Co‐treatment with IL‐2 is considered to promote the persistence of CD8+ Tregs in patients, as required for ex vivo culture.3, 103, 104, 105, 106, 107 Encouraging results were obtained in HSCT patients treated with low dose IL‐2, expanding a functional CD4+Foxp3+ Treg subset associated with a lower incidence of GVHD while maintaining a low viral infection incidence158, 159 (NCT00539695). This evidence concerns the gene CD4 and graft versus host disease.