DCLK1 Suppresses Tumor-Specific Cytotoxic T Lymphocyte Function Through Recruitment of MDSCs via the CXCL1-CXCR2 Axis.

Background & Aims: Gastrointestinal cancer stem cell marker doublecortin-like kinase (DCLK1) is strongly associated with poor outcomes in colorectal cancer (CRC). Although DCLK1's regulatory effect on the tumor immune microenvironment has been hypothesized, its mode of action has not been shown previously in vivo, which hampers the potential intervention based on this molecule for clinical practice.

Methods: To define the immunomodulatory mechanisms of DCLK1 in vivo, we generated DCLK1 tumor cells by Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) and developed subcutaneous and intestinal orthotopic transplantation tumor models. Tumor tissues were harvested and subjected to immunofluorescence staining, flow cytometry analysis of tumor-infiltrating immune cell populations, tumor myeloid-derived suppressor cell (MDSC) sorting by isolation kit and then co-culture with spleen T cells, and RNA sequencing for transcriptomic analysis.

Results: We found that DCLK1 tumor cells lose their tumorigenicity under immune surveillance. Failed tumor establishment of DCLK1 was associated with an increase in infiltration of CD8 T cells and effector CD4 T cells, and reduced numbers of MDSCs in the tumor tissue. Furthermore, DCLK1 promoted the up-regulation of C-X-C motif ligand 1, which recruits MDSCs in CRC through chemokine C-X-C motif receptor 2. The ability of in vivo tumor growth of DCLK1 tumor cells was rescued by C-X-C motif ligand 1 overexpression. Collectively, we validated that DCLK1 promotes tumor growth in CRC through recruitment of T-cell-suppressive MDSCs.

Conclusions: DCLK1-mediated immune suppression in tumor models allows escaping from the host's antitumor response. Because DCLK1 is one of the most common markers in gastrointestinal tumors, these results identify a precise therapeutic target for related clinical interventions.