Estimation of heterokaryon formation and hybridoma growth in murine and human cell fusions.

Four mouse myelomas commonly used for cell fusions (X63.Ag8.653, SP2/0, NS1, P3U1), 3 human myeloma-like cell lines (ARH77, U-266, GM1500) and 3 human x mouse hybridomas (SPAZ4, SA2, SA3) were compared for their heterokaryon formation and successful hybridoma growth after cell fusion with polyethylene glycol. The cells were stained with different fluorescent dyes which do not alter hybridoma growth or antibody secretion. After fusion myeloma cells containing at least 1 nucleus from a lymphocyte (heterokaryons) were counted from fluorescence photomicrographs and the heterokaryon frequency was calculated. Mouse myelomas fused at a frequency of 1-7%, whereas human myeloma lines showed a higher heterokaryon frequency ranging from 3-25%. In mouse fusions almost every well contained growing hybridomas showing a minimum hybridoma frequency of 2/10(6) lymphocytes. In human fusions the SPAZ4 and SA2 lines showed a heterokaryon frequency nearly as good as mouse myelomas, whereas U-266 yielded no growing hybridomas despite 20% heterokaryon frequency. Furthermore, human cell lines showed a high tendency of multikaryon formation whereas this phenomenon was rarely observed with murine and murine x human heterohybrids. In individual fusion experiments no correlation was found between heterokaryon formation and the number of growing hybridomas. Thus, our study shows that defects in hybridoma growth may not always result from lack of a successful fusion and human hybridomas might be more sensitive to post-fusion conditions.