Vladimir Khristov

In Pursuit of Authenticity: Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium for Clinical Applications

Induced pluripotent stem cells (iPSCs) can be efficiently differentiated into retinal pigment epithelium (RPE), offering the possibility of autologous cell replacement therapy for retinal degeneration stemming from RPE loss. The generation and maintenance of epithelial apical‐basolateral polarity is fundamental for iPSC‐derived RPE (iPSC‐RPE) to recapitulate native RPE structure and function. Presently, no criteria have been established to determine clonal or donor based heterogeneity in the polarization and maturation state of iPSC‐RPE. We provide an unbiased structural, molecular, and physiological evaluation of 15 iPSC‐RPE that have been derived from distinct tissues from several different donors. We assessed the intact RPE monolayer in terms of an ATP‐dependent signaling pathway that drives critical aspects of RPE function, including calcium and electrophysiological responses, as well as steady‐state fluid transport. These responses have key in vivo counterparts that together help determine the homeostasis of the distal retina. We characterized the donor and clonal variation and found that iPSC‐RPE function was more significantly affected by the genetic differences between different donors than the epigenetic differences associated with different starting tissues. This study provides a reference dataset to authenticate genetically diverse iPSC‐RPE derived for clinical applications.

Primary Cilium-Mediated Retinal Pigment Epithelium Maturation Is Disrupted in Ciliopathy Patient Cells

SUMMARY Primary cilia are sensory organelles that protrude from the cell membrane. Defects in the primary cilium cause ciliopathy disorders, with retinal degeneration as a prominent phenotype. Here, we demonstrate that the retinal pigment epithelium (RPE), essential for photoreceptor development and function, requires a functional primary cilium for complete maturation and that RPE maturation defects in ciliopathies precede photoreceptor degeneration. Pharmacologically enhanced ciliogenesis in wild-type induced pluripotent stem cells (iPSC)-RPE leads to fully mature and functional cells. In contrast, ciliopathy patient-derived iPSC-RPE and iPSC-RPE with a knockdown of ciliary-trafficking protein remain immature, with defective apical processes, reduced functionality, and reduced adult-specific gene expression. Proteins of the primary cilium regulate RPE maturation by simultaneously suppressing canonical WNT and activating PKCδ pathways. A similar cilium-dependent maturation pathway exists in lung epithelium. Our results provide insights into ciliopathy-induced retinal degeneration, demonstrate a developmental role for primary cilia in epithelial maturation, and provide a method to mature iPSC epithelial cells for clinical applications.

Polarized Human Retinal Pigment Epithelium Exhibits Distinct Surface Proteome on Apical and Basal Plasma Membranes

Surface proteins localized on the apical and basal plasma membranes are required for a cell to sense its environment and relay changes in ionic, cytokine, chemokine, and hormone levels to the inside of the cell. In a polarized cell, surface proteins are differentially localized on the apical or the basolateral sides of the cell. The retinal pigment epithelium (RPE) is an example of a polarized cell that performs a variety of functions that are dependent on its polarized state including trafficking of ions, fluid, and metabolites across the RPE monolayer. These functions are absolutely crucial for maintaining the health and integrity of adjacent photoreceptors, the photosensitive cells of the retina. Here we present a series of approaches to identify and validate the polarization state of cultured primary human RPE cells using immunostaining for RPE apical/basolateral markers, polarized cytokine secretion, electrophysiology, fluid transport, phagocytosis, and identification of plasma membrane proteins through cell surface capturing technology. These approaches are currently being used to validate the polarized state and the epithelial phenotype of human induced pluripotent stem (iPS) cell derived RPE cells. This work provides the basis for developing an autologous cell therapy for age-related macular degeneration using patient specific iPS cell derived RPE.

Validation of iPS Cell-Derived RPE Tissue in Animal Models

Previous work suggests that replacing diseased Retinal Pigment Epithelium (RPE) with a healthy autologous RPE sheet can provide vision rescue for AMD patients. We differentiated iPSCs into RPE using a directed differentiation protocol. RPE cells at the immature RPE stage were purified and seeded onto either electrospun poly(lactic-co-glycolic acid) (PLGA) scaffolds or non-biodegradable polyester cell culture inserts and compared the two tissues. In vitro, PLGA and polyester substrates produced functionally similar results. Following in vitro evaluation, we tested RPE tissue in animal models for safety and function. Safety studies were conducted in RNU rats using an injection composed of intact cells and homogenized scaffolds. To assess function and develop surgical procedures, the tissues were implanted into an acute RPE injury model pig eye and evaluated using optical coherence tomography (OCT), multifocal ERG (mfERG), and histology. Subretinal injection studies in rats demonstrated safety of the implant. Biodegradability and biocompatibility data from a pig model demonstrated that PLGA scaffold is safe, with the added benefit of being resorbed by the body over time, leaving no foreign material in the eye. We confirmed that biodegradable substrates provide suitable support for RPE maturation and transplantation.

A switchable positive and negative air pressure device for efficient and gentle handling of nanofiber scaffolds

A scaffold handling device (SHD) has been designed that can switch from gentle suction to positive pressure to lift and place nanofiber scaffolds. In tissue engineering laboratories, delicate fibrous scaffolds, such as electrospun nanofiber scaffolds, are often used as substrates for cell culture. Typical scaffold handling procedures include lifting the scaffolds, moving them from one container to another, sterilization, and loading scaffolds into cell culture plates. Using tweezers to handle the scaffolds can be slow, can damage the scaffolds, and can cause them to wrinkle or fold. Scaffolds may also acquire a static charge which makes them difficult to put down as they cling to tweezers. An SHD has been designed that enables more efficient, gentle lifting, and placement of delicate scaffolds. Most of the parts to make the SHD can be purchased, except for the tip which can be 3D-printed. The SHD enables more reliable handling of nanofiber scaffolds that may improve the consistency of biomanufacturing processes.

Induced Pluripotent Stem Cell-Derived Autologous Cell Therapy for Age-Related Macular Degeneration

Photoreceptor cell death associated with advanced age-related macular degeneration (AMD) is triggered by degeneration of retinal pigment epithelium (RPE). Replacement of the atrophied RPE cell layer has previously shown potential to preserve visual acuity in autograft surgeries. However, these procedures are risky and complicated. RPE cells derived from patient-specific induced pluripotent stem (iPS) cells can be reproducibly manufactured as a tissue on a surgically compatible substrate and transplanted back into the patient’s eye potentially with no risk of immune rejection. Using a developmentally guided differentiation protocol we have manufactured autologous RPE tissue from AMD patients on a biodegradable scaffold. In vitro, this tissue demonstrates morphological, molecular, and functional attributes that are similar to the native tissue. We have confirmed safety and efficacy of this tissue in vivo in an RPE injury pig model. Our results provide a potential treatment for AMD using autologous iPS cells.