Pancreatic Cancer Stem-Like Cells With High Calreticulin Expression Associated With Immune Surveillance.

OBJECTIVE Pancreatic cancer stem-like cells (P-CSLCs) are thought to be associated with poor prognosis. Previously, we used proteomic analysis to identify a chaperone pro-phagocytic protein calreticulin (CALR) as a P-CSLC-specific protein. This study aimed to investigate the association between CALR and P-CSLC. METHODS PANC-1-Lm cells were obtained as P-CSLCs from a human pancreatic cancer cell line, PANC-1, using a sphere induction medium followed by long-term cultivation on laminin. To examine the cancer stem cell properties, subcutaneous injection of the cells into immune-deficient mice and sphere formation assay were performed. Cell surface expression analysis was performed using flow cytometry. RESULTS PANC-1-Lm showed an increased proportion of cell surface CALR-positive and side-population fractions compared with parental cells. PANC-1-Lm cells also had higher frequency of xenograft tumor growth and sphere formation than PANC-1 cells. Moreover, sorted CALRhigh cells from PANC-1-Lm had the highest sphere formation frequency among tested cells. Interestingly, the number of programmed death-ligand 1-positive cells among CALRhigh cells was increased as well, whereas that of human leukocyte antigen class I-positive cells decreased. CONCLUSION In addition to the cancer stem cell properties, the P-CSLC, which showed elevated CALR expression on the cell surface, might be associated with evasion of immune surveillance.