Role of Macrophages in Brain Tumor Growth and Progression

Abstract

The role of macrophages in the growth and the progression of tumors has been extensively studied in recent years. A large body of data demonstrates that macrophage polarization plays an essential role in the growth and progression of brain tumors, such as gliomas, meningiomas, and medulloblastomas. The brain neoplasm cells have the ability to influence the polarization state of the tumor associated macrophages. In turn, innate immunity cells have a decisive role through regulation of the acquired immune response, but also through humoral cross-talking with cancer cells in the tumor microenvironment. Neoangiogenesis, which is an essential element in glial tumor progression, is even regulated by the tumor associated macrophages, whose activity is linked to other factors, such as hypoxia. In addition, macrophages play a decisive role in establishing the entry into the bloodstream of cancer cells. As is well known, the latter phenomenon is also present in brain tumors, even if they only rarely metastasize. Looking ahead in the future, we can imagine that characterizing the relationships between tumor and tumor associated macrophage, as well as the study of circulating tumor cells, could give us useful tools in prognostic evaluation and therapy. More generally, the study of innate immunity in brain tumors can boost the development of new forms of immunotherapy.

Innate and Adaptive Immunity Linked to Recognition of Antigens Shared by Neural Crest-Derived Tumors

“…Sometimes in meningiomas infiltration by tumor-associated macrophages (TAMs) may be very pronounced, especially in cases of meningiomas that carry isolated monosomy 22, where the immune infiltrates also contain greater numbers of cytotoxic T and NK-cells that are associated with an increased anti-tumoral immune response. In line with this, the presence of regulatory T cells is usually limited to a small fraction of all meningiomas [87]. These studies reflect an attempted immune response.…”

“…Ml macrophages can produce high levels of inducible nitric oxide synthase (iNOS) to promote arginine metabolism into nitric oxide and citrulline and high levels of proinflammatory cytokines. M2 macrophages express scavenger receptors, mannose receptors and IL-10 and are involved in tissue remodelling, immune modulation and tumor progression [87]. Interestingly, M2-type macrophages in vestibular schwannomas relate to angiogenesis and volumetric tumor growth [88].…”

Novel Immune-Related Gene Signature for Risk Stratification and Prognosis of Survival in Lower-Grade Glioma

“…In current study, it was found that the M2-type macrophage was significantly enriched in primary LGG. Despite the glioma was defined as "cold tumor" with very little infiltrative immune cells, the proportions of macrophage can still constitute up to 30-50% in the TME of glioma (Guadagno et al, 2018). Additionally, the predictive values of immune cells have been extensively investigated.…”

A multi-layered systems approach for renal cell carcinoma

“…Taken together, these studies demonstrate a previously unknown role for IL34 in progression of RCC and suggest it as an important potential target. IL34 has been also shown to promote tumor progression and metastasis in other tumor types such as osteosarcoma [60][61][62][63][64][65][66] . The effect of IL34 and CSF-1 blockade was recently explored using specific blocking antibodies 58 .…”