Human Mesenchymal Stem Cell Secretome Driven T Cell Immunomodulation Is IL-10 Dependent

The Human Mesenchymal Stem Cell (hMSC) secretome has pleiotropic effects underpinning its therapeutic potential. hMSC serum-free conditioned media (SFCM) contains a variety of cytokines, with previous studies linking a changed secretome composition to physoxia. The Jurkat T cell model allowed the efficacy of SFCM vs. serum-free media (SFM) in the suppression of immunological aspects, including proliferation and polarisation, to be explored. Cell growth in SFM was higher [(21% O₂ = 5.3 × 10⁵ ± 1.8 × 10⁴ cells/mL) and (2% O₂ = 5.1 × 10⁵ ± 3.0 × 10⁴ cells/mL)], compared to SFCM [(21% O₂ = 2.4 × 10⁵ ± 2.5 × 10⁴ cells/mL) and (2% O₂ = 2.2 × 10⁵ ± 5.8 × 10³ cells/mL)]. SFM supported IL-2 release following activation [(21% O₂ = 5305 ± 211 pg/mL) and (2% O₂ = 5347 ± 327 pg/mL)] whereas SFCM suppressed IL-2 secretion [(21% O₂ = 2461 ± 178 pg/mL) and (2% O₂ = 1625 ± 159 pg/mL)]. Anti-inflammatory cytokines, namely IL-4, IL-10, and IL-13, which we previously confirmed as components of hMSC SFCM, were tested. IL-10 neutralisation in SFCM restored proliferation in both oxygen environments (SFM/SFCM^+antiIL-10 ~1-fold increase). Conversely, IL-4/IL-13 neutralisation showed no proliferation restoration [(SFM/SFM^+antiIL-4 ~2-fold decrease), and (SFM/SFCM^+antiIL-13 ~2-fold decrease)]. Present findings indicate IL-10 played an immunosuppressive role by reducing IL-2 secretion. Identification of immunosuppressive components of the hMSC secretome and a mechanistic understanding of their action allow for the advancement and refinement of potential future cell-free therapies.