We have recently developed a protein-free medium (PFS) able to support the growth of Chinese hamster ovary (CHO) cells in suspension. Upon further supplementation with some plant protein hydrolysates, medium performances reached what could be observed in serum-containing media [Burteau et al. In Vitro Cell. Dev. Biol.-Anim. 39 (2003) 291]. Now, we describe the use of rice and wheat protein hydrolysates, as non-nutritional additives to the culture medium to support productivity and cell growth in suspension or in microcarriers. When CHO-320 cells secreting recombinant interferon-gamma (IFN-c) were cultivated in suspension in a bioreactor with our PFS supplemented with wheat hydrolysates, the maximum cell density increased by 25% and the IFN-c secretion by 60% compared to the control PFS. A small-scale perfusion system consisting of CHO-320 cells growing on and inside fibrous microcarriers under discontinuous operation was first developed. Under these conditions, rice protein hydrolysates stimulated recombinant IFN-c secretion by 30% compared to the control PFS. At the bioreactorscale, similar results were obtained but when compared to shake-flasks studies, nutrients, oxygen or toxic by-products gradients inside the microcarriers seemed to be the main limitation of the system. An increase of the perfusion rate to maintain glucose concentration over 5.5 mM and dissolved oxygen (DO) at 60% was able to stimulate the production of IFN-c to a level of 6.6 lg h À1 g À1 of microcarriers after 160 h when a cellular density of about 4 · 10 8 cell g À1 of carriers was reached.Abbreviations: AU -arbitrary units; CHO -Chinese hamster ovary; DO -dissolved oxygen; LDH -lactate deshydrogenase; IFN-c -interferon-gamma; PFA -protein-free medium for adhesion; PFS -protein-free medium for suspension; RP -rice protein hydrolysates; WP -wheat protein hydrolysates.

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