Approximately 2 Million people globally suffer from RP & currently there’s no cure.
We’ve broken down each study that’s looking into Stem Cells for RP in detail, but we know it’s a lot to digest.
At the start of the article, we’ve provided an initial summary of what all the research is telling us.
If you want to look at any study in particular, use the Content Table on the left to go to a particular study, or the conclusion at the end of the article.
We hope this is helpful!
RP Research Snapshot
What the research says about Stem Cells for RP
Stem cell research for retinitis pigmentosa (RP) is still at an early stage. Most studies are small and focused on learning whether these treatments are safe, not on curing the disease. Only a few trials have reached later stages, and none have shown that stem cells can restore lost vision.
How stem cells are working in trials right now
In current studies, stem cells are mainly being used as support cells, not replacement parts. Researchers believe the cells release helpful signals that protect stressed retinal cells, reduce damage, and help remaining vision cells work a little better for a period of time. In some trials, this has led to small or temporary improvements, or slowed vision loss, but the disease usually continues.
Safety so far
Across studies, stem cell treatments for RP have been mostly safe in the short term when done in controlled clinical trials. Serious problems are rare, but some eye-related risks have occurred, especially with more invasive procedures. Because follow-up is often short, long-term safety is still not fully known.
So far, the results from stem cell studies for retinitis pigmentosa are mixed and limited.
Most studies do not restore lost vision.
People do not regain normal eyesight or reverse the disease.
Some people see small or short-term improvements.
In several trials, vision stayed stable for a while, or improved slightly. This might mean better light sensitivity, a small improvement in side vision, or daily tasks feeling a bit easier. These effects are often temporary.
In many cases, vision eventually continues to decline.
Even when improvements happen, the disease usually keeps progressing over time.
Results depend on the type of cells and how advanced the disease is.
People with earlier-stage RP and more remaining retinal cells tend to see better results than those with very advanced disease.
In simple terms:
Stem cells may help support struggling eye cells for a while, but they do not rebuild the eye or cure RP. Scientists are still trying to understand which treatments work best, for whom, and for how long.
Ongoing Trials Looking at Stem Cell Research for RP
Here we look at trials that are currently running for RP. These trials have already started and are not recruiting.
Cedars-Sinai Phase 1 / 2a Trial: Neural Progenitor Cell Transplant for RP: United States
You can read the full study details on their Clinical Trials Page.
This is an early-stage, first-in-human clinical trial being conducted in the United States.
The main goal is to test the safety of transplanting a specific type of stem-derived support cell into the retina of people with retinitis pigmentosa (RP).
Because this is a very early trial, the primary focus is safety. Any potential vision benefit is considered exploratory.
Who Is Running This Trial?
This study is sponsored and run by Cedars-Sinai Medical Center.
The study also lists the California Institute for Regenerative Medicine (CIRM) as a collaborator.
The principal investigator is David Liao, MD, PhD, based at Retina-Vitreous Associates Medical Group in Beverly Hills, California.
Dates
- Study start date: July 22, 2021
- Estimated primary completion date: July 2026
- Estimated study completion date: July 2026
Participants
- Estimated total enrollment: 16 participants
- Age: 18 years and older
- Condition: Diagnosed retinitis pigmentosa
To be eligible, participants must:
- Have a confirmed diagnosis of retinitis pigmentosa
- Show typical signs of RP, such as:
- Night blindness
- Retinal pigment changes
- Narrowed visual fields
- Abnormal electroretinography (ERG) showing rod dysfunction
- Have moderate to advanced vision loss, depending on the study group
- Be medically able to undergo eye surgery
People are excluded if they:
- Have other significant eye diseases that could interfere with surgery or measurements
- Have had recent eye surgery or certain eye injections
- Have serious uncontrolled medical conditions, active infections, or recent cancer
- Are currently using certain immunosuppressive or steroid medications
- Have previously taken part in gene therapy or cell-based therapy studies
- Cannot safely undergo anesthesia or comply with study follow-up
Study Details
The study is testing the safety of injecting CNS10-NPC, a type of human neural progenitor cell, into the subretinal space (a space underneath the retina) of one eye.
This is a:
- Phase 1 / 2a study
- Single-center study
- Open-label study (both doctors and participants know the treatment is given)
- Non-randomized study
- Sequential dose-escalation study
Treatment Groups
All participants receive a single injection into one eye only.
Group 1A
- Vision: 20/200 or worse
- Dose: 300,000 cells
- Participants: 3
Group 1B
- Vision: 20/200 or worse
- Dose: 1,000,000 cells
- Participants: 3
Group 2
- Vision: between 20/80 and 20/200
- Dose: 1,000,000 cells
- Participants: 10
Participants are treated one at a time within each group, with waiting periods between surgeries for safety monitoring.
Types of Cells Used
The treatment uses human neural progenitor cells called CNS10-NPC.
- Neural progenitor cells are early-stage cells from the nervous system.
- They are not fully developed nerve cells, but cells that can mature into certain supportive nerve-related cells.
- In this study, the cells are described as being derived to become astrocytes, which are a type of support cell found in the nervous system.
Cell Source (as stated in the study record)
- The cells are described as clinical-grade human fetal cortical-derived neural progenitor cells
- The cells originally came from a single donated human fetal brain tissue sample.
- That tissue was used to create a permanent cell line, which is grown in the lab and used for the trial.
Delivery Method
- One-time surgical injection
- Delivered into the subretinal space of one eye, it’s injected into a small space underneath the retina in one eye.
- No repeat doses in this study
What They’re Measuring
Primary Focus: Safety
Participants are followed for at least 12 months to monitor:
- Any side effects or serious adverse events
- Blood tests (blood counts and metabolic panels)
- Urine tests
- Immune responses, including donor-specific antibodies
- Changes in vision and visual fields
- Retinal structure using optical coherence tomography (OCT)
Additional Measurements
Researchers also assess:
- Retinal thickness and structure
- Visual field size and sensitivity
- Electroretinography (ERG), which measures retinal electrical activity
- Patient-reported vision function using the VFQ-25 questionnaire
- Changes in the rate of vision loss over time
These additional measures are exploratory and are not designed to prove effectiveness.
Next Steps
Follow-Up Schedule
Participants are followed for approximately 15 months after treatment.
During follow-up visits:
- Safety is continuously monitored
- Vision tests and retinal scans are repeated
- Researchers look for signs that the cells remain in the retina and whether vision changes over time
STREAM Phase 1 / 2 Trial: hESC-Derived RPE Patch Implantation for RP: France
You can read the full study details on its ClinicalTrials.gov record (ID: NCT03963154).
This is an early-stage clinical trial being conducted in France.
The main goal is to test the safety of surgically implanting a laboratory-made retinal support cell patch into the eye of people with retinitis pigmentosa caused by a known genetic mutation.
