CD37 and B-cell chronic lymphocytic leukemia: While the impact of Fcγ receptor engagement cannot be completely ruled out, particularly in regard to cytotoxicity in CLL B-cells which express FcγRIIb, the pre-B 697 cell line used for mutant CD37 studies is unlike mature B-cells in that it lacks FcγRII (Suzuki et al., 2002; Lapalombella et al., 2012).