Abstract

Tumor-associated MUC4 mucin hasconsiderable potential as an immunotherapy target for pancreatic cancer. Inprevious studies, we developed dendritic cell (DC) vaccines which elicited MUC4antigen-specific cytotoxic T lymphocyte (MS-CTL) response against tumor cellsin vitro. Due to the observation that MS-CTL apoptotic rate increasedsignificantly when co-cultured with MUC4+ tumor cells compared with T2 cells,we investigated whether high expression levels of MUC4 in pancreatic cancercells would have an effect on the significant increase of apoptosis rate ofMS-CTLs. First, the adverse influence of regulatory T cells (Tregs) waseliminated by CD8+ T lymphocyte sorting before the induction of MS-CTLs. Then,we constructed clonal MUC4-knockdown HPAC pancreatic cancer sublines withdifferent MUC4 expression for co-incubation system. By utilizing appropriatecontrol to rule out the possible apoptosis-induced pathway of intrinsicactivated cell-autonomous death (ACAD) and analogous antigen-dependentapoptosis of CTL (ADAC) in our study system, further analysis of the effect ofMUC4 membrane-expression, supernatants and blockade of CTL surface Fas receptoron MS-CTL apoptosis was carried out. The results demonstrated that the level ofMUC4 membrane expression strongly positively correlated with MS-CTL apoptosisand the influence of supernatants and Fas-blockade did not significantlycorrelate with MS-CTL apoptosis. This evidence suggested that there may be anovel counterattack pathway of pancreatic cancer cells, which is aMUC4-mediated, cell contact-dependent and Fas-independent process, to induceCTL apoptosis. Therefore, further exploration and understanding of thepotential counterattack mechanisms is beneficial to enhance the efficacy ofMUC4 specific tumor vaccines.