Leukemogenesis-associated antigen in HTLV-I-transformed rabbit cells

The presence of a leukemogenesis-associated antigen was investigated in an experimental model of adult T-cell leukemia in (B/J x Chbb:HM)F1 rabbits, where adult rabbits develop leukemia within 1-2 weeks following inoculation with HTLV-I-transformed syngeneic cell lines. Leukemogenic activity was found in some but not all HTLV-I-transformed cell lines, and was associated with leukocytosis-inducing activity which was assayed by inoculating these cells into adult rabbits of the parental Chbb:HM strain. The leukemogenic cell line diminished or lost the leukemogenic and leukocytosis-inducing activities during prolonged culture in vitro. A mouse mAb was raised which recognized an antigen uniquely expressed on the cell surface of the leukemogenic cell lines. This antigen was present, however, in all HTLV-I-transformed cells examined and the mAb immunoprecipitated the same 65 kD glycoproteins from both leukemogenic and non-leukemogenic cell lines. Taken together, the antigenic epitope seemed to be expressed on the cell surface in such a manner as to be accessible to the mAb in leukemogenic but not non-leukemogenic cells. The analyses of various cell lines revealed that this antigen was an endogenous antigen and not a viral antigen. The antibody was cytotoxic in vitro against leukemogenic cell lines in the presence of complement, and administration of this antibody to leukemic rabbits resulted in an abrupt decrease in the peripheral blood leukocyte number, leading to remission of the disease.