Transplantation of clinical-grade human induced pluripotent stem cell derived cardiac tissues contributes to functional recovery in a rat myocardial infarction model
Authors: Osada H , Masumoto H , Kawatou M , Ikeda T , Tabata Y , Minatoya K , Yamashita J.K 
Published: November 2020

Abstract

Background
Clinical-grade human induced pluripotent stem cells (iPSCs) established from a healthy volunteer are currently being considered as a quality controlled cell source for regenerative therapy. Transplantation of three-dimensional bioengineered cardiac tissues composed of human iPSC-derived cardiovascular cell lineages is reported to hold potential for cardiac functional recovery.

Purpose
The aims of this study were to evaluate tissue conformation and cellular viability of human iPSC-derived cardiac tissues (HiCTs) generated from clinical-grade cells and to validate functional efficacy of HiCT transplantation.

Methods
Clinical-grade human iPSC lines were simultaneously differentiated into cardiovascular cell lineages by a high-density monolayer culture. The differentiation efficacy was analyzed by flow cytometry. We seeded the cells on temperature responsive culture dishes to form cell sheets. HiCTs are generated by stacking 5 cell sheets with insertion of gelatin hydrogel microspheres (GHMs) between each sheet to promote oxygen and nutrition supply. Characteristics of the HiCTs are histologically and immunohistochemically evaluated. The HiCTs were transplanted onto an athymic nude rat myocardial infarction (MI) model. Cardiac function was evaluated by echocardiography and cardiac magnetic resonance imaging (MRI) until 4 weeks after surgery, and compared to those in animals with sham operation and with cell sheet stacks without GHMs [GHM(−)].

Results
Flow cytometry at differentiation day15 revealed cellular components as follows: 52.5±1.4% of cardiomyocytes (cardiac isoform of troponin-T+), 9.8±0.7% of vascular endothelial cells (VE-cadherin+), 14.8±1.8% of vascular mural cells (PDGFRβ+) and 0.2±0.1% of undifferentiated cells (TRA-1-60+). HiCTs were significantly thicker [GHM(−) vs HiCT: 357.3±81.5 vs 723.0±84.0μm, p&lt;0.05], composed of higher area of cardiomyocytes (27.7±7.9 vs 71.9±15.5mm2, p&lt;0.05) and endothelial cells (CD31+) (1.6±0.7 vs 9.2±1.5mm2, p&lt;0.05), free from hypoxia (HIF-1α+) (3.1±0.1 vs 0.8±0.2%, p&lt;0.05) and cell death (TUNEL+) (3.2±0.1 vs 1.4±0.3%, p&lt;0.05) after 7 days of in vitro culture. Echocardiography revealed significantly lower left ventricular end diastolic volume (LVEDV) and higher left ventricular ejection fraction (LVEF) in HiCT group [sham (n=27) vs GHM(−) (n=12) vs HiCT (n=12): LVEDV; 1.4±0.1 vs 1.3±0.1 vs 0.9±0.1mL, p&lt;0.0001/LVEF; 55.3±1.1 vs 58.2±2.3 vs 78.2±1.5%, p&lt;0.0001]. Cardiac MRI showed lower LVEDV and higher LVEF as well [sham (n=8) vs GHM(−) (n=6) vs HiCT (n=6): LVEDV; 0.7±0.03 vs 0.7±0.03 vs 0.6±0.02mL, p&lt;0.01 / LVEF; 39.2±2.1 vs 43.8±1.4 vs 54.0±2.8%, p&lt;0.001].

Conclusions
We conclude that HiCTs generated from clinical-grade cells hold sufficient viability and tissue conformation suitable for functional recovery validated by a rat MI model. Clinical-grade human iPSCs potentially serve as a reasonable cell source for stem cell-derived product transplantation therapy with foreseeable clinical applications.

Funding Acknowledgement
Type of funding source: Other. Main funding source(s): Japan Agency for Medical Research and Development (AMED), Invited Research Project of Institute for Advancement of Clinical Transnational Science, Kyoto University Hospital