Stem cell grafts for reconstruction of ocular surface

[caption id="attachment_6875" align="alignnone" width="750"] Total corneal conjunctivalization after burn and after a failed traditional autologous limbal transplantation. Image from Paolo Rama MD[/caption]   Autologous cultivated limbal stem cell grafts give good and stable long-term clinical results and have several advantages in the reconstruction of compromised ocular surface due to disease or severe trauma, according to Paolo Rama MD. “Stem cells can be cultured under appropriate culture conditions and can be implanted and remain viable and functional in the long-term. Furthermore, the surgical procedure is simple and reproducible, and cells on fibrin can easily be handled and transported,” Dr Rama said in his EuCornea Medal Lecture at the 7th EuCornea Congress in Copenhagen, Denmark. Dr Rama explained that ocular surface diseases are challenging and complex and that corneal transparency is the final goal of treatment. “A healthy ocular surface is absolutely necessary for the preservation of corneal transparency. Traditional corneal transplants cannot be successful when the ocular surface is impaired,” he said. Much of Dr Rama’s research has focused on limbal stem cell deficiency (LSCD), a disorder often caused by chemical or thermal injury, multiple surgeries, severe infections, or immunologically mediated diseases such as Stevens-Johnson syndrome and atopic keratoconjunctivitis. As early as 1960, pioneering work by Strampelli and Barraquer, and later refined by Kenyon, showed that autologous limbal transplantation was effective for treatment of unilateral LSCD. In 2012, Sangwan et al revised the technique with simple limbal epithelial transplantation (SLET), which required less donor tissue than conventional autografting and which did not require a specialist laboratory for cell expansion. Despite the advantages of the technique, limbal autografts remained a limited option for treating LSCD, said Dr Rama. “There are potential risks for the healthy donor eye, it is not repeatable in case of failure and it is only possible in cases of unilateral LSCD. Furthermore, patients are often fearful about the procedure and surgeons carry a heavy responsibility in the presence of complications,” he said. The revised version of the technique, SLET, also falls short of the optimal solution for LSCD, said Dr Rama. “Studies by Li et al have shown that outgrowths from human limbal explants show a rapid decline in proliferative potential, with transient amplifying cells rather than stem cells migrating on to the surface. There was also a progressive decline in the number of epithelial progenitor cells observed during culture on amniotic membrane. So we need more studies to determine the long-term survival of this procedure,” he said. EFFECTIVE TREATMENT Dr Rama said that ex-vivo expanded cultured stem cells may offer the most viable and effective treatment for LSCD, following on from the pioneering work by Dr Howard Green at Harvard Medical School, who developed the first therapeutic application of cultured cells using keratinocytes for the regeneration of epidermis on severely burned patients. “Thousands of third-degree burned patients have now been grafted in many countries with permanent epidermal regeneration over more than a 20-year period,” said Dr Rama. He noted that the wide variation in the results achieved, ranging from 0% to 100% success rates, depended on a factors such as the properties of the cultured graft, surgical technique to prepare the wound surface and control 
of postoperative infections. In ophthalmology, the first application of the technique by Pellegrini et al successfully restored damaged corneal surfaces with autologous cultivated corneal epithelium in three patients. The autologous limbal cells were cultured on fibrin and clinical-grade 3T3-J2 feeder cells. In a study published in 2010, Dr Rama and co-workers used autologous limbal stem cells cultivated on fibrin to treat 112 patients with corneal damage, most of whom had burn-dependent LSCD. Permanent restoration of a transparent, renewing corneal epithelium was attained in 76.6% of eyes, with failures occurring within the first year. Restored eyes remained stable over time, with up to 10 years of follow-up, said Dr Rama. Buoyed by these positive results, the technique to use autologous limbal stem cells for ocular surface repair and regeneration has been recently approved by the European Commission (Holoclar™) as a commercially available stem cell therapy for use in cases of blindness caused by burning. While autologous cultivated limbal stem cell grafts offer clear advantages over many current methods of ocular surface reconstruction, the complexity and costs of the procedure may inhibit its initial uptake, said Dr Rama. Nevertheless, he said that Holoclar™offers too many advantages not to gain more widespread use in clinical practice over 
the long-term. He compared the situation to that which existed in cataract surgery over 20 years ago, before the advent of phacoemulsification. “Phacoemulsification took more 
than 20 years of research and development to become a routine and safe procedure for cataract surgery. So you should ask your colleagues in cataract if they consider as misguided the early efforts and investment and initial high costs of the phacoemulsification procedure. The reality is that innovative procedures are often not convincing and convenient in the beginning, but later may show clear advantages before becoming routine,” he said. Paolo Rama: rama.paolo@hsr.it