Tokyo's Heartseed Confirms Efficacy of iPS Cell-Derived Heart Muscle Transplants in Clinical Trial

Groundbreaking Results from Heartseed's iPS Cell Therapy

Heartseed, a Tokyo-based venture company originating from Keio University, announced on Friday, December 13, 2025, that a clinical trial has confirmed the efficacy of transplanting cardiac muscle derived from induced pluripotent stem (iPS) cells. The trial involved 10 patients suffering from severe heart failure, with no major safety issues reported. This significant development marks a crucial step forward in regenerative medicine for cardiovascular diseases.

Clinical Trial Design and Patient Cohorts

The clinical trial, which commenced in 2022, focused on patients with ischemic heart diseases, including cardiac infarction and angina pectoris. The therapeutic approach involved transplanting cardiomyocyte spheroids, which are clusters of cardiac muscle cells created from iPS cells. Participants were divided into two distinct groups to evaluate dose-dependent outcomes:

• A low-dose cohort received 50 million transplanted cardiac muscle cells.
• A high-dose cohort received 150 million transplanted cardiac muscle cells.

The trial meticulously assessed various outcomes, including the heart's ability to pump blood and overall cardiac functions.

Demonstrated Efficacy and Safety Profile

The results from both cohorts were highly encouraging. In the low-dose group, four out of five patients showed improvements or maintenance of cardiac functions one year post-transplantation compared to their pre-transplant levels. Notably, one patient's six-minute walk distance significantly increased from 150 meters to 500 meters, indicating substantial functional improvement. The high-dose cohort also exhibited a positive trend toward improved cardiac functions six months after transplantation.

Crucially, the trial confirmed an excellent safety profile, with no major safety concerns identified in either group. Specifically, there was no evidence of tumor formation or arrhythmia, which are critical considerations in stem cell therapies. The transplanted cardiomyocyte spheroids are expected to integrate and grow within the heart, contributing to sustained improvements in cardiac function.

Path to Regulatory Approval and Future Impact

Following these successful clinical findings, Heartseed is now conducting final data analysis and advancing preparations for regulatory submission. The company aims to submit an application for manufacturing and marketing approval by the end of 2026, with the ambitious goal of making this innovative treatment practically available to patients by 2027. This breakthrough offers new hope for millions worldwide suffering from severe heart failure, potentially transforming the landscape of cardiovascular regenerative medicine.