Darryl R. Davis

Validation of the Cardiosphere Method to Culture Cardiac Progenitor Cells from Myocardial Tissue

Background At least four laboratories have shown that endogenous cardiac progenitor cells (CPCs) can be grown directly from adult heart tissue in primary culture, as cardiospheres or their progeny (cardiosphere-derived cells, CDCs). Indeed, CDCs are already being tested in a clinical trial for cardiac regeneration. Nevertheless, the validity of the cardiosphere strategy to generate CPCs has been called into question by reports based on variant methods. In those reports, cardiospheres are argued to be cardiomyogenic only because of retained cardiomyocytes, and stem cell activity has been proposed to reflect hematological contamination. We use a variety of approaches (including genetic lineage tracing) to show that neither artifact is applicable to cardiospheres and CDCs grown using established methods, and we further document the stem cell characteristics (namely, clonogenicity and multilineage potential) of CDCs. Methodology/Principal Findings CPCs were expanded from human endomyocardial biopsies (n = 160), adult bi-transgenic MerCreMer-Z/EG mice (n = 6), adult C57BL/6 mice (n = 18), adult GFP+ C57BL/6 transgenic mice (n = 3), Yucatan mini pigs (n = 67), adult SCID beige mice (n = 8), and adult Wistar-Kyoto rats (n = 80). Cellular yield was enhanced by collagenase digestion and process standardization; yield was reduced in altered media and in specific animal strains. Heparinization/retrograde organ perfusion did not alter the ability to generate outgrowth from myocardial sample. The initial outgrowth from myocardial samples was enriched for sub-populations of CPCs (c-Kit+), endothelial cells (CD31+, CD34+), and mesenchymal cells (CD90+). Lineage tracing using MerCreMer-Z/EG transgenic mice revealed that the presence of cardiomyocytes in the cellular outgrowth is not required for the generation of CPCs. Rat CDCs are shown to be clonogenic, and cloned CDCs exhibit spontaneous multineage potential. Conclusions/Significance This study demonstrates that direct culture and expansion of CPCs from myocardial tissue is simple, straightforward, and reproducible when appropriate techniques are used.

Cardiospheres Recapitulate a Niche-Like Microenvironment Rich in Stemness and Cell-Matrix Interactions, Rationalizing Their Enhanced Functional Potency for Myocardial Repair†‡§

Cardiac stem cells (CSCs) are promising candidates for use in myocardial regenerative therapy. We test the hypothesis that growing cardiac‐derived cells as three‐dimensional cardiospheres may recapitulate a stem cell niche‐like microenvironment, favoring cell survival and enhancing functional benefit after transplantation into the injured heart. CSCs and supporting cells from human endomyocardial biopsies were grown as cardiospheres and compared with cells cultured under traditional monolayer condition or dissociated from cardiospheres. Cardiospheres self‐assembled into stem cell niche‐like structures in vitro in suspension culture, while exhibiting greater proportions of c‐kit+ cells and upregulated expression of SOX2 and Nanog. Pathway‐focused polymerase chain reaction (PCR) array, quantitative real‐time PCR, and immunostaining revealed enhanced expression of stem cell‐relevant factors and adhesion/extracellular‐matrix molecules (ECM) in cardiospheres including IGF‐1, histone deacetylase 2 (HDAC2), Tert, integrin‐α2, laminin‐β1, and matrix metalloproteinases (MMPs). Implantation of cardiospheres in severe combined immunodeficiency (SCID) mouse hearts with acute infarction disproportionately improved cell engraftment and myocardial function, relative to monolayer‐cultured cells. Dissociation of cardiospheres into single cells decreased the expression of ECM and adhesion molecules and undermined resistance to oxidative stress, negating the improved cell engraftment and functional benefit in vivo. Growth of cardiac‐derived cells as cardiospheres mimics stem cell niche properties with enhanced “stemness” and expression of ECM and adhesion molecules. These changes underlie an increase in cell survival and more potent augmentation of global function following implantation into the infarcted heart. STEM CELLS 2010;28:2088–2098

Magnetic Targeting Enhances Engraftment and Functional Benefit of Iron-Labeled Cardiosphere-Derived Cells in Myocardial Infarction

Rationale: The success of cardiac stem cell therapies is limited by low cell retention, due at least in part to washout via coronary veins. Objective: We sought to counter the efflux of transplanted cells by rendering them magnetically responsive and imposing an external magnetic field on the heart during and immediately after injection. Methods and Results: Cardiosphere-derived cells (CDCs) were labeled with superparamagnetic microspheres (SPMs). In vitro studies revealed that cell viability and function were minimally affected by SPM labeling. SPM-labeled rat CDCs were injected intramyocardially, with and without a superimposed magnet. With magnetic targeting, cells were visibly attracted toward the magnet and accumulated around the ischemic zone. In contrast, the majority of nontargeted cells washed out immediately after injection. Fluorescence imaging revealed more retention of transplanted cells in the heart, and less migration into other organs, in the magnetically targeted group. Quantitative PCR confirmed that magnetic targeting enhanced cell retention (at 24 hours) and engraftment (at 3 weeks) in the recipient hearts by ≈3-fold compared to nontargeted cells. Morphometric analysis revealed maximal attenuation of left ventricular remodeling, and echocardiography showed the greatest functional improvement, in the magnetic targeting group. Histologically, more engrafted cells were evident with magnetic targeting, but there was no incremental inflammation. Conclusions: Magnetic targeting enhances cell retention, engraftment and functional benefit. This novel method to improve cell therapy outcomes offers the potential for rapid translation into clinical applications.

