Gene therapy for choroideremia using an adeno-associated viral vector encoding Rab escort protein 1: the REGENERATE open-label trial

Article history

The research reported in this issue of the journal was funded by the EME programme as award number 12/66/35. The contractual start date was in August 2015. The draft manuscript began editorial review in October 2023 and was accepted for publication in December 2023. The authors have been wholly responsible for all data collection, analysis and interpretation, and for writing up their work. The EME editors and production house have tried to ensure the accuracy of the authors’ manuscript and would like to thank the reviewers for their constructive comments on the draft document. However, they do not accept liability for damages or losses arising from material published in this article.

Copyright statement

Copyright © 2024 Cehajic-Kapetanovic et al. This work was produced by Cehajic-Kapetanovic et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This is an Open Access publication distributed under the terms of the Creative Commons Attribution CC BY 4.0 licence, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. See: https://creativecommons.org/licenses/by/4.0/. For attribution the title, original author(s), the publication source – NIHR Journals Library, and the DOI of the publication must be cited.

2024 Cehajic-Kapetanovic et al.

Background

Choroideremia is an inherited retinal disease, affecting approximately 1 in 50,000 people, which presents with the same symptoms as a rod–cone dystrophy – beginning in childhood with nyctalopia, followed by gradual loss of peripheral vision and progressive constriction of visual fields, and ultimately resulting in loss of central vision in late adulthood once the degeneration affects the fovea. Choroideremia is caused by null mutations in the CHM gene located on the X-chromosome, and thus has an X-linked recessive mode of inheritance. Males are therefore severely affected by this disease, whereas female carriers present with a range of phenotype severities dependant on the extent and timing of X-chromosome inactivation. 1–3

As the central cone photoreceptors are generally preserved until the late stages of choroideremia, due to the centripetal nature of the degeneration, patients usually retain good visual acuity until degeneration encroaches on the fovea. 4–7 Fundus examinations of patients with choroideremia reveal characteristic centripetal retinal degeneration (Figure 1).

FIGURE 1.

Retinal degeneration in a moderately advanced choroideremia patient. (a) Fundus photograph showing the characteristic centripetal retinal degeneration and (b) fundus autofluorescence image showing the autofluorescent areas of the surviving retinal pigment epithelium and remaining functional retina.

The CHM gene encodes Rab escort protein 1 (REP1), which facilitates intracellular vesicular trafficking. Null mutations in the CHM gene cause a deficiency of REP1 protein, leading to degeneration of the retinal pigment epithelium (RPE), followed by secondary degeneration of photoreceptors and the choroid. 8,9 REP1 mediates the addition of prenyl groups (prenylation) to Rab GTPases, which are needed to anchor the Rabs to the membranes of intracellular organelles and vesicles to enable intracellular trafficking between the retina and RPE. 10 In choroideremia, the absence of functional REP1 causes impaired Rab membrane association. This subsequently leads to impaired intracellular trafficking that disrupts cell homeostasis and causes accumulation of intracellular deposits in the RPE, resulting in retinal degeneration. 11–13 Degeneration primarily occurs in the RPE causing characteristic pigment clumping, before secondary degeneration of photoreceptors and the choroid. 13–15 The disease presents as a rod–cone degeneration, since rods are more vulnerable to RPE degeneration due to their reliance on RPE visual cycle retinal isomerisation. Cones may survive longer because their oxygen requirements from the residual choroidal circulation are less and Mueller cells may compensate for RPE cell deficiency and partly sustain the cone visual cycle. 13,14

Rationale

Gene therapy, a procedure whereby a disease is treated at the genetic level by intracellular delivery of a therapeutic transgene, is an appealing strategy for treating choroideremia. The slow rate of degeneration means that there is a long therapeutic window before cell death occurs. In addition, virtually all cases reported so far are functionally null mutations and are often predicted to result in the severe truncation or absence of endogenous REP1 protein. 13,16 This is useful because the product of the therapeutic gene will not compete with a large pool of mutant protein. This would limit dominant negative effects and, in theory, would mean that only a small amount of functional REP1 protein would be needed to arrest degeneration. 17

Furthermore, the eye is an attractive site for gene therapy for several reasons. Surgical access is relatively straightforward and gene therapy products can be administered directly to cells in the outer retina (photoreceptors and RPE) by subretinal injection. Potential adverse events can be detected and monitored directly via ocular examination. Therapeutic outcomes can be measured directly using non-invasive assessments of visual function and retinal anatomy, with an untreated contralateral eye available as a control. The risk of systemic immune reactions is reduced by the anatomical compartmentalisation of the eye and the immunological privilege provided by the blood–retina barrier. Moreover, the small tissue volume of the subretinal space means that the therapeutic dose required to treat the retina is several thousand times lower in comparison with doses required for treatment of other organs, further reducing the risk of systemic adverse reactions.

