CD19 and cancer: While the CD19-CAR T cells retargeted by the CD19-4D5scFv protein lysed ErbB2+ cancer cells with similar efficacy as the ErbB2-CAR T cells, we found a substantially lower toxicity against the healthy fibroblasts at the CD19-4D5scFv protein doses that were still effective for mediating the ErbB2+ cancer cell killing.