The AttSite Recombinase Technology from Intrexon, Blacksburg, VA, utilizes specific DNA sequences and proprietary recombinase enzymes to catalyze the insertion of a gene of interest at a specific location in the host cell genome. Using this technology, we have developed Chinese Hamster Ovary (CHO) cell lines that have incorporated attB recombination sites at highly transcriptionally active loci or 'hot spots' within the cell genome. Subsequently, these attB site containing host cell lines could then be used for the expression of future Centocor products. Candidate production cell lines would be generated by a simple recombination event. Since the therapeutic gene of interest would preferentially integrate into the pre-selected high-expressing attB site, candidate cell lines would consistently express high levels of the gene of interest. We have been able to demonstrate that the AttSite Recombinase Technology could be a valid approach for the development of high-expressing production cell lines.