CD4 and neoplasm: Opposite to MMR, the expression of major histocompatibility complex class II (MHC-II) on macrophages is associated to anti-tumor response and antigen presentation to CD4+ T cells: Nbs targeting MHC-II were labeled with 18F and successfully applied for the detection of mouse model of pancreatic cancer by immuno-PET/CT, showing a good tumor-to-background ratio [100].