Because this is a Phase 1 / 2 study, the primary focus is safety and tolerability.
Any potential improvement in vision or retinal structure is considered preliminary and exploratory.
Who Is Running This Trial?
This study is sponsored and run by Centre d’Etude des Cellules Souches.
The trial is conducted at a single hospital site in Paris, France:
- Centre Hospitalier National d’Ophtalmologie des Quinze-Vingts
- The principal investigator is:Stéphane Bertin, MD
Dates
- Study start date: August 19, 2019
- Estimated study completion date (including long-term follow-up): December 15, 2026
Participants
- Actual enrollment: 7 participants
- Planned enrollment: 12 participants
- Age range: 18 to 65 years
- Condition: Retinitis pigmentosa caused by a confirmed monogenic mutation affecting RPE function
Genetic requirement
Participants must have a genetic test confirming a mutation in one of the following genes:
- RPE65
- LRAT
- MerTK
These genes are involved in visual signaling at the level of the retinal pigment epithelium (RPE).
Study cohorts
Participants are divided into two sequential groups:
Cohort 1 (advanced disease)
- Legally blind
- Visual acuity ≤ 20/200 in the best eye
Cohort 2 (less advanced disease)
- Visual acuity between 20/63 and 20/200 in the worst eye
- Visible photoreceptor outer nuclear layer (ONL) on OCT imaging
General eligibility requirements
Participants must:
- Be able to comply with long-term follow-up
- Meet contraception requirements during and after the study treatment period (for men and women of child-bearing potential)
Key exclusions include
- Contraindication to general anesthesia
- Prior gene therapy or cell therapy
- Active hepatitis B, hepatitis C, or HIV
- Positive anti-HLA antibodies
- Pregnancy or breastfeeding
- Other eye diseases that interfere with retinal evaluation
- Recent participation in another clinical trial
- Contraindications to immunosuppressive / immunomodulating therapy (including MMF)
Study Details
What Are They Studying?
The study is testing the safety of implanting a patch made of retinal pigment epithelium (RPE) cells derived from human embryonic stem cells.
This is a:
- Phase 1 / 2 study
- Single-center study
- Open-label study (no masking)
- Non-randomized study
- Sequential cohort study
Treatment Method
All participants receive one treatment only, in one eye.
- The treated eye is the eye with worse vision
- The treatment is a single central subretinal implantation
The implant consists of:
- A monolayer sheet (patch) of human embryonic stem cell-derived retinal pigment epithelium (hESC-derived RPE)
- Surgically placed under the retina (subretinal space)
There are no repeat doses in this study.
Types of Cells Used
- Retinal pigment epithelium (RPE) cells
- Derived from human embryonic stem cells (hESCs)
- Product name: ISTEM-01
RPE cells are support cells in the retina that help maintain photoreceptor health and function.
Cell preparation details
The study record does not provide:
- Specific surface markers
- Manufacturing protocols
- Differentiation markers
- Cell purity or maturity markers
No additional laboratory characterization details are included in the publicly available record.
What They’re Measuring
Primary Focus: Safety
Safety and tolerability are assessed over 56 weeks by monitoring:
- Adverse events
- Serious adverse events
Secondary and Exploratory Assessments
Researchers also assess:
- Position of the implanted patch using serial retinal imaging
- Placement of the patch using spectral-domain OCT
- Retinal blood vessel leakage or perfusion using fluorescein angiography
- Thickness of the RPE layer using B-mode orbital ultrasound
- Visual function tests
- Eye fundus appearance
- Signs of photoreceptor survival
An exploratory test includes:
- Full-field stimulus threshold testing (D-FST) to assess light sensitivity
These measurements are not designed to prove effectiveness, only to observe biological and functional signals.
Next Steps
Follow-Up Schedule
- Participants are followed for 56 weeks after implantation
- After this period, participants enter a long-term follow-up study lasting an additional 4 years
During follow-up:
- Safety monitoring continues
- Retinal imaging and vision testing are repeated
- Researchers monitor whether the patch remains in place and whether retinal structure or visual function changes over time
Completed Trials Looking at Stem Cell Research for RP
Here we look at all the completed trials that have been completed since 2020.
Phase I University of California, Davis Trial: Autologous CD34+ Bone Marrow Stem Cells for RP: USA 2025
The study results were published in the journal Ophthalmology Science in 2025.
This study looked at whether a specific population of bone-marrow repair cells, called CD34⁺ stem cells, taken from a patient’s own bone marrow, could be safely injected into the eye of people with advanced retinitis pigmentosa, and whether there were early signs of benefit for vision over 6 months.
CD34⁺ cells are not retinal or Mesenchymal cells. They are naturally occurring bone-marrow stem and progenitor cells involved in tissue repair and blood-vessel support.
The main goals were:
- To evaluate the safety of intravitreal (inside-the-eye) injection of autologous CD34⁺ bone-marrow stem cells
- To confirm the feasibility of harvesting, preparing, and injecting these cells on the same day
- To explore whether vision, visual fields, retinal structure, and daily visual function remained stable or showed signs of improvement
This was a Phase I, prospective, open-label, single-arm clinical trial.
“Open-label” means both doctors and patients knew the treatment was being given.
Only one eye per patient was treated.
The study was conducted at the University of California, Davis Eye Center and registered on their clinical trials page.
Results Summary
The treatment did not restore lost vision, but visual acuity and visual fields remained stable or showed small improvements in several patients, suggesting a possible supportive effect.
The treatment was generally safe, with no serious or lasting treatment-related complications reported.
The researchers do not believe the cells turned into retinal cells; instead, they believe the cells worked by releasing protective biological signals that helped remaining retinal cells function better.
Participants
Participants:
- 7 patients with retinitis pigmentosa
- 5 men, 2 women
Age range:
- 35 to 70 years
Disease stage:
- Moderate to advanced retinitis pigmentosa
- All patients had significant visual field loss
- Many had vision restricted to within 10 degrees
Disease characteristics:
- Progressive loss of night and peripheral vision
- Flat electroretinography (ERG) signals in all participants
- Genetic testing varied and was not required for inclusion
Inclusion highlights:
- Clinical diagnosis of retinitis pigmentosa
- Age ≥18
- Best-corrected vision between 20/60 and 20/400 or severe visual-field constriction
- Ability to complete follow-up testing
Exclusions:
- Other eye diseases contributing to vision loss
- Active infection or immune suppression
- Blood or bone-marrow disorders
- Conditions affecting bone-marrow health
Study Details
Procedure
Delivery Method
Cells were injected directly into the vitreous cavity of the eye (intravitreal injection).
This approach was chosen because:
- It avoids retinal surgery
- It is less invasive than subretinal injection
- CD34⁺ cells can migrate toward damaged retinal tissue
- The goal is biological support, not cell replacement
Only one eye was treated per patient.
