CD33 and acute myeloid leukemia: To create CD33 | CD16b Tmod constructs, we began with a set of 4 CD33 CARs (CAR1-4) that were sensitive enough to respond to CD33 in AML-derived cell lines and two other cells lines (HeLa and K562) transfected with CD33 mRNA (Supplementary Figure 2; see Methods).