In the clinical study by Chellappa et al. analysis of blood samples of idelalisib-treated CLL patient showed a reduced frequency of KI-67 expressing, proliferating CD8+ effector T-cells during idelalisib treatment for two out of three patients (136), suggesting that PI3Kδ inhibition might not be beneficial for CD8+ T-cell mediated tumor control as well as their clearance of pathogens. Here, CD8A is linked to B-cell chronic lymphocytic leukemia.