Comparison of two kinds of methods to determine the titer of recombinant retrovirus containing beta-globin gene based on G418 selection

A retrovirus-based system to stably silence hepatitis B virus genes by RNA interference

RNA interference (RNAi) might be an efficient antiviral therapy for some obstinate illness. Herein, a retrovirus-based RNAi system was developed to drive expression and delivery of Hepatitis B virus (HBV)-specific short hairpin RNA (shRNA) in HepG2 cells. The levels of HBsAg and HBeAg and that of HBV mRNA were dramatically decreased by this RNAi system in HepG2 cells transfected with Topo-HBV plasmid. Retrovirus-based RNAi thus may be useful for therapy in HBV and other viral infections and provide new clues for prophylactic vaccine development.

Knockdown of mouse adult beta-globin gene expression in MEL cells by retrovirus vector-mediated RNA interference

RNA interference (RNAi) efficiently induces sequence-specific gene silencing in mammalian cells through short interfering RNA (siRNA) of 21-23 nucleotides synthesized in vitro or expressed by DNA-based vector. However, introduction of siRNA into mammalian cells by transfection limits the application of RNAi, especially when it is necessary to generate long-term gene silencing in vivo. Virus vector-mediated RNAi provides an alternative to transfection. In the present study, we investigated such transduction system and showed that retrovirus vector-mediated RNAi can substantially down-regulate expression of mouse adult beta-globin gene in MEL cells. The results suggest that retrovirus vector-delivered RNAi may find its use in functional genomics and in gene therapy.

Retrovirus vector-mediated stable gene silencing in human cell

RNA interference (RNAi) is the mechanism of sequence-specific, post-transcriptional gene silencing initiated by short interfering RNAs (siRNAs) homologous to the gene being suppressed. siRNAs, which mediate sequence-specific mRNA degradation, are duplexes of about 21-23 nucleotides with 3'-overhangs synthesized in vitro or expressed by DNA-based vector. However, these systems rely on transfection for delivery and cannot generate long-term gene silencing in vivo. This obstacle may be circumvented by recently developed retrovirus- and lentivirus-delivered RNAi. Here, we describe a retroviral system for delivery of siRNA into cells, which can substantially down-regulate the expression of human p53 gene in human HepG2 cells. What's more, the G1 and S phases of cell cycle change dramatically in p53-down-regulated cells. These results indicate that retrovirus vector-delivered RNAi may be used in functional genomics and in gene therapy.

Evaluation of optimal expression cassette in retrovirus vector for beta-thalassemia gene therapy

Trials of retroviral vector-mediated human beta-globin gene transfer were hampered by low titers, unstable vector transmission, and low-level expression of transferred gene. With the goal of optimizing the retrovirally encoded human beta-globin gene expression cassette for gene therapy of beta-thalassemia, we generated 3 series of vector constructs (a total of 12 constructs) and investigated the effects of the proximal promoter, 3' - enhancer, and derivatives from the beta-locus control region or alpha-major regulatory element on virus titer, vector transmission stability, and gene expression. The virus titers for 9 of the 12 vector constructs ranged between 2.8 x 10(4) cfu/mL and 1.0 x 10(6) cfu/mL. We found that proviral DNA was intact in most G418- resistant murine erythroleukemia (MEL) cell clones for 5 vector constructs, while obvious genetic instability was observed for 4 other vector constructs. MEL cells harboring the intact provirus were induced to differentiate, and human beta-globin gene expression was analyzed with RNase protection assay. The percentage of human beta-globin transcript relative to endogenous murine alpha-globin transcript were 101.8 +/- 64.3% (n = 10), 40.1 +/- 28.7% (n = 4), 31.1 +/- 31.9% (n = 12), 52.4 +/- 11.2% (n = 12), and 53.6 +/- 8.6% (n = 12) for the 5 constructs, respectively, demonstrating the development of optimized retroviral vectors for beta-globin gene therapy with murine erythroid cell lines as a model. Unexpectedly, we also documented that the point mutation 8700(C-->T) in DNase I hypersensitive site 2 (HS2) core fragment might contribute to low-level expression of the human beta-globin gene, based on a comparison of results from transfected and transduced MEL cells and sequence analysis of proviral DNA.