Type 1 Diabetes is an autoimmune disease, in which insulin secreting β cells are destroyed by cytotoxic lymphocytes T. Clear onset of disease is still unknown. The aim of the Master thesis is to investigate the effect of microRNA carried by vesicles on exocytosis of cytotoxic lymphocytes in type 1 Diabetes in patients and to compare the effect to the healthy individuals. Possible miRNA could serve as a biomarker in development of the Diabetes. We transfected isolated peripheral blood mononuclear cells with DOTAP-miRNA vesicles. The effect of vesicles microRNA on exocytosis of cytotoxic lymphocytes was measured with a test of cytotoxicity CD107a. Eight healthy individuals and eight patients with diabetes were included in our study. We found, that miR-375 has a higher effect on exocytosis of cytotoxic lymphocytes in both investigated groups. We proved, that there is no difference in effect of miR-375 on cells between patient and healthy individuals. We measured the secretion of cytokines TNF-α, IL-1β and IL-6 with a commercial kit for detection of extracellular cytokines in three healthy individuals and three patients. We wanted to show the effect of vesicle miRNA on secretion of cytokines. We found, that miR-375 has a higher effect on secretion of cytokines in comparison with RNA41 in both investigated groups, but the difference in effect of miR-375 between patients and healthy individuals was not statistically significant.