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Updated: Jul 12, 2025
Cell Surface Receptor Identification Using Genome-Scale CRISPR/Cas9 Genetic Screens
Published on: June 6, 2020
A CRISPR activation screen identifies MUC-21 as critical for resistance to NK and T cell-mediated cytotoxicity
Dong-Hee Lee1, Hyejin Ahn1, Hye-In Sim2,3
1Department of Convergence Medicine, Asan Institute for Life Sciences, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, South Korea.
Background:
Immunotherapy has significantly advanced cancer treatments, but many patients do not respond to it, partly due to immunosuppressive mechanisms used by tumor cells. These cells employ immunosuppressive ligands to evade detection and elimination by the immune system. Therefore, the discovery and characterization of novel immunosuppressive ligands that facilitate immune evasion are crucial for developing more potent anti-cancer therapies.
Methods:
We conducted gain-of-function screens using a CRISPRa (CRISPR activation) library that covered the entire human transmembrane sub-genome to identify surface molecules capable of hindering NK-mediated cytotoxicity. The immunosuppressive role and mechanism of MUC21 were validated using NK and T cell mediated cytotoxicity assays. Bioinformatics tools were employed to assess the clinical implications of mucin-21 (MUC21) in cancer cell immunity.
Results:
Our genetic screens revealed that MUC21 expression on cancer cell surfaces inhibits both the cytotoxic activity of NK cells and antibody-dependent cellular cytotoxicity, but not affecting complement-dependent cytotoxicity. Additionally, MUC21 expression hinders T cell activation by impeding antigen recognition, thereby diminishing the effectiveness of the immune checkpoint inhibitor, anti-PD-L1. Moreover, MUC21 expression suppress the antitumor function of both CAR-T cells and CAR-NK cells. Mechanistically, MUC21 facilitates immune evasion by creating steric hindrance, preventing interactions between cancer and immune cells. Bioinformatics analysis revealed elevated MUC21 expression in lung cancer, which correlated with reduced infiltration and activation of cytotoxic immune cells. Intriguingly, MUC21 expression was higher in non-small cell lung cancer (NSCLC) tumors that were non-responsive to anti-PD-(L)1 treatment compared to responsive tumors.
Conclusions:
These findings indicate that surface MUC21 serves as a potent immunosuppressive ligand, shielding cancer cells from NK and CD8+T cell attacks. This suggests that inhibiting MUC21 could be a promising strategy to improve cancer immunotherapy.
Insights
Mucin-21 (MUC21) is a novel immunosuppressive ligand on cancer cells that shields them from immune attacks. Inhibiting MUC21 may enhance cancer immunotherapy effectiveness, especially for non-small cell lung cancer (NSCLC).
Area of Science:
- Cancer Immunology
- Molecular Biology
- Immunotherapy
Background:
- Cancer immunotherapy shows promise but is limited by tumor-induced immunosuppression.
- Tumor cells use immunosuppressive ligands to evade immune detection and destruction.
- Identifying novel immunosuppressive ligands is crucial for improving anti-cancer therapies.
Purpose of the Study:
- To identify novel surface molecules involved in immune evasion.
- To investigate the role of mucin-21 (MUC21) in hindering anti-tumor immunity.
- To explore the clinical relevance of MUC21 in cancer.
Main Methods:
- CRISPR activation (CRISPRa) screens of the human transmembrane sub-genome to identify immune-evading surface molecules.
- NK and T cell mediated cytotoxicity assays to validate MUC21's immunosuppressive function.
- Bioinformatics analysis to assess MUC21's clinical implications in cancer immunity.
Main Results:
- MUC21 expression inhibits NK cell and antibody-dependent cellular cytotoxicity, but not complement-dependent cytotoxicity.
- MUC21 hinders T cell activation and reduces the efficacy of anti-PD-L1 therapy by creating steric hindrance.
- Elevated MUC21 in lung cancer correlates with reduced immune cell infiltration and is higher in anti-PD-(L)1 non-responsive NSCLC tumors.
Conclusions:
- Surface MUC21 acts as a potent immunosuppressive ligand, protecting cancer cells from NK and CD8+ T cell-mediated attacks.
- Targeting MUC21 represents a potential strategy to enhance the efficacy of existing cancer immunotherapies.
- MUC21's role in immune evasion highlights its potential as a therapeutic target for improving patient outcomes.
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