The exposure of calreticulin (CRT) on the plasma membrane can precede anthracycline-induced apoptosis and is required for cell death to be perceived as immunogenic. Mass spectroscopy, immunofluorescence and immunoprecipitation experiments revealed that CRT co-translocates to the surface with another endoplasmic reticulum-sessile protein, the disulfide isomerase ERp57. The knockout and knockdown of CRT or ERp57 inhibited the anthracycline-induced translocation of ERp57 or CRT, respectively. CRT point mutants that fail to interact with ERp57 were unable to restore ERp57 translocation upon transfection into crt À/À cells, underscoring that a direct interaction between CRT and ERp57 is strictly required for their co-translocation to the surface. ERp57 low tumor cells generated by retroviral introduction of an ERp57-specific shRNA exhibited a normal apoptotic response to anthracyclines in vitro, yet were resistant to anthracycline treatment in vivo. Moreover, ERp57 low cancer cells (which failed to expose CRT) treated with anthracyclines were unable to elicit an anti-tumor response in conditions in which control cells were highly immunogenic. The failure of ERp57 low cells to elicit immune responses and to respond to chemotherapy could be overcome by exogenous supply of recombinant CRT protein. These results indicate that tumors that possess an intrinsic defect in the CRT-translocating machinery become resistant to anthracycline chemotherapy due to their incapacity to elicit an anticancer immune response. The conventional treatment of cancer relies upon radiotherapy and chemotherapy, two procedures that supposedly mediate their therapeutic effects solely by intrinsic mechanisms of tumor cell death and without direct participation by the host immune system. Nevertheless, there are specific circumstances in which conventional anti-cancer treatments can induce a modality of cell death that is immunogenic, whereby dying cells elicit a tumor-specific immune response culminating in elimination of tumor cells. Although most chemotherapeutic agents kill tumor cells through a morphologically indistinguishable apoptotic pathway, they differ in their capacity to stimulate immunogenic as opposed to nonimmunogenic cell death. 1 Recently, we reported that tumor cells undergoing immunogenic cell death translocate intracellular calreticulin (endo-CRT) to their plasma membrane (PM) surface (ecto-CRT), facilitating tumor cell recognition and engulfment by dendritic cells (DC) and subsequent T-cellmediated elimination of the tumor. 2 Accordingly, anthracyclines and g-irradiation, which elicit immunogenic cell death, induce CRT exposure whereas other proapoptotic agents that induce non-immunogenic cell death fail to induce ecto-CRT. [2][3][4] Depletion of CRT abolishes the immunogenicity of cell death elicited by anthracyclines, whereas addition of exogenous CRT or enforced surface exposure of CRT by pharmacological agents that favor CRT translocation can enhance the immunogenicity of cell death. 2,4 An additional signal emitted during ...