Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 20 2 2021 04 17 221 232 EN Katayoun Bahman Soufiani Department of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Ali Akbar Pourfathollah Department of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Mahin Nikougoftar Zarif Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran Ehsan Arefian Department of Microbiology, School of Biology, College of Science, University of Tehran, Tehran, Iran 2021 01 15 2021 03 06 Conditioned medium (CM) derived from mesenchymal stem cells (MSCs) contains bioactive molecules including microRNAs (miRs) that could be a potential tool for controlling cancer cells' behavior. Due to the properties of CM, this study assesses the effects of miR-34a related MSC-CM on tumor behavior through the evaluation of migration, invasion, apoptosis, and PDL1 expression in breast cancer cell lines. The miR-34a overexpression vector or scramble control was produced using lentiviral vectors, DNA cloning, and the transfection of the HEK-293T cell line. It was then transduced into human adipose-derived mesenchymal stem cells (hAD-MSCs). MSC-CMs were collected and added onto MDA-MB-231 cell lines. The functional evaluations were performed by transwell, wound healing, and Annexin V/PI methods on the treated MDA-MB-231 cell lines. The PDL1 expression was also assessed by Real-time PCR and western blot. The findings of this study showed that ectopic miR‑34a expression was significantly upregulated in manipulated hASC with miR-34a (p<0.0001). Treatment of MDA-MB-231 cell line with miR-34a-hAD-MSC-CM, scramble-hAD-MSC-CM, or hAD-MSC-CM displayed not only a reduction in the number of migrated or invaded cells (p=0.01) but also an increase in the apoptotic cells in the test group (p=0.02) when compared to the control groups. It also showed down-regulation in the gene (p=0.05) and protein expression levels of PDL1 in the test group. The results of the present study showed that simultaneous application of miR-34a and MSC-CM can be considered as a new method for changing the cancerous microenvironment; and therefore, as a potential strategy in breast cancer therapy. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/3096 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/3096/1701