Browsing by Author "De Villiers, Ann-Marie"
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- ItemProduction and glycosylation of a recombinant protein from Chinese hamster ovary (CHO) cells(Stellenbosch : Stellenbosch University, 2012-12) De Villiers, Ann-Marie; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Recombinant glycoproteins are important biopharmaceuticals, providing solutions for numerous previously untreatable illnesses, in everything from cancer to infertility. Most recombinant biopharmaceuticals are produced in mammalian cells due to their ability to provide the correct post-translational processing for use in humans. The post-translation processing influences many of the protein’s properties including pharmacokinetics, bioactivity, secretion, half-life, solubility, recognition and antigenicity. The aim of this thesis is to further study the upstream production of a glycosylated recombinant protein produced by Chinese hamster ovary (CHO) cells on production scale within the confines of an existing process. The process in question uses adherent CHO cells to produce a glycosylated recombinant hormone. As with most recombinant protein production processes, this process has two sections to the upstream production: a seed train to grow enough cells to inoculate production, and a production section, which focuses on the production of a recombinant protein. The seed train is predominantly conducted in roller bottles, while the production section takes place in perfusion bioreactors, where the cells are attached to microcarriers, with spin-filters for cell retention. The whole process uses medium with serum. There are two process challenges regarding an existing recombinant-protein production process: 1. The gradual increase, over the past several campaigns, of the final population doubling level of the cells (which must remain within certain specified limits) at the end of the seed train. 2. The low glycosylation levels of the product seen in certain campaigns, which meant that a certain number of final product batches were below the specified acceptable glycosylation limits. Following a literature survey several controlled process variables were chosen for investigation and hypotheses made on their effect on the seed train or glycosylation. To investigate their effect on the PDL and cell growth in the seed train: - Medium volume: decreasing the medium volume will yield a lower PDL due to slower cell growth caused by lower glucose availability. - Seeding density: if cells obtain confluence by the time they are harvested, decreasing the seeding density will yield a higher PDL. - Cultivation temperature: decreasing the temperature ought to decrease the growth rate. - Medium feed temperature: there will be no significant difference to the cell culture when pre-heated or cold medium is used. Aeration: using vent caps will increase the oxygen content of the medium in the roller bottles and the cell growth, yielding a higher PDL. To investigate their effect on glycosylation during production: - pH: better glycosylation will be seen at pH 6.9, than at pH 6.7. - Perfusion rate: a higher perfusion rate will lead to better glycosylation due to increased glucose and glutamine concentrations. In the seed train, the only factor that significantly influenced the final PDL was the seeding density. Cell growth was inhibited once cells reached confluence, so lowering the seeding density lead to a higher PDL. It is recommended to use a high seeding density to ensure a lower PDL. Historic data indicated that the seeding density was not the cause of the apparent increase of the final PDL, as all previous campaigns had been seeded with a high seeding density. What then became apparent was that the final PDL remained relatively constant during a campaign and that the increase in final PDL occurred between campaigns. It appears that the apparent increase in the final PDL is due to differences in cell counting between operators as each new campaign was managed by different operators. It is recommended that a mechanical cell counter be used to verify cells counts and to maintain a standard between campaigns. In the bioreactors, varying the pH proved to have no significant effect on the glycosylation levels. However, both the initial perfusion rate and the specific perfusion rate proved to be important from both historical data and the data generated during these experiments. Lower levels of the initial perfusion rate lead to better glycosylation and it is recommended that an initial perfusion rate of 1.0 volumes/day be used. The relationship between the specific perfusion rate and the glycosylation appears to be non-linear and requires further study, for now it is recommended that the specific perfusion rate be kept below 0.3 volumes/day/109 cells. Probable reasons for the unsatisfactory glycosylation seen in certain runs could also be proposed from these two factors: • RP33-133 : Very high specific perfusion rate • RP32-135 : High initial perfusion rate and very high specific perfusion rate • RP32-138 : High initial perfusion rate • RP33-139 : High initial perfusion rate Further research is recommended into the effect of the specific perfusion rate as well as the specific glucose consumption rate and the specific glutamine concentration on the glycosylation.