The lack of quantitative descriptions of mammalian culture kinetics limits the ability to optimally design and control cell culture bioreactors. This limitation is ad dressed by developing mathematical equations relating the initial growth rate and the antibody productivity of the hybridoma cell line, CRL-1606, to its environmental state. This initial rate approach, in contrast with steady state analysis of chemostat cultures, approximates steady state behavior, since the rates were measured over brief time intervals and at low cell concentrations (< 50,000 cells/mL). The advantage of this approach is that it is much faster than the chemostat approach.An equation for the growth rate was developed that superimposed Monod equations in serum and glutamine with "noncompetitive" -type inhibition constants were inversely proportional to the lactate and ammonium concentrations. The Monod constant is critical for relating initial, low cell level culture states to other states.Lactate was found to be the only environmental parameter that significantly inhibited antifibronectin monoclonal antibody production by the CRL-1606 hybridomas. Volumetric productivity was strictly related to culture viability, which was observed to decline at growth rates below 0.02 h(-1). Lactate was also found to significantly inhibit ammonium production.

The growth rate of the hybridoma cell line ATCC-CRL-1606 in low serum medium declines rapidly with time after inoculation. To characterize this phenomenon, the stability of the growth-promoting activity of serum was investigated. The activity of serum was found to de grade with time, and was stabilized by alterations in the medium formulation that acted to lower the oxidation/reduction potential. This included both the addition of thiols and the elimination of disulfides from the medium. Additionally, cysteine and other thiols were shown to stimulate growth in low serum, low cell density cultures, suggesting that thiols may be rate-limiting in low serum medium. Stimulation of growth by thiol addition was less significant at high cell levels, implying that the cells themselves may be acting to reduce their environment. A hypothesis is presented based on these results which suggests that the actual rate-limiting moieties in low serum cultures may be dithiols.

Mammalian cell culture in hollow fiber reactors is hampered by oxygen limitation. Diffusive oxygen transport from the fiber wall to the cells can be enhanced by increasing the sugace area for oxygenation andlor decreasing the penetration depth. One strategy for improving of sugace area to penetration depth ratio is to increase the number offibers in the reactor. An alternative way to manipulate this ratio is to grow the cells inside the fibers rather than on the outside. The theoretical analysis presented indicates that this is favorable when the volume of the extracapillary space exceeds that of the fiber lumen by a factor four or more. The impact of growing the cells on the inside of the fibers on other aspects of mammalian cell culture in hollow fiber reactors, including mass transport from the bulk ofthe medium flowing through the reactor to the fiber wall, is discussed.