Retroviral heterogeneity in mouse lymphomas.

Provirus modifications which can occur in tumors may lead to tumor antigenic variants. To investigate this possibility we compared the restriction fragment length patterns of mouse mammary tumor virus (MMTV), murine leukemia virus and xenotropic and mink cell-focus inducing (MCF)-related sequences, using Southern blot analysis, in a panel of Balb/c and C57BL/6 lymphomas, some of which were known to express novel histocompatibility (H) antigens. The results indicate differences in amplification and novel integration sites of retroviral sequences in all tumors analyzed, the number of new sequences depending on the specific retroviral sequence. A relationship has been found between integration of new MMTV sequences and a known susceptibility to lysis by syngeneic alloactivated lymphocytes in the same group of tumors. The possibility that retroviruses can induce the expression of novel histocompatibility antigens on tumors is discussed.