What if, in people with blinding retinal disease, one could simply introduce healthy photoreceptor cells derived from stem cells in a dish into the retina and restore vision?
It’s a temptingly simple strategy to cure blindness, but the approach faces a number of scientific hurdles, including introduced cells that die quickly or don’t integrate with the retina.
A new study, published in Stem Cell Reports, overcomes these challenges and marks significant progress toward cell-based therapy. The work, led by a team from the University of Pennsylvania School of Veterinary Medicine, in collaboration with researchers from the University of Wisconsin-Madison, Children’s Hospital of Philadelphia and the National Institutes of Health’s National Eye Institute (NEI), introduced precursors to human photoreceptor cells in the retina of dogs. A cocktail of immunosuppressants allowed the cells to survive for months in the recipients’ retinas, where they began to form bonds with existing retinal cells.
“In this study, we wanted to know if we could improve the surgical delivery of these cells to the subretinal space; two, image the cells in vivo; three, improve their survival; and four, see them migrate to the layer of the retina where they should be and begin to integrate,” said William Beltran, professor of ophthalmology at Penn Vet and senior author of the study. “The answer to all those questions was yes.”
Beltran and Gustavo Aguirre of Penn Vet have long been interested in tackling retinal blindness disorders, and they have had great success to date in producing corrective gene therapies for conditions with known causative genes. But for many cases of hereditary retinal degeneration, no gene has been identified. In other patients, the disease is so advanced that no photoreceptor cells remain intact enough for gene therapy. In either scenario, a regenerative medicine approach, where photoreceptors can be completely re-cultured, would be extremely valuable.
To develop a cell therapy, Beltran’s team joined groups led by John Wolfe of CHOP and Penn Vet; David Gamm at the University of Wisconsin-Madison; and Kapil Bharti at the NEI, in a consortium supported by the NEI’s Audacious Goals Initiative for Regenerative Medicine. The collaboration combined Beltran’s team’s expertise in canine models of retinal degeneration and extensive experience in cell-based therapy approaches from the Wolfe, Gamm and Bharti labs.
Photoreceptor cells, which are made up of rods and cones, form a layer of the outer retina that is crucial for initiating the process of vision, converting the energy of light into an electrical signal. To function properly, they must form a connection or synapse with cells of the inner retina to transmit the visual information. So the goal of this cell therapy is to recreate this layer and enable it to integrate with the other cell types of the retina to pass signals from one layer to the next.
In the current work, the team used stem cell-derived precursors from human photoreceptor cells developed in the Gamm lab to serve as the basis for the cell therapy. Working with the Bharti lab, they developed a new surgical approach to inject the cells labeled with fluorescent markers into the retinas of seven dogs with normal vision and three with some form of hereditary retinal degeneration, then used a variety of non-invasive imaging techniques to track the cells over time.
“Using a large animal model that undergoes a naturally occurring form of retinal degeneration and has a human-sized eye was essential to optimize a safe and efficient surgical procedure to deliver doses of cells to patients. could be used,” says Gamm.
The researchers found that cell uptake was significantly better in the animals with retinal degeneration compared to those with a normal retina.
“What we showed was that, if you inject the cells into a normal retina that has its own photoreceptor cells, the retina is virtually intact and serves as a physical barrier so that the introduced cells don’t connect to the second-order neurons in the brain.” retina, the bipolar cells,” says Beltran. “But in three dogs that were in an advanced stage of retinal degeneration, the retinal barrier was more permeable. In that environment, cells had a better ability to move to the correct layer of the retina.”
Because the transplanted human cells could be interpreted by the dog’s immune system as foreign entities, the researchers did what would be done in other tissue transplant procedures: They gave the dogs immunosuppressants. The trio of drugs had previously been tested by Oliver Garden, a veterinary immunologist at Penn Vet at the time of the study, who is now dean of Louisiana State University School of Veterinary Medicine.
Indeed, while the injected cell populations decreased significantly in dogs not receiving the immune-suppressing drugs, cell numbers decreased but then persisted in the dogs given the cocktail.
Further characterization of the introduced cells revealed evidence of potential synapses. “We saw that yes, some seem to shake hands with those second-order neurons,” Beltran says. “There appeared to be contact.”
The next phase of this project will be to continue optimizing the therapy and then test whether there is a functional response – in other words, improved vision – in the recipients.
William Beltran is a professor of ophthalmology and director of the Department of Experimental Retinal Therapies at the University of Pennsylvania School of Veterinary Medicine.
Beltran’s co-authors of the work were Penn Vet’s Ana Ripolles-Garcia, Natalia Dolgova, Svetlana Savina, John H. Wolfe, Oliver A. Garden, and Gustavo D. Aguirre; the University of Wisconsin-Madison M. Joseph Phillips, Allison L. Ludwig, Sara A. Stuedemann, Uchenna Nlebedum, and David M. Gamm; and Arvydas Maminishkis, Juan Amaral and Kapil Bharti of the National Eye Institute.
This study was supported by the National Institutes of Health (grants EY029890, EY06855, and EY031230), Fighting Blindness Canada, Foundation Fighting Blindness, Research to Prevent Blindness, the Van Sloun Fund for Canine Genetic Research, Retina Research Foundation, Emmett A. Humble Distinguished Directorship of the McPherson Eye Research Institute, the Sanford and Susan Greenberg End Blindness Outstanding Achievement Prize, and the Sandra Lemke Trout Chair in Eye Research.
Stem Cell Reports
Subject of research
Systemic immunosuppression promotes survival and integration of subretinal implanted human ESC-derived photoreceptor precursors in dogs.
Article publication date