FIG 1.

Mechanisms of immune evasion of neuroblastoma (NB). NBs may evade the immune destruction mediated by cytotoxic T cells (CTLs) and natural killer (NK) cells through multiple mechanisms, including the following: (1) immunosuppressive tumor microenvironment mediated by myeloid-derived suppressor cells (MDSCs)¹⁴⁷; (2) rarity of somatic mutations or neoantigens recognizable by classic T-cell receptors (TCRs) and downregulation of HLA class I molecules and antigen processing and presenting pathways; (3) expression of immunosuppressive tumor antigens such as gangliosides and sialic acids and membrane complement inhibitors; and (4) upregulation of multiple immune checkpoint inhibitors on immune effector cells and NB tumor cells. DCs, dendritic cells; IFN, interferon; IL, interleukin; iNOS, inducible nitric oxide synthase; ROS, reactive oxygen species; TGF-β, transforming growth factor-β; Treg, regulatory T cells.