Caspase-8 Mutation Promotes HNSCC Development and Resistance to Anti–PD-1

Heterozygous mutations of the gene encoding caspase-8 protease occur in 10% of human head and neck squamous cell carcinomas (HNSCCs). Cell line studies indicate that these mutations block apoptosis induced by death ligands. However, the in vivo role of caspase-8 mutations in the development of HNSCC and their impact on response to immune checkpoint blockade have not been determined. We generated mice with heterozygous, epithelium-specific knock-in of a representative, HNSCC-associated caspase-8 mutation (D305G). The impact of the caspase-8 mutation was assessed following treatment with the carcinogen 4-nitroquinoline-1-oxide (4NQO) in drinking water. Treatment of the D305G caspase-8 mutant mice with 4NQO resulted in a greater number of tongue tumors per mouse and a higher percentage of advanced-stage invasive carcinomas than was observed in 4NQO-treated mice with wild-type caspase-8, and tumors from the mutant mice were more resistant to anti–PD-1. We also engineered the murine oral cancer cell line MOC1 for heterozygous expression of caspase-8 mutations. Tumors generated from these engineered cells in syngeneic, immunocompetent mice demonstrated reduced responsiveness to anti–PD-1, relative to tumors with wild-type caspase-8. Further, the caspase-8 mutant tumors displayed reduced intratumoral and splenic CD8⁺ T cells and impaired recruitment of monocytes and dendritic cells during PD-1 blockade. Collectively, these findings demonstrate that caspase-8 mutation promotes carcinogen-induced HNSCC development and resistance to anti–PD-1. Investigation of caspase-8 mutations as potential biomarkers of poor response to immunotherapy in patients with HNSCC is warranted.