Nature 537, 412–428 (2016); doi:10.1038/nature19317 In this Letter, owing to errors introduced by the typesetters, ‘CXCR5+’ should have been ‘CXCR5−’ at two places in the Abstract, to read as follows: “…more potent cytotoxicity than the CXCR5− subset…” and “…greater therapeutic potential than the CXCR5− subset …”.