Intra-myocardial transplantation of human adipose tissue derived marrow stromal cell based three dimensional microtissues into the porcine heart

Aims: Stem cells have been repeatedly suggested for cardiac regeneration after myocardial infarction (MI). However, the low retention rate of applied single cell suspensions limits the efficacy of current therapy concepts. Taking advantage of three dimensional (3D) cellular self-assembly prior to transplantation may be beneficial in this regard. In this pilot study we demonstrate the principal feasibility of intramyocardial delivery of in-vitro generated stem cell based 3D microtissues (3D-MTs) in a pig model.

Methods: 3D-MTs were generated from ion-oxide (MPIO) labeled human adipose tissue derived mesenchymal stem cells (ATMSC) using a modified hanging drop method. Eight pigs (33 ± 2 kg) comprising six healthy ones and two with chronic MI in the left ventricle (LV) anterior wall were included. The pigs underwent intramyocardial transplantation of 16 × 10³ 3D-MTs (1250 cells/MT; accounting for 2 × 10⁷ single ATMSC) into the anterior wall (n = 6)/the MI border zone (n = 2) of the LV using a 3D NOGA mapping guided, catheter-based approach. Clinical follow up (FU) was performed for up to 6 weeks and in vivo cell tracking was performed using serial MRI imaging. Thereafter, the hearts were harvested and assessed by PCR and immunohistochemistry.

Results: Intramyocardial transplantation of human ATMSC based 3D-MTs was successful in seven animals (87.5%) while one pig (without MI) died during the NOGA mapping due to sudden cardiac arrest. During FU no arrhythmogenic, embolic or neurological events occurred in the treated pigs. Serial MRI imaging confirmed the intramyocardial presence of the 3D-MTs by detection of the intracellular ion-oxide MPIOs during FU. After harvest, intramyocardial presence of 3D-MTs was confirmed by positive PCR screening for human specific beta-2 microglobulin and was further verified by positive immunohistochemistry for human-specific MHC-1, ALU-Sequence and anti-FITC detecting the fluorochrome-labeled part of the MPIOs. The 3D-MTs appeared to be viable, integrated and showed an intact micro architecture.

Conclusions: We demonstrate the principal feasibility and safety of intra-myocardial delivery of in vitro generated stem cell based 3D-MTs. Multimodal cell-tracking strategies comprising advanced imaging and in vitro tools allow for in vivo monitoring and post mortem analysis of transplanted 3D-MTs. The concept of 3D cellular self-assembly represents a promising application format that may go beyond currently applied single cell approaches.