Progression of transplanted SJL/J lymphomas attributed to a single aggressive H-2Ds-negative lymphoma

Spontaneously arising, H-2Ds-positive SJL/J lymphomas have been reported to become irreversibly more aggressive and H-2Ds-negative upon successive transplantation in syngeneic mice. In an effort to determine whether this process was one of tumor progression, we sought to: (a) establish whether a clonal relationship exists between readily transplantable aggressive SJL/J lymphomas and their respective indolent predecessors; and (b) identify genetic events critical to the process of acquisition of increased malignancy. Examination of putatively distinct, aggressive, H-2Ds-negative lymphomas, including the long term transplantable line RCS5, revealed them to have the same heavy and light immunoglobulin chain gene rearrangement patterns, a characteristic karyotype marked by nine chromosomal abnormalities, and approximately ten newly acquired ecotropic murine leukemia proviruses at similar genomic sites. Independent, spontaneously arising H-2Ds-positive lymphomas, in early transplant, were found to be genetically distinct from the respective more malignant H-2Ds-negative tumors to which they gave rise during successive transplantation. The data are interpreted as indicating that the aggressive H-2Ds-negative tumors in this study originated from a common source, most likely the RCS5 tumor, rather than through progression of separate spontaneously arising SJL/J lymphomas. It cannot be concluded which of the multiple genetic abnormalities of the H-2Ds-negative tumors were critical to their highly malignant phenotype. However, chromosomal abnormalities and newly acquired murine leukemia proviruses are discussed as to the roles they might play in SJL/J lymphomas.