The aim of this study was to elucidate whether the IgG humoral immune response to breast cancer cells is directed to the aberrant mucin-1 (MUC1) associated to this type of cancer. To this aim, an adaptation of immunohistochemistry (IHC) was performed on samples of 45 breast cancer tissues, 12 benign disease tissues, and 31 normal tissues, incubated with matched serum samples from the same patients. Each serum sample was also incubated, with a modified immunocytochemistry (ICC), with MCF7 cells. In both techniques, serum was employed instead of the primary antibody. In the case of IHC, the reactivity with sera diminished when added after previous incubation of the tumor/tissue with an anti-MUC1 mAb; the reduction in reactivity was: from 93% to 44% in breast cancer tissues, and from 100% to 67% in benign disease tissues. The reactivity of normal samples (36%) remained unchanged. In the case of ICC, the reactivity with sera decreased after incubation with anti-MUC1 mAb from 71% to 16% in breast cancer tissues, from 83% to 0% in benign disease tissues, and from 52% to 10% in normal serum samples. These results were confirmed employing siRNA MUC1 transient gene knockdown. By Western blot analysis – after immunoprecipitation (IP) of the circulating MUC1– and ELISA, the TF antigen was detected in circulating MUC1 in all breast cancer and benign samples while Tn was detected in 38% of the samples. The existence of IgG autoantibodies against aberrantly glycosylated MUC1 may have a protective role and may contribute to a better prognosis in some patients. Enhancement of this natural immune response may constitute an alternative therapeutic strategy.
