In an effort to improve transient gene expression (TGE) in Chinese hamster ovary (CHO) cells, the combinatorial engineering of polyoma virus large T-antigen (PyLT) and Bcl-x(L) in CHO DG 44 cells was performed. The developed cell line (CHOP-off-Bcl-x(L)), which constitutively expresses PyLT and inducibly expresses Bcl-x(L), is capable of episomal replication with the use of the DNA expression vector encoding PyOri, EBNA-1, and OriP (pWP-Ang-EBNA/OriP-PyOri) and it is apoptosis-resistant. When the recombinant antibody was transiently expressed, this combinatorial engineering in the CHO cells resulted in a more than twofold increase in the product titer in various culture conditions such as batch, fed-batch, and cultures with sodium butyrate additions. Taken together, the data obtained here demonstrate that the use of the CHOP-off-Bcl-xL cell line can enhance the TGE significantly, which facilitates early stage product development in the pharmaceutical industry. (C) 2012 Elsevier Ltd. All rights reserved.