Cell Type & Source
- Autologous bone-marrow–derived CD34⁺ stem cells
- Cells came from the patient’s own bone marrow (not a donor)
Cell Preparation & Quality
Cells were not cultured or expanded.
Preparation steps:
- Bone marrow (50–100 mL) was aspirated from the hip bone
- Processing occurred under GMP (cleanroom) conditions
- Mononuclear cells were isolated using a Ficoll density gradient
- CD34⁺ cells were positively selected using the CliniMACS system
Cells were defined by expression of:
- CD34⁺ (stem/progenitor cell marker)
Quality and release criteria included:
- Cell viability >70%
- Negative Gram stain (no bacteria)
- Acceptable endotoxin levels
- Sterility testing initiated
- Low contamination with T cells (CD3⁺ cells ~1%)
This resulted in a CD34⁺-enriched cell product, not a pure population.
No genetic modification, long-term culturing, or expansion was performed.
Dosage
- Dose range: ~1.6 to 7.05 million viable CD34⁺ cells
- Average dose: ~3.26 million cells
- Injection volume: 0.1 mL
- Frequency: Single injection only
- Vehicle: Sterile saline
Key Results
Safety (Primary Endpoint)
Overall safety profile:
- Generally well tolerated
- No immune rejection (autologous cells)
- No infections, tumors, or severe inflammation
Reported side effects:
- One patient had temporary cells in the front of the eye
- Mild, short-term increase in eye pressure
- Resolved within 24 hours
Serious adverse events:
- None attributed to the treatment
Effectiveness (Exploratory Outcomes)
Visual Acuity:
- Vision remained stable or slightly improved in all patients at 6 months
- No sustained treatment-related vision loss
Visual Fields:
- 5 of 7 patients showed stable or increased visual-field sensitivity
- Changes were modest and variable
Retinal Structure (OCT):
- Retinal thickness remained stable
- No evidence of retinal regeneration
- No structural damage from treatment
Quality of Life:
- Vision-related daily function scores improved in assessed patients
- Improvements were modest but meaningful for daily activities
How the Cells Worked
The researchers do not believe CD34⁺ cells turned into retinal or photoreceptor cells.
Instead, they believe the cells worked through paracrine (supportive) effects:
- CD34⁺ cells migrate toward injured retinal tissue
- They release growth factors and protective signals
These signals may:
- Support surviving retinal cells
- Improve blood-vessel function
- Reduce stress in degenerating retina
In simple terms:
- The cells acted as biological support cells
- They helped remaining vision cells cope better
- They did not rebuild or replace damaged retina
This also explains why:
- Effects were modest
- Disease progression eventually continued
Final Thoughts (Tab 4)
What We Don’t Know (Limitations)
- Very small study (7 patients)
- No placebo or sham injection
- Short follow-up (6 months for primary outcomes)
- Advanced disease stage in most participants
- Long-term durability is unknown
- Optimal dosing and repeat injections not studied
Researchers’ Conclusion
This Phase I study shows that intravitreal injection of autologous CD34⁺ bone-marrow stem cells is feasible and appears safe in patients with retinitis pigmentosa. While the treatment did not regenerate retina or cure the disease, early functional signals suggest that CD34⁺ cells may support remaining retinal cells through biological signaling rather than cell replacement. The authors recommend larger, controlled trials to further evaluate safety, dosing, and potential benefit.
Kobe City Eye Hospital / RIKEN Trial: Allogeneic iPSC-Derived Retinal Organoid Sheets for RP: Japan 2023
The study results were published in the journal Cell Stem Cell in 2023.
This study looked at whether lab-grown retinal tissue (retinal organoid sheets) made from donor-induced pluripotent stem cells (iPSCs) could be safely transplanted under the retina of people with advanced retinitis pigmentosa
And whether the transplanted tissue could survive long-term and show early signs of retinal function over a 2-year period.
Retinal organoid sheets are not injections of loose stem cells. They are structured pieces of developing retinal tissue that contain immature photoreceptors and retinal support cells.
The main goals were:
- To evaluate the long-term safety of subretinal transplantation of allogeneic iPSC-derived retinal organoid sheets
- To confirm whether the transplanted retinal tissue could survive and remain stable for up to 2 years
- To explore whether there were early signals of visual or light-response function, without expecting vision restoration
This was a prospective, open-label, single-arm clinical trial.
- “Open-label” means both doctors and patients knew the treatment was being given
- Only one eye per patient was treated
- The study was conducted at Kobe City Eye Hospital, with research support from RIKEN
- The trial was registered in Japan (jRCTa050200027)
Results Summary
Effectiveness: The treatment did not restore vision, but one patient showed small, temporary improvements in light sensitivity and visual task performance.
Safety: The treatment was generally safe, with no tumors, no immune rejection, and no uncontrolled cell growth observed over 2 years.
How the cells worked: The transplanted cells survived and matured locally as retinal tissue but showed limited evidence of functional integration with the patient’s existing retinal circuitry.
Participants
Participants:
- 2 patients with advanced retinitis pigmentosa
- 1 woman (67 years old), 1 man (42 years old)
Disease stage:
- Severe, late-stage retinitis pigmentosa
- Both patients had vision reduced to hand-motion or near hand-motion levels
Disease characteristics:
- Long-standing night blindness
- Severe visual field constriction
- Extensive loss of photoreceptors
- Inner retinal layers and optic nerve still partially preserved
Genetics:
- One patient had a known RP-related gene mutation (EYS)
- One patient had no identified mutation on a 50-gene panel
Inclusion highlights:
- Clinical diagnosis of advanced retinitis pigmentosa
- Severe vision loss with limited remaining treatment options
- Ability to undergo retinal surgery and long-term follow-up
Exclusions:
- Other eye diseases explaining vision loss
- Conditions increasing surgical risk
- Contraindications to immunosuppression
Study Details
Procedure
Delivery Method
- Subretinal transplantation (under the retina)
Retinal organoid sheets were surgically placed into areas where:
- The inner retina was still present
- Some retinal pigment epithelium (RPE) remained
This approach was chosen because:
- Photoreceptor replacement requires direct contact with retinal circuitry
- Intravitreal injection would not allow structured tissue integration
- The goal was cell replacement, not just biological support
Only one eye per patient was treated.
Cell Type & Source
- Allogeneic iPSC-derived retinal organoid sheets
- Cells came from a donor iPSC line, not from the patient
- The iPSC line was selected to reduce immune mismatch risk
- These were retinal tissue sheets, not single-cell suspensions.
Cell Preparation & Quality
Cells were produced under clinical-grade (GMP) conditions.
