B7-H1 is expressed by tumor-associated DCs and inhibits T-cell proliferation. (A) As described in Figure 1, immunohistochemical staining for B7-H1 was performed in patient biopsy specimens. B7-H1 expression by stromal monocyte-derived cells, identified by CD11c (shown), S-100, or CD68 staining, was determined. (B) Single-cell suspensions were generated from spleen (shown) or lymph node biopsy specimens obtained from PTCL patients (n = 5). Cells were stained with an isotype control (closed histogram) or anti–B7-H1 (open histogram) and B7-H1 expression on CD11c⁺CD14⁻ DCs determined. A representative example is shown. (C) Tissue specimens obtained from PTCL patients (n = 7) were double stained with antibodies to human CD11c (red) and B7-H1 (green) and viewed by fluorescent microscopy, as described in “Patient samples, immunohistochemistry, and immunofluorescence assay.” A representative example is shown (original magnification ×100). (D-E) Immature or LPS-matured DCs (4 × 10⁵/well) generated from normal-donor monocytes were cocultured with allogeneic, CFSE-labeled T cells (4 × 10⁶/well) for 6 days in the presence of an isotype control or anti–B7-H1 (4 μg/mL), as shown. T-cell activation, demonstrated by increasing forward scatter (D), and proliferation, indicated by CFSE dilution (E), were analyzed. The data shown are representative of at least 3 similarly performed experiments.