BPI700-Fcγ1700 chimeric gene expression and its protective effect in a mice model of the lethal E. coil infection

Background Infections caused by gram-negative bacteria （GNB） often lead to high mortality in common clinical settings. The effect of traditional antibiotic therapy is hindered by drug-resistant bacteria and unneutralizable endotoxin. Few effective methods can protect high risk patients from bacterial infection. This study explored the protection of adeno-associated virus 2 （AAV2）-bacteriacidal permeability increasing protein 700 （BPI700） -fragment crystallizable gamma one 700 （Fcγ1700） chimeric gene transferred mice against the minimal lethal dose （MLD） of E.coli and application of gene therapy for bacterial infection. Methods After AAV2-BPI700-Fcγ1700 virus transfection, dot blotting and Western blotting were used to detect the target gene products in Chinese hamster ovary-K1 cells （CHO-Klcells）. Reverse transcription-polymerase chain reaction and immunohistochemical assay were carried out to show the target gene expression in mice. Modified BPI-enzyme linked immunosorbent assay was used to identify the target gene products in murine serum. The protection of BPI700-Fcγ1700 gene transferred mice was examined by survival rate after MLD E. coli challenge. Colony forming unit （CFU） count, limulus amebocyte lysate kit and cytokine kit were used to quantify the bacteria, the level of endotoxin, and proinflammatory cytokine. Results BPI1-99-Fcγ1 protein was identified in the CHO-K1 cell culture supernatant, injected muscles and serum of the gene transferred mice. After MLD E. coli challenge, the survival rate of AAV2-BPI700-Fcγ1700 gene transferred mice （36.7%） was significantly higher than that of AAV2-enhanced green fluorescent protein （AAV2- EGFP） gene transferred mice （3.3%） and PBS control mice （5.6%）. The survival rate of AAV2-BPI700-Fcγ1700 gene transferred mice treated with cefuroxime sodium was 65.0%. The bacterium number in main viscera, the levels of endotoxin and proinflammatory cytokine （tumor necrcsis factor-α and interleukin-1β） in serum of the AAV2-BPI700-Fcγ1700 gene transferred mice were markedly lower than that of PBS control mice （P〈0.01）. Conclusions AAV2-BPI700-Fcγ1700 gene transferred mice can resist MLD E. coli infection through expressing BPI1-199-Fcγ1 protein. Our findings suggested that AAV2 mediated BPI700-Fcγ1700 gene delivery could be used for protection and treatment of clinical GNB infection in high-risk individuals.