B cell response to tumor antigens is associated with depletion of B progenitors in murine colocarcinoma

Background. B cells that produce antibodies to autologous tumor antigens have been found in patients with colon cancer; the significance of this phenomenon remains unknown. Normally, the elimination of autoreactive B cells occurs in the bone marrow during their maturation. We studied the production of antibodies to syngeneic tumor antigens and the maturation of bone marrow B cells in experimental colocarcinoma model. Methods. BALB/c mice and syngeneic CT26 colon cancer cell line were used. Reactivity of serum antibodies was tested in Western blot analysis and flow cytometry against CT26 antigens. The number of bone marrow B lineage cells was evaluated with specific antibodies and flow cytometry analysis. Results. A significant decrease in the number of B cell precursors occurred in tumor-bearing mice; it normalized 3 weeks after the removal of CT26 tumors. The number of mature B cells was normal. Serum antibodies from tumor-bearing mice recognized intracellular and not surface antigens of CT26 cells. Conclusion. Experimental colon cancer induces B cell response to intracellular, but not surface, tumor cell antigens and restricts the B cell repertoire by depleting their precursors.