Selection of potentially autoreactive t-cell receptors in nmethyl-n-nitrosourea-induced and spontaneous thymic lymphoma

Injection of the carcinogen N-methyl-N-nitrosourea (MNU) into young AKR mice induces a high incidence (>90%) of thymic lymphoma. In contrast to spontaneous lymphoma which develops in aging untreated AKR mice, MNU-induced lymphoma occurs prior to 6 mo of age and is not a consequence of proviral integration. Although distinct molecular mechanisms are responsible for the generation of MNU-induced versus spontaneous tumors, both types of lympbomas frequently express a CD4+8+CD3+HSAhi phenotype and are monoclonal. The current study was undertaken to determine if the Vβ repertoire expressed by MNU-induced and spontaneous lymphomas is representative of that observed in normal AKR thymocytes. We evaluated Vβ representation on primary spontaneous and MNU-induced thymic lymphomas in immunofluorescence assays using a panel of monoclonal antibodies to specific TCR Vβ gene products. Approximately 58% (15/26) of the MNU-induced and 71%% (5/7) of the spontaneous lymphomas expressed a specific Vβ determinant. Compared to the Vβ distribution in thymocytes from young AKR mice, we observed a greater than expected frequency of MNU-induced lymphomas that expressed Vβ6, Vβ8 and Vβ9. Interestingly, Vp8, but not Vβ6 or Vβ9, was overrepresented on spontaneous lymphomas supporting the notion that spontaneous and MNUinduced tymphomas have different etiologies. These data suggest a skewing of the TCR Vβ repertoire in MNU-induced and spontaneous lymphomas that reflects a nonrandom selection process perhaps as a consequence of stimulation by an endogenous peptide or superantigen within the thymic microenvironment. To distinguish between these possibilities, PCR amplification, cloning and sequencing of the TCR complementaritydetennining region 3 (CDR3) is underway. Supported by CA37912 and Bruce McMUlian Jr. Foundation.