Most gene therapies developed thus far as potential treatments for inherited retinal diseases have utilised recombinant adeno-associated virus (AAV) particles as vectors to deliver therapeutic transgenes to target cells in the retina. 18 Different AAV serotypes have slight differences in their capsid proteins and consequently in their cell selectivity. AAV serotype 2 (AAV2) has shown high affinity for photoreceptors and RPE cells. 19 Therapeutic administration is effected by injection of a suspension of AAV2 vector particles into the subretinal space, which are subsequently taken up by photoreceptors and RPE cells. Voretigene neparvovec (Luxturna^®), an AAV2 vector-based gene therapy for treatment of RPE65-associated inherited retinal disease manufactured by Hoffmann-La Roche AG (Basel, Switzerland), became the first retinal gene therapy to be approved by the US Food and Drug Administration (FDA). 20 Following subsequent approval by the European Medicines Agency (EMA),21 Luxturna is now available as an NHS treatment. 22

This gene therapy for choroideremia uses an AAV2 vector containing the coding sequence for human REP1 protein, regulated by a ubiquitous cytomegalovirus-enhanced chicken β-actin promoter and a woodchuck hepatitis virus post-transcriptional regulatory element (WPRE). The vector, designated as AAV2-REP1, was first tested in human subjects in a phase I/II safety and dose escalation study (NCT01461213) at Oxford (UK). A cohort of six participants was initially treated with a dose of up to 1 × 10¹⁰ vector particles administered subretinally in one eye, followed by a cohort of eight participants treated with a higher dose of up to 1 × 10¹¹ vector particles. Initial results were promising with gains in best corrected visual acuity (BCVA) of 11 and 21 letters recorded in the treated eyes of two participants at 6 months post treatment. 17 Two serious adverse events (SAEs) occurred during the clinical trial, comprising a case of retinal thinning due to surgical complications and a case of postoperative inflammation, but otherwise the study data confirmed the safety and possible efficacy of the AAV2-REP1 vector for treatment for choroideremia. 23

An additional 18 choroideremia patients were subsequently treated with a dose of up to 1 × 10¹¹ particles of the same AAV2-REP1 vector administered subretinally in one eye – 6 participants in a phase I/II study (NCT02077361) at Edmonton (Canada), 6 participants in a phase II study (NCT02553135) at Miami (USA) and 6 participants in a phase II study (NCT02671539) at Tübingen (Germany). These studies showed that the AAV2-REP1 vector was generally well tolerated, with a subset of participants achieving clinically significant improvements in BCVA. 24–26 One SAE involving a case of postoperative inflammation was reported in the Edmonton study, resulting in a loss of BCVA (nine letters) in the treated eye of the relevant participant, but it was also reported that surgery had been difficult in the case of this participant, for whom subretinal air and haemorrhage had complicated the subretinal administration of the AAV2-REP1 vector. There were no cases of postoperative inflammation reported in the 12 choroideremia patients treated in Tübingen and Miami. In the Tübingen study, a pre-existing degenerative macular hole opened up in one of the participants during surgery but subsequently closed spontaneously. In the Miami study, two participants developed an atrophic retinal hole in a non-functioning macular area.

In view of these satisfactory clinical outcomes, which indicated that gene therapy for choroideremia using the AAV2-REP1 vector demonstrated a good safety profile and sustained gains in BCVA in a proportion of trial participants,27 the REGENERATE (REP1 gene replacement therapy) phase II study (NCT02407678) was initiated to assess the efficacy of gene therapy (dose of up to 1 × 10¹¹ particles of the AAV2-REP1 vector administered subretinally in one eye) in 30 choroideremia patients at an earlier stage of the disease and therefore still possessing substantial areas of surviving retinal tissue, thereby facilitating the measurement of area changes in order to assess the effect of gene therapy on retinal deterioration.

Another biotechnology company, Spark Therapeutics (Philadelphia, PA, USA), now owned by Hoffmann-La Roche AG (Basel, Switzerland), has initiated a phase I/II safety and dose escalation study (NCT02341807) of a similar AAV2 vector construct which does not contain WPRE. 28 Fifteen choroideremia patients were recruited, of whom 5 participants were treated with a dose of up to 5 × 10¹⁰ vector genomes administered subretinally in one eye, and 10 participants were treated with a higher dose of up to 1 × 10¹¹ vector particles. BCVA returned to within 15 letters of baseline in all but 2 patients (of whom 1 developed acute foveal thinning and the other developed a macular hole). No incidents of intraocular inflammation were reported.

