Objective: To construct HBV and HCV-specific HLA-A2-peptide tetramers, and to direct clinical therapy.
Methods: Recombinant class I HLA-A2 heavy chains and beta-2 M were produced in Escherichia coli cells transformed with pBV220 vectors. Only the extracellular domain of class I heavy chain was expressed, following modification by replacement of the C-terminal domain with a substrate sequence for BirA biotinylation. HLA-A2-BSP was folded in the presence of beta-2 microglobulin and a specific peptide to form a peptide-MHC complex. The MHC complexes were biotinylated using purified BirA enzyme. Biotinylated MHC-peptide complexes were purified. Tetramers were generated by mixing biotinylated protein complex with streptavidin-PE at a molar ratio of 4:1. Then analysis of stained PBMCs was performed using FACScan and CellQuest software.
Results: The expression levels of pBV220-HLA-A2-BSP and beta-2M were 46% and 48% of total bacterial proteins estimated from SDS - PAGE, respectively. And they were mainly located in the insoluble fraction of the cell as inclusion bodies and the proportion were about 85% and 90%, respectively. The purity of pBV220-HLA-A2-BSP and beta-2M was above 95% analyzed by SDS-PAGE, and the concentration of pBV220-HLA-A2-BSP and beta-2M was about 1.5 g/L and 1.2 g/L, respectively. Using the constructed HLA-A2-peptide tetramer to detect the HBV/HCV-specific CTL, the HBV-specific CD8(+) frequencies were 1.84% and 0.02% - 0.68% of the total CD8(+) T cells in acute and chronic HBV hepatitis, respectively. As an additional control, an HLA-A2/HCV tetramer was tested in the acute and chronic HBV hepatitis. The frequencies never exceeded 0.02% of the total CD8(+) T cell number. Similar low levels of background staining were also detected in the HLA-A2(+) or A2(-) healthy control. The HCV-specific CD8(+) frequency was 0.02 - 0.72% of the total CD8(+) T cells in chronic HCV hepatitis. The same frequencies of control were detected.
Conclusion: High-efficient expressions of HLA-A0201-BSP and beta-2m proteins lay a good foundation for further expression and purification in prokaryotic system and constructing MHC class I-peptide tetramer complexes to study the function of CTLs. Especially, using these two HBV and HCV-specific tetramer can detect the frequencies of the HBV/HCV-specific CD8(+) T cells directly in vitro.