Monoclonal antibody T-199 directed against human medulloblastoma: characterization of a new antigenic system expressed on neuroectodermal tumors and natural killer cells.

A monoclonal antibody (mAb) (T-199) of IgG1 isotype was raised against medulloblastoma by immunizations of mice with the medulloblastoma cell line TE-671. Studies of the specificity of mAb T-199 on cell lines as well as fresh frozen sections of normal and malignant tissues revealed the antigen in high amounts on the cell surface of neuroectodermally derived tumors such as medulloblastoma, neuroblastoma, retinoblastoma, and astrocytoma. Some melanomas and a subgroup of rhabdomyosarcomas also expressed the antigen. In contrast, mesenchymal tumors, osteosarcomas, and Ewing's sarcomas did not bear the T-199 antigen. Reactivity of T-199 with normal tissues has not been found with few exceptions; in certain areas of the brain, especially in the cerebellum and part of the hypothalamus, in the adrenal glands, and in the pancreatic islet cells small amounts of antigen were detectable. Natural killer cells could also be demonstrated to express the T-199 antigen similar to the NKH-1 antigen. However, despite some striking similarities, the antigens or antigen epitopes recognized by mAbs T-199 and NKH-1 are not identical. Therefore, mAb T-199 seems to detect a unique differentiation antigen on neuroectodermal tumors, coexpressed in low amounts on normal neuroectodermally derived cells and natural killer cells. The pattern of reactivity and the biochemical properties of the T-199 antigen are different from other cell surface markers for neuroectodermal cells coexpressed on natural killer cells or T-cells (HNK-1, NKH-1, or Thy-1). Biochemical analysis of the T-199 antigen showed that it is a heat-labile protein.