Transient production of biopharmaceutical proteins

The creation of stable mammalian cell lines for biopharmaceutical production often require several months, and is unfavourable for the rapid production of multiple drug candidates for screening in the early stages of development. Biopharmaceutical production by transient transfection provides a possible alternative of quickly producing these early stage drug candidates. The Epi-CHO transient expression system, which consists of a Chinese hamster ovary (CHO) cell line (CHO-T) expressing the murine polyomavirus Large T-Antigen (LT), emonstrated enhanced transient recombinant protein production. The aim of this study was to prolong transient recombinant protein prod.Jction of the Epi-CHO expression system by creating a CHO cell line expressing both LT and EBNA1 (ECHO-T). The pEBNA1-LT expression vector encoding LT and EBNA1 was constructed and transfected into CHO-K1. A total of 20 clones were isolated from the antibioticresistant pool and screened for the expression of functional LT and EBNA1. PCR analysis showed 16 of the 20 clones was positive for EBNA1 and LT DNA. Of the 16 clones, six were positive for EBNA1 and LT expression by RT-PCR. Detection of LT and EBNA1 by immunofluorescence showed positive staining for the P7-G3 clone. Western blotting suggested the P7-G3 clone was: positive for EBNA1, and clones P3-C7 and P7-E2 were positive for LT. A plasmid replication assay confirmed the expression of functional LT in all six clones. Plasmid maintenance assay confirmed clone P7-G3 as the ECHO-T clones to express functional EBNA1. The P7-G3 clone demonstrated prolonged and sustained transient recombinant protein expression when compared to CHO-T. The P7-G3 clone achieved sustained transient protein expression for 32 days in the absence of selection, the longest currently reported for CHO cells