Optimization of electrofusion parameters for efficient production of murine hybridomas

Several factors which affect the production of murine hybridomas by electrofusion using SP2/0 myelomas were examined. These factors included the ionic composition, specific resistance and osmotic strength of the fusion medium, proteolytic pretreatment of the cells, and field strength of the single, rectangular, 15 or 20 microseconds electric pulse. Individual experiments were observed by phase microscopy, video-recorded, and subsequently analyzed. The efficiency of hybridoma formation was measured by the number of hybrid colonies which survived HAT medium selection. In most cases, the peak efficiency occurred when the pulse field was between 3 and 4 kV/cm. Ca++ and Mg++, in 0.1 and 0.5 mM concentrations, respectively, helped to prevent large-scale SP2/0 lysis following pulse application. Reduction of the osmolarity of the fusion medium allowed for an approximate two-fold increase in the hybrid production efficiency. However, other variations, including an increase of the specific resistance of the medium to 1.7 x 10(4) omega cm, and a reduction of the pulse width to 15 microseconds, allowed significantly higher efficiencies. Dispase pretreatment of the myelomas led to additional improvements when using a 15 microseconds pulse. The data suggest that for this system, the highest efficiencies are obtained by maximizing the attractive polarization forces between cells, while adjusting the ionic composition and pulse parameters to preserve myeloma viability.