Improving performance of mammalian cells in fed-batch processes through "bioreactor evolution".

The amount of recombinant product obtained from mammalian cells grown in a bioreactor is in part limited by achievable cell densities and the ability of cells to remain viable over extended periods of time. In an attempt to generate cell lines capable of better bioreactor performance, we subjected the DG44 Chinese Hamster Ovary (CHO) host cell line and a recombinant production cell line to an iterative process whereby cells capable of surviving the harsh conditions in the bioreactor were selected. This selective process was termed "bioreactor evolution". Following the selective process, the "evolved" host cells attained a 2-fold increase in peak cell density and a 72% increase in integral cell area. Transient transfection experiments demonstrate that the evolved cells have the same transfection efficiency and the same secretory potential as the initial cells. The "evolved" host was also found to contain a large subpopulation of cells that did not require insulin for growth. From this, a new population of growth-factor-independent cells was obtained. These improvements in host properties should prove beneficial in the expression of recombinant proteins in fed-batch processes. The selective process was also applied to a recombinant production cell line. The evolved cells from this selection exhibited a 38% increase in peak cell density, a 30% increase in integral cell area, and a 36% increase in product titer. These increases were obtained without any appreciable impact on product quality, demonstrating the usefulness of this simple approach to improve the performance of recombinant cell lines.

A soluble BAFF antagonist, BR3-Fc, decreases peripheral blood B cells and lymphoid tissue marginal zone and follicular B cells in cynomolgus monkeys.

BAFF (also known as BLyS), a member of the tumor necrosis factor superfamily, plays a critical role in the maturation and development of B cells. BAFF has three receptors on B cells, the most crucial of which is BR3. In this study, we demonstrate the biological outcome of BAFF blockade in cynomolgus monkeys using a soluble fusion protein consisting of human BR3 and human IgG1 Fc. In vitro, BR3-Fc blocked BAFF-mediated survival and proliferation of cynomolgus monkey B cells. Weekly treatment of cynomolgus monkeys with BR3-Fc for 13 to 18 weeks resulted in significant B-cell reduction in the peripheral blood and in lymphoid organs. CD21(high) B cells in lymphoid tissues, a subset analogous to human marginal zone B cells, expressed nearly twofold higher BR3 levels than did CD21(med) B cells. Lymphoid tissue flow cytometric analysis showed that BR3-Fc reduced this CD21(high) B-cell subset to a greater extent than it reduced CD21(med) B cells. Dual-label immunohistochemistry and morphometric image analysis supported these results by demonstrating that BR3-Fc reduced a significant proportion of the B cells within the splenic inner and outer marginal zones. These findings should prove very useful in guiding the desired therapeutic use of BR3-Fc for autoimmune diseases in the clinic.