Janus or Hydra: The Many Faces of T Helper Cells in the Human Tumour Microenvironment.

ABSTRACT

CD4+ T helper (TH) cells are key regulators in the tumour immune microenvironment (TIME), mediating the adaptive immunological response towards cancer, mainly through the activation of cytotoxic CD8+ T cells. After antigen recognition and proper co-stimulation, naïve TH cells are activated, undergo clonal expansion, and release cytokines that will define the differentiation of a specific effector TH cell subtype. These different subtypes have different functions, which can mediate both anti- and pro-tumour immunological responses. Here, we present the dual role of TH cells restraining or promoting the tumour, the factors controlling their homing and differentiation in the TIME, their influence on immunotherapy, and their use as prognostic indicators.