Heart failure affects an estimated 38 million people worldwide and is typically caused by cardiomyocyte (CM) loss or dysfunction. Although CMs have limited ability to regenerate, a large pool of non-myocytes, including cardiac fibroblasts (CFs), exist in the postnatal heart. In vivo reprogramming of non-myocytes into functional CMs is emerging as a potential new approach to treat heart failure and substantial proof-of-concept has been achieved in this new field. However, challenges remain in terms of clinical application. First, reported human reprogramming cocktails often consist of five to seven factors that require multiple AAV vectors for delivery. Thus, a less complex cocktail that is able to fit into one AAV vector is needed for this technology to impact human health. Second, the lack of specificity in AAV tropism further complicates the safety and regulatory landscape. A means to limit the expression of reprogramming factors to target cells is critical for maximizing long-term safety. Lastly, although promising studies in small animals have already been reported, safety and efficacy results in large animal MI models are critical to justify cardiac reprogramming in human clinical trials.
We have developed a novel human cardiac reprogramming cocktail that consists of only two transcription factors and one miRNA. This new cocktail has been engineered into a single AAV cassette to efficiently reprogram human CFs into cardiomyocytes. We also substantially improved transduction of hCFs through AAV capsid engineering and eliminated CMs expression through a microRNA de-targeting method. Moreover, our novel cardiac reprogramming gene therapy improved cardiac function in both rat and swine MI models upon delivery at various time-points after MI without inducing arrhythmias. Given these promising safety and efficacy results in larger animals, we endeavor to translate direct cardiac reprogramming for clinical application.
In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application