Gene Therapy during Cardiac Surgery: Role of Surgical Technique to Minimize Collateral Organ Gene Expression

Effective gene therapy for heart failure has not yet been achieved
clinically. The aim of this study is to quantitatively assess the
cardiac isolation efficiency of the molecular cardiac surgery with
recirculating delivery (MCARD™) and to evaluate its efficacy as a means
to limit collateral organ gene expression. 10(14) genome copies (GC) of
recombinant adeno-associated viral vector 6 encoding green fluorescent
protein under control of the cytomegalovirus promoter was delivered to
the nine arrested sheep hearts. Blood samples were assessed using
real-time quantitative polymerase chain reaction (RT QPCR). Collateral
organ gene expression was assessed at four-weeks using
immunohistochemical staining. The blood vector GC concentration in the
cardiac circuit during complete isolation trended from 9.59±0.73 to
9.05±0.65 (log GC/cm(3)), and no GC were detectable in the systemic
circuit (P<0.001). The washing procedure performed prior to relinquishing the cardiac circuit decreased the systemic blood vector GC concentration >800-fold (P<0.001), consistent with >99%
isolation efficiency. Conversely, incomplete isolation resulted in
equalization of vector GC concentration in the circuits, leading to
robust collateral organ gene expression. MCARD™ is an efficient,
clinically translatable myocardial delivery platform for cardiac
specific gene therapy. The cardiac surgical techniques utilized are
critically important to limit collateral organ gene expression.