Secreted calreticulin mutants subvert anticancer immunosurveillance

Mutations of the gene coding for calreticulin (CALR) that cause the loss of the C-terminal KDEL motif abolish its retention in the endoplasmic reticulum and cause CALR to be secreted from cells. Specific CALR mutants bearing a novel C-terminus can precipitate the manifestation of myeloproliferative diseases via the autocrine activation of the thrombopoietin receptor. We recently employed the retention using selective hooks (RUSH) technology to monitor CALR trafficking and demonstrated the secretion of C-terminally truncated variants of CALR in vitro and in vivo. Of note, extracellular CALR inhibited the phagocytosis of dying cancer cells by dendritic cells (DC). Via this mechanism, mutant CALR induced immunosuppression, which decreased the efficacy of immunogenic anticancer chemotherapies and PD-1 blockade.