CD4 and cystic fibrosis: Specifically, we showed that CF patients can stratify CF into two groups based on Treg frequencies, CD4+ T cell surface phenotype (CD25 and CTLA-4) and cytokine production by CD4+/CD8+ T cells (IFNγ, TNFα, CD107a, and IL-2), with at-risk patients exhibiting a distinct deficiency in TNFα.