Defining the Cellular Basis for Therapeutic Angiogenesis: Characterisation of Progenitor Cell Populations

Abstract

Cardiovascular disease is currently the leading cause of death worldwide. Despite improvement in management, there remain a significant number of “no option” patients who are not eligible for traditional treatments. Clearly there is an unmet clinical need to better serve these individuals. There has been much hype over the use of cell therapy for therapeutic angiogenesis as a treatment for these “no option” patients. While preclinical studies of various cells types have been promising, the potential of cell therapy has failed to translate with clinical trials showing mixed outcomes. This may be due to issues such as the use of heterogeneous cell populations, varying cell-processing techniques, cell numbers and delivery methods. This thesis investigates the use of bone marrow-derived mononuclear cells (BMMNCs), two endothelial progenitor cell subtypes, mesenchymal stem cells (MSCs) and fibroblasts as a cell therapy for neovascularisation in a murine hindlimb ischaemia model using a low (2x105) and high (1x106) cell dose and two different delivery methods (intramuscular and intravenous) to determine the most effective treatment for the augmentation of blood flow recovery. Cell kinetics and efficacy were longitudinally compared in vivo using bioluminescence imaging coupled with laser Doppler perfusion imaging (LDPI) to dynamically track cell homing, survival and engraftment and recovery. The study found that a cell number threshold exists for cell therapy efficacy and that intramuscular transplantation is the most effective delivery method for successful cell therapy. The outgrowth endothelial cell (OEC) endothelial progenitor subtype were found to be the most effective cell of all those tested, with only OEC therapy being able to affect recovery at the lowest cell dosage used. At the higher cell dosage tested, although OECs were most effective BMMNCs were also able to augment blood flow recovery, implicating them as a good second choice for cell therapy if there is limited time for ex vivo cell expansion as would be required with OEC therapy. Novel analyses of LDPI data using sigmoid recovery functions and Area Under Curve analyses showed that OEC therapy had significantly greater overall efficacy as well as an earlier day of 50% recovery. These novel parameters will be useful in further investigations of LDPI data as they allow for broader analyses of treatment parameters that can be used to compare therapies. This thesis also outlines the discovery of a murine peripheral blood mononuclear cell-derived outgrowth endothelial cell that may be a prospective cell therapy. More studies need to be carried out to characterise and confirm this potential. In conclusion, this thesis identifies intramuscular transplantation of OECs to be the most effective cell type for augmentation of blood flow recovery in ischemic conditions. However, further investigations need to be carried out to determine the translatability of these findings to a human setting.