Preparation and identification of human soluble sPD-L1 and its antibodies / 生物工程学报

This study reports the preparation and identification of soluble programmed death-1 (PD-1) ligand-1 (sPD-L1) and its antibodies of mouse origin. Immobilized metal ion affinity chromatography was used to perform on-column refolding with simultaneous purification of denatured sPD-L1, and soluble sPD-L1 with purity of 95% was obtained. The purified sPD-L1 was verified by immunoblotting using a commercial goat-anti-human PD-L1 antibody. An ELISA-based assay showed that it also had high binding activity for its cognate receptor PD-1. Furthermore, mouse anti-sPD-L1 antiserum of high titer was raised using the purified sPD-L1 as an immunogen, and the specific IgG antibodies were purified using sPD-L1-HiTrap affinity chromatography. In addition, a sensitive sandwich ELISA was established using the purified IgG antibodies together with the commercial goat antibodies. In conclusion, the preparation of soluble sPD-Ll and its antibodies provide the basis for detection of the potential anti-PD-L1 antibodies and soluble PD-L1 in humans as well as for further investigation of its in vivo bioactivities and characterization of its potential receptors.

Improved expression of HLA-A* 2402-BSP in Escherichia coli and its tetramer preparation / 生物工程学报

HLA-A* 2402 is one of the most frequently encountered HLA-A alleles in East Asian populations. In order to study the CD8+ T cell responses in Chinese populations, we have described the generation and functional test of HLA-A* 2402 tetramer loaded with HCMV pp65(341-349) peptide (QYDPVAALF, QYD). The cDNA of HLA-A* 2402 heavy chain was cloned by RT-PCR from one of the donors. DNA fragment encoding the ectodomain of HLA-A* 2402 heavy chain fused at its carboxyl-terminal a BirA substrate peptide (BSP) was amplified by PCR with the cloned heavy chain cDNA as a template. The wild-type gene of HLA-A* 2402-BSP was not expressed in Escherichia coli (E. coli), while mutant HLA-A* 2402-BSP gene with optimized codons was overexpressed as inclusion bodies in E. coli. Furthermore, the soluble HLA-A* 2402-QYD monomers were generated by in vitro refolding of washed inclusion bodies in the presence of beta2-microglobulin and QYD peptide. The tetramer was subsequently formed by mixing HLA-A* 2402-QYD monomers with streptavidin-PE at a molar ratio of 4:1. Flow cytometry analysis indicated that this tetramer possessed binding activity with specific CTL from HLA-A24+ donors and the frequencies of tetramer-binding CTL were 0.09% - 0.37% within total CD8+ T cells. This tetrameric agent provides a powerful tool to explore the secrets of CTL responses against HCMV antigens in HLA-A* 2402 individuals.