The responses of naive CD4+ T cells to high dose IL-7 correlated with absolute CD4+ T cell counts in ICL patients (Fig. S2E, RICL = 0.65, p<0.05), emphasizing the relevance of impaired IL-7 responses in the loss of CD4+ T cell homeostasis characteristic of ICL. Here, IL7 is linked to idiopathic CD4 lymphocytopenia.