This significant increase in expression at the mRNA level was corroborated using a functional assay; the production of L-kynurenine by IDO in the T-H-SF-MSCs (mean ± SD: 12.611 ± 0.561 μM) and T-RA-SF-MSCs (mean ± SD: 5.507 ± 1.360 μM) significantly increased compared with the control samples of H-SF-MSCs (mean ± SD: 0.119 ± 0.561 μM) and RA-SF-MSCs (mean ± SD: 0.047 ± 1.2646 μM) (Figure 5B). Here, IDO1 is linked to rheumatoid arthritis.