Abstract Body: Background
Human induced pluripotent stem cell (hiPSC)-derived cardiac cells provide a powerful platform for disease modeling and drug discovery. While 3D cardiac tissues can recapitulate structural and functional aspects of heart disease, modeling cardiac inflammation remains challenging due to the lack of immune components.

Research Question
Can incorporation of hiPSC-derived macrophages into 3D mature cardiac tissues enable physiological and pathological modeling of cardiac inflammation?

Goals
To establish a 3D human cardiac tissue model containing macrophages that recapitulates inflammatory responses and functional alterations observed in human heart diseases.

Methods
We generated macrophages from hiPSCs and incorporated them into 3D engineered cardiac tissues composed of mature cardiomyocytes and other non-cardiac cells. Phenotypic characterization of macrophages was performed, and cardiac tissue function was evaluated under physiological and inflammatory conditions.

Results
Macrophages successfully integrated into 3D cardiac tissues and exhibited phenotypes resembling cardiac-specific macrophages. Under physiological conditions, their presence enhanced both systolic and diastolic function of the tissues. In contrast, under pathological conditions, aberrant inflammatory activation accompanied by impaired contractile function and fibrotic remodeling—none of which were observed in cardiac tissues without macrophages. Importantly, single-cell RNA sequencing analysis under pathological conditions revealed distinct macrophage–fibroblast interactions associated with cardiac inflammation and fibrosis within the tissues.

Conclusion
These findings demonstrate that this platform enables the investigation of cellular crosstalk between macrophages and fibroblasts that drives inflammatory and fibrotic remodeling in the human heart.