ReNeuron shares clinical data on stem cell vision loss therapy

ReNeuron has presented detailed data from a phase 1/2a clinical trial of its stem cell treatment for retinitis pigmentosa. Shares in ReNeuron fell more than one-third after the release of top-line data at the start of the month, but the biotech argued the detailed results are positive for its prospects. 

The phase 2a portion of the study enrolled 10 patients with the genetic vision loss disorder retinitis pigmentosa. Each received 1 million cells isolated from fetal retinas in one of their subretinal spaces. The trial was designed to assess the theory that the human retinal progenitor cells can slow, stop or reverse vision deterioration by comparing each patient’s treated and untreated eyes. 

Data presented in April showed the vision in the treated eyes of the first three patients improved by more than 20 letters from baseline on a visual acuity scale. However, the results from the next five patients were less impressive, dragging the average two-month improvement from baseline down to 5.4 letters.

Pravin Dugel, a consultant to ReNeuron and clinical ophthalmology professor, provided more details (PDF) on what changed between the first and second updates at an event in San Francisco over the weekend. 

Dugel highlighted the performance of two subjects who experienced events related to the surgical procedure or patient selection. The events led to vision loss. After 90 days, one of those patients had suffered a more than 40-letter deterioration in their treated eye. The other patient had experienced a more than 10-letter decline. 

Data on the two subjects partly explain why the results presented this month were worse than the data shared on the first three patients in April. However, the other three recently treated patients who did not suffer adverse events only experienced relatively small improvements in their vision.

When the two patients who suffered adverse events are included in the analysis, the untreated eyes of the patients improved by more than the treated eyes at the 90-day cutoff. After removing those two patients, the average control-adjusted improvement in the treated eyes is 9.5 letters. 

Dugel concluded his presentation by saying the phase 1/2a results will “provide a better understanding of optimal patient selection and surgical procedure standardization for future study design.” ReNeuron now plans to talk to its advisers and regulatory agencies about the design of its next retinitis pigmentosa clinical trial.