Sub-retinal transplantation of human iPSC-derived retinal sheets: A promising approach for the treatment of macular degeneration

Retinal degenerative diseases affect millions of people worldwide, and legal blindness is generally associated with the loss of cone photoreceptors located in the retinas central region called the macula. Currently, there is no treatment to replace the macula. Addressing this unmet need, we employed control isogenic and hypoimmunogenic induced pluripotent stem cell (iPSC) lines to generate spontaneously polarized retinal sheets (RSs). They presented the advantage of facile customization and large-scale production, exhibiting a polarized 3D architecture within a 2D cell culture environment, thus readily adaptable for clinical applications. RSs were enriched in retinal progenitor and cone precursor cells, which could differentiate into mature S- and M/L-cones in long-term cultures. Single-cell RNA-seq analysis showed that RSs recapitulate the ontogeny of the developing human retina and are devoid of pluripotent stem cells. Isolation of neural rosettes for sub-retinal transplantation effectively eliminated unwanted cells such as RPE cells. In a porcine model of chemically induced retinal degeneration, grafts integrated the host retina and formed a new, yet immature, photoreceptor layer, exhibiting viability for up to 2 months. In one transplanted animal that met all criteria, including correct apicobasal orientation and seamless graft integration, functional and immunohistochemical assays suggest that grafts exhibited responsiveness to light stimuli and established putative synaptic connections with host bipolar neurons. This study underscores the potential and challenges of iPSC-derived RS for clinical applications while establishing the optimal methodology and conditions for RS transplantation, thus paving the path for future long-term functional investigations using RS grafts.