In vivo phenotypes of herg1-positive and herg1-negative leukemia blasts. Repopulation assay in NOD-SCID mice, inoculated with (1) herg1-negative (herg1⁻) and herg1-positive (herg1⁺) leukemia blasts from primary AML; two herg1⁻ cases (cases A10 and A13 in Table 1) and two herg1⁺ cases (cases A34 and A42 in Table 1) were injected; (2) HL60 and of HL60 cells transfected with herg1a cDNA (hERG1-HL60). In these cells, herg1a mRNA expression was checked by RQ-PCR (Table 3). Data are representative of at least 3 mice per group. (A) Immunohistochemistry (IHC) with anti-mCD34 antibody on BM of mice inoculated with herg⁻ (left) and herg⁺ (right) leukemia blasts from primary AML (magnification 250×). The arrows indicate CD34-positive vessels. (B) IHC with anti-hMHCI antibody on BM of mice inoculated with HL60 (left) and hERG1-HL60 (right) (magnification 200×). The arrows indicate niches of leukemia blasts. Inset, IHC with anti-hERG1 antibody on BM of mice injected with hERG1-HL60 (magnification 400×). The arrow indicates hERG1-positive leukemia cells. (C) IHC with anti-hMHCI on the liver of mice inoculated with herg⁻ (left) and herg⁺ (right) leukemia blasts (magnification 400×). The arrow indicates niches of leukemia blasts. (D) IHC with anti-hMHCI on spleen of mice inoculated with HL60 (left) and hERG1-HL60 (right) (magnification 200×). The arrow indicates niches of leukemia blasts. Images were acquired on a Leica DM 4000B microscope with a Leica DFC 320 photocamera (Leica Microsystems) (PL Fluotar 40×/0.70, PL Fluotar 100×/1030 OIL objective). To determine BM angiogenesis, BM sections were stained with anti-CD34 antibodies. Vascular morphometric parameters were quantified following the procedure used by Korkolopoulou et al,³⁰  with Leica DC Viewer software.