- This study investigates the combination of ibrutinib, fludarabine and pembrolizumab for treatment of CLL. Fludarabine is a well-tolerated drug that has been used widely to treat CLL. Also, fludarabine can kill both malignant B cells and T cells that support the growth of leukemia cells. Pembrolizumab targets immune checkpoint molecules and enhances the cell-killing activity of T cells. With this approach we hope to achieve a greater reduction in CLL cells than with single agent ibrutinib and to restore healthier immune system that could contribute to durable responses.