Generation of a stable anti-human CD44v6 scFv and analysis of its cancer-targeting ability in vitro.

CD44v6 is a cancer-associated antigen that mainly expresses in a subset of adenocarcinomas. Therefore, in this study, anti-human CD44v6 single-chain variable fragment (scFv) has been selected and characterized because it is the first step of primary importance towards the construction of a novel cancer-targeted agent for cancer diagnosis and therapy. In our study, anti-human CD44v6 scFv was selected from a human phage-displayed scFv library based on its ability to bind in vitro to CD44v6 antigen. Subsequently, immunofluorescent staining and Western blot analyses were performed to measure the binding characteristics of this scFv. In addition, flow cytometric analysis was done to verify its cancer-targeting ability in vitro. And a flow cytometry-based assay was used to determine its equilibrium dissociation constant (K (D)). Finally, one functional anti-CD44v6 scFv was selected and characterized. Nucleotide sequencing verified that it was an incomplete scFv gene but had a variable heavy chain (V(H)) alone. However, anti-CD44v6 scFv demonstrated cell-binding and antigen-binding activities by immunofluorescent staining and Western blot analyses. Furthermore, flow cytometric analysis proved that this scFv specifically targeted CD44v6-expressing cancer cells other than CD44v6 non-expressing normal cells or tumor cells in vitro. The K (D) of this scFv was calculated to be 7.85 +/- 0.93 x 10(-8) M. In summary, the selected human scFv against CD44v6 has specific binding activity and favorable binding affinity despite lacking a variable light chain (V(L)). Moreover, it can effectively and specifically target CD44v6-expressing cancer cells. All these characteristics make anti-CD44v6 scFv a promising agent for cancer detection and anti-cancer therapy.