The 'Danse Macabre'-Neutrophils the Interactive Partner Affecting Oral Cancer Outcomes

Abstract

Over the past few decades, tremendous advances in the prevention, diagnosis, and treatment of cancer have taken place. However for head and neck cancers, including oral cancer, the overall survival rate is below 50% and they remain the seventh most common malignancy worldwide. These cancers are, commonly, aggressive, genetically complex, and difficult to treat and the delay, which often occurs between early recognition of symptoms and diagnosis, and the start of treatment of these cancers, is associated with poor prognosis. Cancer development and progression occurs in concert with alterations in the surrounding stroma, with the immune system being an essential element in this process. Despite neutrophils having major roles in the pathology of many diseases, they were thought to have little impact on cancer development and progression. Recent studies are now challenging this notion and placing neutrophils as central interactive players with other immune and tumor cells in affecting cancer pathology. This review focuses on how neutrophils and their sub-phenotypes, N1, N2, and myeloid-derived suppressor cells, both directly and indirectly affect the anti-tumor and pro-tumor immune responses. Emphasis is placed on what is currently known about the interaction of neutrophils with myeloid innate immune cells (such as dendritic cells and macrophages), innate lymphoid cells, natural killer cells, and fibroblasts to affect the tumor microenvironment and progression of oral cancer. A better understanding of this dialog will allow for improved therapeutics that concurrently target several components of the tumor microenvironment, increasing the possibility of constructive and positive outcomes for oral cancer patients. For this review, PubMed, Web of Science, and Google Scholar were searched for manuscripts using keywords and combinations thereof of "oral cancer, OSCC, neutrophils, TANs, MDSC, immune cells, head and neck cancer, and tumor microenvironment" with a focus on publications from 2018 to 2021.

Keywords: immune cells; innate immunity; interaction; myeloid cells; neutrophil; oral cancer; tumor microenvironment.

Figure 1

Effect of neutrophils and other immune cell sub-phenotypes on tumorigenesis. Immune cells such as CD8⁺ T, M1 TAMs, DCs, NK, and N1 TANs exhibit an anti-tumor response and aid in tumor regression. On the other hand, tumorigenic cells such as Treg, M2 TAMs, tolerogenic DCs, N2 TANs, and MDSCs, exhibit pro-tumor response and aid in tumor progression. There is complex interplay within the anti- and pro-tumor cell groups, as well as interaction of neutrophils with these cell groups to drive tumorigenesis in the TME ecosystem.

Figure 2

Tumorigenic role of TANs (N2) and MDSCs in the suppression of T-cell responses. N2 TANs differentiate into MDSC, an activated and more immunosuppressive neutrophil phenotype. Both N2 and MDSC produce Arg 1 and upregulate PD-L1 to cause T-cell anergy by modulating PD-L1/PD-1 signaling. N2 and MDSC also produce nitric oxide (NO) which initiates the TNF-α pathway to induce CD8⁺ T-cell death, via apoptosis. N2 and MDSC hinder anti-tumor T-cell function by anergy and apoptosis and promote tumor progression.

Figure 3

Neutrophil engagement with dendritic cells in the TME can result in immune-suppressive or immune-promotion of cancer pathology. Classical/conventional DC1 cells (cDC1) are the predominant subtype orchestrating an anti-tumor response through the interplay with N1 TAN, CD8⁺ cytotoxic T (CD8+ T) and natural killer (NK) cells. N1s produce several alarmins and cytokines that induce DC maturation, TME recruitment, and the initiation of anti-tumor adaptive immunity. DCs in-turn induce N1 proliferation and survival through cytokine/chemokine release, Type l IFNs, β-defensins and direct interaction MAC-CEACAM1/DC-SIGN receptor engagement. N1-induced DCs have a greater propensity to engage with and enhance the functions of anti-tumor CD8⁺ T cells, Th1, and NK cells to induce cytotoxic killing of tumor cells. On the other hand, N2 TANs and MDSCs have a suppressive role on DC functions and promote tumorigenic tolerant DCs. Reduction in N2 produced CCL4 leads to decreased cDC tumor infiltrate, an βincrease in N2 CXCL8 and CLL2 contributes to tumor progression and invasion pathways, N2–DC cell interaction HMGB1-TIM3, and IL-10 production leads to inhibition of cDCs. The inhibition of cDCs further compromises other anti-tumor immune cells (NK, CD8⁺ T) and allows for suppressive cells (N2, MDSC, Treg, tolerogenic DCs) to promote tumor growth.

Figure 4

Interaction of cancer-associated fibroblasts in promoting N2 function and tumorigenesis. Cancer-associated fibroblasts (CAFs) induce tumorigenic N2 by various interactions. CAF associated molecules such as TGF-β, CXCR2, and SDF-1α, promote cancer cell expression of CXCL6 and TGF-β, which aid in N2 polarization and TME recruitment. CAF produced IL-6 induces STAT3 signaling pathways that modulates PD-L1/PD-1 interaction between N2 and CD8⁺ T cells and aids in tumor cell death resistance. CAF associated chemokine CCL7 also aids in N2 recruitment to TME by chemotaxis. Other CAF associated molecules contribute to N2 NETosis and the production of proteases such as NE, MMPs, and cathepsin to degrade and remodel ECM and promote tumor invasion and metastasis.

Figure 5

Neutrophil networks affecting oral cancer outcomes. Neutrophils interact with anti-tumor and suppressive immune cells in the complex TME ecosystem. TME recruited neutrophils, TANs (tumor-associated neutrophils) polarize to a N1 anti-tumor phenotype in the presence of IFN-β, and to a N2 tumorigenic phenotype with TGF-β. N1 neutrophils upregulate several molecules such as cathepsin-G, MPO, MIP-1 α/β, IFN- β, TNF-α, IL-8, and TSP-1, to induce other immune cells and also execute N1 functions such as ADCC, ROS, and iNOS-induced cytotoxicity. N1 induce M1 TAM, NK (IL-18, 1L-15), T cells (IL-12, CCL1, CCL20, MCP-1) and DCs (LL-37, TNF-α, HMG-B1, defensins, lactoferrin, cell interaction Mac-1/CEACAM1–DC-SIGN). DCs further aid in N1 induced NK via IL-12, and NK aid in N1 induced DC via CCL5 and XCL1. N1 induced DCs further promote CD8⁺ T cells and Th1 cells. Interaction of these anti-tumor immune cells with N1 promotes tumor death. On the other hand, N2 neutrophils promote suppressive cells such as MDSC, Treg, and M2 and function via molecules such as MMP-9, VEGF, TGF-β, NETs, CLL4, and IL-10. N2 and MDSC inhibit anti-tumor T cells via Arg-1, TNF-α, and NO; and NK cells via NO and CXCR1/2. These lead to tumor growth and metastasis.

Figure 6

Immunoediting during tumorigenesis. 1. Initiation of cancer with transformation of healthy cells. 2. Robust response from innate and adaptive immune cells such as N1 neutrophils, CD8⁺ T, M1 TAM, NK, and cDC1, producing key cytokines IFNγ and TNFα to eliminate the cancer cells. 3. Equilibrium between the immune cell response and cancer growth in the presence of proinflammatory cytokines. Overtime, more resistant tumor variants arise that can evade the immune response and escape. 4. Tumor growth and progression in the presence of immune suppressive cells such as Tregs, N2 neutrophils, MDSCs, M2 TAMs, and tolerogenic DCs, producing key anti-inflammatory cytokines 1L-10 and TGF-β. Anti-tumor immune cells are suppressed in this highly tumoricidal environment.