PO-02-244 AAV6-MEDIATED GFP GENE TRANSFER INDUCES TACHYARRHYTHMIAS IN A PORCINE MODEL OF AV BLOCK

Abstract

Green fluorescent protein (GFP) is a reporter widely utilized to evaluate gene transfer efficiency and used as control in therapeutic overexpression strategies. Although it is frequently considered to be an innocuous protein, there is also evidence indicating interference with contractile function and electrophysiological properties, potentially leading to cardiac dilation and functional deterioration. Cognizant of these possible limitations, we considered GFP gene transfer to provide a valuable starting point to evaluate local gene transfer and its potential deleterious effects. To evaluate gene transfer efficiency and potential pro-arrhythmic effects in a porcine model of complete atrioventricular block (CAVB). A total of eight pigs were implanted with a pacemaker, after which a radiofrequency ablation CAVB was generated. Four weeks after induction of the model the animals received catheter-based intramyocardial injections of saline, AAV6-CMV-GFP or were not injected at all. All animals were then observed for four more weeks. Monitoring included weekly pacemaker interrogations. Ventricular arrhythmias were assessed by means of increase in maximum heart rates and pacemaker dependency. Four weeks post-ablation all pigs displayed maximal heart rates of 75 ± 16,9 bpm which notably increased in AAV6-CMV-GFP-injected animals two weeks post-treatment (240 ± 10 bpm; Figure A), but not in the control animals (n = 5, 78 ± 29,5 bpm; Figure A). Electronically paced beats showed a remarkable reduction in transduced animals two weeks post-injection (40 ± 37,36 %; Figure B). Although GFP is commonly used in gene transfer studies, our experiments reveal the occurrence of ventricular arrhythmias after treatment. Mechanistically, these arrhythmias could be triggered by local tissue damage stemming from a possible inflammatory response exacerbated by a reaction to the capsid and transgene. As a result, locally injected AAV6-CMV-GFP should not be used as a control transgene in large animal studies to validate cardiac gene therapies.