Induced pluripotent stem cells as custom therapeutics for retinal repair: progress and rationale

Abstract

Human pluripotent stem cells have made a remarkable impact on science, technology and medicine by providing a potentially unlimited source of human cells for basic research and clinical applications. In recent years, knowledge gained from the study of human embryonic stem cells and mammalian somatic cell reprogramming has led to the routine production of human induced pluripotent stem cells (hiPSCs) in laboratories worldwide. hiPSCs show promise for use in transplantation, high throughput drug screening, "disease-in-a-dish" modeling, disease gene discovery, and gene therapy testing. This review will focus on the first application, beginning with a discussion of methods for producing retinal lineage cells that are lost in inherited and acquired forms of retinal degenerative disease. The selection of appropriate hiPSC-derived donor cell type(s) for transplantation will be discussed, as will the caveats and prerequisite steps to formulating a clinical Good Manufacturing Practice (cGMP) product for clinical trials.

Keywords: clinical good manufacturing practice; human induced pluripotent stem cells; induced pluripotent stem cells; photoreceptor; retina; retinal pigmented epithelium; transplantation.

Figure 1

Optic vesicle-like structures (OVs) derived from human induced pluripotent stem cells (hiPSCs) can form layered retinal structures containing photoreceptor-like cells with potential to form synapses. (A) After 20 days of differentiation, proliferating Ki67+/VSX2+ retinal progenitor cells derived from hiPSCs form a structure resembling the optic vesicle in vivo. (B) An inner layer consisting of post-mitotic HuC/D+ neurons and an outer neuroblastic layer of Ki67+/VSX2+ retinal progenitors can be detected by 50 days. (C) A similar pattern is observed at day 50 with the retinal ganglion cell marker BRN3 and the retinal progenitor marker SOX2. (D) RECOVERIN+ cells with the morphology of immature photoreceptors are located in the outermost layer of the OV where they (E) send processes towards the inner neuronal layers of hiPSC-OVs by day 70. (F) Synaptic proteins such as SYNAPTOPHYSIN are expressed in RECOVERIN+ cells by 90 days, indicating the potential for synapse formation. Scale bar = 50 μm (panels A, B and C); 20 μm (panel D); 10 μm (panel E); 5 μm (panel F).

Figure 2

(A) A large number of RECOVERIN+ cells is present in bulk cultures of isolated hiPSC-OVs at day 90. (B) Upon dissociation of day 90 hiPSC-OV cultures, an enriched population of CRX+/RECOVERIN+ photoreceptor-like cells can be obtained. (C) Compared to the number of RECOVERIN+ cells, relatively few GFAP+ glia are found in dissociated day 90 hiPSC-OVs. Scale bar =100 μm.

Figure 3

Flowchart depicting the potential role of hiPSCs in retinal transplantation therapies relative to current and future hESC-based trials.