The diagnosis of blastic plasmacytoid dendritic cell neoplasm (BPDCN) has been based on the expression status of multiple markers, including CD123. TCF4 was discovered recently to be an obligatory master regulator of plasmacytoid dendritic cells. We postulated that a tissue-based assay designed to detect dual CD123 and TCF4 expression would provide a highly reliable and practical marker for BPDCN in biopsy material. We designed, optimized, and validated a dual-color TCF4/CD123 immunohistochemistry stain for use in formalin-fixed paraffin-embedded tissue sections. The performance characteristics of the TCF4/CD123 stain were evaluated in 48 confirmed BPDCN cases. TCF4/CD123 coexpression was detected reproducibly in plasmacytoid dendritic cells. In BPDCN, the TCF4/CD123 stain showed coexpression in all (48/48; 100%) cases analyzed. Cases with concurrent samples from different anatomic sites showed comparable staining characteristics. In contrast, of 464 non-BPDCN cases comprising a wide range of hematolymphoid neoplasms and cutaneous lesions that might enter in the differential diagnosis of BPDCN, we identified dual expression of TCF4 and CD123 in only 1 case of B-lymphoblastic leukemia/lymphoma. On the basis of these findings, the TCF4/CD123 dual-color immunohistochemical stain had an analytic sensitivity of 100% and a specificity of 99.8%. Receiver operator characteristic analysis demonstrated an area under the curve of 1.000 (95% confidence interval: 0.999-1.000). In summary, the dual-color TCF4/CD123 immunohistochemistry stain provides a robust standalone and cost-effective assay for the diagnosis of BPDCN.

The potential of CD123-targeted therapies in acute lymphoblastic leukemia/lymphoma remains largely unexplored. We examined CD123 expression levels in a large cohort of patients with acute lymphoblastic leukemia/lymphoma and assessed the in vitro impact of IMGN632, a conjugate of CD123-binding antibody with a novel DNA-alkylating payload. CD123 expression on leukemic blasts was surveyed using multicolor/multiparameter flow cytometry. The in vitro effect of IMGN632 was evaluated on B acute lymphoblastic leukemia/lymphoma cell lines and primary B acute lymphoblastic leukemia/lymphoma blasts. The study cohort (n=213) included 183 patients with B acute lymphoblastic leukemia/lymphoma and 30 with T acute lymphoblastic leukemia/lymphoma. CD123 expression was more prevalent in B acute lymphoblastic leukemia/lymphoma than in T acute lymphoblastic leukemia/lymphoma (164/183, 89.6% versus 13/30, 43.3%; P <0.0001), and within B acute lymphoblastic leukemia/lymphoma CD123 expression was more prevalent in Philadelphia chromosome-positive patients than in Philadelphia chromosome-negative patients (96.6% versus 86.3%; P =0.033). In T acute lymphoblastic leukemia/lymphoma, 12/13 (92.3%) patients with CD123-positive blasts had either early T precursor (ETP) or early non-ETP immunophenotype. IMGN632 was highly cytotoxic to B acute lymphoblastic leukemia/lymphoma cell lines, with half maximal inhibitory concentrations (IC 50 ) between 0.6 and 20 pM. In five of eight patients’ samples, low picomolar concentrations of IMGN632 eliminated more than 90% of the B acute lymphoblastic leukemia/lymphoma blast population, sparing normal lymphocytes. In conclusion, CD123 expression is prevalent across acute lymphoblastic leukemia/lymphoma subtypes, and the CD123-targeted antibody-drug conjugate IMGN632 demonstrates promising selective activity in preclinical models of B acute lymphoblastic leukemia/lymphoma.

