Sunil Srivastava, MD, examines why and how optical coherence tomography characteristics may be predictive of the efficacy of the injections.
A phase 2 study of the efficacy of the intravitreal injection of allogeneic human retinal progenitor cells (hRPCs) (jCell, jCyte Inc.) to treat retinitis pigmentosa (RP) showed that in the group of patients who received the high-dose treatment, a correlation was seen between the outcomes and the optical coherence tomography (OCT) baseline parameters, i.e., the mid-subfield mean ellipsoidal zone (EZ) thickness and the mean central foveal thickness (CFT), according to Sunil Srivastava, MD, a staff physician, Cleveland Clinic Cole Eye Institute, Cleveland.
EZ recession and more generally the thinning of the outer zone have become potential structural surrogates for RP severity.
Considering this, Srivastava and colleagues conducted a phase 2b study to identify objective factors that can better predict the efficacy of hRPCs on baseline spectral-domain OCT (SD-OCT) images in patients who might be more responsive to this treatment.
The investigators identified a subgroup of patients who had fewer variable measurements, and the subgroup’s readable SD-OCT volumetric data were analyzed from 29 eyes of 29 patients with advanced RP (sham treatment, n = 10; low-dose treatment, n = 9; high-dose treatment n = 10).
The investigators proceeded by processing frame-by-frame macular cube scans using automated segmentation followed by EZ mapping with manual correction for segmentation errors by masked graders.
A three-dimensional volume map of the EZ-retinal pigment epithelium (RPE) for the entire macular cube generated the mean foveal thickness within the subfield or mid-subfield, mean CFT, and EZ-RPE subfield or mid-subfield volume and thickness (with or without fluid).
The changes in the correlational analysis between each OCT parameter and the changes in each of the phase 2b trial endpoints, including the best-corrected visual acuity, contrast sensitivity, kinetic visual fields, low luminance mobility test, and a visual function questionnaire from baseline to 12 months, were recorded.
The study showed moderate to strong correlations in all trial endpoints in the high-dose treatment group that received 1 injection of 6 x 106 cells in the mean CFT and the mid-subfield mean EZ thickness, Srivastava reported.
Greater values in each parameter corresponded to greater improvements in the end point. The low-dose treatment (3 x 106cells) did not demonstrate a significant relationship.
“These results suggested a correlation between outcomes and OCT baseline parameters of the mid-subfield mean EZ thickness and mean CFT in the high-dose treatment group,” the investigators concluded. “Because of both the small number of patients and post hoc nature of the analyses, these results should be viewed cautiously.
A certain minimal EZ or mean CFT may facilitate selection of a population with the greatest chance for a treatment response in a phase 3 study from the neurotrophic effects of hRPCs in RP patients.”
Sunil Srivastava, MD
This article was adapted from Dr. Srivastava’s presentation at the Association for Research in Vision and Ophthalmology’s 2021 virtual annual meeting. Srivastava is a consultant to jCyte.