Retinal gene therapy in patients with choroideremia: initial findings from a phase 1/2 clinical trial

Abstract

Background: Choroideremia is an X-linked recessive disease that leads to blindness due to mutations in the CHM gene, which encodes the Rab escort protein 1 (REP1). We assessed the effects of retinal gene therapy with an adeno-associated viral (AAV) vector encoding REP1 (AAV.REP1) in patients with this disease.

Methods: In a multicentre clinical trial, six male patients (aged 35-63 years) with choroideremia were administered AAV.REP1 (0·6-1·0×10(10) genome particles, subfoveal injection). Visual function tests included best corrected visual acuity, microperimetry, and retinal sensitivity tests for comparison of baseline values with 6 months after surgery. This study is registered with ClinicalTrials.gov, number NCT01461213.

Findings: Despite undergoing retinal detachment, which normally reduces vision, two patients with advanced choroideremia who had low baseline best corrected visual acuity gained 21 letters and 11 letters (more than two and four lines of vision). Four other patients with near normal best corrected visual acuity at baseline recovered to within one to three letters. Mean gain in visual acuity overall was 3·8 letters (SE 4·1). Maximal sensitivity measured with dark-adapted microperimetry increased in the treated eyes from 23·0 dB (SE 1·1) at baseline to 25·3 dB (1·3) after treatment (increase 2·3 dB [95% CI 0·8-3·8]). In all patients, over the 6 months, the increase in retinal sensitivity in the treated eyes (mean 1·7 [SE 1·0]) was correlated with the vector dose administered per mm(2) of surviving retina (r=0·82, p=0·04). By contrast, small non-significant reductions (p>0·05) were noted in the control eyes in both maximal sensitivity (-0·8 dB [1·5]) and mean sensitivity (-1·6 dB [0·9]). One patient in whom the vector was not administered to the fovea re-established variable eccentric fixation that included the ectopic island of surviving retinal pigment epithelium that had been exposed to vector.

Interpretation: The initial results of this retinal gene therapy trial are consistent with improved rod and cone function that overcome any negative effects of retinal detachment. These findings lend support to further assessment of gene therapy in the treatment of choroideremia and other diseases, such as age-related macular degeneration, for which intervention should ideally be applied before the onset of retinal thinning.

Funding: UK Department of Health and Wellcome Trust.

Figure 1

Retinal detachment in patients' eyes exposed to vector Images show the retina in patients 1–6 (A, D, G, J, M, and P, respectively) and the corresponding baseline autofluorescent retina (B, E, H, K, N, and Q, respectively). The area of autofluorescent retinal pigment epithelium exposed to vector is annotated on each panel in mm². The limits of the retinal detachment are indicated by the green dotted line and the injection site is indicated with a green dot. The corresponding autofluorescence images and measurements in the retinal pigment epithelium at 6 months are shown in panels C, F, I, L, O, and R. The area of the retinal pigment epithelium did not change substantially 6 months after surgery, although focal loss of autofluorescence superior to the injection site was noted in patient 3 (I). In patients 4 and 6, more than one injection was required to detach the fovea (additional green lines).

Figure 2

Microperimetry at baseline and 6-month follow-up in both eyes of patients with choroideremia given gene therapy Snellen equivalents and microperimetry measurements are shown for both eyes. The left column shows measurements at baseline in patients 1–6 (A, C, E, G, I, and K, respectively) and the right column shows the results 6 months after surgery (B, D, F, H, J, and L, respectively). The eyes injected with vector are indicated by a green icosahedron. The stimulus points from the baseline measurements are stored in the software and mapped onto identical regions of retina during follow-up testing. Black dots indicate points not seen at 0 dB. The movement of the left fundus image in patient 1 (A, B) represents a real shift in fixation (figure 3). The white arrow in panel L is adjacent to the site of the subretinal injection. Although there was thinning in this area, it become the most sensitive point in this retina at 26 dB (fovea 21 dB).

Figure 3

Detailed analysis of retinal function and structure in patients with choroideremia (A) Pre-surgery and (B) 6 months post-surgery analysis of patient 1 showing a shift in the cloud of variable fixation (blue dots; B, white arrow) into the area of retina exposed to vector (dotted white line), but away from the area of surviving autofluorescent retinal pigment epithelium (white solid line) that was not exposed to vector. The increase in retinal sensitivity also correlated anatomically with the region of surviving retina exposed to AAV.REP1 (C, dotted line) and residual outer retina identified with optical coherence tomography scanning (D, green arrow). The thin fovea and injection site can be seen on either side of the residual retina (green arrow). Green dot (L) is the mean centre of all fixation points. ETDRS=Early Treatment for Diabetic Retinopathy Study (a standard vision test). AAV=adeno-associated virus. REP1=Rab escort protein 1.

Figure 4

Vector doses administered to and vision changes in patients with choroideremia (A) Western blot showing REP1 expression from aliquots of 1:10 residual diluted vectors that were removed from syringes after administration to patients and applied to a human cell line (HT1080) in culture. Also shown are the positive (hREP1) and negative controls (lysate from non-transduced cells) and the loading control (α tubulin). (B) Changes in best corrected visual acuity in ETDRS letters in each of the six patients. Horizontal lines represent baseline levels and the columns represent changes at 6 months in the treated (green) and fellow eyes (blue). (C) Shows the changes in retinal sensitivity measured with microperimetry before and 6 months after surgery in the treated and control eyes. The improvement in the treated eyes was correlated with the dose of vector genome particles per mm² in the surviving retina. hREP1=human Rab escort protein 1 (tagged protein positive control). REP1=Rab escort protein 1. ETDRS=Early Treatment for Diabetic Retinopathy Study (a standard vision test). AAV=adeno-associated virus. *Patients 1 and 4 with the greatest improvement in retinal sensitivity also had notable improvements in visual acuity.