FOLR1 and neoplasm: Future evaluation must address potential on-target, off-tumor toxicity of FOLR1 CAR T cells, as FOLR1 is expressed in healthy tissues (kidney, intestine, lung, retina, placenta, and choroid plexus; ref. 35), and prior studies with a T cell bispecific antibody targeting FOLR1 have demonstrated severe lung toxicity in nonhuman primates (36).