Avoiding rapid growth at high cell densities: a potentially important optimisation criterion for hybridoma cultures

Effect of feed rate on growth rate and antibody production in the fed-batch culture of murine hybridoma cells

Batch and fed-batch cultures of a murine hybridomacell line (AFP-27) were performed in a stirred tankreactor to estimate the effect of feed rate on growthrate, macromolecular metabolism and antibodyproduction. Macromolecular composition was foundto change dynamically during batch culture ofhybridoma cells possibly due to active production ofDNA, RNA and protein during the exponential phase.Antibody synthesis is expected to compete with theproduction of cellular proteins from the amino acidpool. Therefore, it is necessary to examine therelationship between cell growth in terms of cellularmacromolecules and antibody production. In this study,we searched for an optimum feeding strategy bychanging the target specific growth rate in fed-batchculture to give higher antibody productivity whileexamining the macromolecular composition. Concentratedglucose (60 mM) and glutamine (20 mM) in DR medium(1:1 mixture of DMEM and RPMI) with additional aminoacids were fed continuously to the culture and thefeed rate was updated after every sampling to ensureexponential feeding (or approximately constantspecific growth rate). Specific antibody productionrate was found to be significantly increased in thefed-batch cultures at the near-zero specific growthrate in which the productions of cellular DNA, RNA,protein and polysaccharide were strictly limited byslow feeding of glucose, glutamine and other nutrients. Possible implications of these results are discussed.

Specific growth rate as a parameter for tracing growth-limiting substances in animal cell cultures

The specific growth rate (mu) reaches its maximum very early during culture (at 20 h), but declines again thereafter so that no exponential growth phase occurs in batch cultures of hybridoma cells. This growth rate limitation depends neither on exhaustion of any of the macro-nutrients, nor on inhibition by metabolic byproducts (Ljunggren and Häggström, 1994). Intermittent additions of serum, after 20 and 40 h of culture, resulted in exponential growth throughout the growth phase. Insulin was found to be the main component responsible for the growth rate increasing effect. Intermittent additions of serum or insulin to a dual substrate (glucose and glutamine) limited fed batch culture increased the growth rate also here, and the results indicate the existence of a minimum growth rate (about 0.02 h-1) at a threshold glutamine level (0.005 mM). Serum and insulin additions markedly enhanced the glucose consumption and lactate formation rates, a metabolic effect that was not coupled to the increase in mu. The reduced concentrations of glucose and glutamine in substrate limited fed batch cultures suppressed substrate consumption rates and byproduct formation (lactate, ammonium, alanine, other amino acids) even in the serum and insulin stimulated cultures and rendered the energy metabolism much more efficient than in batch culture. Further, the serum and insulin stimulated cells growing in substrate limited fed batch culture produced almost 4-times more antibodies, from the same amount of nutrients as supplied to the batch grown cells.

Methods and strategies available for the process control and optimization of monoclonal antibody production

The objective of this paper is to explore the range of methods and strategies available for the process control and optimization of monoclonal antibody production by hybridoma cell culture. Emphasis will be placed on the choice of the level of complexity incorporated into the process control and optimisation procedure. It will be shown that the behaviour of hybridomas in culture is influenced by sophisticated cellular metabolic activities and various interactive environmental factors and that the understanding and modelling of the way hybridomas grow in the bioreactor should enable optimisation of bioreactor operating conditions to achieve maximum monoclonal antibody formation. However, due to the lack of on-line instrumentation of important biological variables and the incomplete knowledge of hybridoma cultivation process, there exist many limitations and challenges to the advent of applications of process control and optimisation in this field. To solve the problem, introduction of industrially practical biological measurements and development of new control concepts are inevitable. At the end of this paper, we shall discuss possible schemes for the control of the physiological state of cells in order that balanced cell growth and maximum monoclonal antibody synthesis may be achieved.