Single-cell proteomics maps circulating monocyte dynamics in advanced head and neck squamous cell carcinoma

It remains unclear whether metastatic progression in head and neck squamous cell carcinoma (HNSCC) is accompanied by functional remodeling of circulating immune cells at the proteome level. To address this question, we applied single-cell proteomics (SCP) to cryopreserved peripheral blood mononuclear cells (PBMCs) from three patients with HNSCC representing distinct stages of metastatic progression and two healthy donors. Proteomic analysis of 619 individual PBMCs resolved major immune cell populations, with up to 1,638 proteins quantified per cell. Trajectory inference, clustering, and differential abundance analyses revealed proteomic remodeling associated with disease progression, with the most pronounced changes occurring within a monocyte cluster composed exclusively of cells from patients with nodal metastasis. This population showed increased abundance of interferon-related proteins, HLA molecules, and myeloid immunoregulatory signatures, consistent with an activated, interferon-associated monocyte state. In parallel, lymphocytes showed reduced coordinated abundance of proteins associated with activation, cytotoxicity, and degranulation, consistent with altered cytotoxic effector programs across disease stages. Overall, these findings reveal distinct proteomic states in circulating monocytes and lymphocytes associated with HNSCC progression and identify selective remodeling of the monocyte compartment in nodal metastatic disease.