Isolation and expansion of functionally-competent cardiac progenitor cells directly from heart biopsies

The adult heart contains reservoirs of progenitor cells that express embryonic and stem cell-related antigens. While these antigenically-purified cells are promising candidates for autologous cell therapy, clinical application is hampered by their limited abundance and tedious isolation methods. Methods that involve an intermediate cardiosphere-forming step have proven successful and are being tested clinically, but it is unclear whether the cardiosphere step is necessary. Accordingly, we investigated the molecular profile and functional benefit of cells that spontaneously emigrate from cardiac tissue in primary culture. Adult Wistar-Kyoto rat hearts were minced, digested and cultured as separate anatomical regions. Loosely-adherent cells that surround the plated tissue were harvested weekly for a total of five harvests. Genetic lineage tracing demonstrated that a small proportion of the direct outgrowth from cardiac samples originates from myocardial cells. This outgrowth contains sub-populations of cells expressing embryonic (SSEA-1) and stem cell-related antigens (c-Kit, abcg2) that varied with time in culture but not with the cardiac chamber of origin. This direct outgrowth, and its expanded progeny, underwent marked in vitro angiogenic/cardiogenic differentiation and cytokine secretion (IGF-1, VGEF). In vivo effects included long-term functional benefits as gauged by MRI following cell injection in a rat model of myocardial infarction. Outgrowth cells afforded equivalent functional benefits to cardiosphere-derived cells, which require more processing steps to manufacture. These results provide the basis for a simplified and efficient process to generate autologous cardiac progenitor cells (and mesenchymal supporting cells) to augment clinically-relevant approaches for myocardial repair.

Remote magnetic navigation-assisted catheter ablation enhances catheter stability and ablation success with lower catheter temperatures.

Background: It has been suggested that remote magnetic navigation (RMN) may provide enhanced catheter stability and substrate contact to aid in ablation. To date, no study has examined this claim. Accordingly, we compared the characteristics of the successful ablation of atrioventricular reentry tachycardia (AVNRT) using RMN with a matched population ablated using a conventional (CON) manual approach.

Atrioventricular Block as the Initial Manifestation of Cardiac Sarcoidosis in Middle-Aged Adults

Atrioventricular block (AVB) can be caused by several conditions, including cardiac sarcoidosis (CS). The prevalence of CS causing this presentation in a North American population has not been investigated and was the purpose of this study.

Intrinsic cardiac origin of human cardiosphere-derived cells

AIMS Cardiosphere-derived cells (CDCs) are in clinical development as a regenerative cell product which can be expanded ex vivo from patient cardiac biopsies. Cardiosphere-derived cells are clonogenic, exhibit multilineage differentiation, and exert functional benefits in preclinical models of heart failure. The origin of CDCs remains unclear: are these cells endogenous to the heart, or do they arise from cells that populate the heart via blood-borne seeding? METHODS AND RESULTS Right ventricular endomyocardial biopsies were obtained from cardiac transplant recipients (n = 10, age 57 ± 15 years), and CDCs expanded from each biopsy. Donor-recipient mismatches were used to probe the origin of CDCs in three complementary ways. First, DNA analysis of short-tandem nucleotide repeats (STRs) was performed on genomic DNA from donor and recipient, then compared with the STR pattern of CDCs. Second, in two cases where the donor was male and the recipient female, CDCs were examined for the presence of X and Y chromosomes by fluorescence in situ hybridization. Finally, in two cases, quantitative PCR (qPCR) was performed for individual-specific polymorphisms of a major histocompatability locus to quantify the contribution of recipient cells to CDCs. In no case was recipient DNA detectable in the CDCs by STR analysis. In the two cases in which a female patient had received a male heart, all CDCs examined had an X and Y chromosome, similarly indicating exclusively donor origin. Likewise, qPCR on CDCs did not detect any recipient DNA. CONCLUSION Cardiosphere-derived cells are of endogenous cardiac origin, with no detectable contribution from extra-cardiac seeding.

