IL21 and infection: We report that recovery of functional CD4+ T‐cell pathogen responses occurs 9‐ to 12 month post‐alloHSCT and, based on antigen‐specific in vitro responses, identify a panel of cytokines (IFN‐γ, IL‐1β, IL‐4, IL‐6, IL‐17, IL‐21 and IL‐31), with potential for immune‐profiling and infection risk prediction.