Independent immunoglobulin class-switch events occurring in a single myeloma cell line.

Five gamma 2a-producing cell lines, all derived from the gamma 2b-producing mouse myeloma MPC11, were analyzed for changes in gene structure. Also examined was a cell line (ICR9.7.1) that acts as an intermediate to some of these class switches. All six of the MPC11 variants have undergone DNA rearrangement. Rearrangement sites in the gamma 2a-producing cells are different in each case and generally do not involve tandem repeat sequences. An enhancer for heavy chain gene transcription was deleted in at least one of these cell lines as a result of its class-switch rearrangement. DNA sequence analysis of cloned genes from two of the MPC11 variants revealed shared sequences at their rearrangement breakpoints. The same sequences are found at the breakpoints of two additional immunoglobulin gene rearrangements in MPC11.