Aim and objectives

The aim of the REGENERATE study was to investigate the efficacy and safety of a single subretinal injection of AAV2-REP1 in participants with a confirmed diagnosis of choroideremia over an assessment period of 24 months post treatment.

Study design

The REGENERATE study is an open-label Phase II clinical trial investigating the efficacy and safety of AAV2-REP1 vector-mediated gene therapy for treatment of choroideremia.

In contrast to other interventional studies, the REGENERATE study recruited choroideremia patients at an earlier stage of the disease and therefore still possessing substantial areas of surviving retinal tissue. The intention behind this study design was to facilitate the measurement of changes in area of surviving RPE (determined by fundus autofluorescence) in order to assess the effect of gene therapy on retinal deterioration.

Whereas in changes in BCVA and other measures of visual function in the treated eye could be compared against baseline values, assessment of the anatomical rate of degeneration ideally required the untreated contralateral eye to be used as an internal control. This condition required, in turn, the inclusion of participants having a fairly symmetrical disease. In consequence, randomisation of treatment of one eye or the other was also required to avoid selection bias.

Equality, diversity and inclusion

According to the 2021 Census, the total population of England and Wales was 59.6 million, broadly composed of the following ethnic groups: 81.7% white (48.7 million), 9.3% Asian (5.5 million) and 9.0% black/mixed/other (5.4 million). As choroideremia is a rare disease affecting approximately 1 in 50,000 people, it was therefore anticipated that the pool of prospective participants for the REGENERATE study consisted of approximately 1000 white, 100 Asian and 100 black/mixed/other choroideremia patients.

In view of the significant challenges in achieving the recruitment target of the REGENERATE study considering the limited pool of choroideremia patients meeting the inclusion criteria, it was not possible to arrange special provisions for recruitment of ethnically diverse trial participants representative of the overall demographic profile of the country.

Patient and public involvement

Choroideremia patients were invited to help with writing patient information sheets, including their feedback on suitable fonts and layouts for sight-impaired persons. The medical charity Fight for Sight was also approached for help in public communication of the aims and objectives of the REGENERATE trial and how choroideremia patients could get involved.

Fight for Sight also co-ordinated a fundraising campaign with the assistance of the Tommy Salisbury Choroideremia Fund, which raised funds for the purchase of an ophthalmic operating microscope with an integrated optical coherence tomography (OCT) scanner for use in the REGENERATE study. OCT operating microscopes have an integrated scanner providing a head-up display of a cross-section of the retina in real time for the surgeon, thereby permitting subretinal delivery of the vector to be achieved more safely and accurately.

Sample size

As this was an exploratory study to assess a new end point (comparative change from baseline in the area of surviving RPE in the treated and control eyes, determined by fundus autofluorescence), there was no predetermined power calculation to determine the number of trial participants. Instead, data from this trial will be used for future power calculations. A sample size of 30 participants in the REGENERATE study was deemed sufficiently statistically powered to show a signal in the primary end point of efficacy (comparative change from baseline in BCVA in the treated and control eyes) based on power calculations from the original phase I/II study (NCT01461213).

Study set-up

The REGENERATE study was listed on the U.S. National Library of Medicine ClinicalTrials.gov database on 3 April 2015: National Clinical Trial identifier (NCT02407678). The study was also registered in the International Standard Randomised Controlled Trial Number (ISRCTN) registry on 18 April 2016: reference ISRCTN15602229. Clinical trial authorisation was given by the Medicines and Healthcare products Regulatory Agency on 11 November 2015: European Union Drug Regulating Authorities Clinical Trials database number 2015-001383-18. Recruitment commenced on 16 August 2016 and closed on 23 May 2019.

Independent oversight of the REGENERATE study was provided by the Trial Steering Committee that received recommendations from the independent Data and Safety Monitoring Committee. (The members of the trial oversight committees are listed in Appendix 2.)

Study setting

The REGENERATE study was conducted at two NHS eye hospitals, namely, the Oxford Eye Hospital and Moorfields Eye Hospital. These sites were selected based on their expertise and prior experience in conducting clinical trials of retinal gene therapies and their access to specialist clinics for patients with inherited retinal diseases.

