Research progress on the role of immune cells in the tumor microenvironment in the development and progression of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC), the most common type of head and neck malignancy, has a poor prognosis owing to its high invasiveness and high rate of cervical lymph node metastasis. The tumor microenvironment (TME) is a complex microenvironment that is essential for tumor cell survival. Tumor-associated immune cell (TAIC), the main stromal cell of TME, regulates the proliferation, invasion, epithelial-mesenchymal transformation (EMT), and anti-tumor immunity of OSCC. M2-tumor-associated macrophages (TAMs) promote the invasion and metastasis of OSCC through the macrophage migration inhibitory factor/NOD-like receptor family pyrin domain containing 3/interleukin (IL)-1β axis, while N2-tumor-associated neutrophils (TANs) regulate the proliferation and EMT of OSCC through the Janus kinase 2/signal transducer and activator of transcription 3 pathway. Meanwhile, myeloid-derived suppressor cells (MDSCs) accelerate the progression of OSCC by secreting IL-6, IL-10, and transforming growth factor (TGF)-β; T cells promote inflammation by secreting IL-17 and inhibit inflammation-mediated tumor immune response by secreting IL-10 and TGF-β; and natural killer (NK) cells recognize and attack OSCC cells to inhibit OSCC progression. TAIC interaction network also regulates OSCC progression. M2-TAMs regulate the invasion and metastasis of OSCC by promoting T cell apoptosis through the secretion of IL-10 and programmed death-ligand (PD-L) -1, while N2-TANs inhibit T cell proliferation and cytotoxicity by secreting LOX-1 and arginase-1. MDSCs inhibit the proliferation and anti-tumor effects of CD8⁺ T cells through the inactivation of programmed cell death (PD)-1/PD-L1 signaling. Additionally, MDSCs inhibit the proliferation of T cells by decreasing the expression of the CD3-zeta chain and interferon-γ (IFN-γ). Moreover, tumor-infiltrating lymphocytes and NK cells were found to be positively correlated in OSCC progression. Therefore, target regulation, related signaling pathways, and the interaction network of TAIC may serve as promising therapeutic targets in the immunotherapy of OSCC. In this review, we summarize the recent research on the effects of TAIC and their interaction network in the TME in the progression of OSCC and explore its application in the early diagnosis and treatment of OSCC.