Inflammatory Conditions Promote Resistance to Immune Checkpoint Inhibitors in High Microsatellite Instability Colorectal Cancer

Inflammatory conditions caused by obstruction or perforation are common complications in colorectal cancer (CRC) and play important roles in tumor progression and immunosuppression. However, the significance of inflammatory conditions in the tumor response to immune checkpoint inhibitors (ICIs) remains unclear. We found a high microsatellite instability (MSI-H) CRC patient (Patient 1) whose primary tumor progressed and liver metastasis regressed during PD-1 blockade after having inflammatory conditions. Then, in 73 MSI-H CRCs, inflammatory conditions during ICI treatment were correlated with a poor tumor response, and an elevated NLR was associated with a poor immune status and resistance to ICIs. An organoid-T cell coculture model demonstrated an inhibited local immune response to treatment instead of systemic immunosuppression in Patient 1. Single-cell RNA sequencing suggested that neutrophils suppress the immune microenvironment mostly through CTLA-4-associated pathways. Therefore, inflammatory conditions in MSI-H CRCs correlate with resistance to ICIs through neutrophil-associated immunosuppression. Additional CTLA-4 blockade may improve the sensitivity to PD-1 blockade. Single-cell RNA sequencing (scRNA-seq) was conducted using the primary tumor of Patient 1. An scRNA-seq library was prepared using the DNBelab C4 system as previously described. Briefly, the single-cell suspension was transformed into the scRNA-seq library of barcodes through the steps of droplet encapsulation, emulsification and fragmentation, mRNA capture bead collection, reverse transcription, cDNA amplification and purification. An indexed sequencing library was constructed according to the manufacturer's instructions. The sequencing library was quantified using the Qubit SSDNA Assay Kit (Thermo Fisher Scientific). DIPSEQ T1 was used for sequencing libraries at the National Gene Bank (CNGB). -------------------------------------------------------------- Authors state "raw data are not available for this Series due to patient privacy concerns and human genetic resources policy in China".