Direct Comparison of Different Stem Cell Types and Subpopulations Reveals Superior Paracrine Potency and Myocardial Repair Efficacy With Cardiosphere-Derived Cells
Authors: Tao-Sheng Li, PhD., Ke Cheng, PhD., Konstantinos Malliaras, MD, et al. Journal of the American College of Cardiology 2012; 59(10): 942-953; doi:10.1016/j.jacc.2011.11.029.
Background: Many types of stem cells have been used clinically in attempts to treat damaged hearts. The discovery of cardiac stem cells within the heart and the development of a technique for expansion of cardiosphere-derived cells (CDCs) has given researchers a new option in the use of stem cells for regenerative therapy.
Purpose: To evaluate the success of various types of human stem cells in myocardial repair in mice and to determine if cardiosphere-derived cells offer enhanced heart repair capabilities when compared to stem cells derived from other tissues.
Methods: For in vitro studies, all cells types were cultured in the same formulation of media. After three days, growth factor production was evaluated. Supernatant from each cell culture was tested for angiopoietion-2 (Ang-2), fibroblast growth factor basic (bFGF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF-1), platelet-derived growth factor (PDGF), stromal cell-derived factor (SDF-1), and vascular endothelial growth factor (VEGF-A) via colorimetric ELISA. Cardiomyogenic differention was evaluation by immunostaining with an anti-human Troponin-T antibody following 7 days of culture. Angiogenic potency was evaluated using a kit for imaging and measurement of tube formation. Lastly, resistance to oxidative stress was evaluated using a kit for detection of apoptotic (dying) cells.
For in vivo studies, acute myocardial infarction was induced in male SCID-beige mice. Hearts were injected at four time-points with one of four stem cell preparations: CDCs (cardiosphere-derived cells), BM-MSCs (bone marrow-derived mesenchymal stem cells), AD-MSCs (adipose tissue-derived mesenchymal stem cells), and two concentrations of BM-MNCs (bone marrow-derived mononuclear cells. Three weeks after treatment, left ventrical ejection fraction (LVEF) was determined by echocardiography. Engraftment of implanted human cells was detected by immunostaining with human nuclear antigen (HNA). Differentiation of implanted human cells into cardiomyocytes was determined by immunostaining with monoclonal antibodies to human-specific α-sarcomeric actin (α-SA). Cell engraftment was measured by detection of the SRY gene located on the male Y chromosome via quantitative PCR and reported as a number of engrafted cells per heart.
Results: For in vitro studies, only the CDCs secreted large amounts of all six growth factors tested. All other cell types were deficient in production of one or more growth factors. Approximately 9% of CDCs expressed troponin T, indicating differentiation into cardiomyocytes. This value was <1% for the other cell types. All cell types formed capillary-like networks, but the mean tube length was greater for the CDCs. All three stem cell types showed a similar resistance to oxidative stress. The BM-MNCs showed a deficiency in this area. For in vivo studies, quantitative image analysis showed higher engraftment in in mice implanted with CDCs than other cells. The number of cardiomyocytes derived from the transplanted cells was also greater in mice implanted with human CDCs. Hearts implanted with CDCs contained fewer apoptotic cells.
Findings of Note: Unsorted cardiosphere-derived cells were tested vs. an equal number of purified cardiac stem/progenitor cells positive for c-kit+. Unsorted CDCs produced higher amounts of paracrine (growth) factors and greater overall benefit to the infarcted heart.
To ensure that observed cell type differences were not donor-related, various cell types were isolated from individual rats and tested for growth factor expression in vitro. In the rat model involving a single donor, the CDCs produced higher levels of HGF, IGF-1, and VEGF (the three factors tested for the rat model) than the other cell types, confirming the results seen in the human study.
The author also mentioned a recently-published report on a Phase 1 trial using CDCs. Lancet 2012 Feb 14 [E-pub ahead of print] doi: 10.1016/S0140-6736(12)60195-0.
Author’s Conclusion: In a head-to-head comparison of four different cell types, cardiosphere-derived cells outperformed bone marrow-derived mesenchymal stem cells, adipose tissue-derived mesenchymal stem cells, and bone-marrow derived mononuclear cells when tested in vitro and in vivo for use in regenerative therapy in ischemic hearts. The results of this study indicate strong potential for the use of CDCs in regenerative heart therapy.
Reviewer’s Comments: This paper gave some interesting insight into a rapidly-growing field. Though bone marrow-derived stem cells have been used to treat Leukemia and related disorders for many years, the use of cellular therapy to treat a wide range of conditions, from heart damage to diabetes to neurodegenerative diseases now appears possible. The ability to grow stem cells in conjunction with related cells in culture may enable treatment with a patients’ own cells, increasing the chance of success. Recent developments in the field of regenerative medicine and stem cell research are truly exciting and encouraging.