br Myocardial regeneration after allogeneic stem cell therap

Myocardial regeneration after allogeneic stem cell therapy Moreover, as outlined above, a consensus is gaining ground that most of the favourable effects of cell transplantation protocols used until now exert their beneficial effect by a paracrine mechanism of the transplanted TAK-875 over the surviving myocardial cells at risk and/or through the activation of the endogenous myocardial regenerative capacity represented by the eCSCs (Gnecchi et al., 2008; Hatzistergos et al., 2010). If this is correct, then there seems to be little advantage in the use of autologous cells because a similar, and perhaps enhanced, effect can be obtained by the administration of the proper growth factors, the appropriate cell type isolated from allogeneic sources or a combination of both. Allogeneic cells can be produced in large quantities beforehand, stored frozen before their use and made available at all times. That would allow their use not only for the treatment of the pathological remodelling once it has developed but soon after the acute insult to prevent or diminish the pathological remodelling. Unresolved clinical questions related to the use of allogeneic stem cells in the treatment of patients with AMI remain the identification of the optimal cell population and also the method(s) and time of administration. As previously stated, to be widely available and compatible with current clinical standard of care for AMI, an intracoronary method for delivery at the time of the primary revascularization is the most feasible. Also, direct myocardial injection during revascularization surgery is highly realistic. Mesenchymal stem cells (MSC) have a broad repertoire of secreted trophic and immunodulatory cytokines, however they also secrete factors that negatively modulate CM apoptosis, inflammation, scar formation and pathological remodelling (Ranganath et al., 2012). Moreover, it is questionable whether they are the optimal cell to use in terms of survival and homing to and engraftment in the myocardium since only ~3–4% of the cells administered intracoronary are retained in the myocardium (Dauwe et al., 2011). Furthermore, MSCs can be large and become entrapped in the microvasculature and impede their entry into the myocardium. Recently, Marban et al. (Malliaras et al., 2012) have tested the safety and efficacy of using allogeneic, mismatched Cardiosphere-Derived Cells (CDCs) in infarcted rats. Allogeneic CDC transplantation resulted in a robust improvement of fractional area change (~12%), ejection fraction (~20%), and fractional shortening (~10%), which was sustained for at least 6months. Furthermore, allogeneic CDCs stimulated endogenous regenerative mechanisms (recruitment of c-kitpos eCSCs, angiogenesis) and increased myocardial VEGF, IGF-1 and HGF. We have previously shown that eCSCs that express high levels of the transcription factor GATA-4 exert a paracrine survival effect on CMs through increased IGF-1 secretion and induction of the IGF-1R signalling pathway (Kawaguchi et al., 2010). Furthermore, unlike other cell types (Abdel-Latif et al., 2007; Hofmann et al., 2005), CSCs have a very high tropism for the myocardium. When administered through the systemic circulation the majority of CSCs home and nest into the damaged myocardium (Ellison et al., 2013). Under proper culture conditions it is possible to clone and expand a single rodent, porcine or human eCSC to up to 1x1011 cells without detectable alteration of karyotype, loss of differentiating properties or the phenotype of the differentiated progeny (Ellison et al., 2011). These cloned cells produce a repertoire of pro-survival, anti-inflammatory and cardiovascular regenerative growth factors such as: IGF-1, HGF, TGF-β1 superfamily, including activins and BMPs, neuregulin-1, periostin, and BMP-10 among others (Waring et al., 2012). For this reason, we decided to test whether these cloned and in vitro expanded cells, when administered into allogeneic animals, would be the source of a more complex and physiologic mixture of growth and differentiating factors which, through a paracrine effect, would produce a robust activation of the eCSCs with more rapid maturation of their progeny. It was expected that once their short-term effect had been produced and the auto/paracrine feedback loop of growth factor production has been activated in the eCSCs, the allogeneic cells would be eliminated (presumably by apoptosis) and that the regeneration triggered by activated eCSCs would be completely autologous. c-kitpos eCSCs do not express either MHC-II locus or the co-activator molecules CD40, CD80, CD86, ICOS-l, and express low levels of MHC-I antigens. They also have strong immunomodulatory properties in vitro when tested in the mixed lymphocyte reaction with high expression of PD-L1/programmed cell death-1 [unpublished]. We therefore expected the cloned in vitro expanded cells to survive long enough in the allogeneic host to produce their paracrine effect before being eliminated by the host immune system.