Hyperglycemia Inhibits Cardiac Stem Cell–Mediated Cardiac Repair and Angiogenic Capacity

Background— The impact of diabetes mellitus on the cardiac regenerative potential of cardiac stem cells (CSCs) is unknown yet critical, given that individuals with diabetes mellitus may well require CSC therapy in the future. Using human and murine CSCs from diabetic cardiac tissue, we tested the hypothesis that hyperglycemic conditions impair CSC function. Methods and Results— CSCs cultured from the cardiac biopsies of patients with diabetes mellitus (hemoglobin A1c, 10±2%) demonstrated reduced overall cell numbers compared with nondiabetic sourced biopsies (P=0.04). When injected into the infarct border zone of immunodeficient mice 1 week after myocardial infarction, CSCs from patients with diabetes mellitus demonstrated reduced cardiac repair compared with nondiabetic patients. Conditioned medium from CSCs of patients with diabetes mellitus displayed a reduced ability to promote in vitro blood vessel formation (P=0.02). Similarly, conditioned medium from CSCs cultured from the cardiac biopsies of streptozotocin-induced diabetic mice displayed impaired angiogenic capacity (P=0.0008). Somatic gene transfer of the methylglyoxal detoxification enzyme, glyoxalase-1, restored the angiogenic capacity of diabetic CSCs (diabetic transgenic versus nondiabetic transgenic; P=0.8). Culture of nondiabetic murine cardiac biopsies under high (25 mmol/L) glucose conditions reduced CSC yield (P=0.003), impaired angiogenic (P=0.02) and chemotactic (P=0.003) response, and reduced CSC-mediated cardiac repair (P<0.05). Conclusions— Diabetes mellitus reduces the ability of CSCs to repair injured myocardium. Both diabetes mellitus and preconditioning CSCs in high glucose attenuated the proangiogenic capacity of CSCs. Increased expression of glyoxalase-1 restored the proangiogenic capacity of diabetic CSCs, suggesting a means of reversing diabetic CSC dysfunction by interfering with the accumulation of reactive dicarbonyls.

Human Blood and Cardiac Stem Cells Synergize to Enhance Cardiac Repair When Cotransplanted Into Ischemic Myocardium

Background— Blood-derived circulatory angiogenic cells (CACs) and resident cardiac stem cells (CSCs) have both been shown to improve cardiac function after myocardial infarction. The superiority of either cell type has long been an area of speculation with no definitive head-to-head trial. In this study, we compared the effect of human CACs and CSCs, alone or in combination, on myocardial function in an immunodeficient mouse model of myocardial infarction. Methods and Results— CACs and CSCs were cultured from left atrial appendages and blood samples obtained from patients undergoing clinically indicated heart surgery. CACs expressed a broader cytokine profile than CSCs, with 3 cytokines in common. Coculture of CACs and CSCs further enhanced the production of stromal cell–derived factor-1&agr; and vascular endothelial growth factor (P⩽0.05). Conditioned media promoted equivalent vascular networks and CAC recruitment with superior effects using cocultured conditioned media. Intramyocardial injection of CACs or CSCs alone improved myocardial function and reduced scar burdens when injected 1 week after myocardial infarction (P⩽0.05 versus negative controls). Cotransplantation of CACs and CSCs together improved myocardial function and reduced scar burdens to a greater extent than either stem cell therapy alone (P⩽0.05 versus CAC or CSC injection alone). Conclusions— CACs and CSCs provide unique paracrine repertoires with equivalent effects on angiogenesis, stem cell migration, and myocardial repair. Combination therapy with both cell types synergistically improves postinfarct myocardial function greater than either therapy alone. This synergy is likely mediated by the complimentary paracrine signatures that promote revascularization and the growth of new myocardium.

Functional Impairment of Human Resident Cardiac Stem Cells by the Cardiotoxic Antineoplastic Agent Trastuzumab

Trastuzumab (TZM), a monoclonal antibody against the ERBB2 protein, increases survival in ERBB2‐positive breast cancer patients. Its clinical use, however, is limited by cardiotoxicity. We sought to evaluate whether TZM cardiotoxicity involves inhibition of human adult cardiac‐derived stem cells, in addition to previously reported direct adverse effects on cardiomyocytes. To test this idea, we exposed human cardiosphere‐derived cells (hCDCs), a natural mixture of cardiac stem cells and supporting cells that has been shown to exert potent regenerative effects, to TZM and tested the effects in vitro and in vivo. We found that ERBB2 mRNA and protein are expressed in hCDCs at levels comparable to those in human myocardium. Although clinically relevant concentrations of TZM had no effect on proliferation, apoptosis, or size of the c‐kit‐positive hCDC subpopulation, in vitro assays demonstrated diminished potential for cardiogenic differentiation and impaired ability to form microvascular networks in TZM‐treated cells. The functional benefit of hCDCs injected into the border zone of acutely infarcted mouse hearts was abrogated by TZM: infarcted animals treated with TZM + hCDCs had a lower ejection fraction, thinner infarct scar, and reduced capillary density in the infarct border zone compared with animals that received hCDCs alone (n = 12 per group). Collectively, these results indicate that TZM inhibits the cardiomyogenic and angiogenic capacities of hCDCs in vitro and abrogates the morphological and functional benefits of hCDC transplantation in vivo. Thus, TZM impairs the function of human resident cardiac stem cells, potentially contributing to TZM cardiotoxicity.