FCGR1A and Burkitt lymphoma: In addition, H22(Null)-dPBD killed THP-1 cells to the same extent as H22(IgG1)-dPBD, whereas neither H22(IgG1)-dPBD nor H22(Null)-dPBD had any cytotoxic activity against Ramos cells, a Burkitt’s lymphoma cell line that does not express CD64 (Figures 2B, C), suggesting that H22-dPBD functions in a CD64-specific manner.