CD4 and B-cell chronic lymphocytic leukemia: Although differences in basal pSTAT5 levels between the two subsets were much higher in some patients treated with ibrutinib compared to both healthy controls and untreated patients with advanced CLL, a significant increase in ∆pSTAT5 relative to Tcon cells was found only in the FOXP3+ subset of CD4+ T-cells from patients treated with CIT.