Transplanted T-ALL infiltrates multiple organs, remodels the myeloid compartment, and remains dependent on myeloid support for survival in vitro. (A) Survival of nonirradiated CD45.1⁺ mice transplanted with primary LN3 (CD45.2⁺) T-ALL cells was followed. Each line represents results from a cohort of mice transplanted with a distinct primary T-ALL sample. (B) Quantification of the frequencies of T-ALL cells (CD45.2⁺) within the indicated organs of leukemic transplant mice. Graph depicts cumulative data from 3 to 8 experiments, each with a distinct color-coded primary T-ALL. Bars represent means + standard error of the mean (SEM); circles represent individual mice. Graphs depict the number (C) and frequency (D) of viable T-ALL cells 6 or 7 days after culture in the presence or absence of enriched myeloid cells from the TME. T-ALL cells and myeloid cells were isolated from the indicated organs of leukemic mice that had been transplanted with primary LN3 T-ALL cells. Graphs depict cumulative data from 6 to 8 experiments, each with a distinct transplanted T-ALL sample; circles represent the average of 2 or 3 technical replicate wells per experiment. Graphs depict the number of cells of the indicated subsets (E) and frequencies of myeloid subsets (F) within the myeloid compartment (CD11b⁺ and/or CD11c⁺ cells) of spleens from tumor-free and LN3 T-ALL–transplanted mice. Graphs depict cumulative data from 5 or 6 independent experiments, each with a distinct color-coded primary T-ALL. Bars represent means + SEM; circles represent individual mice. (G) Representative immunofluorescent images of transplanted LN3 T-ALL cells and myeloid cells in the indicated organs. Immunostaining for T-ALL cells (CD45.2; green), F4/80 (red), CD11c (magenta), and DAPI (blue) is shown. Scale bars, 100 μm. *P < .05, **P < .01, ***P < .001, paired (C-D) and unpaired (E-F) Student t tests. ns, not significant.