Foxp3, short for forkhead box protein 3, is a member of the forkhead transcription factor family. It is mainly expressed in a subset of CD4+ T-cells, known as regulatory T cells (Tregs), and is crucial for their function. Foxp3 suppresses the function of NFAT and NFκB, leading to the suppression of many genes like IL-2 and effector T-cell cytokines. It also acts as a transcription activator for genes such as CD25, CTLA4, GITR, and folate receptor 4 [2].

In the tumor microenvironment (TME), Tregs expressing Foxp3 impede immune surveillance of tumors and suppress antitumor immune responses [1]. In breast cancer, the increase and decrease of Foxp3+ Tregs seem to correlate with patient survival or prognosis, but the results are controversial, with some studies reporting poor prognosis with Foxp3+ expression and others showing the opposite [3]. In lung cancer, most data suggest that Foxp3 is correlated with an unfavorable prognosis [4].

In conclusion, Foxp3 is essential for the development and function of Tregs, which play a key role in maintaining immune homeostasis. In diseases such as cancer, especially in the context of the TME, Foxp3-expressing Tregs can influence disease prognosis. The study of Foxp3, particularly through in vivo models like KO/CKO mouse models, helps in understanding its role in immune-related diseases and provides potential targets for therapeutic intervention.