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There are different subtypes of brain tumors, classified according to the origin of the abnormally proliferated glial cells. Glioblastoma multiforma (GBM) is the grade 4 of brain tumors, gliomas, with the least life expectancy. microRNAs (miRNAs) are small, single stranded, non-coding RNAs with 20-25 nt length with post-transcriptional gene regulatory activities. An altered expression of miRNAs is linked to developmental disorders and some diseases, most importantly cancers. miR-21 is a well-known microRNA, overexpressed in almost all cancer types, including brain tumors. It targets several genes with vital roles in cellular pathways involve in proliferation, invasion and metastatic behaviors. Exosomes are 30-100 nm extracellular vesicles which are packed with various molecules, including miRNAs. Here, we suppressed miR-21 expression level in HEK-293T cells by transfecting them with the miRZip-21 vector. However, when U87-MG cells were cultured in the presence of exosomes isolated from conditioned medium of engineered HEK-293T cells derived exosomes, we did not observe any suppressing effect on host cells’ miR-21 expression level. Moreover, by analyzing the effects of miRZip-21-enriched cell’s conditioned media on three other brain cell lines including 1321N1, A-172 and DAOY, cell type-specific effects of exocrine miRZip-21 were revealed. These data suggested that cell lines from different brain tumor subtypes could exert different responses to microRNA-based therapies, based on their cellular origin and clinical behaviors.