CD22 and acute lymphoblastic leukemia: To observe the treatment response of a two-dose regimen of inotuzumab ozogamicin(inotuzumab), a monoclonal antibody targeting CD22, for patients with heavily treated relapsed/refractory B-cell acute lymphoblastic leukemia(R/R B-ALL), including those failed or relapsed after chimeric antigen receptor(CAR)-T-cell therapy.