Granulocyte-Colony Stimulating Factor (G-CSF)is a small protein that stimulates the bone marrow to produce more of a particular class of white blood cells called granulocytes and release them into the bloodstream. A commercially available version of G-CSF called Filgrastim (Neupogen) is used to boost the immune system of cancer patients whose immune systems have taken a beating from chemotherapy.
Because several clinical trials have shown that implanting bone marrow mononuclear fractions into the hearts of heart attack patients can improve the heart health of some heart attack patients, clinicians have supposed that injecting heart attack patients with drugs like filgrastim, which moves many bone marrow-derived cells into the bloodstream might also provide some relief for heart attack patients.
Nice idea, but it does not seem to work. Two clinical trials, STEMMI and REVIVAL-2, have given G-CSF to heart attack patients at different times after their heart attacks. Unfortunately both studies have failed to show a difference from the placebo.
In the REVIVAL-2 study, 114 patients were enrolled, and 56 received 10 micrograms per kilogram body weight G-CSF for five days, and the remaining patients received a placebo treatment. G-CSF and the placebo were administered to patients five days after the hearts were successfully reperfused by percutaneous coronary intervention (this is a fancy way of saying stenting). This study was double-blinded, placebo-controlled and well designed. Unfortunately, when patients were studied seven years after treatment, there were no statistically significant differences between the treatment and the placebo groups when it came to the number of deaths, heart attacks, and strokes. Thus, the authors conclude that G-CSF administration did not improve clinical outcomes for patients who had a heart attack (see Birgit Steppich, et al, Atherosclerosis and Ischemic Disease 115.4, 2016).
A second clinical trial, the STEMMI trial, was a prospective trial in which G-CSF treatment was begun 10-65 hours after reperfusion. Here again, there were no structural differences between the placebo group and the G-CSF-treated group six months after treatment and a five-year follow-up analysis of 74 patients revealed no differences in the occurrence of major cardiovascular incidents between the two treatment groups (R.S. Ripa, and others, Circulation 2006; 113: 1983-1992).
The STEM-AMI clinical trial also showed no differences in clinical outcomes after G-CSF treatment as compared to placebo in 60 patients after three years (F. Achilli, and others, Heart 2014, 100: 574-581).
Why does this technique fail? It is possible that the white blood cells that are mobilized by G-CSF are low-quality and do not express particular genes. A study in rats has shown that G-CSF infusion increases the number of progenitor cells in the bloodstream, but fails to increase the number of progenitor cells in the heart after a heart attack (D. Sato, and others, Experimental Clinical Cardiology, 2012; 17:83-88). In order for cells to home to the infarcted heart, they must express particular proteins on their surfaces. For example, the cell surface protein CXCR4 is known to play an integral role in progenitor cell homing, along with several other proteins (see Taghavi and George, American Journal of Translational Research 2013; 5:404-411; Shah and Shalia, Stem Cells International 2011;2011:536758; Zaruba and Franz, Expert Opinion in Biological Therapy 2010; 10:321-335). Indeed, Stein and others have shown that progenitor cells mobilized with G-CSF in human patients lack CXCR4 and other cell adhesion proteins thought to play a role in homing to the infarcted heart (Thromb Haemost 2010;103:638-643).
Therefore, even though all of these studies have not uncovered a risk in G-CSF treatment, the consensus of the data seems to be there no clinical benefit is conferred by treating heart attack patients with G-CSF.