Improved downstream processing.
ZFNs can be used to improve downstream processing by knocking out genes that encode interfering host-cell proteins. If the
CHO cell line contains an endogenous protein that copurifies with the r-protein during chromatographic purification, additional
and costly steps may be required to remove the endogenous protein. ZFNs can be used to knock out the gene that encodes this
endogenous protein. Another potential target may be a protein within the CHO cell that binds the therapeutic r-protein. By
knocking out the gene that encodes such a protein, growth and productivity can be improved. The CHO host cell may also produce
proteolytic enzymes that could degrade the product before purification. Diminishing protease expression can minimize this
The risk of prion or viral infection can be mitigated through genome editing. Retroviral titer in a cell could be reduced
by targeting and removing retroviral elements. Additionally, viral uptake pathways can be targeted, conferring resistance
to viral attack. Similarly, genes for prion proteins can be targeted and removed.
Combining ZFN modifications.
Another benefit of ZFNs is that multiple modifications can be performed in the same clone. Desirable ZFN modifications can
be trait stacked into the same cell line, enabling the potential development of a "super" CHO line precisely engineered to
efficiently produce safe and effective therapeutic proteins.
Genomic changes improve productivity
Genome editing has vastly improved since the creation of the DUKXB11 cell line. Since 2009, SAFC has applied the ZFN technology
to the development of robust CHO cell lines by introducing genomic changes that improve the productivity and processing characteristics
of biopharmaceutical manufacturing cell lines. More than 30 specific modifications are available to the biopharmaceutical
industry. Through microarray experiments, several key genes that impact cell growth and productivity have been identified
SAFC has several R&D scientists who identify and validate new genetic alterations that are relevant to the biopharmaceutical
industry. They have created the CHOZN GS (GS-/-) and CHOZN DHFR (DHFR -/-) knock-out cell lines. Other available cell lines
include knock-outs of GGTA (-/-) and CMAH (-/-), which result in cell lines that produce r-proteins without alpha-gal or Neu5Gc
Kate Achtien is an R&D scientist at SAFC, firstname.lastname@example.org