Figure 6. MSCs with inducible expression of human IDO promote tumor growth through modulation of immune cells.

(A-C) Effects of MSCs with inducible human IDO (hIDO) expression on tumor growth. Wild type C57BL/6 mice or iNOS^−/− mice were injected i.m. in the thigh with B16-F0 melanoma cells (0.5 × 10⁶) (A, B) or EL4 lymphoma cells (0.5 × 10⁶) (C), and then administered i.p. with MSCs having inducible hIDO-expression (MSC-IDOi1), or constitutive hIDO-expression (MSC-IDOc1; positive control), wild type (wt) MSCs, or negative control MSCs (MSC-control) (1 × 10⁶ cells) every 2 days, with or without 1-MT (2 mg/ml) supplementation in drinking water. After 14 days, mice were sacrificed and resultant tumors were excised and weighed. (D) Distribution of immune cell subpopulations within tumor tissue. Cells were harvested from the tumors in (A), stained for the indicated markers, and analyzed by flow cytometry. The number of CD3⁺ T cells, CD4⁺ T cells, CD8⁺ T cells, CD4⁺ Foxp3⁺ T cells (regulatory T cells, Tregs), NKG2D⁺ cells (NK cells) and CD19⁺ cells (B cells) as a percentage of total cells within the tumor are shown. *p <0.05, **p < 0.01, ***p <0.001.