Morphological and cytochemical characteristics of leukaemic promyelocytes

Atypical Rearrangements in APL-Like Acute Myeloid Leukemias: Molecular Characterization and Prognosis

Acute promyelocytic leukemia (APL) accounts for 10–15% of newly diagnosed acute myeloid leukemias (AML) and is typically caused by the fusion of promyelocytic leukemia with retinoic acid receptor α (RARA) gene. The prognosis is excellent, thanks to the all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) combination therapy. A small percentage of APLs (around 2%) is caused by atypical transcripts, most of which involve RARA or other members of retinoic acid receptors (RARB or RARG). The diagnosis of these forms is difficult, and clinical management is still a challenge for the physician due to variable response rates to ATRA and ATO. Herein we review variant APL cases reported in literature, including genetic landscape, incidence of coagulopathy and differentiation syndrome, frequent causes of morbidity and mortality in these patients, sensitivity to ATRA, ATO, and chemotherapy, and outcome. We also focus on non-RAR rearrangements, complex rearrangements (involving more than two chromosomes), and NPM1-mutated AML, an entity that can, in some cases, morphologically mimic APL.

Current first- and second-line treatment options in acute promyelocytic leukemia

Outcome of acute promyelocytic leukemia (APL) has remarkably improved during the last 30 years, especially after the identification of PML-RARA oncogene as a key in the pathogenesis of APL and all-trans retinoic acid as therapeutic agent. Arsenic trioxide has been recently demonstrated to be the most effective single antileukemic agent and it has also showed synergistic action when combined with all-trans retinoic acid, decreasing relapse rate especially in low/intermediate-risk settings. Therapeutic advances led to complete remission rates of more than 90%, modifying disease history. In relapse setting, arsenic trioxide-based regimens showed efficacy for the achievement of second molecular complete remission. The most challenging issue in APL management remains the significant early deaths rate, nowadays the principal reason for treatment failure.

Acute myeloid leukemia with t(16;16) (p13;q22) showing a new CBFB-MYH11 fusion transcript associated with an atypical leukemic blasts morphology

Acute myeloid leukemia (AML) cases with inv(16)(p13q22) or t(16;16)(p13;q22) are characterized by multiple CBFB-MYH11 fusion transcripts, type A being the most frequent. Rare fusion variants are frequently correlated with an atypical cytomorphology, but their biologic and prognostic significance is unclear. We report a case of acute myeloid leukemia with a balanced t(16;16)(p13;q22) and additional monosomy 13 showing a new CBFB-MYH11 fusion transcript variant. The patient also showed an atypical morphology of bone marrow blasts, since about 15% of all blasts showed bilobed nuclei but there was no pathologic eosinophilia. The biologic and prognostic implications of this rare association are discussed.

Flow cytometric immunobead assay for fast and easy detection of PML-RARA fusion proteins for the diagnosis of acute promyelocytic leukemia

The PML–RARA fusion protein is found in approximately 97% of patients with acute promyelocytic leukemia (APL). APL can be associated with life-threatening bleeding complications when undiagnosed and not treated expeditiously. The PML–RARA fusion protein arrests maturation of myeloid cells at the promyelocytic stage, leading to the accumulation of neoplastic promyelocytes. Complete remission can be obtained by treatment with all-trans-retinoic acid (ATRA) in combination with chemotherapy. Diagnosis of APL is based on the detection of t(15;17) by karyotyping, fluorescence in situ hybridization or PCR. These techniques are laborious and demand specialized laboratories. We developed a fast (performed within 4–5 h) and sensitive (detection of at least 10% malignant cells in normal background) flow cytometric immunobead assay for the detection of PML–RARA fusion proteins in cell lysates using a bead-bound anti-RARA capture antibody and a phycoerythrin-conjugated anti-PML detection antibody. Testing of 163 newly diagnosed patients (including 46 APL cases) with the PML–RARA immunobead assay showed full concordance with the PML–RARA PCR results. As the applied antibodies recognize outer domains of the fusion protein, the assay appeared to work independently of the PML gene break point region. Importantly, the assay can be used in parallel with routine immunophenotyping for fast and easy diagnosis of APL.

