[Construction of Expression Vector for Human CD40-Ig Fusion Protein and Its Expression in COS-7 Cells].

CD40/CD40L, besides B7/CD28, is an alternative important costimulation signal transduction pathway. It plays a pivotal role in T cell activation. Moreover, it may play a critical role at many levels of sensitization and effector phases of allograft rejection. In order to get the fusion protein of human CD40 extracelluar region and IgG 1 Fc fragment, and investigate the potential role of blocking CD40/CD40L costimulation pathway in immunotherapy, total RNA was extracted from human lymphoma cell line Daudi, and CD40 gene extracelluar region was amplified by RT-PCR. The PCR products were inserted into pGEM T Easy vector, and the cloning vector pGE40 was obtained. The DNA sequence was analyzed by automatic DNA sequencer. After sequencing, the transient expressing vector was constructed by inserting correct fragment into pIG vector, which contains the genomic human IgG1 Fc (hinge, CH2 and CH3) gene. Hence the recombinant fusion expression vector was constructed successfully, and named after pIG/40 Ig. Then, COS-7 cells were transfected through DEAE-Dextran/chloroquine method. The CD40-Ig fusion protein expressed in COS-7 cell culture supernatant was identified by sandwich ELISA and Western blot. Result showed that the CD40-Ig fusion protein can be detected by sandwich ELISA in the cell culture supernatant. Western blot analysis also showed that it could react with McAbs of mouse anti-human CD40 G28-5 and mouse anti-human Ig gamma chain. There is only one obvious band at the position of relative molecular weight 50 kD, and it is equivalent to the expected value. Above all, the recombinant fusion expression vector pIG/40 Ig was constructed, and CD40-Ig fusion protein gene was expressed in COS-7 cells successfully. It could be laid a foundation to investigate the potential role of CD40/CD40L pathway as the target of GVHD prevention and therapy.