Characterization and applications of Nanobodies against human procalcitonin selected from a novel naive Nanobody phage display library

Background: Nanobodies (Nbs) are single-domain antigen-binding fragments derived from the camelids heavy-chain only antibodies (HCAbs). Their unique advantageous properties make Nbs highly attractive in various applications. The general approach to obtain Nbs is to isolate them from immune libraries by phage display technology. However, it is unfeasible when the antigens are toxic, lethal, transmissible or of low immunogenicity. Naive libraries could be an alternative way to solve the above problems. Results: We constructed a large camel naive phage display Nanobody (Nb) library with great diversity. The generated library contains to 6.86 x 10(11) clones and to our best of knowledge, this is the biggest naive phage display Nb library. Then Nbs against human procalcitonin (PCT) were isolated from this library. These Nbs showed comparable affinity and antigen-binding thermostability at 37 degrees C and 60 degrees C compared to the PCT Nbs from an immune phage-displayed library. Furthermore, two PCT Nbs that recognize unique epitopes on PCT have been successfully applied to develop a sandwich enzyme-linked immunosorbent assay (ELISA) to detect PCT, which showed a linear working range from 10-1000 ng/mL of PCT. Conclusion: We have constructed a large and diverse naive phage display Nb library, which potentially functioning as a good resource for selecting antigen-binders with high quality. Moreover, functional Nbs against PCT were successfully characterized and applied, providing great values on medical application.