Expression of immune checkpoint genes across multiple pediatric tumor types. Gene expression of (A) PD-L1, (B) PD-L2, (C) B7-H3, and (D) IDO1 across various pediatric hematologic malignancies (white bars), central nervous system tumors (light gray bars), solid tumors (gray bars), and osteosarcoma (dark gray bar). Statistical significance (p ≤ 0.05) was determined using one-way ANOVA with Holm-Sidak’s multiple comparison test. P values are indicated for each pairwise comparison (vs. osteosarcoma). B-ALL, B-acute lymphoblastic leukemia; T-ALL, T-acute lymphoblastic leukemia; MLL, mixed lineage leukemia; AML, acute myeloid leukemia; LGG, low-grade glioma; EPD, ependymoma; HGG, high-grade glioma; MB, medulloblastoma; CPC, choroid plexus carcinoma; RMS, rhabdomyosarcoma; MEL, melanoma; RB, retinoblastoma; ACT, adrenocortical tumor; OS, osteosarcoma.