Multicellular human cardiac organoids transcriptomically model distinct tissue-level features of adult myocardium

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been widely used for disease modeling and drug cardiotoxicity screening. To this end, we recently developed human cardiac organoids (hCOs) for modeling human myocardium. Here, we perform a tran-scriptomic analysis of various in vitro hiPSC-CM platforms (2D iPSC-CM, 3D iPSC-CM and hCOs) to deduce strengths and limitations of these in vitro models. We further compared iPSC-CM models to human myocardium samples. Our data shows that the 3D in vitro environ-ment of 3D hiPSC-CMs and hCOs stimulates expression of genes associated with tissue formation. hCOs demonstrated diverse physiologically relevant cellular functions compared to hiPSC-CM only models. Including other cardiac cell types within hCOs led to more transcriptomic similarly to adult myocardium. hCOs lack matured cardiomyocytes and immune cells which limits a complete replication of human adult myocardium. In conclusion, 3D hCOs are transcriptomically similar to myocardium, and future developments of engineered 3D cardiac models would benefit from diversifying cell populations, especially immune cells.