The biological characteristics of adult CD34+ acute promyelocytic leukemia

We aimed to explore the expression of CD34 and its impact on the disease outcome in patients with APL. The study comprised 40 de novo APL patients. Diagnostic tools included peripheral blood and bone marrow morphology and cytochemistry, immunophenotyping, cytogenetic studies, and PML/RARα fusion gene detection using RT-PCR. CD34 was expressed in 13 (32.5%) of cases with higher expression in M3v compared to M3 subtype. All M3v cases were CD34+, while only 7.4% of M3 cases were CD34+. CD34+ cases were associated with significant higher white blood cell count and peripheral blood promyelocytes. No significant association was found between PML/RAR-α isoform and molecular remission. CD34+ expression was significantly associated with decreased incidence of molecular remission and increased incidence of early death. The overall survival of patients with WBC count >11 × 103/μl was inferior to patients with WBC count <11 × 103/μl, but no significant differences were observed in overall survival between CD34- and CD34+ or between bcr1 and bcr3 groups. Immunophenotypic analysis for CD34 could distinguish an APL subset with different biological characteristics and adverse prognostic outcome.

Detection of fusion genes at the protein level in leukemia patients via the flow cytometric immunobead assay

Nowadays, the presence of specific genetic aberrations is progressively used for classification and treatment stratification, because acute leukemias with the same oncogenetic aberration generally form a clinically and diagnostically homogenous disease entity with comparable prognosis. Many oncogenetic aberrations in acute leukemias result in a fusion gene, which is transcribed into fusion transcripts and translated into fusion proteins, which are assumed to play a critical role in the oncogenetic process. Fusion gene aberrations are detected by karyotyping, FISH, or RT-PCR analysis. However, these molecular genetic techniques are laborious and time consuming, which is in contrast to flow cytometric techniques. Therefore we developed a flow cytometric immunobead assay for detection of fusion proteins in lysates of leukemia cell samples by use of a bead-bound catching antibody against one side of the fusion protein and fluorochrome-conjugated detection antibody. So far, we have been able to design such fusion protein immunobead assays for BCR-ABL, PML-RARA, TEL-AML1, E2A-PBX1, MLL-AF4, AML1-ETO and CBFB-MYH11. The immunobead assay for detection of fusion proteins can be performed within 3 to 4 hours in a routine diagnostic setting, without the need of special equipment other than a flow cytometer. The novel immunobead assay will enable fast and easy classification of acute leukemia patients that express fusion proteins. Such patients can be included at an early stage in the right treatment protocols, much faster than by use of current molecular techniques. The immunobead assay can be run in parallel to routine immunophenotyping and is particularly attractive for clinical settings without direct access to molecular diagnostics.

Does microgranular variant morphology of acute promyelocytic leukemia independently predict a less favorable outcome compared with classical M3 APL? A joint study of the North American Intergroup and the PETHEMA Group

Few studies have examined the outcome of large numbers of patients with the microgranular variant (M3V) of acute promyelocytic leukemia (APL) in the all-trans retinoic acid era. Here, the outcome of 155 patients treated with all-trans retinoic acid-based therapy on 3 clinical trials, North American Intergroup protocol I0129 and Programa para el Estudio de la Terapéutica en Hemopatía Maligna protocols LPA96 and LPA99, are reported. The complete remission rate for all 155 patients was 82%, compared with 89% for 748 patients with classical M3 disease. The incidence of the APL differentiation syndrome was 26%, compared with 25% for classical M3 patients, and the early death rate was 13.6% compared with 8.4% for patients with classical M3 morphology. With a median follow-up time among survivors of 7.6 years (range 3.6-14.5), the 5-year overall survival, disease-free survival, and cumulative incidence of relapse for patients with M3V were 70%, 73%, and 24%, respectively. With a median follow-up time among survivors of 7.6 years (range 0.6-14.3), the 5-year overall survival, disease-free survival, and cumulative incidence of relapse among patients with classical M3 morphology were 80% (P = .006 compared with M3V), 81% (P = .07), and 15% (P = .005), respectively. When outcomes were adjusted for the white blood cell count or the relapse risk score, none of these outcomes were significantly different between patients with M3V and classical M3 APL.

