Secretion of biologically active human interleukin-2 and interleukin-4 from genetically modified tobacco cells in suspension culture.

Biologically active human interleukin-2 (IL-2) and IL-4, key lymphokines involved in immune regulation, were produced and secreted into the medium by genetically modified Nicotiana tabacum cells grown in suspension culture. Secretion through the plasma membrane and cell wall into the medium was facilitated by the natural mammalian leader sequences. IL-2 and IL-4 were detected in the medium at concentrations of 0.10 and 0.18 microgram/mL, respectively, although higher levels were detected within the lymphokine-producing cells (approximately 0.80 microgram/mL for IL-2 and approximately 0.28 microgram/mL for IL-4). By Western blot, IL-4 was found to be secreted as two small polypeptides with molecular masses of approximately 18-20 kDa. The biological activity of IL-2 was determined by cell proliferation of the IL-2-dependent murine CTLL-2 cell line, while that of IL-4 was determined by cell proliferation of the CTLL-2 cell line [CT.h4S] which was stably transfected with the human IL-4 receptor. These findings indicate that plant suspension culture can be used to produce and secrete into the medium a variety of biologically active mammalian proteins that are of clinical and diagnostic relevance.