These findings directly parallel the on‐target but off‐tumor B‐cell aplasia observed with targeting the hematologic shared tumor/tissue‐differentiation antigen CD19 using CARs.34 Taken together, these results emphasize the critical need to develop TCRs specific for antigens that are selectively, if not exclusively, expressed by cancer cells and not essential normal tissues. The gene discussed is CD19; the disease is neoplasm.