IL21 and neoplasm: eHSP90α exposed on the surface of tumour released autophagosomes can induce TLR2–MyD88–NF-κB signalling cascade and stimulate CD4+ T cells to produce IL-6 that functions in an autocrine manner to promote the production of IL-10 and IL-21, which create a favourable environment to facilitate tumour growth and metastasis in a melanoma mouse model [125] (Fig. 3).