Application of microRNA Targeted 3′UTRs to Repress DHFR Selection Marker Expression for Development of Recombinant Antibody Expressing CHO Cell Pools

A proline metabolism selection system and its application to the engineering of lipid biosynthesis in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells are the leading mammalian cell host employed to produce complex secreted recombinant biotherapeutics such as monoclonal antibodies (mAbs). Metabolic selection marker technologies (e.g. glutamine synthetase (GS) or dihydrofolate reductase (DHFR)) are routinely employed to generate such recombinant mammalian cell lines. Here we describe the development of a selection marker system based on the metabolic requirement of CHO cells to produce proline, and that uses pyrroline-5-carboxylase synthetase (P5CS) to complement this auxotrophy. Firstly, we showed the system can be used to generate cells that have growth kinetics in proline-free medium similar to those of the parent CHO cell line, CHOK1SV GS-KO™ grown in proline-containing medium. As we have previously described how engineering lipid metabolism can be harnessed to enhance recombinant protein productivity in CHO cells, we then used the P5CS selection system to re-engineer lipid metabolism by over-expression of either sterol regulatory element binding protein 1 (SREBF1) or stearoyl CoA desaturase 1 (SCD1). The cells with re-engineered proline and lipid metabolism showed consistent growth and P5CS, SCD1 and SREBF1 expression across 100 cell generations. Finally, we show that the P5CS and GS selection systems can be used together. A GS vector containing the light and heavy chains for a mAb was super-transfected into a CHOK1SV GS-KO™ host over-expressing SCD1 from a P5CS vector. The resulting stable transfectant pools achieved a higher concentration at harvest for a model difficult to express mAb than the CHOK1SV GS-KO™ host. This demonstrates that the P5CS and GS selection systems can be used concomitantly to enable CHO cell line genetic engineering and recombinant protein expression.

We have engineered a proline P5CS metabolism selection system in CHO cells

P5CS proline selection was used to engineer lipid metabolism in CHO cells

P5CS selection was stable for at least 100 generations

P5CS and GS selection systems were used together to engineer lipid and mAb expression

Lipid metabolism P5CS engineered CHO cells give enhanced recombinant protein expression

Comprehensive characterization of dihydrofolate reductase-mediated gene amplification for the establishment of recombinant human embryonic kidney 293 cells producing monoclonal antibodies

Human embryonic kidney 293 (HEK293) cells with glycosylation machinery have emerged as an alternative host cell line for stable expression of therapeutic glycoproteins. To characterize dihydrofolate reductase/methotrexate (DHFR/MTX)-mediated gene amplification in HEK293 cells, an expression vector containing dhfr and monoclonal antibody (mAb) gene was transfected into dhfr-deficient HEK293 cells generated by knocking out dhfr and dhfrl1 in HEK293E cells. Due to the improved selection stringency, mAb-producing parental cell pools could be generated in the absence of MTX. When subjected to stepwise selection for increasing MTX concentrations such as 1, 10, and 100 nM, there was an increase in the specific mAb productivity (q_mAb ) of the parental cell pool upon DHFR/MTX-mediated gene amplification. High producing (HP) clones with a q_mAb of more than 2-fold of the corresponding cell pool could be obtained using the limiting dilution method. The q_mAb of most HP clones obtained from cell pools at elevated MTX concentrations significantly decreased during long-term culture (3 months) in the absence of selection pressure. However, some HP clones could maintain high q_mAb during long-term culture. Taken together, a stable HP recombinant HEK293 cell line can be established using DHFR/MTX-mediated gene amplification together with dhfr^- HEK293 host cells.

Expression vector cassette engineering for recombinant therapeutic production in mammalian cell systems

Human tissue plasminogen activator was the first recombinant therapy protein that successfully produced in Chinese hamster ovary cells in 1986 and approved for clinical use. Since then, more and more therapeutic proteins are being manufactured in mammalian cells, and the technologies for recombinant protein production in this expression system have developed rapidly, with the optimization of both upstream and downstream processes. One of the most promising strategies is expression vector cassette optimization based on the expression vector cassette. In this review paper, these approaches and developments are summarized, and the future strategy on the utilizing of expression cassettes for the production of recombinant therapeutic proteins in mammalian cells is discussed.

