Retinitis pigmentosa (RP) is an inherited retinal degenerative disease that leads to progressive vision loss and blindness. In recent years (2022–2025), stem cell-based therapies have shown growing promise as potential treatments for RP, aiming to replace lost photoreceptors or support remaining retinal cells. Below we review key clinical trials and research efforts from the United Kingdom, United States, China, and other countries, focusing on therapies that could be feasible in the near future. A summary table of major studies is provided at the end for quick reference.
United Kingdom (UK)
- ReNeuron’s hRPC Therapy (Phase 2a Trial) – Discontinued: UK-based biotech ReNeuron conducted trials of an allogeneic human retinal progenitor cell (hRPC) therapy (subretinal injections of photoreceptor progenitor cells) for RP. A Phase 2a trial (with sites in the UK, USA, and Spain) was halted in early 2022 due to surgical complications and limited efficacy, and the RP program was discontinued. This setback underscored the challenges of safely delivering cells into the subretinal space in advanced RP patients.
- Photoreceptor Patch (Preclinical, UCL) – Patch Implant for Late-stage RP: Researchers at University College London (UCL) are developing a micro-engineered photoreceptor cell patch derived from stem cells to implant into the retina. The tiny scaffold is designed to hold and support new photoreceptor cells. In animal models, the team is evaluating surgical implantation, biocompatibility, and integration of these cells. This approach aims to restore vision in late-stage RP regardless of the genetic cause by replacing lost photoreceptors on a supportive patch.
- Hypoimmunogenic “Off-the-Shelf” Cells (Preclinical, Newcastle) – Universal Donor Cells: At Newcastle University, Prof. Majlinda Lako’s group (with Retina UK funding) is exploring hypoimmunogenic pluripotent stem cells that can evade immune rejection. By genetically engineering stem cells to be “invisible” to the immune system and then differentiating them into rod and cone photoreceptor precursors, the goal is to create an “off-the-shelf” stem cell therapy applicable to a broad range of RP patients. This proof-of-concept study (started 2023) will transplant these photoreceptor precursors into RP mouse models to assess integration and vision rescue. If successful, it could enable ready-made cell transplants for many patients without the need for immunosuppression.
United States (USA)
- jCyte’s jCell Therapy (Phase 2b → Phase 3) – Intravitreal Retinal Progenitor Cells: California-based jCyte, Inc. is leading an advanced program with jCell, an allogeneic human retinal progenitor cell therapy delivered via intravitreal injection. In a Phase 2b trial, a single injection of 6 million retinal progenitor cells led to significant vision improvements in a subset of patients: treated RP patients gained ~16 letters in visual acuity vs ~2 letters in sham controls at 12 months, along with improvements in visual field and low-light mobility. The therapy was well tolerated (minimally invasive intravitreal delivery). These encouraging results prompted the FDA to grant jCell a Regenerative Medicine Advanced Therapy (RMAT) designation. As of early 2024, jCyte had a positive Type B meeting with the FDA and is preparing a pivotal Phase 3 trial in the second half of 2024. This upcoming trial will further evaluate efficacy in a refined target population and could pave the way for the first approved stem cell therapy for RP if successful.
- UC Davis CD34+ Stem Cell Trial (Phase 1) – Autologous Bone Marrow Stem Cells: A team at UC Davis Health completed a Phase 1 trial using patients’ own CD34+ bone marrow stem cells injected into the vitreous of the eye. Results published in 2024 showed the approach was safe and possibly effective: the procedure had no serious adverse effects, and 4 of 7 treated RP patients showed measurable vision improvements. The rationale is that CD34+ cells release growth factors and home to injured retinal tissue, providing neuroprotective support. Most participants reported subjective vision improvements corroborated by functional tests. Given these promising early outcomes, the researchers plan to expand to a larger trial to further assess efficacy. This mutation-agnostic, autologous approach could complement cell replacement strategies by slowing degeneration.
