Translational cell based therapies to repair the heart : Translational cell based strategies to repair the heart

Cardiovascular disease comprising of Coronary Artery Disease (CAD) and Valvular Heart Disease (VHD) represents the leading disease in western societies accounting for the death of numerous patients. CAD may lead to heart failure (HF) and despite the therapeutic options for HF which evolved over the past years, the incidence of HF is continuously increasing with a higher percentage of aged people. Similarly, an increase of VHD can be observed and although valve replacement represents the most common therapy strategy for VHD, approximately 30% of the treated patients are affected from prosthesis-related problems within 10 years. While mechanical valves require lifelong anticoagulation treatment, bioprosthetic valves present with continuous degeneration without the ability to grow, repair or remodel. The concept of regenerative medicine comprising of cell-based therapies, bio engineering technologies and hybrid solutions has been proposed as a promising next generation approach to address CAD and VHD. While myocardial cell therapy has been suggested to have a beneficial effect on the failing myocardium, heart valve tissue engineering has been demonstrated to be a promising concept to generate living, autologous heart valves with the capability to grow and to remodel which may be particularly beneficial for children. Although these regenerative strategies have shown great potential in experimental studies, the translation into a clinical setting has either been limited or has been too rapid and premature leaving many key questions unanswered. The aim of this thesis was the systematic development of translational, cell-based bio engineering concepts addressing CAD (part A) and VHD (part B) with a particular focus on minimally invasive, transcatheter-based implantation techniques. In the setting of myocardial regeneration, in the second chapter the intrinsic regenerative potential of the heart is investigated. Myocardial samples were harvested from all four chambers of the human heart and were assessed for resident stem/progenitor cell populations. The results demonstrated that BRCP+ cells can be detected within the human heart and that they were more abundant than their c-kit+ counterparts. In the non-ischemic heart they were preferentially located in the atria while following ischemia, their numbers were increased significantly in the left ventricle. There were no c-kit+/BCRP+ co-expressing stem/progenitor cell populations suggesting that these two markers are expressed by two distinct cell populations in the human heart. Although these results provided a valuable snapshot at cardiac progenitor cells after acute ischemia, the data also indicated that the absolute numbers of cells acquiring a myocardial phenotype are rather low and further effort is needed to upscale such cells into clinically relevant numbers. In chapter three, it is demonstrated that human bone marrow and adipose tissue derived mesenchymal stem cells can be efficiently isolated via minimally invasive procedures and expanded to clinically relevant numbers for myocardial cell therapy. Thereafter, these cells were tested in a uniquely developed intrauterine, fetal, preimmune ovine myocardial infarction model for the evaluation of human cell fate in vivo. After the successful intrauterine induction of acute myocardial infarction, the cells were intramyocardially transplanted and tracked using a multimodal imaging approach comprising MRI, Micro CT as well as in vitro analysis tools. The principal feasibility of intra-myocardial stem-cell transplantation following intra-uterine induction of myocardial infarction in the preimmune fetal sheep could be demonstrated suggesting this as a unique platform to evaluate human cell-fate in a relevant large animal-model without the necessity of immunosuppressive therapy. In chapter four, adipose tissue derived mesenchymal stem cells (ATMSCs) were processed to generate three dimensional microtissues (3D-MTs) prior to transplantation to address the important issue of cell retention and survival. Thereafter, the ATMSCs based 3D-MTs were transplanted into the healthy and infarcted porcine myocardium using a catheter-based, 3D electromechanical mapping guided approach. The previously used MRI based tracking concept was successfully translated into this preclinical model allowing for the in vivo monitoring of 3D-MTs. To address Valvular Heart Disease (part B), in chapter five, marrow stromal derived cells were used to develop a unique autologous, cell-based engineered heart valve in situ tissue engineering concept comprising of minimally-invasive techniques for both, cell harvest and valve implantation. Autologous marrow stromal derived cells were harvested, seeded onto biodegradable scaffolds and integrated into self-expanding nitinol stents, before they were transapically delivered into the pulmonary position of non-human primates within the same intervention while avoiding any in vitro bio-reactor period. The results of these experiments demonstrated the principal feasibility of generating marrow stromal cell-based, autologous, living tissue engineered heart valves (TEHV) and the transapical implantation in a one-step intervention. In chapter six, this concept was then successfully applied to the high-pressure system of the systemic circulation. After detailed adaption of the TEHV and stent design to the anatomic conditions of an orthotopic aortic valve, marrow stromal cell-based TEHV were implanted into the orthotopic aortic position. The implantation was successful and valve functionality was confirmed using fluoroscopy and trans-esophageal echocardiography. While displaying an ideal opening and closing behaviour with a sufficient co-aptation and a low pressure gradient, there were no signs of coronary occlusion or mal-perfusion. In conclusion, the results of this thesis represent a promising portfolio of translational concepts for cardiovascular regenerative medicine addressing CAD and VHD. In particular, it was demonstrated that mesenchymal stem cells / multipotent stromal derived cells represent a clinically relevant cell source for both myocardial regeneration and heart valve tissue engineering. It was shown that the preimmune fetal sheep myocardial infarction model represents a unique platform for the in vivo evaluation of human stem cells without the necessity of immunosuppressive therapy. Moreover, the concept of transcatheter based intramyocardial transplantation of mesenchymal stem cell-based 3D-MTs was introduced to enhance cellular retention and survival. Finally, in the setting of VHD it could be shown that marrow stromal cell based issue engineered heart valves can successfully generated and transapically implanted into the pulmonary and aortic position within a one-step intervention.