Enrichment of phage displaying human Fab. (A) Phage output-to-input ratios increased approximately 50-fold over the 3 cell panning rounds, indicating the enrichment of phage displaying human Fab with cell-surface reactivity. (B) Polyclonal phage from the 3 cell panning rounds were analyzed for cell-surface reactivity in a whole-cell ELISA by using PBMCs derived from patient α with untreated B-CLL and mouse anti–phage mAb conjugated to HRP as detecting antibody. Shown are signals after subtraction of the signal obtained for the detecting antibody alone.