- BlueRock/Opsis Photoreceptor Program (IND stage) – iPSC-derived Photoreceptors: In 2024, BlueRock Therapeutics (a US biotech owned by Bayer) announced FDA clearance of an IND application for OpCT-001, an induced pluripotent stem cell-derived therapy for primary photoreceptor diseases. Developed in partnership with Opsis Therapeutics (USA) and Fujifilm Cellular Dynamics, OpCT-001 consists of iPSC-derived photoreceptor precursor cells aimed at diseases like RP. With the IND cleared, a US Phase 1 trial is expected to commence, marking one of the first trials transplanting lab-grown photoreceptors in humans. This effort underscores a trend in the USA toward replacement of photoreceptors using iPSC technology, building on extensive preclinical work showing transplanted human photoreceptor cells can integrate and restore visual responses in animal models.
Aside: Another novel U.S. approach comes from Endogena Therapeutics, which in 2022 launched a Phase 1/2a trial of EA-2353, a small molecule intended to activate endogenous retinal stem/progenitor cells in RP. While not a cell transplant, it represents a regenerative strategy to spur the patient’s own cells to repair the retina.
China
- CAS/Beijing hESC-RPE Trial (Phase 1) – Embryonic RPE Cell Transplant: In China, researchers have focused on retinal pigment epithelium support to preserve photoreceptors. A Phase 1 clinical trial sponsored by the Chinese Academy of Sciences (lead by Prof. Qi Zhou) investigated subretinal transplantation of human embryonic stem cell-derived RPE cells in RP patients. The study (NCT03944239) began in 2020 with the goal of assessing safety and changes in visual acuity, visual fields, and retinal structure post-transplant. Although the trial reached its planned end in 2021, detailed results have not been formally published as of 2025. A recent review notes the trial’s status is uncertain, suggesting that safety and efficacy data are still pending or under analysis. This trial is notable as one of the first in China to use an hESC-derived retinal cell therapy for RP, reflecting China’s growing investment in stem cell therapeutics.
- Stem Cell Clinical Practice – MSC Treatments: In the past few years, some hospitals in China have offered experimental mesenchymal stem cell (MSC) treatments for RP, although robust clinical trial data from China are limited. Chinese researchers contribute significantly to global stem cell research and have published encouraging findings on MSC-derived exosomes and other neuroprotective mechanisms in retinal degeneration. However, most MSC use in RP in China has been through small studies or medical practice rather than large, controlled trials. The global evidence (including a large 82-patient trial in Turkey) indicates umbilical cord MSC injections can be delivered safely, with short-term improvements in visual acuity and fields observed at 6-month follow-ups. China’s regulatory environment is tightening around stem cell clinics, and more rigorously monitored trials are anticipated. As of 2025, China’s primary officially registered RP stem cell trial is the RPE transplant above, but additional research is ongoing in laboratories (e.g. generating patient-specific retinal organoids for disease modeling and exploring iPSC-derived retinal cells).
Other Notable International Efforts
- Japan – iPSC-Derived Retinal Sheets (Phase 1): Japan has been at the forefront of iPSC-based therapies. In an open-label study in 2020, a team led by Dr. Masayo Takahashi transplanted allogeneic iPSC-derived retinal organoid sheets into the subretinas of two patients with advanced RP. After 2 years, the grafted sheets survived stably with increased retinal thickness at the transplant site and no serious adverse events. Visual function decline in the treated eyes was slower than in the untreated eyes, although significant vision restoration was not yet achieved. These results, published in Cell Stem Cell (Dec 2023), demonstrate the safety and long-term survival of transplanted retina tissue in humans. Japan is continuing this Phase 1 trial (jRCTa050200027) to treat additional RP patients, marking a major milestone in stem cell therapy – the first transplantation of lab-grown retinal tissue in humans.
