miR-155 deficiency in donor T cells does not abrogate GVL effects. (A) Whole body bioluminescent signal intensity of recipient mice. Mice were imaged on day 10 and day 20. (B) Histopathologic analysis of spleen and liver tissues of the different mice cohorts. Histopathologic examination at lower power (original magnification ×100) revealed extensive nodular leukemic infiltration in the liver in the BM alone recipients, whereas no infiltrates were seen in recipients who received splenocytes, either from WT or miR-155–deficient mice (top panels). Middle top panels: The same liver sections are shown at larger magnification (original magnification ×200). Note in the BM alone the many large anaplastic cells with pleomorphic, multilobular large nuclei and frequent mitosis figures. Last 2 bottom panels: Spleen sections at lower (top) and higher (bottom) magnification. Note the complete replacement of the spleen by the large anaplastic cells in the BM alone group. The arrows point to normal spleen. There were no leukemic infiltrations in the recipient groups who received either WT or miR-155–deficient splenocytes. (C) Survival of lethally irradiated mice transplanted with WT or miR-155–deficient splenocytes plus BM P815 leukemic cells. Survival comparisons were performed using the log-rank test.