Vector shedding and immunology measures in a choroideremia gene therapy trial

Abstract

Purpose : Adeno-associated viral (AAV)-based gene therapy is becoming accepted as a safe and effective treatment for inherited retinal disease. Subretinal AAV gene therapy is theoretically very low risk, however, monitoring in early phase trials is needed to validate this assumption. We report vector shedding and immunology in 9 patients in a phase 2 choroideremia gene therapy trial (ClinicalTrials.gov ID: NCT02407678).

Methods : Patients received subretinal injection of AAV2-REP1 vector (up to 1E+11 genome particles). Intraoperative OCT was used to minimise vitreous reflux. Samples were collected at baseline, 1 day, 1 week and 1 month post-surgery. Saliva, urine, tears and peripheral blood were assessed for presence of AAV-genomes by quantitative PCR. Peripheral blood mononuclear cell (PBMC) and serum fractions were isolated. Cell mediated immune responses were assessed using PBMCs in an enzyme-linked immunosorbent spot (ELISpot) assay with exposure to AAV2 capsids and REP1 mimotopes. Anti-AAV2 neutralising antibody levels in serum were assessed with a cellular assay.

Results : In all samples from 9 patients, only 2 were positive for vector: tear samples from treated eyes 1 day after surgery in patients 2 & 3. Three of 9 patients had positive (>100) baseline anti-AAV2 antibody titres. Two of these patients responded to delivery of the vector with >3x increases in titre during follow-up (patients 3 & 4). Patients with negative baseline titres remained so for the duration. In most patients (7/9), ELISpot responses to REP1 peptide or AAV2 capsid were minimal and unchanged across time (<3x negative control). Patient 6 recorded mildly positive responses to AAV2 capsid (4-6x negative control) during follow-up. Patient 9 showed a mild positive response to REP1 peptide at baseline (>3x negative control), which increased post-surgery (9x & 29x negative control at 1 week and 1 month, respectively). Overall, 4/9 patients had detectable immune responses (2 humoral, 2 cellular). However, no patients displayed systemic symptoms or inflammatory adverse events.

Conclusions : When AAV2-REP1 is given by subretinal injection, vector shedding is very limited. Systemic immune responses are elicited in some patients, particularly those with pre-existing sensitivity. This indicates administration of the viral vector to the eye can be detected by the body, but this is not associated with a clinically noted systemic immune or inflammatory response.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.