Decellularized Hearts, by James Fargnoli

The transplant list for hearts in the US alone is over 3500 and growing. Even when a patient does receive a working donor heart, the risk of organ rejection is significant and the patient is condemned to immunosuppressant treatment for the rest of their lives. Allographic transplants of hearts recellularized with immune compatible cells offer to alleviate the risk of organ rejection. Ultimately, xenographic transplants of recellularized hearts could solve the organ shortage entirely[1].

History

2008 - A research team lead by Harald C Ott repopulates a decellularized cadaveric rat heart with neonatal human cardiac cells and rat aortic endothelial cells exhibiting spontaneous contractions and nascent force generation [2].

2013 - A research team at the University of Pittsburgh Schools of the Health Sciences repopulates a decellularized mouse heart with human induced pluripotent stem cells exibiting spontaneous contractions, force generation, and responsive to drugs[3]

Procedure

A recellularized heart undergoes a process of washing, which removes the cell contents while preserving the Extracellular matrix, often termed the scaffold structure. This consists of cartilage, laminin, and other structural proteins that are integral to the three-dimensional structure. The wash step is currently the most advanced section of the procedure and is typically carried out by one of two methods. Perfusion Decellularization is a method that pumps a detergent through the heart, degrading and washing away lipids, nucleic acids, soluble proteins, and sugars while retaining the structural components of the matrix [2]. Immersion Decellularization is a method of submerging the cellularized heart into a detergent solution and allowing the solution to degrade and wash off lipids, nucleic acids, soluble proteins, and sugars, while retaining the structural components of the matrix[3].

Following the wash, the organ is verified to be acellular through a comnbination of Genomic DNA extraction and histochemical stains[4], [5], [6]. There is a trade-off between the thoroughness of the wash to eliminate cells and the integrity of the decellularized matrix. Upon confirmation, the decellularized heart is reseeded with progenitor cells of either the iPS or embryonic variety. In the heart, at least two types of progenitor cells are used, endothelial and muscle progenitors, respectively for the epithelial lining and cardiomyocyte production.

References

[1] Maher B. How To Build A Heart. Nature 2013; 499: 20-22. [2]Ott HC et al. Perfusion-decellularized matrix: using nature's platform to engineer a bioartificial heart. Nature Medicine 2008; 14: 213-221. [3] Lu TY et al. Repopulation of decellularized mouse heart with human induced pluripotent stem cell-derived cardiovascular progenitor cells. Nature Communications 2013; 4: DOI: 10.1038/ncomms3307. [3] Chen, R.N., Ho, H.O., Tsai, Y.T. & Sheu, M.T. Process development of an acellular dermal matrix (ADM) for biomedical applications. Biomaterials 25, 2679–2686 (2004). [4] Carvalho JL, DeCarvalho PH, Gomes DA, Goes AM. Characterization of Decellularized Heart Matrices as Biomaterials for Regular and Whole Organ Tissue Engineering and Initial In-vitro Recellularization with Ips Cells. Tissue Sci Eng 2012, 8:11. [5] Woods T, Gratzer PF. Effectiveness of three extraction techniques in the development of a decellularized bone–anterior cruciate ligament– bone graft. Biomaterials 2005;26:7339–49. [6]Kakkar R, Grover SR. Theoretical study of molecular recognition by Hoechst 33258 derivatives. J Biomol Struct Dynam 2005;23:37–47.