The genesis of Thy-1-lymphomas in NFS mice exposed to X irradiation

The kinetics of the appearance of potentially leukemic cells (PoLCs) for radiation-induced lymphoma in NFS mice was investigated by the opposite sex (male----female) transplantation assay. The origin of the cells of the lymphomas that developed in the host was decided by sex chromosome markers. The bone marrow and the spleen cells collected from mice 30 days after fractionated irradiation (1.7 Gy X 4) gave rise, upon transfer to 4-Gy-irradiated hosts, to tumors of either donor or host origin. Most tumors of donor origin were thymine-1-negative (Thy-1-) and surface immunoglobulin negative and classified as nonthymic lymphoma, while the tumors of host origin were mainly Thy-1-positive thymic lymphoma. In contrast, neither the bone marrow nor the thymus contained any PoLCs for thymic lymphoma 30 days after split-dose irradiation. These results indicate that PoLCs for Thy-1-lymphoma were induced in the bone marrow and spleens of NFS mice by the split-dose regimen which developed exclusively T-cell lymphomas in the absence of cell grafting.