FIGURE 1.
Antigen affinity of binding fragments is retained in their respective immunotoxin constructs. The four immunotoxins target either CEA or EGFR via either scFv or Fn3. The 3E and FE scFv clones targeting CEA, the C7 fibronectin clone targeting CEA, and the E4 fibronectin clone targeting EGFR were each fused to rGel and titrated for binding affinity on HT-1080(CEA) or A431 cells for CEA or EGFR, respectively. Binding on fixed cells was detected with goat anti-biotin-FITC antibody by flow cytometry. Data were fitted using least-squares regression with a binding isotherm, giving Kd values of 8 nm for 3ErGel, 15 nm for FErGel, 10 nm for C7rGel, and 13 nm for E4rGel.