EphA4 Mediates Pro- and Antitumoral Effects Through Upstream Negative Regulation of AKT in Head and Neck Squamous Cell Carcinoma.

Head and Neck Head and Neck Squamous Cell Carcinoma (HNSCC) is driven by an immunosuppressive tumor microenvironment (TME). We examined the immune-modulatory role of EphA4 in HNSCC using spatial analysis, multi-compartment RNA-sequencing from Oral Cavity Squamous Cell Carcinoma (OCSCC), and three genetically engineered mouse models. Within the HNSCC TME, EphA4 is primarily expressed in Tregs, macrophages, CD8+ T cells, and HNSCC cancer cells. EphA4 in Tregs promotes tumor growth, whereas EphA4 in myeloid cells, CD8+ T cells, and cancer cells limits it. EphA4 mediates these differential effects through shared negative regulation of AKT signaling where its knockout increases AKT activation, leading to reduced Treg immunosuppression, increased M2 macrophage polarization, impaired CD8+ T cell memory differentiation, and enhanced cancer cell proliferation. APY-d3-PEG4, EphA4 inhibitor, reduced tumor growth primarily by targeting Tregs. EphA4 expression on CD8+ T cells correlates with treatment response, representing a potential biomarker, and cell-type-specific targeting via cis-bispecific antibodies offers a promising therapeutic strategy. Interrogating human data shows that EphA4 expression on CD8 correlates to response to treatment, posing it as a potential biomarker for future studies. Mechanistically, our data show EphA4 inhibits AKT signaling, and its inhibition enhances AKT functionality across cell types, yielding opposing effects in cancer.