Aims: This study aimed to investigate the therapeutic potential of a homogenous clonal population of mesenchymal stem cells (cMSC) and their extracellular vesicles (cMSC-EV) subpopulations on isolated rat islets in vitro and in inflammatory-mediated type 1 diabetes (T1D) non-human primate models. Main methods: EV subpopulations were isolated from human bone marrow-derived cMSC supernatant by low- and high-speed ultracentrifuge (EV-20K and EV-U110K) and sucrose density gradient (EV-S110K). The EVs were characterized generally and for the level of albumin, acetylcholinesterase (AChE) activity, co-isolate apoptotic markers, and expression of CD63+/annexin V+. Rat islet-derived single cells (iSCs) proliferation was measured using a Ki-67 proliferation assay. Diabetes was induced by multiple low-dose administrations of streptozotocin in rhesus monkeys. The diabetic monkeys were divided into three groups: the cMSC group, received two injections of 1.5 × 106 cMSC/kg body weight; the EV group received two injections of EVs isolated from 1.5 × 106 cMSC/kg, and the vehicle group received phosphate-buffered saline. Key findings: EV-S110K showed higher AChE activity, lower expression of CD63+/annexin V+, and lower apoptotic co-isolates. EV-S110K induced β-cell proliferation in vitro in a dose-dependent manner. The administration of EV-S110K and/or cMSC in diabetic monkeys demonstrated no significant changes in general diabetic indices and β-cell mass in the pancreas of the monkeys. Both treatments demonstrated a lowering trend in blood glucose levels and reduced pro-inflammatory cytokines. In contrast, regulatory T cells and anti-inflammatory cytokines were increased. Significance: cMSC and cMSC-EV provided initial evidence to attenuate clinical symptoms in inflammatory-mediated T1D non-human primates through immunomodulation. Keywords: Clonal mesenchymal stem cells; Extracellular vesicles; Immunomodulation; Non- human primate; Type 1 diabetes.