Hairy cell leukemia-variant is rare. Only a small number of cases have been reported in the literature with little cytogenetic or molecular data available. In this study, we describe the clinicopathologic and genetic features of 23 patients with hairy cell leukemia-variant (16 men and 7 women) with a median age of 70 years. Most patients had splenomegaly (90%), leukocytosis (77%), and lymphocytosis (82%); no patients had monocytopenia. Histologically, the bone marrow biopsy specimens showed a mixed pattern of predominantly interstitial and lesser intrasinusoidal infiltration by leukemic cells. In bone marrow aspirate smears most cells had villous cytoplasmic features and a small nucleolus. We describe unusual sites of hairy cell leukemia-variant involvement in 4 patients, including brain, omentum, terminal ileum, and skin at the time of initial presentation. Immunophenotyping showed monotypic B-cells positive for pan B-cell antigens, CD11c, and CD103, and negative for CD25 and annexin A1. Conventional cytogenetic or fluorescence in situ hybridization analysis showed deletions of 17p13/TP53 and 11q22/ATM gene in 5/12 (42%) and 2/9 (22%) cases, respectively. Sequencing of the variable region of IGVH showed mutations (>2% deviation from germline) in 40% of the cases assessed. MAP2K1 mutation (p.C121S) was seen in 1 of 14 (7%) patients tested. No BRAF V600E mutations were detected. The patients were treated in a heterogeneous manner, but most often with therapies designed for classical hairy cell leukemia and the 5-year overall survival was 84%. In summary, hairy cell leukemia-variant exhibits a heterogeneous spectrum of clinical, morphologic, immunophenotypic, and genetic features that may overlap with classic hairy cell leukemia and other hairy cell-like B-cell neoplasms. A subset of patients can have an aggressive clinical course. In our experience MAP2K1 mutations are uncommon in this disease.

Summary The differential immunophenotypic characteristics of early T precursor (ETP) acute lymphoblastic leukaemia/lymphoma (ALL) remain incompletely characterized. The study group (n = 142) included 106 (74·7%) men and 36 (25·3%) women with a median age of 34·9 years (range, 2–79) at diagnosis. Patients were subtyped by flow cytometry immunophenotyping as follows: 33 (23·2%) ETP; 32 (22·5%) early non‐ETP; 60 (42·2%) thymic; and 17 (12·1%) mature. Excepting definitional markers, there was a significant differential expression of the markers CD2, CD10, CD33 and TdT between ETP‐ALL and non‐ETP‐ALL. Positive CD33 expression (≥20% of leukaemic blasts) was detected in 21/33 (63%) ETP‐ALL compared with 17/95 (17·9%) non‐ETP‐ALL (P < 0·001). Notably, targeted anti‐CD33 therapy with IMGN779 resulted in significant growth inhibition and increased apoptosis in ETP‐ALL cells in vitro. An 11‐marker T‐ALL immunophenotype score discriminated reliably between ETP and non‐ETP ALL. Longitudinal analysis of ETP‐ALL cases in this study demonstrated that the immunophenotype may be occasionally dynamic but is largely stable over the disease course. In summary, identification of ETP‐ALL might be enhanced by using an 11‐marker T‐ALL immunophenotype score. CD33 expression is frequent in ETP‐ALL, and in vitro data suggest that exploring anti‐CD33 therapy in ETP‐ALL is warranted.

Background/Aims: Risk of ischaemic stroke (IS) was associated with total homocysteine (tHCY). On the other hand, serum selenium (Se) exhibited anti-aging and cardiopreventive effects. Se and tHCY showed relationships in animals but these were contradictory or inconclusive in humans; therefore, we searched for such associations in acute IS. Methods: Ninety-four participants aged around 47 years were identified and 39 patients versus 46 healthy controls were analysed. Clinical, laboratory (blinded) and risk factor questionnaire methods were used. Comparison, correlation and multifactorial regression analyses were applied. Results: IS patients were similar to controls concerning age and gender. IS was prevalent in the carotid system (76.9%); 82.1% had a subacute onset. IS patients expressed higher tHCY (14.65 ± 9.79 µmol/l) and lower Se levels (1.3 ± 0.5 µmol/l). Twice as many IS patients (23%) had optimal Se levels of <1.01 µmol/l. Subjects with hyperhomocysteinaemia (tHCY ≧15 µmol/l) showed lower Se levels during IS; Se accounted for 15.4% of tHCY variations (R = –0.393; p = 0.015) with unit change increasing tHCY by 8.25 units. Se remained predictive of tHCY levels after adjustments (vitamin B₆, fibrinogen, triglycerides). Conclusions: Lower Se was observed during acute IS, being inversely associated with and predicting increased tHCY levels. Of note, there were more IS patients with suboptimal Se than controls.