ABSTRACT Diabetes markedly increases risk of development of atherosclerotic cardiovascular disease (CVD). Human and animal data also show that diabetes prevents the normal repair of damaged arteries that occurs upon circulating LDL cholesterol (LDL-C) reduction. Because of this, patients with diabetes still have greater risk of a cardiovascular event even after statin reduction of LDL-C than individuals without diabetes. Individuals with diabetes have greater platelet aggregation, altered white blood cells, and more vascular inflammation, pathological processes that are improved by LDL-C reduction in unaffected individuals. We hypothesize that by determining response to LDL-C reduction in T1D, we will identify pathways that can be therapeutically targeted to optimize vascular repair and prevent CVD events. These data can also be used to determine patient characteristics that associate with defective response to LDL-C reduction. We propose a clinical study of response to LDL-C reduction in patients with Type 1 diabetes (T1D). We will recruit the patients from two major medical centers, NYU Langone and Mount Sinai that serve diverse communities within New York City. Subjects will be treated for 4 weeks with robust cholesterol-reducing therapies, PCSK9 inhibitors and also either statin (80 mg atorvastatin) or ezetimibe (10 mg). Each subject will serve as their own control and we will determine changes in platelets and white blood cells along with circulating inflammatory factors that occur when LDL-C is markedly reduced. In a subgroup of subjects, changes in vascular inflammation will be determined by assessment of harvested brachial vein endothelial cells and by uptake of 18F-fluordeoxyglucose into arteries. The data will be analyzed by an experienced statistician with expertise in diabetes and CVD risk and will identify the relationship of these changes with HbA1c and glucose variability, and differences between women and men. In addition, the data in T1D will be compared with similar data assessing response to LDL-C in subjects with Type 2 diabetes and controls to determine abnormalities that differ between these two forms of diabetes.