Abstract B099: Tumor progression locus 2 kinase drives pancreatic cancer immune evasion through a MYBL2-CXCL10 signaling axis

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a chronically inflamed tumor microenvironment (TME) driven by persistent activation of innate inflammatory signaling. Tumor progression locus 2 (TPL2; MAP3K8) is a serine/threonine kinase downstream of KRAS that activates both MAPK and NF-κB signaling; however, its tumor-intrinsic role in regulating antitumor immunity remains poorly understood. We investigated the function and mechanism of TPL2 in PDAC using genetically engineered mouse models, orthotopic transplantation models and pharmacologic inhibition. From single-cell RNA sequencing and multiplex immunohistochemistry we demonstrated that TPL2 is predominantly expressed in pancreatic tumor cells rather than stromal or immune populations in both murine and human PDAC. We generated tumor-intrisic conditional deletion of Map3k8 in autochthonous KPPC (p48-Cre/Tp53 flox/flox /LSL-KRas G12D ) mice, which showed significantly delayed tumor progression, reduced tumor burden and prolonged survival. The TME of Map3k8 flox/flox KPPC tumors showed increased infiltration and activation of CD8+ effector T cells and dendritic cells, reduced regulatory T cells and immunosuppressive macrophages, and enhanced tumor cell susceptibility to cytotoxic T-cell killing. Similar immune remodeling was observed in orthotopic tumors generated from Map3k8-deficient PDAC cells and wild-type KPPC mice treated with the clinical-stage TPL2 inhibitor tilpisertib. To define the underlying mechanism, we performed BioID proteomics and identified MYBL2 as a previously unrecognized TPL2-interacting protein. TPL2 promoted phosphorylation of MYBL2 at Thr487, enhancing its transcriptional activity. RNA sequencing revealed that MYBL2 regulates an inflammatory transcriptional program enriched for IL-17 signaling, with CXCL10 emerging as a major downstream effector. CUT&RUN and chromatin immunoprecipitation analyses confirmed direct MYBL2 binding to the Cxcl10 promoter, which was diminished following TPL2 inhibition. Genetic deletion of Mybl2 phenocopied TPL2 deficiency, whereas MYBL2 overexpression accelerated tumor growth and established an immunosuppressive TME that was reversed by Cxcl10 deletion, demonstrating that CXCL10 is a critical downstream mediator of TPL2-MYBL2 signaling. Therapeutically, tilpisertib recapitulated the immune remodeling observed with genetic Map3k8 deletion, prolonged survival, and significantly enhanced the efficacy of gemcitabine plus CTLA-4 blockade in autochthonous KPPC mice. In addition, TPL2 overexpression promoted resistance to KRAS inhibition, whereas KRAS inhibitor-resistant PDAC models exhibited activation of both TPL2 and NF-κB signaling, supporting a role for TPL2 in adaptive resistance to KRAS-targeted therapy. Collectively, these findings identify a previously unrecognized tumor-intrinsic TPL2-MYBL2-CXCL10 signaling axis that promotes immune evasion. Targeting TPL2 remodels the immune TME and improves immunotherapy efficacy,, providing strong rationale for clinical development of TPL2-targeted therapies in PDAC.