preservation of human embryonic stem cell-derived retinal pigment epithelial cells with optimized cryopreservation

Advancing Cryostorage of Human Stem Cell-Derived Retinal Pigment Epithelial Cells

The retinal pigment epithelium (RPE) is a pigmented monolayer of cells required for maintaining the proper function of the retina1. RPE dysfunction and death are closely associated with many retinal degenerative diseases, including age-related macular degeneration, retinitis pigmentosa, and Stargardt disease2,3. RPE replacement therapy is one of the most promising treatment regimens for these diseases4,5,6,7. A stable supply of donor RPE cells is vital for cell therapy. Human embryonic stem cell (hESC)-derived RPE cells are an ideal cell source for cell therapy because they mimic the function of primary RPE cells and can produce a theoretically unlimited supply8. However, the differentiation process is laborious and the shelf-life of the obtained RPE cells is relatively short because of subsequent epithelial-mesenchymal transition (EMT). Therefore, the cryopreservation of hESC-derived RPE cells is an indispensable step required for long-term storage and on-demand distribution9.
Cryopreservation-induced cellular damage can inadvertently compromise therapeutic efficacy10,11. Therefore, recent studies on cryopreservation have proposed that optimal cryogenic storage conditions should be determined when designing cell therapies12. Successful cryopreservation guarantees efficient cell recovery, high viability, and cell function restoration after the freeze-thaw cycle. However, previous studies on the cryopreservation of the adherent monolayers of mammalian cells have reported highly variable (35%-95%) survival rates after thawing13,14,15. Many factors considerably affect the outcomes of cryopreservation, particularly during the freezing stage16,17. Recent research showed that RPE cells frozen at different time points exhibited varied recovery after thawing17. To the best of our knowledge, studies on the determination of the optimal freezing time window for stem cell-derived RPE cells are lacking. In different studies, the cells were frozen at various stages: some cells were frozen shortly after passaging or before confluency or pigmentation8,15,18, whereas others were frozen at other time points9,19,20,21. Furthermore, there is no clear evidence of whether the phase or stage of RPE cells used for cryopreservation affects RPE function after thawing. In our previous study, we demonstrated for the first time that the exponential phase of cell growth (P2D5) is the best stage for the cryopreservation of hESC-derived RPE cells in terms of cell viability and the recovery of cellular properties and functions17.
The method established here aims to cryopreserve hESC-derived RPE at an optimal stage to achieve the best preservation in terms of cell viability and function after thawing. Using the 5-ethynyl-2&#39;-deoxyuridine (EdU) labeling assay to detect the exponential phase of DNA synthesis before cryopreservation, thawed RPE cells exhibited &#62;80% viability and attachment rate, RPE-specific gene expression, polarized cell morphology, pigment epithelium-derived factor secretion, appropriate transepithelial resistance, and phagocytic ability8,17,22. Although this protocol focuses&#160;on hESC-derived RPE cells and not all therapeutic cells are equally cryopreserved, the strategy of freezing in the exponential phase may be applied to many other therapeutic cells.

Author Spotlight: Development of an Efficient and Feasible Method of Retinal Pigment Epithelial Cell Freezing

Cryopreservation of Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells at the Optimal Stage

Our lab aims to better understand the molecular mechanism of retinal diseases, with a focus on unmet medical needs of patients. We aim to develop effective treatments, such as stem-cell-based therapies, for them. Cryopreservation of stem-cell-derived RPE cells is an important step for RPE replacement therapy.Currently, the cells are frozen at various stages, resulting in highly variable survival rates for thawing. This is needed to determine the optimal cell stage for freezing these cells. Our protocol provides a simple, efficient, and inexpensive ways of freezing RPE cells by determining the exponential phase of RPE cells for freezing.It's less dependent of differentiated methods or cell lines.

