Cell Banks and Stability of Antibody Production
The original and fundamental appeal of monoclonal antibodies (mAbs), compared with polyclonal antisera, is the possibility for indefinite production of the same product. However, even well-established cell lines have limited stability in long-term culture
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21 Cell Banks and Stability of Antibody Production Pru Bird and Geoff Hale 1. Introduction The original and fundamental appeal of monoclonal antibodies (mAbs), compared with polyclonal antisera, is the possibility for indefinite production of the same product. However, even well-established cell lines have limited stability in long-term culture and it is necessary to establish a control system to ensure continuity of product supply. This is normally done by a seed lot system. A pool of cells derived from a single clone is frozen in a number of vials (say 100) to create a master cell bank (MCB). This MCB is carefully stored in liquid nitrogen. As required, individual vials are thawed and expanded to provide working cell banks, which might also consist of about 100 vials. Thus up to 10,000 production runs can be initiated before the original cell stock is exhausted. Obviously the number of vials in a bank can be adjusted to meet individual requirements. Working cell banks may not be necessary for experimental or preclinical projects, but you should at all costs avoid depletion of a clinically important master cell bank. There are extensive guidelines for the testing of master and working cell banks that will be used for production of therapeutic products (e.g., 1,2) and it is not our purpose to reiterate them here. Those tests are designed primarily to check the identity of the cell line and to characterize any microbial or viral contaminants. They must be carried out by expert virologists and are usually contracted to suitable commercial organizations. Because the testing process is costly and time consuming, it is important to establish cell banks as early as possible in a new project. However, for the same reasons, it is equally important to choose the optimal cell line, which is both a high producer and is clonally stable. From: Methods in Molecular Medicine, Vol. 40: Diagnostic and Therapeutic Antibodies Edited by: A. J. T. George and C. E. Urch © Humana Press Inc., Totowa, NJ
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It is a sine qua non that cell lines must be truly clonal before making a master cell bank. When receiving a hybridoma or transfectant from another laboratory, the wise production laboratory will first check its mycoplasma status and then reclone it. Many mouse and hetero- hybridomas are notoriously unstable regarding antibody production, and we have found the same to be true of transfectants, particularly several made using the glutamine synthetase (GS) expression system (3,4). It is laborious and time-consuming to check and compare the stability of different clones or transfectants; the normal procedure being to carry out analytical cloning after an appropriate period of continuous culture. Many subclones have to be assessed for antibody secretion to obtain an accurate measure of the heterogeneity of the cell line. Here we describe a simpler procedure whereby the cytoplasmic immunoglobulin within the antibody-producing cells is measured by flow cytometry (5). The concentration of cytoplasmic Ig correlates
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