Abstract Body (Do not enter title and authors here): Background: The role of immune suppressive microenvironment, promulgated by the presence of Myeloid Derived Suppressor Cells (MDSC) have been the major focus of research delineating the underlying mechanisms of cardiovascular diseases (CVD). CCR5, a chemokine receptor, has been associated with both immunosuppressive and inflammatory phenotypes, however, the possible role of CCR5 pertaining to MDSCs in the development of atherosclerosis has not been elucidated yet. Therefore, we investigated the therapeutic potential of CCR5 modulation in early atherosclerosis progression.
Methods: CCR5 receptor-ligand expression was studied with flow cytometry, real time PCR and immunocytochemistry in 65 individuals (25 Healthy controls, 20 young hypercholesterolemic individuals, and 20 stable [Coronary Artery Disease] CAD patients). To induce atherosclerosis, mice were fed high fat diet (HFD) for 6 weeks following partial ligation of left carotid artery in C57BL6 mice. MDSCs phenotype and functionality were assessed using CCR5 inhibitor in vitro (10^-8 M) and in vivo (i.p 3ng/day for 15 days). M-MDSCs phenotype switch, atherosclerotic lesion development and plaque phenotype was studied in vivo.
Results: We observed CCR5 elevation on Monocytic-MDSCs in the early phase of atherosclerosis. M-MDSCs displayed an intermediate phenotype with expression of both pro and anti-inflammatory mediators in early atherosclerosis, a similar trend was observed in inflammatory cytokines stimulated M-MDSCs (in vitro). Notably, DAPTA treatment shifted phenotype of M-MDSCs to anti-inflammatory profile with elevated expression of IL-10 and reduced expression of IFNγ, IL4, and IL22. Further, CCR5 modulation expanded IL10+M-MDSC in vivo. Additionally, DAPTA reduced the migratory potential, reduced cholesterol uptake and improved the functionality (suppression of T cell) of M-MDSCs. Blocking CCR5 with DAPTA led to the formation of stable plaque in HFD-fed mice.

Conclusion: Increased expression of CCR5 coupled with inflammatory cytokine secretion by regulatory cells lead to dysfunctional M-MDSCs in CVD risk factor population. Possibly this dysfunctionality contributes to the development and progression of CVD including atherosclerosis. Our findings show targeting of CCR5 with DAPTA reduces atherogenesis, increases plaque stabilization and corrects phenotypic alterations in immune suppressive M-MDSCs. The functionality and phenotype of M-MDSCs in atherosclerosis, may be ameliorated by targeting CCR5.