Tumor-specific antibodies were analyzed in sera after immunization and tumor challenge as described above. Sera were taken about 3 weeks following the last trAb injection. At this time point, no residual trAb was detected. Tumor cells were pre-incubated with sera on ice; after washing cells, fluorescence-labeled antibody against mouse IgG1 or IgG2a was added. Analysis of IgG-binding tumor cells was subsequently performed using FACS (LSRII flow cytometer; BD Biosciences).