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Transplantation of HLA-typed adult RPE cells can be an effective causal therapy
By using adult HLA-typed cells with the support of postoperative immunosuppressive therapy, the risk of immune rejection is greatly reduced.
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TAORMINA, Italy — Transplantation of HLA-typed adult retinal pigment epithelium (RPE) cells can be an effective causal therapy of geographic atrophy in age-related macular degeneration (AMD). This was shown in a study presented here at the Jules Gonin Club meeting by Gisbert Richard, MD, head of the University Eye Clinic in Hamburg, Germany.
“Geographic atrophy is characterized by a progressive degeneration of the RPE, resulting in secondary atrophy of the choriocapillaris and photoreceptors. At present, there is no effective medical or surgical treatment for it,” Dr. Richard explained.
The first experiments on RPE cell transplantation in AMD were carried out several years ago using fetal RPE cells without additional immunosuppressive therapy. Signs of graft rejection were reported.
“To obviate this problem, we used HLA-typed adult RPE cells from our RPE cell bank and supported the patients with a postoperative course of immunosuppressants. In this way, the risk of immune rejection, which is a major concern for the success of allogenic RPE grafting, was greatly reduced,” he said.
Cell culture
RPE cells were isolated enzymatically from donor eyes and were cultured in a specially designed medium. After multiplication, part of the culture was subcultured for HLA-typing, and the remaining part was cryopreserved for storage in a cell bank.
“HLA-typing is possible with adult human RPE cells,” Dr. Richard said. “However, this is not the only reason why we decided to use adult cells. First of all, they show a lower tendency toward dedifferentiation than fetal cells. Also, our corneal bank can count on a high number of donors, and the number of cells can be further increased by cultivation.”
He explained that both first passage cells and cryopreserved recultivated cells express voltage-dependent CA2+ channels that are characteristic for freshly isolated cells and that cryopreserved cells maintain specific morphologic and functional characteristics in vitro even after storage over a long period of time.
After recultivation of cryopreserved cells for RPE transplantation, membrane integrity and cell number were determined by trypan-blue dye exclusion test.
Transplantation
A total of nine patients, one man and eight women, aged 47 to 78 years, participated in the study. They all suffered from bilateral AMD with geographic atrophy and/or advanced drusen.
“For RPE transplantation, HLA-matched RPE cells were chosen from our bank, showing correspondence on at least four HLA gene loci,” Dr. Richard said.
Preoperatively, patients had a complete ophthalmic examination including fluorescein angiography and optical coherence tomography (OCT). Independent investigators performed vision testing.
“We selected the worse of the two eyes for transplantation. After standard vitrectomy, a small retinotomy was performed temporal or supratemporal to the macula. The retina was detached using a balanced salt solution, and the subretinal fluid was removed,” Dr. Richard said.
“Then, a suspension of RPE cells was injected into the subretinal space using a micropump. A mild cryopexy was applied to the site of retinotomy, and a fluid-gas exchange was performed. Patients were asked to stay in the supine position for 1 hour to allow the injected cells to settle. Subsequently, patients had to stay in the prone position for 1 week to ensure an effective tamponade of the retinotomy,” he added.
No adverse events
Postoperatively, an immunosuppressive therapy was given, consisting of dexamethasone in decreasing doses over a period of 1 week and cyclosporine for 6 months.
“In all patients, the postoperative period was uneventful. No inflammation was seen by slit-lamp biomicroscopy. None of the patients developed retinal detachment. No patients required additional laser treatment,” he said.
As he reported, in some patients, the graft was visible as cell clusters on fundus examination. In one case, choroidal neovascularization developed and could be detected by fluorescein angiography and OCT. In the remaining cases, no edema could be detected during the 6 months of follow-up.
Vision slightly increased in four eyes, remained stable in three eyes and declined in two. Vision did not increase in any of the fellow control eyes. It remained unchanged in six eyes and decreased in three eyes.
Reducing the risk of rejection
“Our study is the first one dealing with transplantation of HLA-typed, cryopreserved adult human RPE cells in patients suffering from geographic atrophy,” Dr. Richard said. “So far, the procedure appears to be safe. None of the patients experienced graft rejection, and this suggests that the risk of allograft rejection after RPE transplantation in the subretinal space can be reduced by the selection of patients, by using HLA-matched RPE cells and by postoperative systemic immunosuppression. This is important, because recent clinical trials and experimental studies in animal models have shown that the immune privilege of the subretinal space is not absolute and static.’
He also stressed the importance of quality and physiological features of cultured human RPE cells for the success of transplantation.
However, the timing of transplantation surgery remains an unsolved problem. It has not been determined whether it would be useful to perform transplantation in an early stage of the disease.
“Surgery must be performed at a time when photoreceptor degeneration is not too advanced, the damage is possibly still reversible,” Dr. Richard said. “However, we believe that, in patients with geographic atrophy, it should be considered a success when further visual loss is prevented or delayed by RPE grafting and before a substantial progression of photoreceptor degeneration occurs. This emphasizes the importance of an RPE cell bank, which enables a prompt supply of HLA-matched RPE cells.”
He also suggested that RPE transplantation could be indicated in some forms of retinitis pigmentosa and macular dystrophies with primary RPE involvement. Candidate diseases for RPE transplantation are, therefore, Leber’s congenital amaurosis, diseases caused by mutations in the retinal transport protein (RP B4), Best’s dominant macular dystrophy (VMD2) and gyrate atrophy.
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Inclusion criteria
Exclusion criteria
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For Your Information:
- Gisbert Richard, MD, is Professor of Ophthalmology and Head of the University Eye Clinic in Hamburg, Germany. He can be reached at University Eye Clinic Hamburg, Martinistr, 52, D-20246 Hamburg, Germany; (49) 40428032301; fax: (49) 40428034906; e-mail: richard@uke.uni-hamburg.de. Dr. Richard has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.