Human Vδ2 T cells are a major source of interleukin-9

V delta 2V gamma 9 T cells are the dominant gamma delta T-cell subset in human peripheral blood. V delta 2 T cells recognize pyrophosphate molecules derived from microbes or tumor cells; hence, they play a role in antimicrobial and antitumor immunity. TGF-beta, together with IL-15, induces a regulatory phenotype in V delta 2 T cells, characterized by forkhead box protein P3 (FoxP3) expression and suppressive activity on CD4 T-cell activation. We performed a genome-wide transcriptome analysis and found that the same conditions (TGF-beta plus IL-15) strongly enhanced the expression of additional genes in V delta 2 T cells, including IKAROS family zinc finger 4 (IKZF4; Eos), integrin subunit alpha E (ITGAE; CD103/ alpha E beta 7), and IL9. This up-regulation was associated with potent IL-9 production as revealed by flow cytometry and multiplex analysis of cell culture supernatants. In contrast to CD4 and CD8 alpha beta T cells, gamma delta T cells did not require IL-4 for induction of intracellular IL-9 expression. Upon antigen restimulation of V delta 2 T cells expanded in vitro in the presence of TGF-beta and IL-15, IL-9 was the most abundant among 16 analyzed cytokines and chemokines. IL-9 is a pleiotropic cytokine involved in various (patho) physiological conditions, including allergy and tumor defense, where it can promote antitumor immunity. Given the conspicuous sensitivity of many different tumors to V delta 2 T-cell-mediated killing, the conditions defined here for strong induction of IL-9 might be relevant for the development of V delta 2 T-cell-based immunotherapy.