CD28 and B-cell chronic lymphocytic leukemia: We suggest that the significantly lower CD28 antigen expression on both subsets of unstimulated T cells and its more profound and long-lasting downregulation after stimulation compared with normal controls as observed in our study may deliver a stronger and prolonged stimulus for CD152 induction and expression on the CD3+/CD4+ and CD3+/CD8+ T-cell subpopulations in B-CLL.