Control of Splicing Efficiency by the Mouse Histone H2a Element in a Murine Leukemia Virus–based Retroviral Vector

While using various human complementary DNA (cDNA) sequences in the context of the murine leukemia virus (MLV)-based retroviral vector, it was found that a retroviral vector containing some human cDNA sequences produces unusually low viral titer. One of those sequences is that for the human IL-1 receptor antagonist protein (IL1RN). The RNA analysis showed that a cryptic splice acceptor sequence is present in the middle of its coding region, resulting in the deletion of the packaging signal sequence and the removal of some coding sequences that lead to low viral titer and a low level of the transgene product. We tested whether the mouse Hist2h2aa1 element (mH2aE), previously shown to suppress the splicing function, could inhibit the cryptic splicing in the context of MLV-based retroviral vectors. It was found that the mH2aE could efficiently suppress such unwanted splicing event, thus increasing the amount of unspliced transcript, which eventually led to the increase in the level of IL1RN expression and viral titer. The mH2aE could also be used to control unusually high splicing activity. Our data suggested that the mH2aE could be used for the fine-tuning of the splicing process, thus improving the level of gene expression and viral titer in the context of retroviral vectors.