Overexpression of the Shh/Ihh ligands in a JAK3-dependent T-ALL mouse model results in a competitive growth advantage and modification of the thymic niche. (A) GLI1 expression levels are strongly correlated with JAK3 levels in T-ALL patients. (B) Kaplan-Meier survival plot showing disease latency in mice transplanted with bone marrow progenitor cells expressing JAK3(M511I), JAK3(M511I)+Shh, or JAK3(M511I)+Ihh. (C) Leukemic cells expressing JAK3(M511I)+Shh or JAK3(M511I)+Ihh show a competitive growth advantage compared with cells expressing either gene alone. The percentage of each subpopulation was measured before injection (starting point) and at leukemia development (end point). (D) Lymph node infiltration in leukemic mice with JAK3(M511I), JAK3(M511I)+Shh, or JAK3(M511I)+Ihh. Pie charts show the number of mice with enlarged inguinal lymph nodes. The images show a representative example of the mesenteric lymph nodes with almost no infiltration in a JAK3(M511I) mouse, but high infiltration for a JAK3(M511I)+Shh mouse. Staining shown for anti-GFP. (E-F) Leukemic T lymphocytes are significantly reduced in blood of JAK3(M511I)+Shh or Ihh mice. (E) Time point (in days) at which the white blood cell count (WBC) exceeds 10 000 cells per µL. (F) Absolute white blood cell count at end point. (G) Gli1 and Gli1 target genes are significantly upregulated in mice expressing the hedgehog ligands. Relative expression of Gli1 target genes in thymic lymphocytes isolated from mice expressing the empty vector or the hedgehog ligands are shown. (H-I) Activation of TECs by hedgehog ligands results in upregulation of Gli1, Gli1 target genes, and ligands correlated with T-cell development. Relative expression of Gli1 target genes (H) and ligands (I), which are physiologically expressed by TECs are shown. **P < .01.