ABSTRACT
Plant cell cultures have been used as expression hosts for recombinant proteins for over two decades. The quality of plant cell culture-produced proteins such as full-size monoclonal antibodies has been shown to be excellent in terms of protein folding and binding activity, but the productivity and yield fell short of what was achieved using mammalian cell culture, in which the key to gram-per-liter expression levels was strain selection and medium/process optimization. We carried out an extensive media analysis and optimization for the production of the full-size human anti-HIV antibody 2G12 in N. tabacum cv. BY-2. Nitrogen source and availability was found to be one key factor for the volumetric productivity of plant cell cultures. Increased amounts of nitrate in the culture medium had a dramatic impact on protein yields, resulting in a 10-20-fold increase in product accumulation through a combination of enhanced secretion and higher stability. The results were scalable from shake flasks to stirred-tank bioreactors, where the maximum yield per cultivation volume was 8 mg L(-1) over 7 days. During the stationary phase, antibody levels were 150-fold higher in nitrogen-enriched medium compared to standard medium. The enhanced medium appeared not to affect antibody quality and activity, as determined by Western blots, surface plasmon resonance binding assays and N-glycan analysis.
Subject(s)
Antibodies, Monoclonal/biosynthesis , Biotechnology/methods , HIV Antibodies/biosynthesis , Nicotiana , Nitrogen/metabolism , Bioreactors , Cell Culture Techniques/methods , Cell Line , Culture Media/chemistry , Humans , Nitrates/metabolism , Recombinant Proteins/biosynthesisABSTRACT
We report the first measurement of a ratio lambda(beta(b))/lambda(beta(c)) of bound-state ((lambda(beta(b))) and continuum-state (lambda(beta(c))) beta(-)-decay rates for the case of bare 207Tl81+ ions. These ions were produced at the GSI fragment separator FRS by projectile fragmentation of a 208Pb beam. After in-flight separation with the Brho-deltaE-Brho method, they were injected into the experimental storage-ring ESR at an energy of 400.5A MeV, stored, and electron cooled. The number of both the 207Tl81+ ions and their bound-state beta(-)-decay daughters, hydrogen-like 207Pb81+ ions, were measured as a function of storage time by recording their Schottky-noise intensities. The experimental result, lambda(beta(b))/lambda(beta(c)) = 0.188(18), is in very good agreement with the value of 0.171(1) obtained from theory employing spectra of allowed transitions.
ABSTRACT
Stopping power and energy-loss straggling of 197Au, 208Pb, and 209Bi projectiles have been measured in different solids (4
