This study evaluates the safety and efficacy of CAR-modified natural killer (NK) cells in patients with relapsed or refractory CD19-positive cancers. The trial involved 11 patients who received HLA-mismatched anti-CD19 CAR-NK cells derived from cord blood. The cells were transduced with a retroviral vector encoding the anti-CD19 CAR, interleukin-15, and inducible caspase 9 as a safety switch. The cells were expanded ex vivo and infused at three doses after lymphodepleting chemotherapy. The results showed that CAR-NK cell infusion was well-tolerated, with no significant toxic effects such as cytokine release syndrome, neurotoxicity, or graft-versus-host disease. Eight out of 11 patients (73%) had a response, including seven with complete remission. The infused CAR-NK cells expanded and persisted at low levels for at least 12 months. The study suggests that CAR-NK cells may be a promising alternative to CAR T cells for treating CD19-positive cancers, offering a safer and more accessible treatment option.This study evaluates the safety and efficacy of CAR-modified natural killer (NK) cells in patients with relapsed or refractory CD19-positive cancers. The trial involved 11 patients who received HLA-mismatched anti-CD19 CAR-NK cells derived from cord blood. The cells were transduced with a retroviral vector encoding the anti-CD19 CAR, interleukin-15, and inducible caspase 9 as a safety switch. The cells were expanded ex vivo and infused at three doses after lymphodepleting chemotherapy. The results showed that CAR-NK cell infusion was well-tolerated, with no significant toxic effects such as cytokine release syndrome, neurotoxicity, or graft-versus-host disease. Eight out of 11 patients (73%) had a response, including seven with complete remission. The infused CAR-NK cells expanded and persisted at low levels for at least 12 months. The study suggests that CAR-NK cells may be a promising alternative to CAR T cells for treating CD19-positive cancers, offering a safer and more accessible treatment option.