Leukemic transformation by the APL fusion protein PRKAR1A-RARα critically depends on recruitment of RXRα

PRKAR1A (R1A)–retinoic acid receptor-α (R1A-RARα) is the sixth RARα–containing fusion protein in acute promyelocytic leukemia (APL). Using the murine bone-marrow retroviral transduction/transformation assay, we showed that R1A-RARα fusion protein could transform bone-marrow progenitor/stem cells. In gel-shift assays, R1A-RARα was able to bind to a panel of retinoic acid response elements both as a homodimer and as a heterodimer with RXRα, and demonstrated distinct DNA-binding characteristics compared with wild-type RARα/RXRα or other X-RARα chimeric proteins. The ratio of R1A-RARα to RXRα proteins affected the retinoic acid response element interaction pattern of R1A-RARα/RXRα complexes. Studies comparing R1A-RARα with R1A-RARα(ΔRIIa) demonstrated that the RIIa protein interaction domain located within R1A was responsible for R1A-RARα homodimeric DNA binding and interaction with wild-type R1A protein. However, the RIIa domain was not required for R1A-RARα–mediated transformation because its deletion in R1A-RARα(ΔRIIa) did not compromise its transformation capability. In contrast, introduction of point mutations within the RARα portion of either R1A-RARα or R1A-RARα(ΔRIIa), previously demonstrated to eliminate RXRα interaction or treatment of transduced cells with RXRα shRNA or a RXRα agonist, reduced transformation capability. Thus, leukemic transformation by APL fusion protein PRKAR1A-RARα is critically dependent on RXRα, which suggests RXRα is a promising target for APL.

Partial characterization of feline myeloperoxidase and investigation of its potential role as an autoantigen in hyperthyroid cats

OBJECTIVE

To partially characterize the cDNA, amino acid sequence, and tertiary structure of feline myeloperoxidase, describe its cellular location in mature granulocytes, and determine whether hyperthyroid cats have anti-myeloperoxidase antibody.

SAMPLE POPULATION

Bone marrow RNA and whole blood from cats of various sources and feline serum samples submitted for measurement of total thyroxine concentration from September 2006 to July 2007.

PROCEDURES

Feline myeloperoxidase cDNA was amplified from bone marrow RNA; presumptive splice sites were determined by comparison with human sequences. Intracellular localization of myeloperoxidase in granulocytes was determined by use of immunofluorescence and electron microscopy, and molecular weight and partial tertiary structure were determined by use of immunoblotting of granulocyte lysates. Anti-human myeloperoxidase (hMPO) antibody was detected via ELISA.

RESULTS

A 2,493-bp sequence encompassing the 2,160-bp cDNA with presumably the same number and size of exons as hMPO was generated. Translation predicted 85% homology with hMPO. Feline myeloperoxidase was localized to neutrophil primary granules, and immunoblotting revealed heavy and light bands with molecular weights similar to those of hMPO. The prevalence of anti-hMPO antibody did not differ between nonhyperthyroid and hyperthyroid cats or among hyperthyroid cats subclassified by treatment modality.

CONCLUSIONS AND CLINICAL RELEVANCE

Moderate homology existed between feline myeloperoxidase and hMPO cDNA and protein. Although findings suggested a similar tertiary structure and function for the 2 proteins, they also suggested that inability to detect a high prevalence of anti-hMPO antibody in hyperthyroid cats may be attributable to antigenic differences between the human and feline proteins rather than a lack of autoantibody.