Immuno-phenotyping of X-linked retinoschisis (XLRS) subjects in a Phase I/IIa AAV8-RS1 gene therapy clinical trial reveals baseline differences in systemic immune cell proportions but minimal further changes after vector administration.

Abstract

Purpose : To report the systemic immune profile of human XLRS subjects at trial baseline (ClinicalTrials.Gov NCT02317887) compared to a healthy population and to compare changes, if any, after vector administration, to assess whether the clinical vector or transgene product trigger a systemic immune response.

Methods : Whole blood samples were collected from XLRS subjects before vector administration (at baseline) and at days 14 and 60 afterward. Age-matched healthy samples were obtained from the NIH blood bank. XLRS subjects were analyzed based on vector dosage (1e9 – 3e11 vg/eye). Adaptive and innate immune cell populations in PBMCs were analyzed using an 18 color flow cytometry panel run on Cytoflex NUV and analyzed with Cytexpert v2.3 software (Beckman Coulter Inc.).

Results : Compared to normal controls, XLRS subjects at baseline showed upregulation in T helper cells and a skewed CD4/CD8 ratio in several participants. Various cell populations of innate immunity like intermediate monocytes, activated T cells, natural killer cells, natural killer T cells and dendritic cells were also altered at baseline. AAV vector administration did not change the immune response significantly. High dosage groups (1 & 3e11 vg/eye) who received immunosuppression showed no marked changes in the immune cell populations.

Conclusions : Immune cell changes in XLRS subjects at baseline suggests that retinal degeneration itself may affect the immune system; we are investigating whether these changes are common to other retinal degenerations. No significant changes were noted after vector administration, except for down-regulation of CD56^-CD11c⁺ dendritic cells at day 60; CD11c facilitates immune regulation and cell adhesion and acts as a receptor for diverse ligands such as iC3b, complement factor Bb and fibrinogen. We are now investigating possible functional importance of systemic immune changes and whether down-regulation of CD11c and associated cytokines are triggered by the AAV8-RS1 vector. This study however confirms that AAV8-RS1 clinical vector is safe and causes minimal immunological disturbances systemically.

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