Calreticulin is an effective immunologic adjuvant to tumor-associated antigens

As a key molecule involved in cell recognition, calreticulin (CRT) may be expressed on the surface of (pre-) apoptotic cells and provide the signal that is recognized by dendritic cells (DCs) or other antigen presenting cells (APCs), which results in phagocytosis. Within the APCs, tumor-associated antigens (TAAs) may be subsequently presented to T lymphocytes, which triggers a specific antitumor immune response. It has been hypothesized that CRT is able to act as the immunologic adjuvant and translocate itself and TAAs to the cell surface and induce a specific antitumor immune response. In the present study, CRT was demonstrated to translocate itself and mucin 1 (MUC1), a breast cancer antigen, to the surface of 4T1 cells and the MUC1-CRT-coated cells were able to induce apoptosis in a time-dependent manner. When DCs were infected with adenovirus containing MUC1-CRT, an increase in T cell proliferation and cytokine production was exhibited. These results suggest that CRT may act as an immunologic adjuvant with MUC1 and induce a strong immune response.