In vivo generation of heart and vascular system by blastocyst complementation

The generation of organs from stem cells by blastocyst complementation is a promising approach to cover the clinical need for transplants. In order to generate rejection-free organs, complementation of both parenchymal and vascular cells must be achieved, as endothelial cells play a key role in graft rejection. Here we used a lineage-specific cell ablation system to produce mouse embryos unable to form both the cardiac and vascular systems. By mouse intraspecies blastocyst complementation we rescued heart and vascular development separately and in combination, obtaining complemented hearts with cardiomyocytes and endothelial cells of exogenous origin. Complemented chimeras were viable and reached adult stage, showing normal cardiac function and no signs of histopathological defects in the heart. Furthermore, we implemented the cell ablation system for rat-to-mouse blastocyst complementation, obtaining xenogeneic hearts whose cardiomyocytes were completely of rat origin. These results represent an advance in the experimentation towards the in vivo generation of transplantable organs. ### Competing Interest Statement The authors have declared no competing interest.