HETEROGENEITY WITHIN POPULATIONS OF RECOMBINANT CHINESE-HAMSTER OVARYCELLS EXPRESSING HUMAN INTERFERON-GAMMA

The Chinese hamster ovary (CHO) cell line has great commercial importa nce in the production of recombinant human proteins, especially those for therapeutic use. Much attention has been paid to CHO cell populati on physiology in order to define factors affecting product fidelity an d yield. Such studies have revealed that recombinant proteins, includi ng human interferon-gamma (IFN-gamma), can be heterogeneous both in gl ycosylation and in proteolytic processing. The type of heterogeneity o bserved depends on the growth physiology of the cell population, altho ugh the relationship between them is complex. In this article we repor t results of a cytological study of the CH0320 line which expresses re combinant human IFN-gamma. When grown in suspension culture,this cell line exhibited three types of heterogeneity: (1) heterogeneity of the production of IFN-gamma within the cell population, (2) heterogeneity of the number of nuclei and mitotic spindles in dividing cells, and (3 ) heterogeneity of cellular environment. The last of these arises from cell aggregates which form in suspension culture: Some cells are expo sed to the culture medium; others are fully enclosed within the mass w ith little or no direct access to the medium. Thus, live cells produci ng IFN-gamma are heterogeneous in their environment, with variable acc ess to O-2 and nutrients. Within the aggregates, it appears that live cells proliferate on a dead cell mass. The layer of live cells can be several cells deep. Specific cell-cell attachments are observed betwee n the living cells in these aggregates. Two proteins, known to be requ ired for the formation of certain types of intercellular junctions, sp ectrin and vinculin, have been localized to the regions of cell-cell c ontact. The aggregation of the cells appears to be an active process r equiring protein synthesis (C) 1995 John Wiley and Sons, Inc.