CD22 and graft versus host disease: With the administration of Tandem CAR-T cells co-targeting CD22 and CD19 (CD22/CD19-targeted scFv-CD137/CD3ζ) after hematopoietic stem cell transplantation (HSCT), more than 14 months of minimal residual disease (MRD)-negative complete remission (CR) was achieved; the patient developed graft-versus-host disease (GVHD), which is clinically manageable.