Ultrathin Polyimide Membrane as Cell Carrier for Subretinal Transplantation of Human Embryonic Stem Cell Derived Retinal Pigment Epithelium

In this study, we investigated the suitability of ultrathin and porous polyimide (PI) membrane as a carrier for subretinal transplantation of human embryonic stem cell (hESC) -derived retinal pigment epithelial (RPE) cells in rabbits. The in vivo effects of hESC-RPE cells were analyzed by subretinal suspension injection into Royal College of Surgeons (RCS) rats. Rat eyes were analyzed with electroretinography (ERG) and histology. After analyzing the surface and permeability properties of PI, subretinal PI membrane transplantations with and without hESC-RPE were performed in rabbits. The rabbits were followed for three months and eyes analyzed with fundus photography, ERG, optical coherence tomography (OCT), and histology. Animals were immunosuppressed with cyclosporine the entire follow-up time. In dystrophic RCS rats, ERG and outer nuclear layer (ONL) thickness showed some rescue after hESC-RPE injection. Cells positive for human antigen were found in clusters under the retina 41 days post-injection but not anymore after 105 days. In rabbits, OCT showed good placement of the PI. However, there was loss of pigmentation on the hESC-RPE-PI over time. In the eyes with PI alone, no obvious signs of inflammation or retinal atrophy were observed. In the presence of hESC-RPE, mononuclear cell infiltration and retinal atrophy were observed around the membranes. The porous ultrathin PI membrane was well-tolerated in the subretinal space and is a promising scaffold for RPE transplantation. However, the rejection of the transplanted cells seems to be a major problem and the given immunosuppression was insufficient for reduction of xenograft induced inflammation.

本研究探讨了超薄多孔聚酰亚胺（polyimide, PI）膜作为载体，用于兔体内人类胚胎干细胞（human embryonic stem cell, hESC）诱导的视网膜色素上皮（retinal pigment epithelial, RPE）细胞视网膜下移植的适用性。本研究通过向皇家外科学院（Royal College of Surgeons, RCS）大鼠行视网膜下悬浮注射，分析hESC-RPE细胞的体内生物学效应。采用视网膜电图（electroretinography, ERG）与组织学方法对大鼠眼部进行检测。在完成PI膜表面性质与通透性能的分析后，我们在兔模型中开展了携带与未携带hESC-RPE细胞的PI膜视网膜下移植实验。对实验兔进行为期3个月的随访，通过眼底摄影、视网膜电图（ERG）、光学相干断层扫描（optical coherence tomography, OCT）及组织学方法对眼部进行评估。实验全程使用环孢素对实验动物进行免疫抑制处理。在营养不良型RCS大鼠中，hESC-RPE细胞注射后，视网膜电图（ERG）与外核层（outer nuclear layer, ONL）厚度均显示出一定程度的组织修复效果。注射后41天，可在视网膜下簇状分布的区域中检测到人源性抗原阳性细胞，但在105天时未再观察到此类阳性细胞。在兔实验模型中，光学相干断层扫描（OCT）结果显示PI膜放置位置良好。但随着随访时间延长，hESC-RPE-PI复合物表面出现色素丢失现象。仅植入PI膜的眼部未观察到明显炎症反应或视网膜萎缩迹象；而在植入hESC-RPE-PI复合物的眼部，移植膜周围可见单核细胞浸润与视网膜萎缩。综上，超薄多孔PI膜在视网膜下间隙中具有良好的组织耐受性，是一种极具应用前景的RPE细胞移植支架材料。但移植细胞的排斥反应仍是当前面临的主要难题，本次使用的免疫抑制方案不足以减轻异种移植诱导的炎症反应。