STC2 and neoplasm: As STC2 was previously shown to form a complex with heme oxygenase-1 (HO-1) to degrade heme in COS-7 cells32, combined with HO-1 is an important mediator of the ability of MSCs to inhibit T-cell responses33, and downregulation of HO-1 in tumor increased the infiltration of cytotoxic CD8+ T cells34, we hypothesized that MSC-derived STC2 might reduce CD8+ Tc1 cells by affecting HO-1 activity.