An Animal Model for Assessing Cardiovascular Cell Therapy with Human Bone Marrow Stem Cells

Ischemic cardiovascular diseases are still the leading cause of morbidity and mortality in the western world. Incomplete surgical myocardial revascularization is a determining factor for early flare of subsequent angina which results in lower patient survival. Cell-based cardiac therapy in the treatment of ischemic heart disease is a new concept that has been studied using numerous cell types, delivery systems, and strategies. Bone-marrow derived stem/progenitor cells (BMDC) have been used in a number of different studies in both animal and human models. Adult BMDC is composed of a multitud of cell types: hematopoietic, mesenchimal, stromal stem cells and other cell types yet to be characterized. More studies are needed to address the timing, relative concentrations, source and route of delivery of each cellular populations in animals models of myocardial ischemia. In vivo studies are clear prerequisites for clinical translation and appropriate animal models are needed.

The aim of this study was to produce a xenogenic large animal model of myocardical infartation and investigate whether this model allows evaluation of angiogenic cell therapy with human BMDC.

The proposed strategy was to develop myocardial ischemia in a human cell graft tolerant sheep model. Chimeric tolerant sheeps were created by human BMDC transplant into early gestational sheep fetuses during the “preimmune” stage. Human CD34+ cells (x = 315×10³) were implanted in 45+3 days sheep fetuses (n = 10) by echocardiographic-guided injection (modified Zanjani model).

Myocardial infarction (MI) was produced by a combined technique of surgical ligature of the first marginal of the circumflex artery and cryoablation with liquid nitrogen achieving an infarction area with total fibrotic replacement (n=8). MI was created in 1 year chimeric sheep and infarcted areas were treated with saline (control group, n=3) or 260×10³ human CD34+cells (treated group, n=7). Animals were euthanazied 1 month after MI and the heart were excised for pathology study. The infarct region was divided for study into three areas respect to the center of the infarct. Blood vessels were identified by BS-1 lectin-histochemistry and capillary density determined.

Our results showed no differences in capillary density in the three areas studied but a slightly increase in arteriolar component in the treated group compared with the control group (not significant). Neither significant differences were observed when comparing epicardial, medium and endocardial areas. No immune rejection or graft vs. host disease were observed in all treated animals.

This study shows that this model is a useful tool for preclinic in vivo evaluation of human cell therapy strategies in ischemic cardiovascular disease. Using human CD34+ cells at doses mentioned above our results did not showed significantly more angiogenesis and arteriogenesis than in the control group. To improve this model, further studies are needed to fully charaterize the role of dose, cell type and time for the angiogenic effect of cell-based therapies. Understanding the potentential of defined lineages of stem cells or undifferentiated progenitors, will lead to better and more focussed clinical trial designs using each cell type indenpendently or in combination, depending on which particular clinical indication is being targeted.

No relevant conflicts of interest to declare.