Cell preparation steps:
- Donor iPSCs were differentiated into 3D retinal organoids
- Retinal tissue was dissected into thin organoid sheets
- Sheets were divided into:
- A transplant portion
- A quality-control portion
Cell identity and markers:
The retinal organoid sheets contained cells expressing markers consistent with:
- Recoverin⁺ (photoreceptor lineage marker)
- CRX⁺ (photoreceptor precursor transcription factor)
- Opsin-positive cells (developing rods and cones)
- Müller glial markers (retinal support cells)
- Horizontal cell markers (important for synapse formation)
Quality and safety testing included:
- Sterility testing
- Viral screening
- Genetic stability checks
- Tumor-formation risk assessment
- No evidence of uncontrolled proliferation (Ki-67 negative over time)
No genetic modification was performed.
Dosage
- Three retinal organoid sheets per treated eye
- Each sheet approximately 0.5 × 1 mm
- Single surgical procedure only
- No repeat dosing
Key Results
Safety (Primary Endpoint)
- Generally well tolerated
- No tumors
- No uncontrolled tissue growth
- No immune rejection detected
Immune response:
- Patients received temporary immunosuppressive therapy
- Blood tests showed no lymphocyte-graft immune reaction
Surgical safety:
- No retinal detachments caused by the grafts
- No long-term inflammation
- Temporary, manageable side effects only
Effectiveness (Exploratory Outcomes)
Visual Acuity:
- No meaningful improvement in visual acuity
- Vision remained largely unchanged
Light Sensitivity (FST testing):
- One patient showed improved sensitivity to light (blue and red stimuli)
- Improvements were modest and not consistently sustained
Visual Fields:
- No significant improvement
- Disease progression appeared slower in the treated eye compared to the untreated eye
Fixation & Visual Tasks:
- One patient showed temporary improvement in:
- Fixation stability
- Letter recognition tasks
Retinal Structure (OCT Imaging)
- Transplanted tissue remained visible and stable for 2 years
- Retinal thickness increased at the graft site
- No abnormal overgrowth
- No migration of transplanted cells outside the target area
How the Cells Worked
The researchers do not believe the transplanted retinal organoid sheets fully restored normal retinal circuitry.
Instead, they believe:
- The organoid sheets survived and matured locally
- Photoreceptor-like cells formed rosette structures
- Limited synapse-like connections may have formed with host retinal cells
In simple terms:
- The graft acted like a small retinal patch
- It may have provided localized light responsiveness
- It did not rebuild the retina or restore vision
This explains why:
- Effects were small and inconsistent
- Vision was not restored
- The disease continued to progress
Final Thoughts
What We Don’t Know (Limitations)
- Extremely small study (2 patients)
- No control or sham surgery group
- Advanced disease stage limits potential benefit
- Functional integration is difficult to measure clinically
- Long-term effects beyond 2 years are unknown
Researchers’ Conclusion
This early study showed that lab-grown retinal tissue can be transplanted safely in people with advanced retinitis pigmentosa and can survive in the eye for at least two years, without tumors or immune rejection. However, the treatment did not restore vision. Based on these safety results, Sumitomo Pharma announced in a press release in 2024 they have received FDA clearance to begin a Phase 1/2 clinical trial in the United States, using fresh (non-frozen) retinal organoid tissue, with the goal of better testing whether this approach can eventually improve vision.
Ankara University Trial: Umbilical Cord Stem Cells for RP: Turkey 2020
The study results were published in the journal Stem Cell Research & Therapy in 2020.
This study looked at whether mesenchymal stem cells taken from Wharton’s jelly (umbilical cord tissue) could safely improve or stabilise vision in people with retinitis pigmentosa.
The main goals were:
- To check safety
- To see whether the treatment could improve vision, retinal structure, and retinal function
This was a prospective, open-label clinical trial.
- “Open-label” means both doctors and patients knew the treatment was being given, and there was no placebo injection. One eye was treated while the other eye acted as an internal comparison.
- The study was conducted at Ankara University Faculty of Medicine in Turkey between April and October 2019.
Results Summary
The treatment showed signs of working, with patients experiencing measurable improvements in vision and retinal health over six months compared with untreated eyes.
The treatment was considered safe, with no serious side effects or immune reactions reported during the study period.
The researchers do not believe the stem cells turned into new eye cells; instead, they believe the cells released helpful signals that supported and re-activated remaining vision cells and reduced ongoing damage.
Participants
Participants: 32 patients (34 treated eyes) with retinitis pigmentosa
Age range: 18 to 58 years
Disease stage: Moderate to advanced RP (Phase 3 clinical research)
Inclusion highlights:
- Confirmed diagnosis of RP (clinical exams, imaging, ERG, and genetic testing)
- Best corrected visual acuity between 50 and 110 ETDRS letters
- Significant visual field loss
Exclusions:
- Other eye diseases (glaucoma, cataracts)
- Diabetes or major systemic illness
- Smoking
- Conditions that could interfere with vision testing
Study Details
Procedure
Delivery Method
Stem cells were injected into the sub-tenon space (the tissue surrounding the eyeball), not inside the eye.
This approach was chosen to reduce the risk of retinal damage.
Cell Type & Source
- Wharton’s jelly–derived mesenchymal stem cells (WJ-MSCs)
- Allogeneic cells (from a single healthy umbilical cord donor, not the patient)
Cell Preparation & Quality
- Cells were expanded in a cGMP-certified laboratory
- Cells were frozen and stored at passage 3 (P3)
- Cell viability was above 90%
Cells were tested for:
- Correct stem cell markers
- Sterility
- Endotoxins
- Genetic stability
Dosage
- 2 to 6 million cells per eye
- Suspended in 1.5 mL saline
- Single injection per treated eye
- Cells were administered within 24 hours of release from storage
Key Results
Safety (Primary Endpoint)
- Excellent safety profile
- No serious eye complications
- No systemic side effects
- No immune rejection
- One patient had a temporary increase in pre-existing nystagmus (eye movement), which resolved
Effectiveness (Vision & Retinal Function)
Visual Acuity
- Improved from 70.5 letters to 80.6 letters
- This change was statistically significant
Visual Field (Side Vision)
- Mean visual field loss improved from −27.3 dB to −24.7 dB
- Indicates more usable peripheral vision
Retinal Structure
- Outer retinal thickness increased
- From ~100 μm to 119 μm
- This layer contains photoreceptors, the cells damaged in RP
Retinal Electrical Activity
- mfERG tests showed improved central retinal responses
- Full-field ERG showed stronger light responses
- Improvements were seen mainly in the central retina, where cells are more likely still alive
Untreated Eyes
- No meaningful changes
- Supports that improvements were treatment-related
How the Stem Cells Worked
The researchers do not believe the stem cells turned into new retinal cells.
