In vivo growth advantage of the MOPC-315 mouse myeloma over its immunoselected variants.

Myeloma cells of the "wild type" that produce complete immunoglobulin molecules and those of the more usual variant type that display only one kind of chain [either light (L) or heavy (H)] were cocultivated ip and sc in syngeneic BALB/c mice. With each of six deliberately selected variants, a progressive increase in the proportion of wild-type cells was observed; the rate of change suggested that these variants had an approximately 10% slower growth rate than that of the wild-type tumor. In contrast, a variant that arose spontaneously overgrew the wild-type cells. The results may account for a) the stable capacity of most wild-type tumors to produce complete immunoglobulin molecules (L- plus H-chains) over many years, even though they frequently generate variant cells that produce only L- or only H-chains; and b) the occasional spontaneous change of myeloma cell populations from predominantly wild-type to variant cells.