Identifying targets present in the tumor microenvironment that contribute to immune evasion has become an important area of research. In this study, we identified EphB4–ephrin-B2 signaling as a regulator of both innate and adaptive components of the immune system. EphB4 belongs to receptor tyrosine kinase family that interacts with ephrin-B2 ligand at sites of cell–cell contact, resulting in bidirectional signaling. We found that EphB4–ephrin-B2 inhibition alone or in combination with radiation (RT) reduced intratumoral regulatory T cells (Tregs) and increased activation of both CD8⁺ and CD4⁺Foxp3⁻ T cells compared with the control group in an orthotopic head and neck squamous cell carcinoma (HNSCC) model. We also compared the effect of EphB4–ephrin-B2 inhibition combined with RT with combined anti-PDL1 and RT and observed similar tumor growth suppression, particularly at early time-points. A patient-derived xenograft model showed reduction of tumor-associated M2 macrophages and favored polarization towards an antitumoral M1 phenotype following EphB4–ephrin-B2 inhibition with RT. In vitro, EphB4 signaling inhibition decreased Ki67-expressing Tregs and Treg activation compared with the control group. Overall, our study is the first to implicate the role of EphB4–ephrin-B2 in tumor immune response. Moreover, our findings suggest that EphB4–ephrin-B2 inhibition combined with RT represents a potential alternative for patients with HNSCC and could be particularly beneficial for patients who are ineligible to receive or cannot tolerate anti-PDL1 therapy.

These findings present EphB4–ephrin-B2 inhibition as an alternative to anti-PDL1 therapeutics that can be used in combination with radiation to induce an effective antitumor immune response in patients with HNSCC.