CD28 and CD86 expression. (A) CD28. The indicated cells were stained with anti-CD28 PE (filled histogram) or isotype control (open histogram) and analyzed by FACS. Top panels show cell lines. Bottom panels show primary myeloma isolates. Primary myeloma cells were purifed from 3 different patient samples (PS; bone marrow aspirates, recurring MM) by CD138 immunomagnetic selection. (B) Extramedullary plasmacytoma. Serial sections from an extramedullary plasmacytoma were stained with hematoxylin/eosin (left panel) or anti–human CD28 (brown staining, right panel). Magnification, 20×/0.40 NA N Plan objective. Representative sections from 1 of 2 patients with intramuscular extramedullary plasmacytomas. (C) CD80 and CD86. The cell lines indicated were stained with isotype control (open histograms), anti-CD80, CD86 mAb, or CTLA4-Ig (closed histograms), and analyzed by FACS. Data are representative of 2 independent experiments.