Detection of Tumor Cell Surface-reactive Antibodies Vaccine-based immunotherapy is being used to treat dogs with primary brain tumors. The vaccines are composed of a lysate of autologous tumor cells, which stimulate an immune response producing tumor specific antibodies that are capable of inducing antibody-dependent cell-mediated cytotoxicity to allogeneic, as well as autologous, tumor cells. This protocol will describe the tumor cell serum antibody-binding assay to measure the tumor-reactive IgG antibody response. Key features of this assay are that it is performed with sera collected from the canine patient prior to and following vaccination as the source of antibodies and canine brain tumor cells used as the target cells.