T-ALL development in NOD-Scid mice. Human T-ALL blasts were identified using CD45-specific antibodies and further characterized with myeloid and lymphoid subset-specific antibodies. Shown are representative results from a group of mice transplanted with the M18 T-ALL sample that carries a sil-tal interstitial deletion (Table 1, additional data). (A) Engraftment levels in the mouse hematopoietic organs. BM indicates bone marrow; SPL, spleen; THY, thymus; LN, lymph nodes. (B) Human B lymphoid and myeloid cells are absent from the BM of T-ALL–transplanted mice. Human CD45⁺ cells were gated according to isotype controls. Expression of CD19 B-cell marker or of CD15 myeloid cell marker was analyzed in the gated human CD45⁺ cell population. (C) May-Grünwald-Giemsa staining of cytospins (top panels). Slides were viewed with a laborlux 5 Leitz microscope (Leitz France, Rueil Malmaison, France) using Leitz microscope lens (oil immersion, ×25). Pictures were acquired using a Sony-CCD iris color video camera (Sony France, Paris, France) and images were processed using Adobe Photoshop software. CD4/CD8 (middle panels), and CD7 (bottom panels) expression analysis of gated human CD45⁺ cells engrafting different hematopoietic sites. Positivity bars were set according to isotype controls. Indicated are percentage of positive cells. ND indicates not done. (D) SCL/TAL1 protein levels in human cells engrafting different hematopoietic organs were determined using Western blot. eEF2k protein levels were used for loading normalization. Negative control (ie, C⁻) are proteins from cells (mouse + human) present in the spleen of a mouse transplanted with M22 T-ALL that does not express SCL/TAL1. (E) PCR analysis of γ-TCR gene rearrangements in the BM, THY, and SPL of a representative mouse transplanted with M18 T-ALL. Cells from patient were used in parallel. Negative (C⁻) control contained water.