Interesting Gizmag article on Ibrutinib with some good background on how lymphocytes work and how CLL and MCL differ. (Ibrutinib trials were done on both).
It is worth looking through the associated pictures. The first explains well how B and T cells work together to clear infections and give future immunity from reinfection. Either click on View All or use this link:
Note that the last image is of a lymphoma cell mass, not a lymphoma cell.