From thymus to tissues and tumors: a review of T cell biology.

T cells are critical orchestrators of the adaptive immune response that optimally eliminates a specific pathogen. Aberrant T cell development and function are implicated in a broad range of human disease including immunodeficiencies, autoimmune diseases, and allergic diseases. Accordingly, therapies targeting T cells and their effector cytokines have drastically improved the care of patients with immune dysregulatory diseases. Newer discoveries concerning T cell mediated antitumor immunity and T cell exhaustion have further prompted development of highly effective and novel treatment modalities for malignancies, including checkpoint inhibitors and antigen-reactive T cells. Recent discoveries are also uncovering the depth and variability of T cell phenotypes: while T cells have long been described using a subset-based classification system, next-generation sequencing technologies suggest an astounding degree of complexity and heterogeneity at the single cell level.