Long-Term Outcome of Administration of c-kit ^POS Cardiac Progenitor Cells After Acute Myocardial Infarction

Abstract

Conclusions:The beneficial effects of CPCs on left ventricular remodeling and dysfunction are sustained for at least 1 year and thus are likely to be permanent. Because transplanted CPCs do not differentiate into mature myocytes, their major mechanism of action must involve paracrine actions. These paracrine mechanisms could be very prolonged because some CPCs engraft, proliferate, and persist at 1 year. This is the first report that transplantation of any cell type in the heart induces a proliferative response that lasts at least 1 year. A major limitation of all of the aforementioned studies, however, is that the follow-up after cell therapy was relatively short (4-6 weeks); consequently, the long-term (≥1 year) effects of CPCs on LV function and structure in experimental models of ischemic cardiomyopathy remain unknown. Similarly, the safety of CPC therapy remains uncertain because potential adverse effects, such as tumor formation, would not be expected to be evident within the 4-to 6-week follow-up of the studies performed to date; a longer time frame is needed to assess this possibility. For the same reason, the long-term fate of transplanted CPCs beyond the first 4 to 6 weeks is essentially unknown.Another fundamental issue that remains to be clarified is the mechanism(s) that underlies the beneficial effects of CPCs.2 Differentiation of transplanted CPCs into myocytes and vascular cells has been thought to play an important role 15 but, as alluded to above, in our previous studies in models of ischemic cardiomyopathy, we did not observe formation of adult myocytes from transplanted cells 9-14 ; however, because in all of these studies 9,11-14 animals were followed-up for only 4 to 5 weeks after cell therapy, the possibility that differentiation of transplanted CPCs into mature myocytes may occur at a later time cannot be ruled out. Because we did not observe any evidence of differentiation of exogenous CPCs, [9][10][11][12][13][14] we have proposed 3 that these cells produce their salubrious effects, at least in part, by activating the pool of endogenous CPCs; however, this possibility has not been substantiated.Thus, several fundamental issues remain to be addressed regarding CPC therapy. From a translational standpoint, before clinical implementation, it is important to assess the long-term safety of CPC therapy and establish, in a rigorous and wellcontrolled experimental model, whether the cardiac reparative benefits of CPC administration are transient or permanent. From a conceptual standpoint, understanding the mechanism of action of exogenous CPCs requires an effort to illuminate the long-term fate of the transplanted cells and to establish whether or not their salubrious effects are mediated by differentiation of the transplanted cells into mature cardiac myocytes.This study was undertaken to elucidate these issues. Specifically, using a well-characterized rat model 9 and a rigorous, blinded study design, we sought to determine i) whether the effects of CPCs on LV function and remodeling after MI ...

Repeated Administrations of Cardiac Progenitor Cells Are Superior to a Single Administration of an Equivalent Cumulative Dose

“…The isolation, characterization, and expansion of CPCs have been previously described 3, 8, 9. Briefly, cardiac cells were isolated from adult male Fischer 344 rats (4–6 months of age).…”

“…Serial echocardiograms were obtained at 5 time points: baseline (3 days before coronary artery occlusion), 30 days after MI (before the first treatment), 35 days after the first treatment (before the second treatment), 35 days after the second treatment (before the third treatment), and 35 days after the third treatment (before euthanasia; Figure 1). The echocardiographic studies were performed as described3, 7, 8, 9, 10 using a Vevo 2100 Imaging System equipped with a 20‐MHz transducer.…”

“…The hemodynamic studies were conducted 35 days after the third treatment, just before euthanasia (Figure 1). The protocol has been described previously 3, 7, 8, 9, 10…”

“…The procedures for Masson's trichrome, picrosirius red, and immunohistochemistry staining and analyses have been described 3, 7, 8, 9, 11, 12. Immunohistochemistry staining was performed with specific antibodies against CD45, wheat germ agglutinin, α‐sarcomeric actin, BrdU , and IdU (Sigma).…”

“…Immunohistochemistry staining was performed with specific antibodies against CD45, wheat germ agglutinin, α‐sarcomeric actin, BrdU , and IdU (Sigma). To assess the fate of the transplanted male CPCs, Y chromosome was detected by fluorescence in situ hybridization according to the modified manufacturer's protocol (ID Labs, London, ON) 3, 8, 13…”