Clonal analysis of limbal epithelial stem cell populations

Xenofree generation of limbal stem cells for ocular surface advanced cell therapy

Background

Limbal stem cells (LSC) sustain the corneal integrity and homeostasis. LSC deficiency (LSCD) leads to loss of corneal transparency and blindness. A clinical approach to treat unilateral LSCD comprises autologous cultured limbal epithelial stem cell transplantation (CLET). CLET uses xenobiotic culture systems with potential zoonotic transmission risks, and regulatory guidelines make necessary to find xenofree alternatives.

Methods

We compared two xenofree clinical grade media and two feeder layers. We used CnT07, a defined commercial medium for keratinocytes, and a modified xenofree supplemented hormonal epithelial medium with human serum (XSHEM). Optimal formulation was used to compare two feeder layers: the gold standard 3T3 murine fibroblasts and human processed lipoaspirate cells (PLA). We tested the expressions of ΔNp63α and cytokeratin 3 and 12 by qPCR and immunofluorescence. Morphology, viability, clonogenicity, proliferation, and cell growth assays were carried out. We also evaluated interleukin 6 (IL-6) and stromal-derived factor 1 (SDF-1) by qPCR and ELISA.

Results

XSHEM maintained better LSC culture viability and morphology than CnT07. Irradiated PLA feeder cells improved the undifferentiated state of LSC and enhanced their growth and clonogenicity stimulating IL-6 secretion and SDF-1 expression, as well as increased proliferation and cell growth when compared with irradiated 3T3 feeder cells.

Conclusions

The combination of XSHEM and PLA feeder cells efficiently sustained LSC xenofree cultures for clinical application. Moreover, PLA feeder layers were able to improve the LSC potential characteristics. Our results would have direct clinical application in CLET for advanced therapy.

Graphical abstract

Ex Vivo Expansion of Human Limbal Epithelial Cells Using Human Placenta-Derived and Umbilical Cord-Derived Mesenchymal Stem Cells

Ex vivo culture of human limbal epithelial cells (LECs) is used to treat limbal stem cell (LSC) deficiency, a vision loss condition, and suitable culture systems using feeder cells or serum without animal elements have been developed. This study evaluated the use of human umbilical cord or placenta mesenchymal stem cells (C-MSCs or P-MSCs, resp.) as feeder cells in an animal/serum-free coculture system with human LECs. C-/P-MSCs stimulated LEC colony formation of the stem cell markers (p63, ABCG2) and secreted known LEC clonal growth factors (keratinocyte growth factor, β-nerve growth factor). Transforming growth factor-β-induced protein (TGFBIp), an extracellular matrix (ECM) protein, was produced by C-/P-MSCs and resulted in an increase in p63⁺ ABCG2⁺ LEC colonies. TGFBIp-activated integrin signaling molecules (FAK, Src, and ERK) were expressed in LECs, and TGFBIp-induced LEC proliferation was effectively blocked by a FAK inhibitor. In conclusion, C-/P-MSCs enhanced LEC culture by increasing growth of the LSC population by secreting growth factors and the ECM protein TGFBIp, which is suggested to be a novel factor for promoting the growth of LECs in culture. C-/P-MSCs may be useful for the generation of animal-free culture systems for the treatment of LSC deficiency.

Limbal Stem Cells from Aged Donors Are a Suitable Source for Clinical Application

Limbal stem cells (LSC) are the progenitor cells that maintain the transparency of the cornea. Limbal stem cell deficiency (LSCD) leads to corneal opacity, inflammation, scarring, and blindness. A clinical approach to treat this condition consists in LSC transplantation (LSCT) after ex vivo expansion of LSC. In unilateral LSCD, an autologous transplant is possible, but cases of bilateral LSCD require allogenic LSCT. Cadaveric donors represent the most important source of LSC allografts for treatment of bilateral LSCD when living relative donors are not available. To evaluate the suitability of aged cadaveric donors for LSCT, we compared three pools of LSC from donors of different ages (<60 years, 60–75 years, and >75 years). We evaluated graft quality in terms of percent of p63-positive (p63+) cells by immunofluorescence, colony forming efficiency, and mRNA and protein expression of p63, PAX6, Wnt7a, E-cadherin, and cytokeratin (CK) 12, CK3, and CK19. The results showed that LSC cultures from aged donors can express ≥3% of p63+ cells—considered as the minimum value for predicting favorable clinical outcomes after LSCT—suggesting that these cells could be a suitable source of LSC for transplantation. Our results also indicate the need to evaluate LSC graft quality criteria for each donor.