Survival, engraftment, and immune evasion of hypoimmune RPE cell transplants in the nonhuman primate

About This Grant

PROJECT SUMMARY Millions of elderly individuals suffer from visual impairment due to dry age-related macular degeneration (AMD), for which effective treatments are limited. In advanced stages of dry AMD, the gradual loss of retinal pigment epithelial (RPE) cells leads to the death of overlying photoreceptors, causing progressive vision loss and eventual blindness. Transplantation of healthy RPE to replace lost/diseased RPE cells have shown in rodent studies to rescue rod and cone photoreceptors, improve retinal electrophysiological responses, and enhance visual thresholds over extended periods. However, these studies have used xenogeneic (across species) cell transplants, which require immune suppression (IS) to prevent the host’s immune system from rejecting the transplanted cells. Similarly, allogeneic (same species) RPE cell transplants in non-immune suppressed models, including pigs and nonhuman primates, are typically rejected within three weeks. Although IS appears currently necessary and sufficient to protect transplanted cells, it raises significant safety concerns, especially for elderly AMD patients who may experience toxic side effects from long-term or indefinite IS use. Additionally, IS introduces challenges such as patient compliance and the risk of rejection with suboptimal dosages. Current Phase I/II clinical trials using allogeneic RPE cells combine multiple IS medications to prevent rejection, but the majority of adverse effects stem from the IS regimen rather than the cell therapy itself. To address the complications of IS, the NIH has initiated an autologous RPE cell trial, despite the high logistical and cost barriers to broad implementation. In contrast, our approach focuses on developing a scalable allogeneic cell-based therapy that can avoid immune rejection, providing greater access, efficiency, and lower costs. We have demonstrated feasibility of this approach in multiple settings including short-term RPE cell transplants in the eye in non-immune suppressed NHPs. In the proposed studies, we will generate multiple lines of allogeneic induced pluripotent stem cells (iPSCs) from nonhuman primates (NHPs) and engineer them to lack expression of class I and II major histocompatibility complexes and to overexpress the “don’t eat me” signal, CD47. We will then optimize the differentiation of these modified iPSCs into RPE cells for transplantation studies in both normal and diseased NHP retinas. Transplantation studies will include short and long-term survival and in diseased retinal conditions to replicate acute version chronic rejection in normal and diseased retinal environments. Finally, we will optimize the use of a safety switch to enable selective removal of cells in the subretinal space should that ever be necessary. These studies will demonstrate the potential of gene-modified RPE cells to evade immune rejection while maintaining a high safety profile and will help identify factors in retinal disease environments that may affect the survival of transplanted RPE cells. Successful completion of these aims will lay the groundwork for translating these studies toward clinical application.