CD4+ T cells can differentiate into T helper (Th)1, Th2, Th17, and Regulatory T (Treg) cells by exposure to various cytokines and cellular interactions that induce expression of specific sets of transcription factors. Differentiation into Th1 cells is promoted through IL-12 and IFN-gamma. These cells are characterized by their secretion of IFN-gamma, IL-10, and TNF-alpha. Differentiation into Th2 cells is promoted by IL-4 in combination with either IL-2, IL-7, or TSLP. through IL-12 and IFN-gamma. These cells are characterized by their secretion of IFN-gamma, IL-10, and TNF-alpha. Th2 cells secrete IL-4, IL-5, IL-9, IL-13, and IL17E/IL-25. Differentiation into the Th17 lineage is promoted by cytokines such as TGF-beta and IL-6, while their survival and expansion are dependent on IL-21 and IL-23. Th17 cells secrete TNF-alpha, IL-6, IL-9, IL-17A, IL-17F, IL-21, IL-22, and (human) IL-26/AK155. The ability to differentiate CD4+ T cells ex vivo into Th1, Th2, Th17, or Treg cells is valuable to researchers who require specific T helper cell subsets for downstream applications, including studies for cell therapy and cancer immunotherapy.