Granulocyte-colony stimulating factor therapy to induce neovascularization in ischemic heart disease

Rasmus Sejersten Ripa
Danish Medical Journal 2012, 59 (3): B4411
Cell based therapy for ischemic heart disease has the potential to reduce post infarct heart failure and chronic ischemia. Treatment with granulocyte-colony stimulating factor (G-CSF) mobilizes cells from the bone marrow to the peripheral blood. Some of these cells are putative stem or progenitor cells. G-CSF is injected subcutaneously. This therapy is intuitively attractive compared to other cell based techniques since repeated catheterizations and ex vivo cell purification and expansion are avoided. Previous preclinical and early clinical trials have indicated that treatment with G-CSF leads to improved myocardial perfusion and function in acute or chronic ischemic heart disease. The hypothesis of this thesis is that patient with ischemic heart disease will benefit from G-CSF therapy. We examined this hypothesis in two clinical trials with G-CSF treatment to patients with either acute myocardial infarction or severe chronic ischemic heart disease. In addition, we assed a number of factors that could potentially affect the effect of cell based therapy. Finally, we intended to develop a method for in vivo cell tracking in the heart. Our research showed that subcutaneous G-CSF along with gene therapy do not improve myocardial function in patients with chronic ischemia despite a large increase in circulation bone marrow-derived cells. Also, neither angina pectoris nor exercise capacity was improved compared to placebo treatment. We could not identify differences in angiogenic factors or bone marrow-derived cells in the blood that could explain the neutral effect of G-CSF. Next, we examined G-CSF as adjunctive therapy following ST segment elevation myocardial infarction. We did not find any effect of G-CSF neither on the primary endpoint--regional myocardial function--nor on left ventricular ejection fraction (secondary endpoint) compared to placebo treatment. In subsequent analyses, we found significant differences in the types of cells mobilized from the bone marrow by G-CSF. This could explain why intracoronary injections of unfractionated bone marrow-derived cells have more effect that mobilization with G-CSF. A number of other factors could explain the neutral effect of G-CSF in our trial compared to previous studies. These factors include timing of the treatment, G-CSF dose, and study population. It is however, remarkable that the changes in our G-CSF group are comparable to the results of previous non-blinded studies, whereas the major differences are in the control/placebo groups. We found that ejection fraction, wall motion, edema, perfusion, and infarct size all improve significantly in the first month following ST-segment myocardial infarction with standard guideline treatment (including acute mechanical revascularization), but without cell therapy. This is an important factor to take into account when assessing the results of non-controlled trials. Finally, we found that ex vivo labeling of cells with indium-111 for in vivo cell tracking after intramyocardial injection is problematic. In our hand, a significant amount of indium-111 remained in the myocardium despite cell death. It is difficult to determine viability of the cells after injection in human trials, and it is thus complicated to determine if the activity in the myocardium tracks viable cells. Cell based therapy is still in the explorative phase, but based on the intense research within this field it is our hope that the clinical relevance of the therapy can be determined in the foreseeable future. Ultimately, this will require large randomized, double-blind and placebo-controlled trials with "hard" clinical endpoints like mortality and morbidity.

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