Generation and preliminary characterization of an antibody library with preferential reactivity to human colorectal cancer cells as compared to normal human blood cells

Abstract

We are developing recombinant polyclonal antibody libraries (PCALs) reactive to human colorectal cancer cells as an anti-cancer therapeutic approach. To test the hypothesis that PCALs with preferential recognition of tumor cells as compared to normal cells could be generated, a Fab phage display library reactive to human colorectal cancer cell lines was absorbed with normal human blood cells. ELISA analysis of the absorbed Fab phage display library showed that 70% of tested clones reacted to colorectal cancer cells. Reactivity of the library to blood cells was reduced 4–10-fold, with many clones unreactive to one or more of the blood cell types. DNA fingerprint analysis of colorectal cancer-binding clones showed that the absorbed library remained polyclonal. The H and L chain V region gene pairs of the absorbed library were transferred in mass from the Fab phage display vector to a mammalian vector and expressed as IgG following transfection into Sp2/0 myeloma cells. ELISA analysis showed that 79% of transfectants expressed IgG and of those 74% were positive for binding to the SW480 human colorectal cancer cell line. A template of 95 SW480-reactive wells was assembled, designated Lib-Col2.1, and IgG purified from a consolidated mass culture. The purified Lib-Col2.1 IgG was compared to the clinically used anti-colorectal cancer mAb 17-1A, by ELISA and flow cytometry, for binding density on SW480 colorectal cancer cells and on normal human blood cells. The results showed that Lib-Col2.1 bound to SW480 cells at higher density than mAb 17-1A and that its binding to normal human blood cells was reduced 2.4–24-fold relative to an unabsorbed anti-SW480 serum. Furthermore, Lib-Col2.1 was more effective than mAb 17-1A at inhibiting the growth of SW480 cells in culture. These results suggest that a polyclonal antibody library with preferential reactivity to cancer cells as compared to normal cells could be generated.