Preservation of Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells with Optimized Cryopreservation

To begin, dissociate the hESC-derived retinal pigment epithelial cells, prepare the cell suspension, and then count the cells. Now, centrifuge the cells at 250g for three minutes at room temperature. Pour out the supernatant, then, resuspend the cell pellet in cryopreservation medium.Next, transfer one milliliter of the cell suspension to a 1.2-milliliter cryogenic vial. Place the cryogenic vials in a freezing container and freeze overnight at minus 80 degrees Celsius. Transfer the vials to liquid nitrogen for long-term storage.To thaw the frozen vials, first heat the culture medium in metallic beads heated to 37 degrees Celsius, pre-fill 10 milliliters of the warmed culture medium into a 15-milliliter tube. Now, remove the cryogenic vials from the liquid nitrogen and place them in an automated thawing system for rapid thawing. Drop 0.5 to one milliliter of the preheated culture medium into the cryogenic vial to ensure gradual cell adaptation.Then, pipet 1.5 to two milliliters of the cell suspension to the 15-milliliter tube with medium. Centrifuge the cells at 250g for three minutes at room temperature. Then, discard the supernatant.Resuspend the pellet in two milliliters of warm medium. Load the cells in a hemocytometer and count them to determine the recovery and survival rates. Culture the thawed cells on basement membrane coated plates in a culture medium with Y27632.The retinal pigment epithelial cells that were frozen on day five in their exponential phase displayed a higher attachment rate after thawing. Relative to their characteristic hexagonal morphology, the cells frozen at other time points had a fibroblastic phenotype. P2 day-five cells displayed higher expression and more properly localized cell markers 28 days after thawing.It was noted that different cryopreservation media performed equally well in achieving high cell viability and attachment post-thawing.

preservation-human-embryonic-stem-cell-derived-retinal-pigment

Research

JoVE Journal

Medicine

Retinal pigment epithelial&#160;(RPE) cells derived from human embryonic stem cells (hESCs) are superior cell sources for cell replacement therapy in individuals with retinal degenerative diseases; however, studies on the stable and secure banking of these therapeutic cells are scarce. Highly variable cell viability and functional recovery of&#160;RPE cells after cryopreservation are the most commonly encountered issues. In the present protocol, we aimed to achieve the best cell recovery rate after thawing by selecting the optimal cell phase for freezing based on the original experimental conditions. Cells were frozen in the exponential phase determined by using the 5-ethynyl-2&#8242;-deoxyuridine labeling assay, which improved cell viability and recovery rate after thawing. Stable and functional cells were obtained shortly after thawing, independent of a long differentiation process. The methods described here allow the simple, efficient, and inexpensive preservation and thawing of hESC-derived RPE cells. Although this protocol focuses on RPE cells, this freezing strategy may be applied to many other types of differentiated cells.

This study provides a detailed protocol for the efficient cryopreservation of human stem cell-derived retinal pigment epithelial cells.

Retinal pigment epithelial&#160;(RPE) cells derived from human embryonic stem cells (hESCs) are superior cell sources for cell replacement therapy in ...

Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cell Dissociation and Optimal Cryopreservation Stage Determination

To begin, dilute a vial of thawed cold basement membrane matrix with 12 milliliters of DM EM F12. Mix the suspension well. Add one cover slip into each well of a 24-well plate.Then, pipette 250 microliters of the dilute matrix solution into each well. Discard the culture medium of the cultured hESC derived retinal pigment epithelial cell plates. Wash the plates two times with one milliliter of preheated PBS per well.Next, add 0.5 milliliters of the cell dissociation reagent to the wells of the culture plates, and incubate them at 37 degrees Celsius for 15 minutes to initiate digestion. After incubation, observe the cells under the microscope to confirm the end of digestion. Now with a one milliliter pipette, gently pipette the cell suspension up and down 10 times.Add preheated culture medium to dilute the suspension. Then, centrifuge it at 250 G for three minutes at room temperature. Pour out the supernatant from the centrifuge tube.Then, re-suspend the cell pellet in two milliliters of the culture medium. Use a pipette to mix the cells 10 to 15 times. Filter the cell suspension through a 40 micrometer cell strainer.Next, count the retinal pigment epithelial cells. Aspirate the coating solution before plating. Then, add one milliliter of the culture medium into each well and seed the cells on the cover slips.After EDU incorporation and staining, capture the images of five random fields with a fluorescence microscope. Calculate the percentage of EDU positive cells. Then, plot the corresponding proportion time curves to generate a growth curve.Lastly, determine the freezing window from the exponential phase for each cell line. The retinal pigment epithelial cells initially lost their characteristic hexagonal morphology, but later regained it in the exponential phase of growth. When the cells were cultured for an additional week, cell proliferation decreased.EDU proliferation assay confirmed that P2 day five cells exhibited a higher proliferation rate, whereas P2 day 11 cells had entered the deceleration phase.