The immobilisation of cells in a perfusion culture allows to obtain a high cell concentration and an ef®cient removal of the catabolites without cell loss. A disadvantage of this system is that the cell density cannot be directly monitored. The cellular metabolism is just followed by online measurements of pH and dissolved oxygen (DO) and off-line determinations of residual metabolites. In this article, we report a high cell density achieved by the cultivation of a hybridoma in a bubblecolumn bioreactor ®lled with hollow glass cylinders. The parameters monitored during the cultivation were pH, temperature, DO, glucose, lactate and monoclonal antibody. The glucose uptake rate was used to estimate the cell concentration along the time. The maximum cell concentration calculated for the considered cultivation time was 2.7´10 7 cell á ml A1 . The glucose concentration in the media decreased stepwise twice, causing a decrease on the speci®c growth rate, while maintaining high antibody productivity levels. Maximum monoclonal antibody productivity was 503 lg á l A1 á day A1 and speci®c productivity, considering calculated cell density, was 0.019 ng á cell A1 á day A1 .
IntroductionAlthough target of a great number of studies, mammalian cell culture kinetics is still not completely understood. It depends on so many factors, including the cell line physiology, media formulation, type of bioreactor, gas supply and operating conditions. Often, the particular characteristics of a given cell line are functions of the culture conditions, including the composition of the medium, the bioreactor type, and the way it is operated [1].The most commonly used basal media for the growth of hybridomas are DME and RPMI 1640, formulated with different concentrations of glucose and glutamine, the major nutrients related to growth in conventional cell culture media, representing cell mass precursors and energy source. The other nutrients do not count for growth limitation, as they are usually supplied in excess. In a comparison between DME and RPMI media, it was concluded that DME seems to be more ef®cient for hybridoma growth, supporting greater number of cells for longer periods than RPMI, while the antibody synthesis depends only on the cell number, regardless of the medium used [2,3].Concerning the culture mode, perfusion culture of mammalian cells allows the maintenance of long-term, high-density and high-productivity cultures. Suspension cultures of hybridoma in a perfusion system makes it dif®cult to control the problems caused by the shear forces and to increase the dilution rate above the maximum speci®c growth rate, permitting to achieve high cellular viability. Several devices have been attempted to retain the cells, with more or less ef®cacy [4±6]. The immobilisation of hybridoma cells in any kind of support allows more ef®cient perfusion and confers more stability to the culture system, therefore, increasing the potential for longer cultures, higher cell density and antibody productivity [7]. The immobilisation condition protect...