Human corneal endothelial cell sheets for transplantation: thermo-responsive cell culture carriers to meet cell-specific requirements

Corneal endothelial diseases lead to severe vision impairment, motivating the transplantation of donor corneae or corneal endothelial lamellae, which is, however, impeded by endothelial cell loss during processing. Therefore, one prioritized aim in corneal tissue engineering is the generation of transplantable human corneal endothelial cell (HCEC) layers. Thermo-responsive cell culture carriers are widely used for non-enzymatic harvest of cell sheets. The current study presents a novel thermo-responsive carrier based on simultaneous electron beam immobilization and cross-linking of poly(vinyl methyl ether) (PVME) on polymeric surfaces, which allows one to adjust layer thickness, stiffness, switching amplitude and functionalization with bioactive molecules to meet cell type specific requirements. The efficacy of this approach for HCEC, which require elaborate cell culture conditions and are strongly adherent to the substratum, is demonstrated. The developed method may pave the way to tissue engineering of corneal endothelium and significantly improve therapeutic options.

[Transplantation of corneal endothelium--chances and challenges]

BACKGROUND

Endothelial keratoplasty is a promising surgical procedure which may replace penetrating keratoplasty in cases of endothelial cell diseases of the cornea. This method may thereby help to prevent postoperative astigmatism and transplant rejection.

METHODS AND RESULTS

A survey of publications reporting about results after endothelial keratoplasty shows that the main problem of this transplantation technique is a postoperative endothelial cell loss which is comparable to or even higher than that observed in penetrating keratoplasty. Improving surgical techniques led to a reduction of the endothelial cell loss, however, cell-based strategies to prevent postoperative cell loss or to enhance the cell densities of donor corneas or endothelial lamellae are rare.

DISCUSSION

This review presents an overview of clinical results after endothelial keratoplasty. Current strategies in the field of cell biology and tissue cultivation of corneal endothelial cells, genetic manipulation of the corneal endothelium and tissue engineering strategies aiming at the production of transplantable endothelial cell sheets are described.

CONCLUSION

The limited availability of donor corneas makes it mandatory to develop methods in the field of tissue engineering in order to improve corneal endothelial cell survival or to increase corneal endothelial cell density, using interdisciplinary approaches.

Physiological features of primary cultures and subcultures of human retinal pigment epithelial cells before and after cryopreservation for cell transplantation

BACKGROUND

One striking disadvantage of in vitro culturing of human retinal pigment epithelial (RPE) cells is the loss of epithelial differentiation and specific cell function during culture. This may be one of the main reasons for the failure of RPE cell transplantation. The aim of this study was to evaluate cell culture conditions ensuring the maintenance of differentiation and function of RPE cells after subcultivation and storage in liquid nitrogen.

METHODS

Enzymatically isolated cells were seeded onto coated culture dishes, cultured with a specially formulated improved growth medium until confluence and then cryopreserved in liquid nitrogen for 16-66 months. HLA class I and II typing was performed before cryopreservation and after thawing. Expression of Ca2+ channels in primary, first-passage and cryopreserved RPE cells was studied using the patch-clamp technique.

RESULTS

After cryopreservation no loss of any HLA antigen was detectable in 12 of 14 cell strains studied. Patch-clamp experiments demonstrated that high-threshold L-type Ca2+ channels, which are typical for freshly isolated cells, could be detected in first-passage and cryopreserved RPE cells only when improved culture conditions were employed, not in conventionally cultured cells. The characteristics of these channels showed little change in subcultured cells compared to primary cultures.

CONCLUSION

This is the first study showing the maintenance of adult human RPE-specific cell differentiation and characteristics in vitro after primary culture and after cryopreservation using improved cell culture methods. The optimization and quality control of cell culture is an important prerequisite for successful cell transplantation.

[Structure of a cell bank for transplantation of HLA-typed, cryopreserved human adult retinal pigment epithelial cells]

BACKGROUND

The transplantation of retinal pigment epithelial cells (RPE) in patients with age-related macular degeneration is discussed as a future therapy. A cornea bank can serve as a source for cells that can be isolated, cultivated, HLA-typed and cryopreserved for subsequent tissue-compatible transplantation.

METHODS

RPE cells are isolated enzymatically from donor eyes and are cultured in a specially designed growth medium. After multiplication, one part of the culture is cryopreserved; the other part is subcultured for HLA-typing. Completely typed and morphologically sufficiently well-differentiated cell cultures are registered on a donor list (RPE cell bank) and can be provided for cell transplantations with matching HLA type in patients suffering from RPE degenerative diseases.

RESULTS

A total of 461 cell cultures have been prepared since 1996; 116 fully typed and well-differentiated cell cultures are stored in our cell bank. Since January 1998 patients who agreed to have an RPE transplantation have been registered on a waiting list. Seven transplantations have already been performed.

CONCLUSION

RPE cells can be stored cryopreserved in a cell bank and can be kept available for transplantation for a prolonged period of time.