Instead, they believe the cells worked by supporting and reactivating existing retinal cells, mainly through:
Paracrine signalling
The cells release helpful molecules (growth factors, cytokines, exosomes).
Reactivating “dormant” photoreceptors
Some retinal cells in RP are weak but not dead. Growth factors may help them function again.
Reducing chronic inflammation
RP involves long-term inflammation that damages the retina over time.
Supporting retinal support cells
Including retinal pigment epithelium (RPE) and Müller glial cells.
The sub-tenon location allowed these signals to diffuse through the sclera into the retina without directly injecting the eye.
Final Thoughts
What We Don’t Know (Limitations)
No placebo group
Because the study was open-label, placebo effects can’t be fully ruled out.
Single dose only
The study did not test repeat injections.
Short follow-up
Only 6 months of data, long-term durability is unknown.
Dose not optimised
The study did not compare different cell doses.
Researchers Conclusion
This study suggests that sub-tenon injection of umbilical cord–derived mesenchymal stem cells is safe for people with retinitis pigmentosa. The treatment showed meaningful short-term improvements in vision, retinal structure, and retinal function, likely by supporting surviving photoreceptors rather than regenerating new ones. While the results are encouraging, larger, controlled trials with longer follow-up are needed to confirm how effective this treatment truly is and how long the benefits last.
Kayseri Acibadem Hospital Trial: Umbilical Cord Stem Cells for RP: Turkey 2020
The study results were published in the International Journal of Ophthalmology in 2020.
This study looked at whether mesenchymal stem cells taken from umbilical cord tissue could safely improve or stabilise vision in people with retinitis pigmentosa.
The main goals were:
To check safety
To see whether the treatment could improve vision and retinal function
This was a prospective, open-label Phase 3 clinical trial.“Open-label” means both doctors and patients knew the treatment was being given, and there was no placebo or untreated control eye. Both eyes could be treated.
The study was conducted at Kayseri Acibadem Hospital in Turkey between January and December 2019.
Results Summary
The treatment showed signs of working, with statistically significant improvements in visual acuity and visual field over six months.
The treatment was considered safe, with no serious eye or systemic side effects reported.
The researchers do not believe the stem cells turned into new retinal cells; instead, they believe the cells worked by releasing supportive growth factors that helped remaining retinal cells function better.
Participants
Participants: 82 patients (124 treated eyes) with retinitis pigmentosa
Median age: 38.5 years
Disease stage: Moderate to advanced RP
Inclusion highlights:
- Age over 18
- Confirmed diagnosis of retinitis pigmentosa
- Best corrected visual acuity worse than 20/50
- Measurable visual field loss
Exclusions:
- Previous eye surgery (except cataract surgery)
- Other eye diseases (glaucoma, uveitis, strabismus)
- Systemic or neurological disease
- Smoking
- Conditions interfering with imaging or vision testing
Study Details
Procedure
Delivery Method
Stem cells were implanted into the suprachoroidal space, a layer between the white of the eye (sclera) and the blood-rich choroid, using a surgical technique.
This location was chosen to avoid injecting directly into the eye while still allowing stem-cell signals to reach the retina.
Cell Type & Source
- Umbilical cord–derived mesenchymal stem cells (UC-MSCs)
- Allogeneic cells (from donated umbilical cords, not from the patient)
Cell Preparation & Quality
Cells were prepared under full GMP (good manufacturing practice) conditions.
Cells were expanded in culture and tested using flow cytometry.
Markers reported:
- Positive markers: CD73, CD90, CD105
- Negative markers: CD34, CD45, HLA-DR
Cell viability was above 90% at the time of use.
Cells were tested for:
- Identity and purity
- Sterility (bacterial and fungal contamination)
- Potency and viability
Dosage
- 5 million stem cells per eye
- Suspended in isotonic solution with human serum albumin
- Single surgical implantation per eye
- Cells were transported at 2–8°C and used within 24 hours
Key Results
Safety (Primary Endpoint)
- No serious eye complications
- No systemic adverse events
- No infections, tumors, or immune reactions
- One patient had a brief episode of temporary vision loss that resolved without permanent damage
Effectiveness (Vision & Retinal Function)
Visual Acuity
- Statistically significant improvement at 1 month and 6 months
- 46% of treated eyes improved
- 42% remained stable
- 12% worsened
Visual Field
- Significant improvement in visual field sensitivity over 6 months
- Suggests better usable vision rather than structural repair
Retinal Electrical Activity
- mfERG testing showed improved electrical responses in the central retina
- Improvements were seen mainly in central retinal areas
- Peripheral retina showed little or no improvement
Retinal Structure
- No measurable changes on OCT or fluorescein angiography
- Central macular thickness remained stable
How the Stem Cells Worked
The researchers do not believe the stem cells differentiated into retinal or photoreceptor cells.
Instead, they believe the cells worked through paracrine signalling, meaning the stem cells released helpful biological signals that supported surviving retinal cells.
Proposed mechanisms include:
- Release of growth factors that support photoreceptor survival
- Re-activating “dormant” retinal cells that are weak but not dead
- Reducing chronic inflammation in the retinal environment
- Supporting retinal support cells rather than replacing them
The suprachoroidal location allowed these signals to diffuse into the retina through natural blood flow without directly entering the eye.
Final Thoughts
What We Don’t Know (Limitations)
- No placebo or untreated control group
- Short follow-up period (6 months only)
- No genetic testing to see which RP subtypes respond best
- No early-stage RP patients included
- No repeat dosing studied
Researchers’ Conclusion
This study suggests that suprachoroidal implantation of umbilical cord–derived mesenchymal stem cells is safe for people with retinitis pigmentosa. The treatment showed meaningful short-term improvements in visual acuity, visual field, and retinal electrical activity, mainly in the central retina. The benefits are believed to come from supportive growth-factor signalling rather than the stem cells turning into new retinal cells. Long-term follow-up and controlled trials are still needed to confirm durability, ideal timing, and which patients benefit most.
Siriraj Hospital (Mahidol University) Trial: Autologous Bone Marrow Stem Cells for RP: Thailand 2020
The study results were published in the journal Stem Cell Research & Therapy in 2021.
This study looked at whether mesenchymal stem cells taken from a patient’s own bone marrow could be safely injected into the eye of people with advanced retinitis pigmentosa, and whether this showed any short-term signs of benefit for vision.
The main goals were:
- To check safety of intravitreal (inside-the-eye) stem cell injection
- To see whether vision, retinal structure, or visual function showed short-term improvement
This was a Phase I, non-randomized, open-label clinical trial.
“Open-label” means both doctors and patients knew the treatment was being given. There was no placebo injection. One eye was treated, and the other eye acted as a comparison.
The study was conducted at Siriraj Hospital, Mahidol University (Bangkok, Thailand), in collaboration with the Thai Ministry of Public Health, between 2012 and 2020.
