Cardiac organoids for myocardial infarction: a new therapeutic approach

Introduction

Cell therapy for myocardial infarction (MI) faces two key challenges: poor cellular integration and the risk of post-transplant arrhythmias.

Aim

Develop a scalable platform for human cardiac organoid (CO) production and evaluate their safety and efficacy in a preclinical swine model of acute MI.

Methods

COs were derived from human iPSCs in stirred-tank bioreactors. A 100 mL protocol was scaled to 1 L to assess robustness and CO characteristics. Twelve immunosuppressed pigs underwent MI induction and were randomized to Short-term CO (8-day follow-up, n=2), Long-term Control (30-day follow-up, n=4), and Long-term CO (30-day follow-up, n=6). Thirty minutes post-MI, treated animals received 3500 COs by intramyocardial injections; controls received vehicle. Engraftment was assessed at 8 and 30 days by immunohistofluorescence (IF) for human nuclear antigen (HNA) and connexin-43 (CX43). Scar content was evaluated by Picrosirius Red staining and spatial transcriptomics. In long-term groups, rhythm was monitored by 15-day ECG Holter recordng; cardiac function and scar size were evaluated by magnetic resonance (MR) at days 2 and 29; and electrophysiological properties and arrhythmia inducibility were evaluated at day 30 using high-density mapping (HDM) and programmed electrical stimulation.

Results

Bioreactor scaling increased output from 7000 COs/100 mL to 50000 COs/1 L while preserving uniform size and multicellular organization, with an endothelial-enriched outer layer and a cardiomyocyte-dense core. IF confirmed the presence of HNA⁺ cells in infarct and peri-infarct regions. At 8 days, COs retained spherical architecture, whereas at 30 days, COs were disaggregated and cells migrated into the surrounding tissue. At 30 days, some HNA⁺ cells expressed CX43, suggesting gap junction formation and potential electrical coupling with host myocardium. Spatial transcriptomics revealed reduced pro-fibrotic gene expression in HNA⁺ regions at 30 versus 8 days. Consistently, collagen quantification showed a mild decrease in collagen I content and a lower collagen I:III ratio in CO-treated animals compared with controls, indicating potentially favorable scar remodeling.

All animals maintained a sinus rhythm without severe ventricular arrhythmias, and electrophysiological testing revealed no group differences. MR showed significant improvements in left ventricular (LV) stroke volume (p=0.05), LV ejection fraction (p=0.034), cardiac output (p=0.010), and cardiac index (p=0.048), along with reduced scar size (p=0.029), exclusively in the Long-term CO group.

Conclusions

This scalable bioreactor platform enables reproducible CO production. Following implantation, COs integrate into the host myocardium, exhibit potential electrical coupling without increasing arrhythmia risk, and are associated with improved cardiac function and attenuated fibrotic remodeling. Larger ongoing studies are expected to further substantiate their therapeutic potential.