Protocol

The REGENERATE study protocol is available at https://fundingawards.nihr.ac.uk/award/12/66/35. The REGENERATE study commenced recruitment on protocol version 2.0, dated 19 October 2015. A number of updates and minor corrections were made to the protocol during the course of the study:

• Version 3.0, dated 14 November 2016, included a change of principal investigator at the Moorfields Eye Hospital site, clarifications of the randomisation and informed consent procedures, an amendment to the interval between screening and surgery, amendments to the schedule of assessments (full ophthalmic examination, viral shedding, immunology and colour vision) and a clarification of the procedures for recording and managing study data.

• Version 4.0, dated 4 January 2017, included amendments to the schedule of assessments (vital signs, blood chemistry, immunology, fundus photography and refraction/BCVA).

• Version 5.0, dated 15 March 2017, included an amendment to the inclusion criterion for BCVA such that candidates must have BCVA better than or equal to 6/60 (20/200; LogMAR 1.0).

• Version 6.0, dated 4 October 2017, included amendments extending the oral prednisolone course and permitting administration of 0.2 ml of the AAV2-REP1 vector.

• Version 7.0, dated 8 July 2020, included updates to the safety reporting section to include parameters for determining the clinical significance of changes in BCVA.

Participants

Allocation for treatment

Participants in the REGENERATE study were assigned to one or both of the following cohorts:

• Cohort 1 included all participants and compared changes in BCVA and other measures of visual function in the treated eye against baseline values.

• Cohort 2 included the subset of participants having symmetrical disease for whom selection of the treated eye was randomised and compared the rate of anatomical degeneration in the treated eye and the untreated contralateral (control) eye.

In participants having asymmetrical disease (and therefore not included in Cohort 2), the decision about which eye to treat was made on clinical grounds and the worse-affected eye was chosen.

Note that randomisation was not used for assigning treatment (vs. placebo/standard care as in randomised controlled trials) to participants included in Cohort 2, but solely for selection of the eye to be treated in these participants for whom the progress of retinal degeneration was relatively symmetrical between the two eyes, defined as

• a difference in BCVA of no more than one line of letters, as measured on an Early Treatment Diabetic Retinopathy Study (ETDRS) chart; and

• no more than 25% difference in the area of surviving RPE, as measured by fundus autofluorescence.

Block randomisation was achieved by creating a numbered list on a Microsoft Excel^® (Microsoft Corporation, Redmond, WA, USA) spreadsheet and using the RANDBETWEEN function to generate a value of zero or one in a random fashion, which was assigned to each number on the list. A value of zero indicated that the right eye was to be treated and a value of one indicated that the left eye was to be treated. Participants in Cohort 2 were then assigned an appropriate number and corresponding randomised value.

Intervention

Adeno-associated virus serotype 2 vector encoding Rab escort protein 1 vector suspension (1 × 10¹² vector particles per ml) was supplied by Nightstar Therapeutics (London, UK), now part of Biogen Inc. (Cambridge, MA, USA). Up to 0.1 ml of AAV2-REP1 vector suspension, corresponding to a dose of up to 1 × 10¹¹ vector particles, was administered to the treated eye by subretinal injection. The dose varied slightly dependent on the amount of residual retina. Hence, in more advanced patients, 0.03–0.05 ml might have been sufficient to detach the target area of retina completely. The concentration of vector remained the same.

The surgical technique for subretinal administration of the AAV2-REP1 vector suspension has been described previously. 17 All surgeries took place at the participating hospital sites using the standard BIOM^® (binocular indirect ophthalmic microscope) operating system. 29 Following a standard vitrectomy to remove the vitreous gel (Figure 2a), the retina was detached with 0.1–0.5 ml of balanced salt solution injected through a subretinal cannula connected to a vitreous injection set. A dose of up to 1 × 10¹¹ vector particles was then injected into the subretinal fluid through the same entry site (Figure 2b).

FIGURE 2.

Surgical procedure for subretinal injection of AAV2-REP1 vector. (a) A standard vitrectomy through an operating system to remove the vitreous gel is followed by (b) injection of vector suspension into the subretinal space.

Control eyes received no intervention.

Assessments

Safety reporting

Statistical methods

Cohort 1 comprised the 30 participants who were enrolled in this study, of whom 28 participants had symmetrical disease and were therefore also assigned to Cohort 2. The statistical analyses were therefore performed on the total cohort comparing visual function and anatomical degeneration in treated versus control eyes.

Summary statistics of each assessed variable was performed for treated eyes versus control eyes. Data involving a comparison of an assessed variable between the treated and untreated eyes (of each participant) were estimated as the difference between the eyes (with a 95% confidence interval), and simple analysis of change from baseline (paired t-test) was performed at 24 months post treatment. As most participants (93%) had symmetric disease, analysis of covariance was deemed unnecessary.