- France – I-STEM “STREAM” Trial (Phase 1/2): In France, a collaboration between the Vision Institute/Quinze-Vingts Hospital in Paris and the I-STEM lab is testing an embryonic stem cell-derived RPE patch for RP caused by monogenic mutations. The STREAM trial (NCT03963154), active since 2019, is implanting RPE cell sheets under the retina in 12 RP patients (two cohorts: end-stage “legally blind” patients and a group with less advanced RP). The patch is similar to those used for macular degeneration, aiming to support photoreceptor survival in RP. The primary goal is to assess safety and tolerability of the implanted RPE, while secondary outcomes include visual function tests and observing whether photoreceptor degeneration slows around the patch. As of 2025, interim safety data are positive (no immune rejections reported), and the trial’s estimated completion is 2026. This effort highlights a global trend of repurposing stem cell RPE implants, originally developed for age-related macular degeneration, for inherited retinal dystrophies like RP.
- Worldwide Meta-Analysis & Other Studies: A 2023 meta-analysis of 21 studies (382 patients) from various countries found that about half of RP patients experienced some visual acuity improvement in the first 6 months after receiving stem cell treatments (of various types), but the benefits often plateaued by 12 months. No significant safety issues were identified aside from occasional procedure-related complications. Notably, treatments delivered to the suprachoroidal space (an emerging technique) showed promising efficacy in RP subgroups. This reflects the broad global interest – from Europe to the Middle East – in stem cell approaches, including mesenchymal stem cells (MSC) via different routes (intravitreal, subretinal, suprachoroidal, etc.) and retinal progenitor or RPE cells. For example, a Phase 3 trial in Turkey using umbilical cord MSCs reported improved vision with no major adverse events at 6 months, and a team in Germany (CRTD Dresden) demonstrated that transplanted human cone photoreceptors could restore light responses in blind mice. These international efforts, both clinical and preclinical, reinforce the feasibility and partial efficacy of stem cell therapies for retinal degeneration, while also emphasizing the need for longer-term follow-up and larger controlled trials.
Summary of Key Stem Cell Trials/Studies for RP (2022–2025)
| Study / Therapy | Location | Stem Cell Type | Phase | Institution / Sponsor | Status (2025) |
|---|---|---|---|---|---|
| jCell (jCyte Inc.) – Intravitreal retinal progenitor cells | USA (multi-center) | Allogeneic retinal progenitor cells (hRPC) | Phase 2b completed; Phase 3 starting | jCyte, Inc. (California, RMAT designated) | Phase 2b showed improved vision; Pivotal trial prep for 2024. |
| ReNeuron hRPC Therapy | UK, USA, Spain | Allogeneic retinal progenitor cells (hRPC) | Phase 2a | ReNeuron (UK) | Discontinued Feb 2022 due to complications & low efficacy. |
| UC Davis CD34+ Autologous | USA (California) | Autologous bone marrow CD34+ stem cells | Phase 1 | University of California, Davis | Completed Phase 1; Safe, 4/7 patients with vision gains. |
| OpCT-001 (BlueRock/Opsis) – iPSC photoreceptors | USA (planned) | Allogeneic iPSC-derived photoreceptor precursors | IND cleared (Phase 1 pending) | BlueRock Therapeutics / Bayer (USA) | IND approved by FDA in 2024; Phase 1 trial initiation expected. |
| Japan iPSC Retinal Sheet | Japan (Kobe) | Allogeneic iPSC-derived retinal organoid sheet | Phase 1 | RIKEN/CiRA, Kobe Eye Center | Treated 2 patients; 2-year safety demonstrated, stable grafts (ongoing enrollment). |
| France “STREAM” RPE Patch | France (Paris) | hESC-derived RPE cell patch | Phase 1/2 | I-Stem & Quinze-Vingts Hospital | Active (not recruiting); interim safety OK, follow-up through 2026. |
| China hESC-RPE Subretinal | China (Beijing) | hESC-derived RPE cells (suspension) | Phase 1 | Chinese Acad. of Sciences (Qi Zhou) | Completed enrollment 2021; Status unknown, results pending. |
| MSC Therapy (Kahraman et al.) | Turkey | Umbilical cord MSC (suprachoroidal injection) | Phase 3 | Türkiye (Int. J. Ophthalmol. 2020) | 82 patients treated; 6-mo vision improvement, no serious adverse events. |
Sources: Selected data drawn from clinical trial registries and recent publications as cited in text (e.g., trial IDs NCT03963154 France; NCT03944239 China; and peer-reviewed results).
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