ABSTRACT
Liver-directed gene therapy, using mainly viral vectors for the genetic cell modification, is a promising therapeutic approach for many genetic and metabolic liver diseases. The recent successful preclinical trials with AAV vectors expose the benefits as well as the limitations of the system. We focused on the development of an alternative non-viral episomal gene transfer system, by inserting the DNA element Scaffold/Matrix Attachment Region (S/MAR) into the free of antibiotic resistance gene miniplasmid vector (pFAR4). We produced pFAR4 derivative experimental vectors, carrying the eGFP gene driven by the composite HCRHPi liver-specific promoter and either lacking (pFAR4-noS/MAR) or containing the S/MAR element in an upstream (pFAR-S/MAR-IN) or downstream (pFAR4-S/MAR-OUT) configuration in relation to the poly-A signal of the eGFP expression cassette. Upon transfer into Huh7 cells by lipofection, vector pFAR4-S/MAR IN showed significantly higher transfection efficiency and eGFP expression than the control vector or the pFAR4-S/MAR-OUT (p < 0.005), estimated by fluorescent microscopy and flow cytometry. Stable transfections were produced only with cultures containing vector pFAR4-S/MAR IN, through the expansion of single colonies, which displayed sustained GFP expression and plasmid copy number per cell of 2.3 ± 0.4, at 3 months of culture. No vector integration events were detected in these cultures by FISH analysis, while the presence of free, circular plasmids was documented by plasmid rescue assay. The presence of S/MAR renders pFAR4 miniplasmid substantially more efficient regarding episomal gene transfer and is suitable for liver-directed studies towards gene therapy applications.
Subject(s)
Gene Transfer Techniques , Genetic Vectors/genetics , Hepatocytes/metabolism , Plasmids , Cell Line, Tumor , Cells, Cultured , Gene Expression , Humans , In Situ Hybridization, Fluorescence , Liver/metabolism , TransfectionABSTRACT
Pregnancy-associated malaria (PAM) arises from sequestration of Plasmodium falciparum-parasitized erythrocytes (PE) in the placenta, leading to chronic symptoms in the expectant mother and serious consequences for fetal development. Placental sequestration has been linked to binding of chondroitin sulphate A (CSA) by the var2CSA variant of PfEMP1 expressed on the PE surface, and a substantial body of evidence shows that the immune response to var2CSA gives an effective protection against PAM. We have expressed the var2CSA-DBL5epsilon domain, derived from a placental isolate from Senegal, as soluble product in Escherichia coli and have shown using different criteria that the recombinant protein is obtained with the native conformation. Using surface plasmon resonance techniques, we have examined binding of DBL5epsilon to placental chondroitin sulphate proteoglycan and CSA; however, the recombinant protein also binds to other sulphated oligosaccharides, with higher affinity in some cases, indicating that the single domain lacks the specificity for CSA shown by the complete extra-cellular region of var2CSA and placental parasites. Recombinant DBL5epsilon was specifically recognized by sera from malaria-exposed Senegalese women in a parity-dependent manner but by sera not from children or males from the same endemic region. Conversely, DBL5epsilon induced antibodies in mice that recognized placental isolates from Benin but not isolates from children. The presence of universal epitopes thus supports DBL5epsilon as an interesting component of var2CSA to be considered for vaccine development.
