mTOR inhibition augments antitumor immune effector response by reprogramming the TP53-mutant, immune-cold HNSCC tumor microenvironment

Abstract

Resistance to immunotherapy remains a major clinical challenge in TP53-mutant head and neck squamous cell carcinoma (HNSCC), a disease subset characterized by immune exclusion, high recurrence, and poor outcomes. Given the constitutive activation of PI3K/AKT/mTOR signaling in TP53-mutant HNSCC and its role in disease progression, we investigated whether the mTOR inhibition (mTORi) could overcome immune resistance and improve outcomes. We evaluated the effects of mTOR inhibitor everolimus in tumor microenvironment (TME) changes, including immune cell infiltration, immune checkpoint expression, and key pathways associated with immune suppression and angiogenesis, to define the mechanisms underlying TME remodeling. Everolimus significantly suppressed tumor growth in syngeneic HNSCC models. At the cellular level, everolimus significantly increased intratumoral CD8+ T cell and dendritic cell (DC) infiltration while reducing regulatory T cell (Treg) accumulation. Mechanistically, everolimus induced a cytokine/chemokine response, marked by increased TNF-α/CXCL10 expression, leading to enhanced immune infiltration. Everolimus also inhibited the HIF-1α/VEGFA pathway, a central driver of immune exclusion and myeloid-derived suppressor cell (MDSC) recruitment. Furthermore, everolimus treatment attenuated PD-1/PD-L1 signaling by reducing PD-1 and PD-L1 expression in T cells and tumor cells, thereby restoring T-cell cytotoxic competence. These findings demonstrate that mTORi with everolimus reverses multiple mechanisms of immune resistance and enhances anti-tumor T cell activity. Collectively, these results support mTORi as a rational therapeutic strategy for TP53-mutant HNSCC and for reprogramming the immune-resistant TME, particularly in patients who are likely to fail immunotherapy.