Evolution-guided evaluation of the inverted terminal repeats of the synthetic transposon Sleeping Beauty

The new frontier in CHO cell line development: From random to targeted transgene integration technologies

Cell line development represents a crucial step in the development process of a therapeutic glycoprotein. Chinese hamster ovary (CHO) cells are the most frequently employed mammalian host cell system for the industrial manufacturing of biologics. The predominant application of CHO cells for heterologous recombinant protein expression lies in the relative simplicity of stably introducing ectopic DNA into the CHO host cell genome. Since CHO cells were first used as expression host for the industrial production of biologics in the late 1980s, stable genomic transgene integration has been achieved almost exclusively by random integration. Since then, random transgene integration had become the gold standard for generating stable CHO production cell lines due to a lack of viable alternatives. However, it was eventually demonstrated that this approach poses significant challenges on the cell line development process such as an increased risk of inducing cell line instability. In recent years, significant discoveries of new and highly potent (semi)-targeted transgene integration systems have paved the way for a technological revolution in the cell line development sector. These advanced methodologies comprise the application of transposase-, recombinase- or Cas9 nuclease-mediated site-specific genomic integration techniques, which enable a scarless transfer of the transgene expression cassette into transcriptionally active loci within the host cell genome. This review summarizes recent advancements in the field of transgene integration technologies for CHO cell line development and compare them to the established random integration approach. Moreover, advantages and limitations of (semi)-targeted integration techniques are discussed, and benefits and opportunities for the biopharmaceutical industry are outlined.

Recent reactivation of a pathogenicity-associated transposable element is associated with major chromosomal rearrangements in a fungal wheat pathogen

Transposable elements (TEs) are key drivers of genomic variation contributing to recent adaptation in most species. Yet, the evolutionary origins and insertion dynamics within species remain poorly understood. We recapitulate the spread of the pathogenicity-associated Styx element across five species that last diverged ∼11 000 years ago. We show that the element likely originated in the Zymoseptoria fungal pathogen genus and underwent multiple independent reactivation events. Using a global 900-genome panel of the wheat pathogen Zymoseptoria tritici, we assess Styx copy number variation and identify renewed transposition activity in Oceania and South America. We show that the element can mobilize to create additional Styx copies in a four-generation pedigree. Importantly, we find that new copies of the element are not affected by genomic defenses suggesting minimal control against the element. Styx copies are preferentially located in recombination breakpoints and likely triggered multiple types of large chromosomal rearrangements. Taken together, we establish the origin, diversification and reactivation of a highly active TE with likely major consequences for chromosomal integrity and the expression of disease.

Progress of Transposon Vector System for Production of Recombinant Therapeutic Proteins in Mammalian Cells

In recent years, mammalian cells have become the primary host cells for the production of recombinant therapeutic proteins (RTPs). Despite that the expression of RTPs in mammalian cells can be improved by directly optimizing or engineering the expression vectors, it is still influenced by the low stability and efficiency of gene integration. Transposons are mobile genetic elements that can be inserted and cleaved within the genome and can change their inserting position. The transposon vector system can be applied to establish a stable pool of cells with high efficiency in RTPs production through facilitating the integration of gene of interest into transcriptionally active sites under screening pressure. Here, the structure and optimization of transposon vector system and its application in expressing RTPs at high level in mammalian cells are reviewed.

Transposon vector-mediated stable gene transfer for the accelerated establishment of recombinant mammalian cell pools allowing for high-yield production of biologics

Stable recombinant mammalian cells are of growing importance in pharmaceutical biotechnology production scenarios for biologics such as monoclonal antibodies, growth and blood factors, cytokines and subunit vaccines. However, the establishment of recombinant producer cells using classical stable transfection of plasmid DNA is hampered by low stable gene transfer efficiencies. Consequently, subsequent selection of transgenic cells and the screening of clonal cell populations are time- and thus cost-intensive. To overcome these limitations, expression cassettes were embedded into transposon-derived donor vectors. Upon the co-transfection with transposase-encoding constructs, elevated vector copy numbers stably integrated into the genomes of the host cells are readily achieved facilitating under stringent selection pressure the establishment of cell pools characterized by sustained and high-yield recombinant protein production. Here, we discuss some aspects of transposon vector technologies, which render these vectors promising candidates for their further utilization in the production of biologics.