Rapid proliferation of CD22 negative leukemic cells after inotuzumab ozogamicin therapy for relapsed acute lymphoblastic leukemia

We report the case of a 48-year-old woman with relapsed B-lineage acute lymphoblastic leukemia(B-ALL)following cord blood transplantation, in which leukemic cell CD22 antigens became negative after a single administration of inotuzumab ozogamicin(InO).At relapse, a major part of leukemic cells expressed CD19 and CD22 antigens, however some leukemic cells were negative for CD22. As treatment with blinatumomab proved ineffective, InO therapy was subsequently initiated