CTLA4 and B-cell chronic lymphocytic leukemia: The expression of miR-155 and miR-34a is significantly increased in CLL cells, affecting the expression of cell cycle regulatory proteins, costimulatory receptors, and immune checkpoints, such as PD-1 (programmed death receptor 1) and CTLA-4 (cytotoxic T-lymphocyte-associated antigen-4), which may lead to immunosuppression and tumor escape from the immune system.