Chromosomal, histopathological and cell surface marker studies on Moloney virus induced lymphomas

Trisomy of chromosome 15 is a common feature in murine T-cell leukemias of chemical, viral and spontaneous origin. It is not present in all T-cell derived lymphomas, however. In order to study whether trisomy 15 was restricted to a specific T-cell subtype, diploid and chromosome 15 trisomic M-MuLV induced leukemias and derived in vitro lines were compared with regard to histology, karyotype, Thy-1,2 and Lyt-1, 2, 3 and 5 antigen expression. Histologically trisomic lymphomas showed a higher mitotic rate, higher peri-cellular reticulum content and less small cell infiltration than diploid tumors. It was not possible to distinguish trisomic from diploid lymphomas in blind tests based on these criterias, however. Trisomic and diploid lymphoma cells were indistinguishable in morphology. Three of nine lymphomas induced by M-MuLV inoculation were trisomic; two of them were thymomas. Transplantation to syngeneic recipients of the opposite sex and study of the sex chromosome marker was used to establish the origin of the enlarged organ. Upon subcutaneous transplantation, trisomic tumors and thymomas grew locally and were of donor cell type whereas splenic lymphomas caused spleen enlargement, as a rule, and were of donor or recipient type. Transplantation of bone marrow from mice infected with M-MuLV as newborns gave rise to lymphomas with the same sex as the donor and established the presence of preleukemic T-cells in the bone marrow of the donor. In vitro lymphoma lines expressed four different patterns of Lyt antigens: (a) 1.2 + , 2.2 + , 3.2 + , 5.1 + (4 lines); (b) 1.2 + , 2.2 − , 3.2 − , 5.1 + (5 lines); (c) 1.2 + , 2.2 + , 3.2 − , 5.1 + (7 lines); (d) individually distinct patterns (3 lines). Each group contained Thy-1.2 − and Thy-1.2 + lines. The trisomic tumors were mostly in group (a), all of them were Thy-1.2 positive. Diploid tumors were randomly distributed largely between groups (b) and (c). Two of three tumors in group (d) were aneuploid (not trisomic for 15). In spite of the differences observed between trisomic and diploid lymphomas, no specific T-cell subset could be assigned to the two groups. This is in line with the finding of trisomy 15 in some B-cell lymphomas suggesting that this anomaly may contribute to the neoplastic change in a variety of lymphocyte subsets, representing different lineages and steps of differentiation.