Figure 1. Workflow for the Differentiation of hPSCs into Retinal Pigment Epithelium (RPE) with STEMdiff™ RPE Culture System

hPSC colonies, previously harvested and seeded as clumps, are put directly into the medium provided in STEMdiff™-ACF RPE Differentiation Kit. Seeding into STEMdiff™ RPE Differentiation Medium A induces cells toward immature RPE. A full medium change is performed on Day 1 with fresh STEMdiff™ RPE Differentiation Medium A and then on Day 2 with STEMdiff™ RPE Differentiation Medium B. On Days 4 and 6, medium changes are performed with fresh STEMdiff™ RPE Differentiation Medium C. On Days 7 and every second day thereafter a medium change is performed with fresh STEMdiff™ RPE Differentiation Medium D. On Day 14, immature RPE cells are enzymatically harvested and subcultured in STEMdiff™-XF RPE Maturation Medium with the addition of STEMdiff™-ACF RPE Plating Supplement from Days 14 to 21 to improve survival after passaging. RPE cells begin to mature over the course of 5 weeks of culture in STEMdiff™-XF RPE Maturation Medium and become fully matured by Day 49, possessing key characteristics such as polygonal shape, polarization, pigmentation and phagocytosis.

Figure 2. Robust and Rapid Generation of Mature Retinal Pigment Epithelial Cells (RPE) across multiple PSC Cell Lines with the STEMdiff™-ACF RPE Differentiation Kit

hPSCs were cultured for 14 Days using STEMdiff™-ACF RPE Differentiation Kit and subsequently subcultured in STEMdiff™-XF RPE Maturation Medium. Flow cytometry expression of RPE markers are shown at Day 14 and Day 49. (A) The percentage of cells expressing PMEL17, RPE65, EZRIN, and CRALBP and (B) Viable cell yields for 4 hPSC cell lines. PMEL17 is expressed at Day 14 and 49 while the other markers are only present at Day 49. Data are reported as mean + SEM; n = 16 -20. (C) A cell pellet of mature RPE cells demonstrates the pigmentation. Maturation is further demonstrated with immunohistochemistry for expression of RPE markers at Day 49. (D, E, F, G) Mature RPE display tight junctions marked by localization of ZO1 and BEST1 to cell junctions. Mature RPE are polarized, expressing EZRIN apically and ZO1 subapically and express proteins required for the visual cycle (RPE65).

Figure 3. Mature Retinal Pigment Epithelial (RPE) Cells Display Key Functionalities Corresponding to RPE Behaviour

hPSC’s were cultured for 14 Days using STEMdiff™-ACF RPE Differentiation Kit and subsequently subcultured on cell culture inserts in STEMdiff™-XF RPE Maturation Medium for 5 weeks. Apical and basal conditioned medium were collected from Mature RPE, and a sandwich ELISA was performed to quantify Vascular Endothelial Growth Factor (VEGF) and Pigment Epithelial Derived Growth Factor (PEDF) secretion. (A, B) Mature RPE secreted more basal VEGF and apical PEDF demonstrating RPE display correct apicobasal polarity. Data shown as mean + SEM; n = 3. (C) Mature RPE were able to generate a strong barrier with high transepithelial resistance (TER). Data shown as mean + SEM; n = 3-6. (D) Mature RPE were fed FITC-labelled bovine photoreceptor outer segments (POS) for 4 to 5 hours prior to being enzymatically dissociated for flow cytometry analysis or fixed with paraformaldehyde for immunostaining. (E) Mature RPE efficiently internalize bovine POS. Data shown as mean + SEM; n = 3. (F) A cross-sectional schematic of the cell insert culture system.