Recruitment

Recruitment commenced on 16 August 2016 and closed on 23 May 2019. The recruitment target of 30 participants was achieved, of whom 28 participants had symmetrical disease and could therefore be included in Cohort 2 (for whom selection of the treated eye was randomised).

The progress of actual recruitment versus initial target recruitment is outlined in Figure 3. An initial delay in recruitment was caused by a temporary interruption in the supply of the AAV2-REP1 vector. As choroideremia is a rare disease, additional delays in recruitment caused challenges in finding choroideremia patients meeting the inclusion criteria.

FIGURE 3.

Initial target recruitment and actual recruitment of trial participants.

Participant flow and baseline characteristics

A total of 30 patients met the inclusion criteria and were recruited into the trial, of whom 12 were treated at the Oxford Eye Hospital and 18 at the Moorfields Eye Hospital. The Consolidated Standards of Reporting Trials flow diagram (Figure 4) shows the participant flow through the REGENERATE trial. Cohort 1 comprised the 30 participants who were enrolled in this study. Cohort 2 comprised the 28 participants who had symmetrical disease and for whom selection of the treated eye was randomised. Table 2 shows the participants’ subject identifiers and their CHM gene variants. Participant demographics are shown in Table 3. All participants were male, 29 were white and mean age was 32.1 years [standard deviation (SD) 8.79].

FIGURE 4.

Participant flow through the REGENERATE trial.

Clinical outcomes

Primary efficacy measure

Comparative change from baseline in best corrected visual acuity in treated and control eyes at 24 months post treatment

The primary efficacy-related end point (comparative change from baseline in BCVA, measured in ETDRS letters, in treated and control eyes at 24 months post treatment) was not statistically different between treated eyes [−2.63 letters, standard error of the mean (SEM) 2.76] and control eyes (+2.67 letters, SEM 0.768) in all 30 participants, including 4 participants with ocular SAEs (p = 0.08) (Figure 5a). The difference reduced to 0.84 letters (SEM 0.996) in the treated group and remained similar in the control group at + 2.5 letters (SEM 1.85) when BCVA was analysed in 26 participants with no ocular SAEs (p = 0.53) (Figure 5b).

FIGURE 5.

Comparative change from baseline in BCVA in treated and control eyes in all 30 participants, including 4 participants with ocular SAEs (a) and 26 participants with no ocular SAEs (b). The tick marks on the y-axis are standard errors of the mean, and the data are normally distributed. (As defined by GraphPad Prism software: ns = not significant, p > 0.05; *p < 0.05; **p < 0.005; ***p < 0.0005; ****p < 0.0001.)

Analysis excluding patients who suffered an ocular SAE is standard policy in pivotal studies as the SAEs are used separately to assess risks of the potential treatment effect. This is the approach taken by the regulatory authorities for pivotal studies since a complication, such as loss of vision, will most likely be an outlier for statistical analyses. Furthermore, by treating the ocular SAEs separately, there is more transparency on a small number of participants having a complication which might otherwise be lost amongst a large number of participants with favourable outcomes.

Key secondary efficacy measures

Comparative change from baseline in mean microperimetry, total microperimetry and central microperimetry (four central points) in treated and control eyes at 24 months post treatment

Mean total microperimetry declined from baseline in treated eyes (−3.67 dB, SEM 0.585) and control eyes (−1.11, SEM 0.189) with statistically significant difference between the groups at 24 months post treatment (p = 0.0004) when analysing all 30 participants, including 4 participants with ocular SAEs (Figure 6a). A smaller decline in the treated group was observed when four participants with ocular SAEs were excluded (treated = −2.83 dB, SEM 0.359; control = −1.22 dB, SEM 0.192; p < 0.0001) (Figure 6b). Mean central microperimetry (average of four central points tested) declined in treated eyes (−2.93 dB, SEM 1.33) and control eyes (0.05 dB, SEM 0.584) at 24 months (p = 0.04) (Figure 6c). The decline in the treated group was less when four participants with ocular SAEs were excluded from the analysis (treated group mean = −1.08 dB, SEM 0.986; control group = −0.02 dB, SEM 0.671), and the difference between the groups at 24 months was no longer statistically significant (p = 0.3) (Figure 6d).

FIGURE 6.

