Combination of FACS and homologous recombination for the generation of stable and high-expression engineered cell lines

Applications of flow cytometry sorting in the pharmaceutical industry: A review

The article reviews applications of flow cytometry sorting in manufacturing of pharmaceuticals. Flow cytometry sorting is an extremely powerful tool for monitoring, screening and separating single cells based on any property that can be measured by flow cytometry. Different applications of flow cytometry sorting are classified into groups and discussed in separate sections as follows: (a) isolation of cell types, (b) high throughput screening, (c) cell surface display, (d) droplet fluorescent-activated cell sorting (FACS). Future opportunities are identified including: (a) sorting of particular fractions of the cell population based on a property of interest for generating inoculum that will result in improved outcomes of cell cultures and (b) the use of population balance models in combination with FACS to design and optimize cell cultures.

Generation of homogeneous cell populations with tunable levels of transgene expression

We describe here a vector construct to establish homogeneous cell populations expressing a recombinant gene of interest (GOI) at tuneable levels, including low expression levels that are difficult to generate using standard cell line development techniques. This is achieved using a tricistronic mRNA that contains an open reading frame for the gene of interest, a first internal ribosome entry site (IRES), an open reading frame for a fluorescent reporter protein (such as green fluorescent protein, GFP), a second IRES and an open reading for an antibiotic resistance gene (such as puromycin N-acetyl-transferase, PAC). The resistance gene allows convenient selection of stable cell populations. The fluorescent reporter protein allows convenient homogeneity and expression stability assessments of the cell line. The expression level of the GOI can be adjusted by using different start codons for the open reading frame. These alternate start codons will initiate the translation of the GOI with different efficiency, leading to cell populations expressing different levels of the GOI, and similar levels of the fluorescent reporter through the first IRES and the puromycin resistance gene through the second IRES to the GOI. Such cell populations are useful tools, for instance to assess the safety of potent targeted therapeutics, as they allow the simplified generations of homogenous cell populations with different levels of target protein expression between populations.

High-throughput sorting of the highest producing cell via a transiently protein-anchored system

Developing a high-throughput method for the effecient selection of the highest producing cell is very important for the production of recombinant protein drugs. Here, we developed a novel transiently protein-anchored system coupled with fluorescence activated cell sorting (FACS) for the efficient selection of the highest producing cell. A furin cleavage peptide (RAKR) was used to join a human anti-epithelial growth factor antibody (αEGFR Ab) and the extracellular-transmembrane-cytosolic domains of the mouse B7-1 antigen (B7). The furin inhibitor can transiently switch secreted αEGFR Ab into a membrane-anchored form. After cell sorting, the level of membrane αEGFR Ab-RAKR-B7 is proportional to the amount of secreted αEGFR Ab in the medium. We further selected 23 αEGFR Ab expressing cells and demonstrated a high correlation (R² = 0.9165) between the secretion level and surface expression levels of αEGFR Ab. These results suggested that the novel transiently protein-anchored system can easily and efficiently select the highest producing cells, reducing the cost for the production of biopharmaceuticals.