A Calsequestrin Cis-Regulatory Motif Coupled to a Cardiac Troponin T Promoter Improves Cardiac Adeno-Associated Virus Serotype 9 Transduction Specificity

Adeno-associated virus serotype 9 (AAV9) is an efficient vector for gene transfer to the myocardium. However, the use of ubiquitous promoters, such as the cytomegalovirus (CMV) promoter, can result in expression of the transgene in organs other than the heart. This study tested if the efficiency and specificity of cardiac transcription from a chicken cardiac troponin T (TnT) promoter could be further increased by incorporating a cardiomyocyte-specific transcriptional cis-regulatory motif from human calsequestrin 2 (CS-CRM4) into the expression cassette (Enh.TnT). The efficiency of luciferase expression from the TnT and Enh.TnT constructs was compared to expression of luciferase under the control of the CMV promoter in both adult and neonatal mice. Overall, expression levels of luciferase in the heart were similar in mice injected with AAV9.TnT.Luc, AAV9.Enh.TnT.Luc and AAV9.CMV.Luc. In contrast, expression levels of luciferase activity in nontarget organs, including the liver and muscle, was lower in mice injected with the AAV9.TnT.Luc compared to AAV9.CMV.Luc and was negligible with AAV9.Enh.TnT. In neonates, in organs other than the heart, luciferase expression levels were too low to be quantified for all constructs. Taken together, the data show that the AAV9 Enh.TnT constructs drives high levels of expression of the transgene in the myocardium, with insignificant expression in other organs. These properties reduce the risks associated with the AAV9-mediated expression of the therapeutic protein of interest in nontarget organs. The excellent cardiac specificity should allow for the use of higher vector doses than are currently used, which might be essential to achieve the levels of transgene expression necessary for therapeutic benefits. Taken together, the findings suggest that the Enh.TnT transcription unit is a potentially attractive tool for clinical cardiac gene therapy in adults.