Effect of membrane-bound complement regulatory proteins on tumor cell sensitivity to complement-dependent cytolysis triggered by heterologous expression of the α-gal xenoantigen.

Engineering malignant cells to express a heterologous α-gal antigen can induce heterograft hyperacute rejection, resulting in complement-dependent cytolysis (CDC) of tumor cells, which has been considered as a novel strategy for antitumor therapy. A549 cells engineered to express Galα1-3Galß1-4GlcNAc-R (α-gal) epitope exhibited strong resistance to CDC treated by normal human serum (NHS) in a previous study. We hypothesized that the expression of membrane-bound complement regulatory proteins (mCRPs) decay accelerating factor (CD55) and protectin (CD59) influenced the efficacy of the α-gal/NHS-mediated antitumor effect to tumor cells in vitro. The present study confirmed that A549 cells expressed high levels of CD55 and CD59, whereas Lovo cells expressed relatively low levels of these proteins. A549 and Lovo cells transfected with plasmids containing or lacking the α-gal epitope were evaluated for their susceptibility to CDC by NHS and detected using a trypan blue exclusion assay. α-gal-expressing Lovo (Lovo-GT) cells were almost completely killed by α-gal-mediated CDC following incubation with 50% NHS, whereas no cytolysis was observed in α-gal expressing A549 (A549-GT) cells. Abrogating CD55 and CD59 function from A549-GT cells by various concentrations of phosphatidylinositol-specific phospholipase C (PI-PLC) or blocking antibodies increased the susceptibility of cells to CDC, and the survival rate decreased significantly comparing to the controls (P<0.05). The findings of the present study indicated that using the α-gal/NHS system to eliminate tumor cells via inducing the complement cascade reaction might represent a feasible approach for the treatment of cancer. However, high levels of mCRP expression may limit the efficacy of this approach. Therefore, an improved efficacy of cancer cell killing may be achieved by combining strategies of heterologous α-gal expression and mCRP downregulation.

[Cloning of splicing variants of alpha1,3-galactosyltransferase cDNA of Chinese Banna Minipig inbred line and its expression in human cells].

OBJECTIVE: To study the transfection and expression of the splicing variants of alpha1, 3-galactosyltransferase cDNA of Chinese Banna Minipig Inbred Line (BMI) in human A549 cells. METHODS: Full length of alpha1,3-GT gene cDNA was amplified by RT-PCR from total RNA of BMI liver tissue and cloned into T-A cloning vector. Two different splicing variants of BMI alpha1,3-GT cDNA were confirmed by sequencing 15 positive clones and inserted respectively into pEGFP-N1 to construct eukaryotic expression vectors pN-GT1 and pN-GT2. The vectors were transfected into human lung adenocacinoma A549 cells and the expression of alpha1,3-GT gene was detected by RT-PCR. The expression of the a-Gal epitopes on transfected cells was confirmed under fluorescent microscope and by flow cytometry using FITC-BS-IB4 lectin. The binding of IgM and complement C3 in human serum to a-Gal on transfected cells were measured by flow cytometry using FITC-anti-IgM and FITC-anti-C3. RESULTS: There was no other splicing variants of alpha1,3-GT cDNA found in BMI except GT1 and GT2, which were 1116 bp and 1080 bp in length respectively, the latter lacks exon 5. The expression of BMI alpha1,3-GT mRNA and the synthesis of a-Gal on A549 cells transfected with either pN-GT1 or pN-GT2 were detected, and the binding of IgM nature antibodies and complements C3 in human serum on transfected A549 cells were observed. The expression level of alpha-Gal and the deposits of IgM and C3 on transffected cells showed no significant difference between pN-GT1 and pN-GT2. CONCLUSION: The splicing variants of alpha1,3-GT cDNA of BMI could express in human cells, which provide the basis for genetic manipulation of the alpha1,3-GT of BMI for future xenotransplantation studies.

[Establishment and identification of human lung adenocarcinoma cell line stably expressing the alpha1, 3-galaetosyltransferase gene from pig].

OBJECTIVES: To establish a human lung adenocarcinoma cell subline A549 that can stably express the Chinese Banna minipig inbred-line (BMI) alpha1 ,3-galactosyltransferase (alpha1 ,3GT) gene and alpha-galactosyl (Gala1-3Galb1-4GlcNAc-R, alpha-gal) epitopic, providing a cell model which expressed xenotransplantation antigens for the further research on the effect of complement dependent cytotoxic lysis of the tumor cells triggered by human natural serum. METHODS: The pEGFP-CMV-GT plasmid containing Banna minipig alpha1 ,3-GT gene was ransfected into A549 cells with lipofectin in vitro. After screened with G418,the single clones were got out and then amplified, the stable transfected cells was named A549-GT. The transcription of alpha1, 3-GT gene in A549-GT cells was detected by RT-PCR. Direct immunofluonrescence methods and flow cytometer were performed to observe the expression of alpha-gal and the binding conditions of IgM and complement C3 in human serum on A549-GT cells. The biological characters of A549-GT cells including morphology, proliferation, and tumorigenesis in nude mice were also examined. RESULTS: After G418 screening, A549-GT that stablely transfected with alpha1, 3-GT gene was obtained and has been passaged for 2 years. The expression of alpha1,3-GT mRNA and alpha-gal was detected continuously and stably in A549-GT. The expression rate of alpha-gal positive cells reached 80.1% +/- 3.2%. The binding of human serum IgM and C3 in human serum on A549-GT cells were founded. Compared with parental A549 cells, its biological characteristics did not change. CONCLUSION: A549-GT cell line stably and continuously expressing alpha1, 3-GT and alpha-gal was established successfully. It provided a useful cell model for the further study of pig alpha1,3-GT gene in tumor immunotherapy.