Results Summary
The treatment showed temporary signs of benefit, with some patients experiencing short-term improvements in visual acuity that faded over time.
The treatment was mostly safe, with mainly mild and temporary side effects, although one serious delayed complication occurred years later and required surgery.
The researchers do not believe the stem cells turned into retinal cells; instead, they believe the cells worked by releasing supportive biological signals that temporarily helped surviving retinal cells function better.
Participants
Participants:
- 14 patients with retinitis pigmentosa
- 9 men, 5 women
Age range:
- 31 to 61 years
Disease stage:
- Advanced retinitis pigmentosa
- Very poor vision at baseline
- Many had little or no measurable retinal electrical activity (ERG)
Inclusion highlights:
- Confirmed diagnosis of retinitis pigmentosa
- Severe visual impairment
- Very limited visual fields
- Non-recordable or severely reduced ERG
Exclusions:
- Other eye diseases that could affect results
- Severe systemic illness (heart, liver, kidney disease, etc.)
- Pregnancy or breastfeeding
- Inability to attend follow-up visits
Study Details
Procedure
Delivery Method
Stem cells were injected directly into the vitreous cavity of the eye (intravitreal injection).
This route was chosen because:
- It is less invasive than retinal surgery
- It allows a higher number of cells to be delivered
- The cells can release helpful signals into the retina
Only one eye was treated. The untreated eye served as a comparison.
Cell Type & Source
- Bone marrow–derived mesenchymal stem cells (BM-MSCs)
- Autologous cells (taken from the patient’s own body, not a donor)
- Bone marrow was taken from the hip bone (iliac crest).
Cell Preparation & Quality
Cells were:
- Isolated from bone marrow
- Expanded in culture under cleanroom (ISO 5 / Grade A) conditions
- Used at passage 3 (P3)
Cells were tested and confirmed to:
Express MSC markers:
- CD73
- CD90
- CD105
Not express blood or immune markers:
- CD34
- CD45
- HLA-DR
Additional quality checks:
- Cell viability ~92% on average
- Sterility testing (bacteria, fungi, mycoplasma)
- Endotoxin testing
Dosage
Three dose groups were tested:
- 1 million cells
- 5 million cells
- 10 million cells
Other details:
- Single injection only
- Injection volume: 50 μL
- Cells suspended in sterile balanced salt solution
Key Results
Safety (Primary Endpoint)
Overall safety profile:
- Mostly mild and temporary side effects
- Short-term inflammation inside the eye was common but resolved
- Temporary eye pressure increases resolved within 24 hours
Reported side effects included:
- Mild eye pain or irritation
- Temporary inflammation
- Occasional cystoid macular edema
- Minor lens position changes in patients with artificial lenses
Serious adverse event:
- One patient developed abnormal fibrous and bone-like tissue inside the eye several years later
- Required surgical removal
- Vision returned to baseline after surgery
Effectiveness (Vision & Retinal Measures)
Visual Acuity:
- Some patients showed temporary improvements in vision
- Improvements typically appeared between 1 and 8 months
- Vision returned to baseline by 12 months
Dose observations:
- The lowest dose (1 million cells) showed the best balance of safety and short-term improvement
Visual Field:
- Mostly stable
- No clear worsening during the study period
Retinal Structure:
- Retinal thickness remained stable
- No evidence of rapid degeneration
Untreated Eyes:
- Showed similar long-term decline
- Suggests short-term changes may be treatment-related but not durable
How the Stem Cells Worked
The researchers do not think the stem cells turned into new eye or retinal cells.
Instead, they believe the stem cells worked mainly by sending helpful signals to the remaining vision cells that were still alive.
In simple terms:
- The stem cells released supportive substances (often called growth factors and anti-inflammatory signals)
- These signals may have helped weakened but living retinal cells work better for a period of time
Researchers also believe:
- These stem cells do not easily enter the retina itself
- Because of this, they were unlikely to rebuild or replace damaged vision cells directly
This helps explain why:
- Some people noticed temporary improvements in vision
- The effects did not last long-term, and vision later returned to baseline
Overall, the treatment appears to have supported existing cells rather than regenerated new ones.
Final Thoughts
What We Don’t Know (Limitations)
- Very small study (14 patients)
- No placebo or sham injection
- Advanced disease stage only
- Single injection only
- Benefits were temporary
- Long-term risks need further study
Researchers’ Conclusion
This study shows that intravitreal injection of a patient’s own cultured bone marrow mesenchymal stem cells is feasible and generally safe in advanced retinitis pigmentosa. The treatment produced temporary visual improvements and appeared to slow disease progression for a limited time, likely by supporting surviving retinal cells rather than regenerating new ones. The researchers recommend future studies using: Lower doses, Earlier-stage patients, Longer follow-up, Possibly cell-free approaches such as exosomes
Pomeranian Medical University Trial: Autologous Lineage-Negative Bone Marrow Cells for Retinitis Pigmentosa: Poland 2021
The study results were published in the journal Stem Cells International in 2021.
This study looked at whether a specific group of early bone-marrow cells, called lineage-negative (Lin⁻) cells, taken from a patient’s own bone marrow, could be safely injected into the eye of people with retinitis pigmentosa, and whether this showed signs of benefit for vision and retinal function over 12 months.
The main goals were:
- To check the safety of intravitreal (inside-the-eye) injection of autologous Lin⁻ cells
- To see whether central vision, visual fields, retinal electrical activity, and quality of life showed measurable improvement
This was a prospective, open-label, non-randomized clinical trial.
“Open-label” means both doctors and patients knew the treatment was being given.
One eye was treated, and the other eye was used as a comparison (fellow eye).The study was conducted at Pomeranian Medical University (Szczecin, Poland) and registered on their clinical trial page.
Results Summary
The treatment showed modest but measurable improvements in central vision and retinal electrical function, especially in patients with earlier-stage disease.
The treatment was generally safe, but a small number of patients developed retinal complications that required surgery.
The researchers do not believe the cells turned into retinal cells; instead, they believe the cells worked by releasing protective and supportive biological signals that helped surviving retinal cells function better.
Participants
Participants:
- 30 patients with retinitis pigmentosa
- 18 men, 12 women
Age range:
- 19 to 64 years
- Average age: ~42 years
Disease stage:
- Mild to moderate retinitis pigmentosa
- All patients still had measurable central vision
- Some retained useful cone (day-vision) function
Disease duration:
- 9 patients with symptoms for less than 10 years
- 21 patients with symptoms for more than 10 years
Inclusion highlights:
- Confirmed clinical diagnosis of retinitis pigmentosa
- Age 18–65
- Best-corrected vision in the treated eye between 0.1 and 0.5 (Snellen equivalent)
- Ability to give informed consent
Exclusions:
- Other eye diseases (glaucoma, advanced cataract, diabetic eye disease, etc.)
