Ex-Vivo Expanded Human Bone Marrow-Derived AC133+ Cells To Treat Myocardial Infarction.

To examine whether ex-vivo expanded human bone marrow (BM)-derived AC133⁺ cells may participate in post myocardial infarction (MI) healing, we have examined the effect of the copper chelator tetraethylenepentamine (TEPA) on the ex-vivo expansion potential of BM-derived stem cell populations and the effect of the resulting ex-vivo expanded AC133⁺ cells in a MI animal model. AC133⁺ cells isolated from human BM, using the CliniMACS device, at purities greater than 90% were expanded in Teflon bags, in the presence of IL-6, TPO, Flt-3 ligand, and SCF with or without TEPA for three weeks. The progenitor cell composition and potential were examined at the end of the treatment time and after long-term incubation in culture. After 3 weeks in TEPA-treated cultures the total nuclear cell expanded more than 200±20 fold. The increase in the CD34⁺, AC133⁺ and AC133⁺/CD38^-cell populations was 17±13, 16±1 and 270±110 - fold, respectively, and the CFU content was 84±28 fold higher than at the initiation of the cultures. Contrary to TEPA treated cultures, the cultures treated in the absence of the chelator lost their progenitor populations by week 5-7 in culture. Ex-vivo expanded AC133⁺ cells for 3 weeks expressed VEGF and VEGF receptor RNA as examined by RT-PCR.

An MI model was established in athymic nude rats by permanent ligation of the left anterior descending coronary artery. Ex-vivo expanded AC133⁺ cells (6x10⁶ cells/rat) or saline (control) were injected at the scar tissue 6 days post MI. Four weeks after cell therapy, the hearts were harvested and examined. Staining for smooth-muscle alpha-actin detected a 1.6-fold increase in capillary and arteriole density in the expanded cell-treated vs. control hearts. Preliminary echocardiographic studies compared 4 weeks post-treatment with those observed prior to treatment. Expanded BM-derived AC133⁺ injection into the infarcted myocardium improved left ventricular (LV) remodeling as demonstrated by increasing LV systolic dimensions only by 11%±4 while increasing by 53%±17 in control animals (p=0.02). Similarly, AC133⁺ cell injection improved LV contractility as demonstrated by increasing fractional shortening (FS) by 58%±44 whereas FS decreased by 20%± 5 in control animals (p=0.14). In addition, AC133⁺ cell injection prevented scar thinning as demonstrated by a decrease in anterior wall thickness of 10%±4 whereas the decrease in anterior wall thickness was 30%±7.5 in control saline-treated animals (p<0.05). Clinical trials examining the safety and feasibility of intra-corronary injection of ex-vivo expanded autologous BM-derived AC133⁺ to patients with ischemic heart disease, are currently in preparation.

Conclusion: A. TEPA allows BM-derived AC133⁺ cells to self renew by permitting proliferation ex-vivo while hindering their differentiation. B. Our preliminary results suggest that injection of ex-vivo expanded BM-derived AC133⁺ cells into infarcted myocardium results in new vessel formation and improves left ventricular function.