Anti-CD33 monoclonal antibody, clone IJN4-5 [CF405M]

Neonatal congenital leukemia (CL) constitutes less than 1% of all childhood leukemia cases and is diagnosed in 1 to 5 per million live births. In the neonatal period acute myeloid leukemia (AML) is described in 56-64% of cases, acute lymphoblastic leukemia (ALL) in 21-38% of cases and mixed-phenotype acute leukemia (MPAL) in less than 5% of cases. Rearrangements of the mixed-lineage leukemia (KMT2A alias MLL) gene are found in > 70% of infant leukemia cases. The incidence of the most frequent KMT2A rearrangements in newborns with congenital MPAL is unknown. We report a male term newborn with "blueberry muffin" syndrome, which had been noted at birth, as a presenting sign of acute leukemia. Eight-color multiparameter flow cytometry showed a blast population corresponding to a myeloid lineage with monocytic differentiation positive for CD33+/CD15+/CD11+/CD64+/HLA-DR+/CD4+, negative for MPO-/CD34-/CD19-/CD79a-/CD117-/CD13-/CD14-/CD36-/cCD3-/CD2-/CD7-, and additionally positive for sCD3 (40%). Mixed-phenotype acute leukemia according to the World Health Organization (WHO) classification was diagnosed with complex translocation t(10;11)(p12;q23) with KMT2A/MLLT10 rearrangement. The patient had an unfavorable response to chemotherapy and died on the 5th day of life.

Background Acute myeloid leukemia (AML) is a hematopoietic malignancy which is biologically, phenotypically and genetically very heterogeneous. Outcome of patients with AML remains dismal, highlighting the need for improved, less toxic therapies. Chimeric antigen receptor T-cell (CART) immunotherapies for patients with refractory or relapse (R/R) AML are challenging because of the absence of a universal pan-AML target antigen and the shared expression of target antigens with normal hematopoietic stem/progenitor cells (HSPCs), which may lead to life-threating on-target/off-tumor cytotoxicity. CD33-redirected and CD123-redirected CARTs for AML are in advanced preclinical and clinical development, and they exhibit robust antileukemic activity. However, preclinical and clinical controversy exists on whether such CARTs are myeloablative. Methods We set out to comparatively characterize in vitro and in vivo the efficacy and safety of 41BB-based and CD28-based CARCD123. We analyzed 97 diagnostic and relapse AML primary samples to investigate whether CD123 is a suitable immunotherapeutic target, and we used several xenograft models and in vitro assays to assess the myeloablative potential of our second-generation CD123 CARTs. Results Here, we show that CD123 represents a bona fide target for AML and show that both 41BB-based and CD28-based CD123 CARTs are very efficient in eliminating both AML cell lines and primary cells in vitro and in vivo. However, both 41BB-based and CD28-based CD123 CARTs ablate normal human hematopoiesis and prevent the establishment of de novo hematopoietic reconstitution by targeting both immature and myeloid HSPCs. Conclusions This study calls for caution when clinically implementing CD123 CARTs, encouraging its preferential use as a bridge to allo-HSCT in patients with R/R AML.