FOXP3 and lymphoproliferative syndrome: Indeed, in mice, invalidating mutations in the Foxp3 gene or specific ablation of Foxp3+ T cells lead to the development of a fatal lymphoproliferative disorder (10–13) and humans with mutations in the FOXP3 gene suffer from the lethal immune-dysregulation polyendocrinopathy enteropathy X linked syndrome (14, 15).