P04

Characterization of pre-existing anti-AAV T Cells using spectral flow cytometry in a cohort of healthy donors

M Schmitt(1) A Avenel(1) G Tilly(2) N Jaulin(1) M Devaux(1) R Xicluna(1) M Guilbaud(1) L Delbos(2) N Degauque(2) O Adjali(1) G Gernoux(1)

1:UMR INSERM 1089; 2:UMR INSERM 1064

Recombinant adeno-associated viruses (rAAV) are efficient tools for in vivo gene transfer as demonstrated by 8 FDA or EMA-approved drugs in the US and Europe. However, their immunogenicity in humans remains a major hurdles to overcome for a successful clinical translation. Indeed, adverse events related to immune system activation following systemic injection of high doses of rAAV into patients have been reported, resulting in some cases in clinical trial hold. This immunotoxicity is partly due to the reactivation of pre-existing anti-AAV T cells  after gene transfer. In a previous  cellular immune response prevalence study in a cohort of healthy donors (n=145), we showed that 24% and 46% of donors have a pre-existing cellular immune response to AAV8 and AAV9 respectively. Here, we aim at studying the phenotype of these anti-AAV8 (n=6) and anti-AAV9 (n=9) T cells by spectral cytometry. Preliminary data on this cohort showed that the cells involved in the anti-AAV8 and anti-AAV9 cellular response are mostly effector memory CD8 T cells (Tꭼꮇ) followed by terminally-differentiated effector memory cell (Tꭼꮇꭱꭺ). Tꭼꮇ cells appear more involved in the anti-AAV9 response, while Tꭼꮇꭱꭺ cells are more implicated in the anti-AAV8 response. Moreover, the co-expression of CD57 and CD27 markers by anti-AAV Tꭼꮇ cells suggests a cytotoxic activity. An in-depth functional characterization of these cells is ongoing. This study will allow to better characterize the preexisting anti-AAV T cells that might be involved in clinical trial adverse events and to develop targeted immunomodulation to prevent deleterious immune responses after rAAV gene transfer.