Comparative change from baseline in mean microperimetry in treated and control eyes: total microperimetry in all 30 subjects, including 4 participants with ocular SAEs (a), total microperimetry in 26 participants with no ocular SAEs (b), central microperimetry in all 30 participants, including 4 participants with ocular SAEs (c) and central microperimetry in 26 participants with no ocular SAEs (d). The tick marks on the y-axis are standard errors of the mean, and the data are normally distributed. (As defined by GraphPad Prism software: ns = not significant, p > 0.05; *p < 0.05; **p < 0.005; ***p < 0.0005; ****p < 0.0001.)

Comparative change from baseline in total area of autofluorescence in treated and control eyes at 24 months post treatment

Total area of autofluorescence declined from baseline in treated eyes (−5.18 mm², SEM 0.797) and control eyes (−2.47 mm², SEM 0.374) with statistically significant difference between the groups at 24 months post treatment (p = 0.0004) (Figure 7a). The difference reduced to −4.31 mm² (SEM 0.578) in the treated group and remained similar in the control group at −2.22 mm² (SEM 0.295) when the analysis at 24 months was performed excluding four participants with ocular SAEs (p = 0.0003) (Figure 7b).

FIGURE 7.

Comparative change from baseline in total area of autofluorescence in treated and control eyes in all 30 participants, including 4 participants with ocular SAEs (a) and 26 participants with no ocular SAEs (b). The tick marks on the y-axis are standard errors of the mean, and the data are normally distributed. (As defined by GraphPad Prism software: ns = not significant, p > 0.05; *p < 0.05; **p < 0.005; ***p < 0.0005; ****p < 0.0001.)

Safety

Of the 30 participants recruited in the REGENERATE trial, 26 participants (87%) completed the study without any long-standing or unresolved adverse events. No participants discontinued from the study, and no systemic adverse events were reported that were plausibly associated with the study. Most adverse events were treatable, controlled and resolved without sequelae (Figure 8). In total, 128 adverse events (Table 4) were reported during the study:

FIGURE 8.

Best corrected visual acuity, central retinal sensitivity (microperimetry) and autofluorescence pattern in a participant (subject 201) with no SAEs over the 24-month assessment period. The patient had no concerns and reported increased colour depth perception at 24 months. (AF = autofluorescence.)

• Twenty-eight adverse events were classified as non-ocular and identified by the reporting clinician as not associated with the surgical procedure or AAV2-REP1 vector. These included two participants treated at the Oxford Eye Hospital (subjects 203 and 209), who each experienced a non-ocular SAE involving gallstones that required hospitalisation for cholecystitis or cholelithotomy.

• One hundred adverse events were classified as ocular, of which:

  • thirty-eight adverse events were not plausibly associated with the surgical procedure or AAV2-REP1 vector.

  • sixty-two adverse events, including six SAEs, were associated with the surgical procedure or AAV2-REP1 vector.

Six ocular SAEs related to the surgical procedure or AAV2-REP1 vector were reported in four participants treated at Moorfields Eye Hospital:

• A suspected unexpected serious adverse reaction (SUSAR) was reported for subject 602 (Figure 9a) for a profound loss of BCVA in the treated eye caused by sustained postoperative inflammation related to the AAV2-REP1 vector that was not responsive to immunosuppression.

• A SUSAR was reported for subject 603 (Figure 9b) for a clinically significant decrease in BCVA in the treated eye caused by recurring postoperative inflammation related to the AAV2-REP1 vector.

• Three SAEs were reported for subject 617 (Figure 9c) for visual impairment involving loss of autofluorescence and reduced central retinal sensitivity in the treated eye, consequent to choroidal inflammation associated with the AAV2-REP1 vector. BCVA remained stable.

• An SAE was reported for subject 620 (Figure 9d) for a clinically significant decrease in BCVA in the treated eye following surgery.

FIGURE 9.

Best corrected visual acuity, central retinal sensitivity (microperimetry) and autofluorescence pattern in four participants (subjects 602, 603, 617 and 620) with the six ocular SAEs over the 24-month assessment period. (a) Subject 602 experienced a profound loss of BCVA in the treated eye caused by sustained postoperative inflammation related to the AAV2-REP1 vector that was not responsive to immunosuppression; (b) subject 603 experienced a clinically significant decrease in BCVA in the treated eye caused by recurring postoperative inflammation related to the AAV2-REP1 vector; (c) subject 617 experienced visual impairment involving loss of autofluorescence and reduced central retinal sensitivity in the treated eye, consequent to choroidal inflammation associated with the AAV2-REP1 vector. BCVA remained stable; and (d) subject 620 experienced a clinically significant decrease in BCVA in the treated eye following surgery. (continued)

Table 4 details ocular and non-ocular adverse events reported during the study.

