RESUMO
The use of multidrug-resistant variant of Sp2/0 mouse myeloma cell line SpEBr-5 as a partner for making mouse hybridoma producing monoclonal antibodies is described here. The resulting hybridoma cell line 1F7 was characterized with a high level of monoclonal antibody production and karyotype containing all normal mouse chromosomes. 1F7 cells were separately selected for resistance to ethidium bromide (EBr) and adriamycin (ADR) and different mechanisms of drug resistance were found in these cell variants. The resistance in ADR-selected 1F7 cells was due to amplification and overexpression of mdr genes. In EBr-resistant 1F7 cells, mdr genes were overexpressed without amplification. Substantially decreased level of Topo II activity in both cell lines also suggests the existence of additional mechanisms for MDR phenotype of hybridoma cells. Finally, adriamycin-resistant 1F7 hybridoma cell variant was found to produce higher level of specific immunoglobulins due to the increased level of Iggamma(2b) heavy chain mRNA.
