Biochemical and biological properties of tumor-associated antigen of bovine leukemia cells

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Enzootic bovine leukosis (EBL) is a lymphoproliferative disease caused by bovine leukemia virus (BLV). The neoplastic cells have tumor-associated antigens (TAA) on their cell surface. Thirteen monoclonal antibodies that identified TAA on EBL cells have been obtained. The properties of the TAA were analyzed by using these monoclonal antibodies. The results obtained in this studies are summerized as follows; 1. According to the reactivities of 13 monoclonal antibodies with 19 individual tumors, TAA were classified into 3 groups: common TAA, partially common TAA and individually distinct TAA. TAA bound to Lentil Lectin-Sepharose 4B column and were thus a glycoprotein. Common TAA with a molecular weight (M.w) of 74,000 (74K) had at least 2 independent antigenic regions coexisting on the molecule. The partially common TAA with a M.w of 64K had at least 4 independent antigenic regions. Individually distinct TAA with a M.w of 64K was located on molecule different from that of the partially common TAA. 2. The specificity of c143, recognized common TAA, binding in vivo for EBL tumor cells was demonstrated. The ^<125>I-labeled c143 F(ad')_2 fragments were injected into athymic mice bearing bovine lymphoid tumor cells. The fragments became preferentially localized in tumor tissues but not in normal tissues, as determined by radioimmunoscintigraphy. 3. An antitumor effect of c143 was tested. Nude mice injected with c143 (200<micrn>g) every other day until 37 days after the tumor transplantation showed significant inhibition of tumor growth when compared with control groups (p<0.05).