Construction of a Natural Human Fab Phage Antibody Library and Screening of Phage Antibody against PD-L1

: Programmed Death Ligand-1(PD-L1) is an important target to drive T cell dysfunction when it connects with Programmed Death-1(PD-1), leading to immune escape of tumor cells, thus anti-PD-L1 antibody shows a promising prospect in the treatment of tumor. In order to construct a large natural antibody library, we collected a large number of lymphocytes of adults and children. The light chain and Fd genes of antibody were amplified by PCR, and the Fab phage antibody library with a library capacity of 4.27×10 9 was constructed. The insertion rates of the light chain library and the Fab library were 90% and 70%, respectively. The cloned sequences identified by PCR showed that all the sequences analyzed were unique, and the amino acid sequences of the CDR regions were diverse, which proved that there was good diversity in the antibody library. The positive clones that bind to PD-L1 were screened by phage ELISA, PCR identification and sequence analysis. In the end, two high-affinity positive clones were determined. The successful construction of this natural phage antibody library provided an effective method for screening human PD-L1 antibodies, which was expected to screen humanized antibodies against various antigens.