PDCD1 and B-cell chronic lymphocytic leukemia: Conversely, other reports highlighted that PD-1 expression is increased on proliferating compared with non-proliferating T cells and that its activation suppresses IFN-γ secretion by CD8+ T cells, while maintaining IL-4 secretion by CD4+ lymphocytes relatively unaffected and contributing to the overall Th2 skewing of T-cell responses observed in CLL patients [58].