Figure 4.

Suppression of T cell proliferation by blockage of ICOS signaling with anti-B7RP-1 scFv clones 223, 311, 323 and 325. Human PBMCs (1 × 10⁵ cells/well) were stimulated with an anti-CD3 mAb (OKT3) and B7RP-1-Fc, which were coated onto the 96-well culture plate in the presence of varying doses (10–1000 nM) of scFv fragments. Cell proliferation was estimated based on the radioactivity of the incorporated [³H] thymidine, after 48 h of cell culture. ICOS-Fc was used as a positive control for the blocking of the ICOS signal. Anti-CD3 (right) indicates the proliferative activity of T cells via exclusive stimulation with an anti-CD3 mAb. The radioactivity incorporated was measured in a scintillation counter and was expressed as cpm.