Retinitis pigmentosa is a group of hereditary diseases of the eye that lead to progressive loss of vision due to cells in the retina becoming damaged and eventually dying.

Pre-clinical studies carried out in disease models by the our academic collaborators have demonstrated that, when transplanted into the retina, our hRPC technology has the potential to preserve existing photoreceptors, potentially reducing or halting further deterioration of vision. In addition, these hRPC cells have been shown to mature into functional photoreceptors that are capable of becoming engrafted into the photoreceptor layer.

A Phase I/IIa clinical trial in RP subjects is currently ongoing in the US. This study which is being conducted at two sites – Massachusetts Eye and Ear Infirmary in Boston and Retinal Research Institute in Phoenix – is an open-label, dose escalation study to evaluate the safety, tolerability and preliminary efficacy of a single, sub-retinal injection of the hRPC stem cell therapy candidate in patients with advanced RP.

The primary endpoint of the study is safety, with patients being followed up for 12 months post-treatment, which includes measurements of visual acuity.  Expansion into the Phase IIa element of this study involves subjects with some retinal functionality, in contrast to the very poor vision and lack of potential for improvement of the subjects in the Phase I. All three subjects in the first cohort of the Phase 2a element of the study have demonstrated a sustained and further improvement in vision compared with their pre-treatment baseline.

These latest results were presented in April 2019 by Jason Comander MD, PhD, Associate Director, Inherited Retinal Disorders Service, Massachusetts Eye and Ear, and Assistant Professor, Harvard Medical School, at the sixth annual Retinal Cell and Gene Therapy Innovation Summit in Vancouver, Canada, which preceded the 2019 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO).

Summary of the preliminary efficacy data (visual acuity measured using the standardised ETDRS chart, five letters per line):

Subject Visual Acuity at Baseline Improvement vs Baseline
First subject 9 letters + 21 letters (120 day follow up)
Second subject 9 letters + 25 letters (60 day follow up)
Third subject 32 letters + 25 letters (60 day follow up)

At most recent follow-up, subjects in the study showed a mean improvement from baseline in visual acuity of + 23 letters in the treated eye.  The untreated control eyes did not show meaningful improvement (mean change from baseline of + 5 letters, range – 2 to + 12 letters).

An improvement of + 23 letters is equivalent to reading an additional four lines of letters on the ETDRS eye chart, the standardised eye chart used to measure visual acuity in clinical trials.  An improvement of at least + 15 letters from baseline on the ETDRS chart is considered to be clinically meaningful by the US Food and Drug Administration (FDA), as stated in their recent guidance on gene therapy for retinal disorders.  As a comparator, the difference between a patient with 20/20 vision and 20/200 vision (the latter being the legal definition for blindness in terms of central visual acuity) would be the equivalent of being able to read an extra ten lines on the ETDRS chart.

Top-line data from this trial is expected in the second half of 2019.

For an article published by the Foundation for Fighting Blindness regarding this trial click here..