Main findings of the study

There has been no signal of possible efficacy of the intervention (in terms of comparative change from baseline in BCVA between treated and control eyes) over the 24-month assessment period.

Overall, BCVA remained relatively stable in treated eyes over the 24-month assessment period. Therefore, in terms of the primary safety-related end point (change from baseline in BCVA in treated eyes at 24 months post treatment), the safety profile of the REGENERATE trial was comparable to other choroideremia gene therapy studies that evaluated the same AAV2-REP1 vector.

Retinal degeneration in choroideremia leads to thin and fragile retinae, making surgical procedures very challenging. Moreover, the RPE at the edges of surviving islands of retinal tissue is very disrupted and may be more susceptible to surgical trauma. A statistically significant deterioration in visual fields was observed in treated eyes compared to control eyes, possibly caused by surgery-induced damage in some treated eyes as manifested by increased loss of autofluorescence and retinal sensitivity at the edges of surviving islands of retinal tissue. The treated eyes underwent retinal detachment prior to injection of the vector suspension into the subretinal space, and this procedure itself can lead to some degree of reduction in central retinal sensitivity and autofluorescence. However, the statistical significance of the comparative reduction in visual fields in treated and control eyes was lost when central retinal sensitivity and area of autofluorescence were analysed in uncomplicated cases. In eyes with no complications, retinal degeneration continued centripetally in both treated and control eyes.

Most adverse events were treatable, controlled and resolved without sequelae. Six SAEs were reported in the treated eyes of four participants: one surgery-related and two inflammation-related SAEs involving clinically significant decreases in BCVA and three SAEs in one participant involving reduction in central retinal sensitivity but with BCVA remaining stable.

Limitations of the study

No evidence of possible efficacy of the intervention was observed, as a meaningful difference in comparative change from baseline in BCVA in treated and control eyes was not discernible over the 24-month assessment period. As choroideremia is a very slow degeneration, BCVA in control eyes did not decline significantly during the assessment period.

Future investigations

Future investigations will include a long-term assessment of BCVA, central retinal sensitivity and area of autofluorescence in REGENERATE trial participants in an observational study (SOLSTICE: NCT03584165). Possible approaches to further the investigation of gene therapy for choroideremia include the optimisation of inclusion criteria for subjects still retaining a healthy central retina which may be more amenable to rescue by gene therapy.

CRediT contribution statement

Jasmina Cehajic-Kapetanovic (https://orcid.org/0000-0002-9956-6412): Data curation (lead), Formal analysis (lead), Investigation (lead), Visualisation (lead), Writing – reviewing and editing (supporting). Marco P Bellini (https://orcid.org/0000-0002-1104-3968): Project administration (lead), Writing – original draft (lead), Writing – reviewing and editing (lead). Laura J Taylor (https://orcid.org/0000-0001-7072-0853): Data curation (supporting), Investigation (supporting), visualisation (supporting), Writing – original draft (supporting). Imran H Yusuf (https://orcid.org/0000-0002-0424-5852): Data curation (supporting), Formal analysis (supporting), Investigation (supporting). Taha Soomro (https://orcid.org/0000-0003-2756-3674): Data curation (supporting), Formal analysis (supporting), Investigation (supporting). Lyndon da Cruz (https://orcid.org/0000-0002-7695-6354): Supervision (equal), Writing – reviewing and editing (supporting). Robert E MacLaren (https://orcid.org/0000-0002-3096-4682): Conceptualisation (lead), Funding acquisition (lead), supervision (equal), Writing – reviewing and editing (supporting). Andrew Stockman: Data curation (supporting), Investigation (supporting). Kanmin Xue: Data curation (supporting), Investigation (supporting). Odysseas Georgiadis: Data curation (supporting), Investigation (supporting). Edward Bloch: Data curation (supporting), Investigation (supporting). Blanca C Flores-Sánchez: Data curation (supporting), Investigation (supporting). Adam M Dubis: Data curation (supporting), Investigation (supporting). Anthony G Robson: Data curation (supporting), Investigation (supporting). Alun R Barnard: Data curation (supporting), Investigation (supporting). Jasleen K Jolly: Data curation (supporting), Investigation (supporting). Andrew R Webster: Funding acquisition (supporting).

