Mesenchymal stromal cells (MSCs) are administered locally to treat sites of inflammation. Local delivery is known to cause MSCs to aggregate into “spheroids,” which alters gene expression and phenotype. While adherent MSCs are highly efficient in their inhibition of T cells, whether or not this property is altered upon MSC aggregation has not been thoroughly determined. In this study, we discovered that aggregation of MSCs into spheroids causes them to lose their T cell-suppressive abilities. Interestingly, adding budesonide, a topical glucocorticoid steroid, alongside spheroids partially restored MSC suppression of T cell proliferation. Through a series of inhibition and add-back studies, we determined budesonide acts synergistically with spheroid MSC-produced PGE2 to suppress T cell proliferation through the PGE2 receptors EP2 and EP4. These findings highlight critical differences between adherent and spheroid MSC interactions with human immune cells that have significant translational consequences. In addition, we uncovered a mechanism through which spheroid MSC suppression of T cells can be partly restored. By understanding the phenotypic changes that occur upon MSC aggregation and the impact of MSC drug interactions, improved immunosuppressive MSC therapies for localized delivery can be designed.

间充质基质细胞（MSCs）局部给药以治疗炎症部位。已知局部递送可导致MSC聚集成“球体”，从而改变基因表达和表型。尽管粘附的MSC在抑制T细胞方面非常有效，但尚未完全确定该性质是否随MSC聚集而改变。在这项研究中，我们发现MSC聚集成球状体会使其失去T细胞抑制能力。有趣的是，将布地奈德，一种局部用糖皮质激素类固醇与球状体一起部分恢复了MSC对T细胞增殖的抑制作用。通过一系列抑制和添加研究，我们确定布地奈德与球状MSC生产的PGE2协同作用，以抑制T细胞通过PGE2受体EP2和EP4增殖。这些发现突出了粘附和球状MSC与人类免疫细胞之间的关键差异，这些差异具有重大的翻译结果。此外，我们发现了一种机制，通过该机制可以部分恢复T细胞的球形MSC抑制。通过了解在MSC聚集后发生的表型变化和MSC药物相互作用的影响，可以设计出用于局部递送的改良的免疫抑制MSC治疗。