thickness decreased with edema resorption (Day 3: 44.5±8 µm; Day 114: 31.4±5 µm). Intraocular pressure remained unchanged (Preop: 11.8±3.6; Postop: 11.7±3.0 mmHg). The grafts did not attract corneal vessels. Mean corneal endothelial cell counts remained stable (Preop: 2506±77 cells/mm2; Postop: 2482±70 cells/mm2). Histology showed nicely integrated grafts, with undisturbed host corneal epithelium, stroma, and endothelium. TEM confirmed the normal aspect of the keratocytes, found in greater number in the grafts, and the absence of inflammatory cells. Spacing between the collagen fibers of the TE-stroma was 33.55±7.21 nm prior to transplantation, due to edema, and 25.90±4.68 nm 4 months after transplantation, with a regular arrangement similar to that of normal native stromas. All results were statistically significant (p<0.05).

Conclusions: The intrastromal TE-corneal stromal grafts remained clear and well-tolerated by the host for 4 months, without disturbance of the endothelial and epithelial layers, and without signs of immunological rejection.

Keywords: 484 cornea: stroma and keratocytes