MUC2 Expression Modulates Immune Infiltration in Colorectal Cancer
Introduction: Colorectal cancer (CRC) is a prevalent malignancy with significant morbidity and mortality worldwide. A deeper understanding of the interaction of cancer cells with other cells in the tumor microenvironment is crucial for devising effective therapeutic strategies. MUC2, a major component of the protective mucus layer in the gastrointestinal tract, has been implicated in CRC progression and immune response regulation.  Method: In this study, we sought to elucidate the relationship between MUC2 expression and immune infiltration within CRC, using in vitro models involving two well-established cell lines, HT-29 and LS-174T. By employing CRISPR-mediated MUC2 knockout, we investigated the influence of MUC2 on tumor immune infiltration and its interplay with T cells and NK cells enriched peripheral blood mononuclear cells (PBMCs) in 3D spheroid cultures.  Results: While MUC2 was more abundant in LS-174T cell line compared to HT-29, its knockout resulted in increased immune infiltration solely in the HT-29 cell line, but not in the LS-174T cell line. We revealed that the removal of MUC2 protein was compensated in LS-174T by the expression of other gel forming mucin proteins (MUC6, MUC5B) commonly expressed in gastrointestinal epithelium, while this was not observed in HT-29 cell line. Discussion: Our study is the first to directly demonstrate that MUC2 acts as a physical barrier to immune infiltration in colorectal cancer (CRC). While it's intuitive to think of mucins like MUC2 as barriers within the gastrointestinal tract, our findings confirm this role in the context of CRC. We observed that in the HT-29 cell line, MUC2 knockout increased immune infiltration, whereas in the LS-174T line, other mucins like Muc6 and Muc5B compensated for the loss of MUC2, maintaining the barrier. These results highlight the complexity of mucin biology in CRC and suggest that targeting mucin expression pathways may offer a promising therapeutic strategy.