- Recent eye surgery
- Active inflammatory or autoimmune disease
- Cancer, major heart, liver, kidney, or neurological disease
- Prior stem cell therapy
- Use of other experimental RP treatments during the study
Study Details
Procedure
Delivery Method
Cells were injected directly into the vitreous cavity of the eye (intravitreal injection).
This route was chosen because:
- It avoids retinal surgery
- It allows cells to release supportive factors inside the eye
- It is less invasive than subretinal approaches
Only one eye per patient was treated. The untreated eye served as a comparison.
Cell Type & Source
- Autologous bone marrow–derived lineage-negative (Lin⁻) cells
- Cells came from the patient’s own bone marrow (not a donor)
Cell Preparation & Quality
Cells were not cultured or expanded.
Preparation steps:
- Bone marrow was processed under GMP (cleanroom) conditions
- Mononuclear cells were isolated
- Mature blood cells were removed using negative selection
Cells were defined as lineage-negative because they did NOT express markers of mature blood cells, including:
- CD2, CD3 (T cells)
- CD14 (monocytes)
- CD15, CD16 (granulocytes)
- CD19 (B cells)
- CD56 (NK cells)
- CD123
- CD235a (red blood cells)
This process enriches for:
- Early hematopoietic stem cells
- Progenitor cells
- Immature stem-like cells with strong signaling activity
No long-term culturing, expansion, or genetic modification was performed.
Dosage
- Dose: 1 million (1 × 10⁶) Lin⁻ cells
- Injection volume: 0.05 mL
- Frequency: Single injection only
- Cell suspension: Sterile phosphate-buffered saline
Key Results
Safety (Primary Endpoint)
Overall safety profile:
- Mostly well tolerated
- No immune rejection (autologous cells)
- No intraocular infection or severe inflammation
Reported side effects:
- Mild, temporary eye irritation
- Transient floaters from injected cells
- Temporary pressure changes controlled during the procedure
Serious adverse events:
- 3 patients developed tractional retinal detachment
- 2 required surgical repair (vitrectomy)
- 1 was mild and monitored without surgery
- Vision returned to baseline after treatment in operated cases
Effectiveness (Vision & Retinal Measures)
Visual Acuity:
- Average improvement of ~4 ETDRS letters at 12 months
- Improvements appeared early and were maintained
- Patients with disease duration under 10 years improved more (≈14 letters)
Retinal Electrical Function (mfERG):
- Significant improvement in central retinal (cone) activity
- Improvements were greater in treated eyes than untreated eyes
- Suggests better functioning of surviving cone cells
Visual Fields:
- Central visual field (10-2 test) showed modest improvement
- Peripheral visual fields did not change significantly
Retinal Structure:
- No major structural changes on OCT
- No evidence of retinal regeneration
Quality of Life:
- Vision-related quality of life improved for up to 9 months
- Improvements correlated with better central visual function
How the Cells Worked
The researchers do not believe the Lin⁻ cells turned into retinal or photoreceptor cells.
Instead, they believe the cells worked mainly through paracrine (supportive) effects:
- The cells released neurotrophic and protective factors (e.g. BDNF)
- These signals likely helped stressed but living retinal cells survive and function better
- The cells acted as biological support cells, not replacement cells
In simple terms:
- The cells helped existing vision cells work better
- They did not rebuild or replace damaged retina
- This explains why improvements were modest and depended on remaining retinal function
Final Thoughts
What We Don’t Know (Limitations)
- Small study (30 patients)
- No placebo or sham injection
- One-time treatment only
- Benefits were functional, not regenerative
- Long-term durability beyond 12 months is unknown
- Retinal detachment risk needs careful consideration
Researchers’ Conclusion
This study suggests that intravitreal injection of autologous lineage-negative bone marrow cells is feasible and relatively safe in selected patients with retinitis pigmentosa. The treatment produced modest improvements in central vision and retinal function, particularly in patients with earlier disease, and likely worked by supporting surviving retinal cells rather than regenerating new ones. The researchers recommend future studies focusing on: Earlier-stage patients Optimizing cell dose and delivery Better risk control Longer follow-up
Phase II jCyte Trial: Repeat Intravitreal Human Retinal Progenitor Cells (jCell) for RP: USA, 2022
You can read more about this on their Clinical Trials Page.
This Phase II clinical trial looked at whether repeat injections of human retinal progenitor cells, called jCell, could be given safely to adults with retinitis pigmentosa who had already received jCell in an earlier study, and how vision changed over 12 months.
The study was sponsored and run by jCyte, Inc, with clinical sites in California and Massachusetts, and was registered on ClinicalTrials.gov.
All participants had already received jCell previously and were returning for a second injection in the same eye.
What Was Being Tested
The study tested human retinal progenitor cells, which are early-stage retinal cells intended to support damaged retina in retinitis pigmentosa.
The study does not state:
- whether the cells were autologous or allogeneic
- whether the cells were fetal, adult, or iPSC-derived
Only the cell type and dose are described.
The Main Goals of the Study
The main goals were:
- To evaluate the safety of repeat intravitreal (inside-the-eye) injection of human retinal progenitor cells
- To monitor vision stability or change after a second injection
- To assess changes in:
- Visual acuity
- Visual fields
- Contrast sensitivity
- Ability to move in low-light conditions
- Visual acuity
This was a Phase II, prospective, open-label, single-arm clinical trial.
- “Open-label” means both doctors and patients knew the treatment was given
- There was no placebo or sham injection
- Only one eye per patient was retreated
Results Summary
On average, vision did not improve after the repeat injection, and most visual measures showed small declines or stability over 12 months.
Adverse events occurred, including serious adverse events; 6.7% of participants experienced serious events judged related or possibly related to the study drug.
The study does not report evidence of cell differentiation or retinal regeneration; the cells were evaluated primarily for safety, not replacement of lost retina.
Participants:
- 30 adults with retinitis pigmentosa
- All had previously received jCell in an earlier study
Sex:
- 17 men (56.7%)
- 13 women (43.3%)
Average age:
- Mean age: 51.6 years
Disease:
- Retinitis pigmentosa
Study eye:
- Right eye: 46.7%
- Left eye: 53.3%
Inclusion Highlights
- Adults aged 18 years and older
- Completed at least 12 months of follow-up after a prior jCell injection
- Adequate blood, liver, and kidney function
- Ability to attend follow-up visits and testing
- Use of contraception when applicable
Key Exclusions
- Significant systemic illness (heart failure, cancer, autoimmune disease, severe lung disease, etc.)
