ICOS expression in ALK⁺ TCL cells. (A) The relative expression of ICOS, CD28, and their ligands by SUDH-L1 cells detected by genome-scale DNA oligonucleotide array. (B) Expression of ICOS mRNA determined by quantitative RT-PCR in the depicted ALK⁺ TCL cell lines compared with a CTCL cell line (MyLa3675) and mitogen-stimulated PBMCs (PBMC/PHA). (C) Expression of the ICOS protein determined by flow cytometry on ALK⁺ TCL- and other TCL-derived cell lines and control cell populations. (Topmost panel) Normal PBMC, PBMC/PHA, and CTCL-derived cell lines. (Top middle panel) ALK⁺ TCL cell lines. (Bottom middle panel) Cell lines from a progressive primary cutaneous CD30⁺ lymphoproliferative disorder (PB-1, 2A, and 2B), T-cell lymphoblastic lymphoma (Jurkat), and germinal center-derived diffuse large B-cell lymphoma (Ly18 and VAL). (Bottom panel) Cell lines from Burkitt lymphoma (Ramos), EBV-mediated B-cell transformation (HH and MM), and Kaposi sarcoma virus-associated body cavity lymphoma (JSC-1, BC-1, and BCBL-1). These results are representative of at least 2 independent experiments. (D) Expression of ICOS in CTCL (left panels) and ALK⁺ TCL (middle and right panels) tissues (original magnification ×400). Microscope: Olympus BX 40; objective: Plan Apox/0.95; camera: Leica DFC 420; software: Leica DFC Twain 6.9.0 and Microsoft Office PowerPoint 2003. Biopsy tissue sections were either formalin-fixed, paraffin-embedded (fp) or snap-frozen (sf) and stained with hematoxylin and eosin or anti-ICOS antibody.