LAUSR

Background: Reparative (alternatively activated or M2-like) macrophages play an important role in post-myocardial infarction (MI) cardiac repair. Transplantation of bone marrow mononuclear cells (BM-MNCs) is an emerging therapy for MI while its therapeutic efficacy in previous clinical trials is not satisfactory. We hypothesized that induced differentiation/polarisation of BM-MNCs to reparative macrophages before transplantation may enhance the effect of BM-MNC transplantation. Purpose: This study aimed to develop a robust in vitro protocol to produce reparative macrophages from BM-MNCs and to establish the pre-clinical proof of concept data for reparative macrophage transplantation for the treatment of MI. Methods & Results: Mouse BM-MNCs were treated with M-CSF plus IL-4, IL-10, TGF-β1 or combinations of these in vitro . The concomitant M-CSF+IL-4 protocol produced the highest rate and number of CD11b + F4/80 + CD206 + macrophages. Expression and secretion of tissue repair-related factors of the produced cells, including IGF-1, TGF-β1, VEGF and IL1-ra, were more extensive compared to BM-MNCs. Then, reparative macrophages, BM-MNCs or PBS only were intramyocardially injected in a mouse MI model. At 4 weeks after treatment, echocardiography demonstrated that reparative macrophage transplantation markedly improved cardiac function (left ventricular ejection fraction; 57.2±1.6%, n=11) compared to both BM-MNC transplantation (48.4±1.3%, n=9) and control group (44.4±2.0%, n=9). Histological studies showed that infarct size was the smallest after reparative macrophage transplantation in association with the greatest tissue repair in the peri-infarct myocardium, including augmented microvascular formation, reduced cardiomyocyte hypertrophy and reduced pathological interstitial fibrosis. It was also found that reparative macrophage transplantation increased host-derived reparative macrophages through TGF-β1 secretion. Conclusion: M-CSF+IL-4 treatment was effective in producing reparative macrophages from BM-MNCs in vitro . Addition of this pre-treatment improved the therapeutic effect of BM-MNC transplantation. Further pre-clinical and clinical development of this advanced cell therapy is warranted.