- Other eye diseases that could affect vision results
- Recent steroid or experimental eye treatments
- Recent cataract surgery or planned surgery within one year
- Known allergy to penicillin, streptomycin, or DMSO
Procedure
Delivery Method
Cells were injected directly into the eye using an intravitreal injection
Why intravitreal injection was used:
- Avoids retinal surgery
- Less invasive than subretinal injection
- Allows broad exposure of the retina
- Designed for biological support, not surgical repair
Only one previously treated eye was retreated per patient.
Cell Type & Source
- Human retinal progenitor cells (hRPCs)
- Also referred to as jCell
- Cell source and donor origin are not specified in the study record
Cell Preparation & Identity
The study does not provide detailed manufacturing steps or culture conditions.
What is specified:
- Single injection of 6.0 million human retinal progenitor cells
- Cells identified as human retinal progenitor cells (hRPCs)
- No markers (e.g. CD markers), differentiation assays, or lineage markers are reported in the provided data
Dosage
- Dose: 6.0 million cells
- Injection volume: Not specified
- Frequency: One repeat injection only
- Route: Intravitreal
- Repeat dosing: Yes (second injection in same eye)
Safety (Primary Endpoint – 12 Months)
Overall safety findings (reported outcomes):
- Any treatment-emergent adverse event: 50.0%
- Events related or possibly related to jCell: 20.0%
- Serious adverse events (all causes): 20.0%
- Serious adverse events related or possibly related to jCell: 6.7%
- Severe adverse events related or possibly related to jCell: 3.3%
Most common non-serious eye event:
- Conjunctival haemorrhage: 20.0%
Deaths during study period:
- 2 participants (6.67%)
- Relationship to treatment not specified
Effectiveness (Secondary Outcomes – Mean Change at 12 Months)
Visual Acuity (BCVA):
- Mean change: −2.34 letters
Visual Fields (KVF area):
- Mean change: −493.96 deg²
Contrast Sensitivity:
- Mean change: −0.57 units
Low-Light Mobility (LLMT):
- Mean change: −0.1 points
Overall, these results indicate no average visual improvement after repeat dosing.
How the Cells Were Thought to Work
The study does not report that the cells:
- Became retinal cells
- Replaced photoreceptors
- Regenerated retinal structure
The trial focused on safety and functional outcomes, and no mechanism of action is formally claimed in the record.
Final Thoughts
What We Don’t Know (Limitations)
- No control or placebo group
- Small study size (30 participants)
- All patients previously treated with jCell
- Vision outcomes were secondary, not primary
- Cell source and manufacturing details not disclosed
- Long-term benefit beyond 12 months unknown
Next Steps
jCyte has started another Phase II, randomized, sham-controlled trial (NCT06912633) to more clearly test whether jCell has a real effect on vision, using a placebo comparison.
This follow-up study is allowed because the repeat-dose trial showed acceptable safety, even though it did not show average visual improvement.
Reviews looking at Stem Cell Research for RP
Here we look at all the reviews analysing Stem Cell Research for RP.
2023 Review on Stem Cell Therapies for Inherited Retinal Diseases: China
You can read more about this review which was published in Stem Cell Research & Therapy.
A team of ophthalmology researchers from Peking University People’s Hospital in Beijing, China, conducted a systematic review and meta-analysis of all available human studies on stem cell therapies for inherited retinal diseases (IRDs), specifically Retinitis Pigmentosa (RP) and Stargardt Disease (STGD).
Their goal was to estimate how safe and effective these treatments are for restoring vision.
Researchers Thoughts Summarized
The treatments appear to be relatively safe, and in many cases showed modest improvements in vision, especially in the first 6 months after treatment.
People with Stargardt Disease saw better and longer-lasting results than those with Retinitis Pigmentosa, who only improved in the short term.
Certain types of stem cells and delivery methods, like umbilical cord stem cells delivered into the suprachoroidal space seemed to work better than others.
The researchers emphasized that while early results are encouraging, there is still a need for larger, better-designed trials to confirm long-term effectiveness and safety.
The team searched PubMed, EMBASE, Web of Science, Cochrane Library, and ClinicalTrials.gov up to August 2023.
They included 21 clinical studies, covering 382 people and 496 eyes (306 people with RP and 76 with STGD).
These were all prospective clinical trials, and some included up to 5 years of follow-up.
Types of Stem Cells Reviewed
- Umbilical cord mesenchymal stem cells (UC-MSCs)
- Bone marrow-derived MSCs
- Adipose-derived MSCs
- Retinal progenitor cells (RPCs)
- Human embryonic stem cell–derived retinal pigment epithelial cells (hESC-RPE)
Delivery Routes Reviewed
- Suprachoroidal space injection (between the white of the eye and the retina)
- Subretinal injection (beneath the retina)
- Intravitreal injection (into the gel of the eye)
- Intravenous infusion (into the bloodstream)
What they were trying to find out
The main goal was to assess how much vision improved (using a scale called logMAR) and how safe the procedures were. They also looked at how different cell types and injection methods affected the outcomes.
Effectiveness
For RP patients, 49% of treated eyes improved at 6 months, but only 30% still showed improvement at 12 months.
The average improvement at 6 months was −0.12 logMAR (meaning better vision).
But by 12 months, the improvement was not statistically significant.
For STGD patients, the results were stronger:
- 60% of eyes improved at 6 months, and 55% at 12 months.
- Vision continued to improve, with average gains of −0.14 logMAR at 6 months and −0.17 logMAR at 12 months.
Mechanism of Action
The researchers believe stem cells may help in several ways:
- Secreting growth and protective factors to support damaged retinal cells
- Replacing or repairing lost photoreceptors or RPE cells
- Reducing cell death and inflammation
- Possibly even transferring useful material to host cells to help them function better
Best Delivery Method
- Suprachoroidal space injection (a newer method) gave the best results and had the fewest side effects, especially for RP.
- Subretinal injection showed promise but carried more risk.
- Intravitreal injection was easier but less effective.
Best Stem Cell Type
Among the stem cell types tested, umbilical cord-derived MSCs (UCMSCs) showed the most consistent benefit for RP.
Safety
Overall, no systemic (whole-body) side effects were reported.
Ocular side effects were rare but included:
- Retinal detachment
- Vitreous hemorrhage
- Epiretinal membrane formation
These were linked to surgical technique, not the stem cells themselves.
No Serious Long-Term Harm was seen in the majority of patients when procedures were done properly.
Stem cell therapy is a promising approach for both Retinitis Pigmentosa and Stargardt Disease, especially in the short term.
Suprachoroidal delivery of umbilical cord stem cells appears particularly effective and safe.
But the researchers caution that long-term results, especially for RP, are uncertain, and the current evidence is still weak due to small study sizes and inconsistent methods.
They strongly recommend larger, randomized controlled trials with longer follow-up and standardized procedures to move the field forward.
Conclusion: What The Research on RP Shows
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