Acknowledgements

The authors would like to thank Sr Anna Rudenko and the other members of the Eye Research Group Oxford clinical trials unit at the Oxford Eye Hospital and Mr Panayiotis Panayiotou and the other members of the clinical team at the Moorfields Eye Hospital for their invaluable assistance in co-ordinating the REGENERATE trial at the Oxford Eye Hospital and Moorfields Eye Hospital, respectively. The authors would also like to thank the members of the REGENERATE Study Group (see Appendix 1), Trial Steering Committee (see Appendix 2) and Data and Safety Monitoring Committee (see Appendix 2) for their important contributions.

The study was sponsored by the University of Oxford and supported by the UK Clinical Research Network, NIHR Oxford Biomedical Research Centre (BRC) and NIHR Moorfields BRC.

Patient data statement

This work uses data provided by patients and collected by the NHS as part of their care and support. Using patient data is vital to improve health and care for everyone. There is huge potential to make better use of information from people’s patient records, to understand more about disease, develop new treatments, monitor safety and plan NHS services. Patient data should be kept safe and secure to protect everyone’s privacy, and it is important that there are safeguards to make sure that they are stored and used responsibly. Everyone should be able to find out about how patient data are used. #datasaveslives You can find out more about the background to this citation here: https://understandingpatientdata.org.uk/data-citation.

Data-sharing statement

All data requests should be submitted to the corresponding author for consideration. Access to anonymised data may be granted following review.

Ethics statement

An application for ethical approval was submitted to the Gene Therapy Advisory Committee (GTAC), the United Kingdom’s national Research Ethics Committee (REC) overseeing clinical trials of gene therapies. Ethics approval was granted by the London – West London and GTAC REC on 16 October 2015: reference 15/LO/1379.

Information governance statement

The University of Oxford is committed to handling all personal information in accordance with the Data Protection Act 2018 and the General Data Protection Regulation (GDPR). This is specified in the University’s data protection policy (https://compliance.admin.ox.ac.uk/data-protection-policy) and in the REGENERATE study protocol. The University of Oxford, as sponsor of the REGENERATE study, is the data controller. If you agreed to participate in the REGENERATE study, information regarding the use of your personal data for research purposes by the University of Oxford is available at https://compliance.web.ox.ac.uk/research-data. Information about your individual rights under the GDPR and the contact details of the University’s Information Compliance Team is available at https://compliance.admin.ox.ac.uk/individual-rights.

Disclosure of interests

Full disclosure of interests: Completed ICMJE forms for all authors, including all related interests, are available in the toolkit on the NIHR Journals Library report publication page at https://doi.org/10.3310/WARA5730.

Primary conflicts of interest: Robert E MacLaren reports financial support from the NIHR via Senior Investigator Award NIHR201338 during the conduct of the study; grants, personal fees and non-financial support from Nightstar Therapeutics (London, UK), now part of Biogen Inc. (Cambridge, MA, USA), during the conduct of the study; grants, personal fees and advisory board honoraria from Gyroscope Therapeutics (London, UK), now part of Novartis International AG (Basel, Switzerland), outside the submitted work; and is a named inventor on international patent WO2012114090 (gene therapy for choroideremia), US patent US20160206704 (subretinal administration of retinal gene therapy) and international patent WO2017153774 (assay for Rab escort protein 1).

Disclaimers

This article presents independent research. The views and opinions expressed by authors in this publication are those of the authors and do not necessarily reflect those of the NHS, the NIHR, the MRC, the EME programme or the Department of Health and Social Care. If there are verbatim quotations included in this publication the views and opinions expressed by the interviewees are those of the interviewees and do not necessarily reflect those of the authors, those of the NHS, the NIHR, the EME programme or the Department of Health and Social Care.

Trial Steering Committee

1. Chairperson: Robert Henderson, Consultant Ophthalmic Surgeon, Great Ormond St Children’s Hospital, London, UK.

2. Independent member: Tim Jackson, Consultant Ophthalmic Surgeon, King’s College Hospital, London, UK.

3. Independent member: Edward Lee, Consultant Ophthalmic Surgeon, Epsom and St Helier Hospital, Carshalton, UK.

4. Non-independent member: Adnan Tufail, Consultant Ophthalmic Surgeon, Moorfields Eye Hospital, London, UK.

Data and Safety Monitoring Committee

1. Chairperson: Tony Moore, Professor of Ophthalmology, University of California San Francisco, San Francisco, USA.

2. Member: David Wong, Professor of Ophthalmology, University of Liverpool, Liverpool, UK.

3. Member: Miles Stanford, Professor of Clinical Ophthalmology, King’s College London, London, UK.

4. Member and statistician: Kashfia Chowdhury, Senior Research Associate, University College London, London, UK.