Engineered transient and stable overexpression of translation factors eIF3i and eIF3c in CHOK1 and HEK293 cells gives enhanced cell growth associated with increased c-Myc expression and increased recombinant protein synthesis

There is a desire to engineer mammalian host cell lines to improve cell growth/biomass accumulation and recombinant biopharmaceutical protein production in industrially relevant cell lines such as the CHOK1 and HEK293 cell lines. The over-expression of individual subunits of the eukaryotic translation factor eIF3 in mammalian cells has previously been shown to result in oncogenic properties being imparted on cells, including increased cell proliferation and growth and enhanced global protein synthesis rates. Here we report on the engineering of CHOK1 and HEK cells to over-express the eIF3i and eIF3c subunits of the eIF3 complex and the resultant impact on cell growth and a reporter of exogenous recombinant protein production. Transient over-expression of eIF3i in HEK293 and CHOK1 cells resulted in a modest increase in total eIF3i amounts (maximum 40% increase above control) and an approximate 10% increase in global protein synthesis rates in CHOK1 cells. Stable over-expression of eIF3i in CHOK1 cells was not achievable, most likely due to the already high levels of eIF3i in CHO cells compared to HEK293 cells, but was achieved in HEK293 cells. HEK293 cells engineered to over-express eIF3i had faster growth that was associated with increased c-Myc expression, achieved higher cell biomass and gave enhanced yields of a reporter of recombinant protein production. Whilst CHOK1 cells could not be engineered to over-express eIF3i directly, they could be engineered to over-express eIF3c, which resulted in a subsequent increase in eIF3i amounts and c-Myc expression. The CHOK1 eIF3c engineered cells grew to higher cell numbers and had enhanced cap- and IRES-dependent recombinant protein synthesis. Collectively these data show that engineering of subunits of the eIF3 complex can enhance cell growth and recombinant protein synthesis in mammalian cells in a cell specific manner that has implications for the engineering or selection of fast growing or high producing cells for production of recombinant proteins.

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We have engineered the overexpression of eIF3i and eIF3c in CHOK1 and HEK293 cells.

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HEK293 cells overexpressing eIF3i had faster growth and increased c-Myc expression.

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Direct stable overexpression of eIF3i in CHOK1 cells was not achievable.

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Overexpression of eIF3c in CHOK1 cells resulted in an increase in eIF3i.

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eIF3c overexpressing CHOK1 cells had enhanced recombinant protein synthesis.

Defining lncRNAs Correlated with CHO Cell Growth and IgG Productivity by RNA-Seq

How the long non-coding RNA (lncRNA) genome in recombinant protein producing Chinese hamster ovary (CHO) cell lines relates to phenotype is not well described. We therefore defined the CHO cell lncRNA transcriptome from cells grown in controlled miniature bioreactors under fed-batch conditions using RNA-Seq to identify lncRNAs and how the expression of these changes throughout growth and between IgG producers. We identify lncRNAs including Adapt15, linked to ER stress, GAS5, linked to mTOR signaling/growth arrest, and PVT1, linked to Myc expression, which are differentially regulated during fed-batch culture and whose expression correlates to productivity and growth. Changes in (non)-coding RNA expression between the seed train and the equivalent day of fed-batch culture are also reported and compared with existing datasets. Collectively, we present a comprehensive lncRNA CHO cell profiling and identify targets for engineering growth and productivity characteristics of CHO cells.

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The CHO cell lncRNA transcriptome is defined using RNA-Seq

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Correlations between lncRNA expression and CHO cell growth and IgG productivity found

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Expression of lncRNAs involved in ER stress correlates to productivity

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Expression of lncRNAs involved in mTOR signaling/growth arrest correlates to growth