Strain- and species-specific immune responses to human adipose stem cell-derived extracellular vesicles: A comparative pharmacological evaluation in mice and human PBMCs

Human adipose stem cell-derived extracellular vesicles (hASC-EVs) have gained attention as potential cell-free therapeutics in regenerative medicine due to their immunomodulatory properties and low immunogenicity. Despite this promise, their immunotoxicity profile remains insufficiently characterized, particularly across species and genetic backgrounds. This study systematically assessed immune responses to repeated high-dose intravenous administration of hASC-EVs in two murine strains-C57BL/6 (inbred) and ICR (outbred)-and in human peripheral blood mononuclear cells (hPBMCs) in vitro. Flow cytometry of murine blood and spleen samples revealed transient, strain-dependent shifts in immune cell populations, including neutrophils, monocytes, macrophages, B cells, and NK cells. Notably, C57BL/6 mice exhibited more pronounced fluctuations than ICR mice, reflecting the role of host genetics in EV-induced immunomodulation. In contrast, hPBMCs exposed to equivalent concentrations of hASC-EVs displayed no significant changes in cell viability, immune cell subset composition, or activation markers over a 24-hour period. While a mild, transient increase in CD86⁺ monocytes was observed at 6 h, this effect normalized by 12 h. These results suggest that hASC-EVs induce minimal and reversible immune responses in vivo and are immunologically inert in human immune cells under the tested conditions. The strain- and species-specific differences observed emphasize the limitations of rodent-only models for predicting human immunotoxicity and support the incorporation of human immune cell assays into preclinical safety assessments of EV-based therapeutics.