Homologous recombination between transferred and chromosomal immunoglobulin kappa genes

Homologous recombination between transferred and chromosomal DNAs provides a means of introducing well-defined, predetermined changes in the chromosomal genes. Here we report that this approach can be used to specifically modify the immunoglobulin genes in mouse hybridoma cells. The test system is based on the Sp6 hybridoma, which synthesizes immunoglobulin M (kappa) specific for the hapten 2,4,6-trinitrophenyl (TNP). As recipient cells, we used the Sp6-derived mutant hybridoma igk14, which has a deletion of the kappa TNP gene and consequently does not synthesize TNP-specific immunoglobulin M. igk14 retains the mu TNP gene and two additional rearranged kappa genes, denoted kappa M21B1 and kappa M21G. As a transfer vector, we used pSV2neo bearing the functionally rearranged TNP-specific V kappa segment. Following DNA transfer by electroporation, we isolated rare transformants which produced normal amounts of the functional kappa TNP chain. Analysis of the DNA of these transformants indicated that in all cases, a functional kappa TNP gene had been formed as the result of a homologous integrative recombination event with the igk14 kappa M21B1 gene. These results suggest that homologous recombination might be used for mapping and introducing immunoglobulin gene mutations and for more conveniently engineering specifically altered immunoglobulins.