High-dose cytarabine plus gemtuzumab ozogamicin as consolidation therapy in patients with favorable- or intermediate-risk acute myeloid leukemia.

Previous prospective randomized trials have investigated the efficacy of gemtuzumab ozogamicin in the frontline treatment of acute myeloid leukemia (AML). We evaluated the efficacy of high-dose cytarabine with GO as consolidation therapy in 20 patients with favorable- or intermediate-risk AML in first complete remission. They included six patients with wild-type nucleophosmin (NPM1) core binding factor (CBF), ten with NPM1-mutated non-CBF, and four with wild-type NPM1 non-CBF. The median follow-up for the entire cohort was 62.0 months. The three-year overall survival (OS) and relapse-free survival (RFS) rates were 72.2% and 77.8%, respectively. OS and RFS were significantly higher for NPM1-mutated non-CBF AML than for wild-type NPM1 non-CBF AML (p = 0.001). We also examined the CD33 single-nucleotide polymorphism (SNP) rs12459419, which has been reported to influence the therapeutic efficacy of GO and CD33 expression. The CD33 expression ratio was higher in CD33 SNP C/C than in C/T (83.1% vs. 49.8%, p = 0.035), but 3-year OS and RFS did not differ significantly. These results suggest that consolidation therapy with high-dose cytarabine plus GO is highly effective in transplant-ineligible elderly patients and may be a reasonable treatment, especially for NPM1-mutated AML.

CRISPR/Cas9 gene editing clarifies the role of CD33 SNP rs12459419 in gemtuzumab ozogamicin-mediated cytotoxicity.

The single-nucleotide polymorphism (SNP) rs12459419 is located at the intron/exon junction of CD33 exon2. When exon2 is skipped by this CD33 SNP, the full-length CD33 (CD33FL) is converted to a short CD33 isoform (CD33D2). Since gemtuzumab ozogamicin (GO) only recognizes CD33FL, the CD33 SNP may affect the clinical efficacy of GO. To elucidate the significance of CD33 SNP on GO reactivity, we leveraged the CRISPR/Cas9 genome-editing system to create OCI-AML3 cell lines with specifically modified CD33 SNPs. Levels of CD33 D2 mRNA were significantly higher in the T/T clone (p < 0.001), but CD33D2 protein was not detectable in any clones. There was no significant difference in CD33FL mRNA expression across edited clones, and CD33FL protein expression was lowest in T/T clones, followed by T/C and C/C. Cytotoxicity assays revealed that the IC50 of GO was significantly lower in T/C and C/C clones than in the T/T clone (p < 0.001). Our study demonstrated a difference in GO-induced cytotoxicity in CD33 SNP-edited clones, clearly indicating that at least one CD33 SNP allele, rs12459419 C, is important for sensitivity to GO.

[Successful induction therapy for acute myeloid leukemia under management with extracorporeal membrane oxygenation].

A 53-year-old woman presented with shortness of breath and hyperleukocytosis and was admitted to our hospital. Shortly after, she went into cardiopulmonary arrest and was resuscitated. Her white blood cell count was 566,000/µl, with 94.5% cup-like blasts positive for MPO staining and FLT3-ITD positive, so she was diagnosed with acute myeloid leukemia (AML) M1. She also had disseminated intravascular coagulation and tumor lysis syndrome. Extracorporeal membrane oxygenation (ECMO) was started to manage bilateral pulmonary thromboembolism that had developed due to deep vein thrombosis, and induction therapy was performed under ECMO. On the third day of illness, the patient developed cerebral hemorrhage. Hematological remission was confirmed on the 39th day of illness. After consolidation therapy with chemotherapy and an FLT3 inhibitor, she underwent allogeneic hematopoietic stem cell transplantation, and remains alive. Case reports suggest strong evidence of mortality benefit from ECMO in patients with hematologic malignancies, particularly when ECMO served as a bridge through chemotherapy. Our patient suffered from cardiopulmonary arrest due to hyperleukocytosis and pulmonary thromboembolism, but was saved by induction of remission under ECMO. Improvements in supportive care should lead to reduction in early deaths during induction therapy.

Correlation of ex vivo and in vivo ammonia production with L-asparaginase biological activity in adults with lymphoid malignancies.

Silent inactivation of L-asparaginase (L-Asp) represents rapid clearance of L-Asp by anti-L-Asp IgG antibodies without clinical symptoms. Measurement of L-Asp activity is the gold standard for diagnosis of silent inactivation, but this test is not commercially available in Japan as of 2023. We evaluated ex vivo and in vivo ammonia production in relation to L-Asp activity. Blood samples from ten adult patients treated with L-Asp were collected to measure ammonia levels and L-Asp activity before the first dose and 24 h after the last dose of L-Asp, during each cycle of treatment. Plasma ammonia levels were analyzed immediately and 1 h after incubation at room temperature, and ex vivo ammonia production was defined as the increase in ammonia concentration. Ex vivo ammonia production correlated with L-Asp activity (R2 = 0.741), and ammonia levels measured immediately after blood collection were moderately correlated with L-Asp activity (R2 = 0.709). One patient with extranodal NK/T-cell lymphoma showed an increase in ammonia levels during the first cycle, but no increase in ammonia levels or L-Asp activity after L-Asp administration during the second cycle. Both ex vivo and in vivo ammonia production and surrogate markers are used for L-Asp biological activity.

[FLT3-ITD and NPM1 mutation positive acute myeloid leukemia with cuplike blasts mimicking acute promyelocytic leukemia].

FMS-like tyrosine kinase 3 (FLT3) inhibitors improve the prognosis of FLT3-internal tandem duplication (ITD)-positive acute myeloid leukemia (AML). Case 1 is a 47-year-old male patient who presented with a white blood cell count (WBC) of 95,700/ml with 94% blast accompanied by cuplike nuclei, lactate dehydrogenase (LDH) of 2,434 IU/l, fibrin degradation products (FDP) of 476 mg/ml, and a bone marrow examination that revealed blastic marrow with chromosome 46, XY, positive FLT3-ITD, and positive nucleophosmin 1 (NPM1) mutation type A. Flow cytometry revealed that blasts were positive for CD33 and negative for CD34, CD117, and human leukocyte antigen-DR isotype (HLA-DR). The patient had no response to idarubicin combined cytarabine; however, qiuzartinib administration resulted in the first complete remission. Case 2 is a 71-year-old female patient, who presented with 94,900/ml of WBC with a 91% blast accompanied with cup-like nuclei, LDH of 19,03 IU/l, FDP of 112 mg/ml, and a peripheral blood examination that revealed chromosome 46, XX, positive FLT3-ITD, and positive NPM1 mutation type B. Flow cytometry revealed that blasts were positive for CD33 and negative for CD34, CD117, and HLA-DR. She had a partial response to venetoclax combined with azacytidine, and qiuzartinib administration resulted in the first complete remission. Both cases were CD34- and HLA-DR-negative with disseminated intravascular coagulation mimicking acute promyelocytic leukemia (APL). Additionally, recognizing the cuplike blasts is useful to differentiate FLT3 mutant AML from APL for the proper use of FLT3 inhibitors.