Expression of antibody genes in tissue culture: structural mutants and hybrid cells.

Detailed information on the nature and frequency of somatic mutations has been derived from studies of the clonal diversification of the myeloma MOPC 21 in tissue culture. A screening procedure is described that permitted the isolation of four spontaneous mutations at the gamma1 structural gene locus. These originate from four mutation events. Two seem to be point mutations: a "nonsense" and a "mis-sense." Of the other two, one is a frameshift leading to mistranslation and early termination, the other a large deletion due to perhaps an intrachromosomal translocation or a mitotic recombination. Fusion between myeloma-producing cells has shown that variable and constant region genes cannot be scrambled. Differentiation from stem to plasma cells seems to involve changes in the primary sequence of the DNA. Fusion between myeloma cells and spleen cells from immunized animals is a satisfactory method for the derivation of permanent tissue culture lines producing specific antibody. The hybrids express the myeloma as well as the specific antibody light and heavy chains. By subcloning and selection, one can derive lines that selectively lose individual chains. Lines that no longer express the myeloma components can thus be derived. The use of appropriate defective variants of the myeloma parental line is another way of avoiding the presence of the myeloma components.