CD4 and neoplasm: The most potent stimulus for class II HLA proteins is IFN-γ, and when CD4+ T cells get activated by recognition of tumour antigens on HLA class II receptors, they produce additional IFN-γ, which subsequently induce further HLA class II expression and subsequent immune activation.36 Tumours surrounded by activated immune cells generally have a less aggressive phenotype than the immune suppressed tumours.