EFFECT OF SERUM-FREE AND SERUM-CONTAINING MEDIUM ON CELLULAR-LEVELS OF ER-BASED PROTEINS IN VARIOUS MOUSE HYBRIDOMA CELL-LINES

BiP, GRP94 and PDI, three endoplasmic reticulum (ER) based proteins ar e involved in the maturation of secretory proteins and might represent a bottleneck in the secretory pathway of monoclonal antibodies (MAB). With the three hybridoma cell lines tested, MAB production kinetics w ere significantly increased for the batch cultures done in serum-free medium (SFM) with respect to those done in serum-containing medium (SC M). It could be established that there was a correlation between the c ellular levels of PDI and GRP94 and the specific MAB production rate. With respect to BiP, no correlation with the MAB production rate was o bserved. The non-producing myeloma cell line X63, used as a reference, showed increased cellular PDI levels when cultivated in SFM. However, in this cell, the cellular GRP94 levels were not significantly influe nced by the medium composition. It was concluded that SFM induced an i ncrease of cellular PDI levels and this elevation seemed to be respons ible for the increase in the specific MAB production rates. On the oth er hand, only MAB producing cells showed an increase in the cellular G RP94 levels which might be a result of increased MAB synthesis. Indeed , 1.13.17 cultivated in SFM supplemented with serum showed a significa ntly reduced (about 50%) specific MAB production rate in comparison to 1.13.17 cultivated in non-serum supplemented SFM. The cellular PDI an d BiP levels did not vary between these conditions of culture, whereas the cellular GRP94 level was about two-fold lower in 1.13.17 cultivat ed in SFM when supplemented with serum than in 1.13.17 cultivated in S FM without further supplementation. These results are discussed with r espect to the medium composition as well as in the context of apparent and potential bottlenecks within the secretory pathway of MAB. (C) 19 97 John Wiley & Sons, Inc.