ALBERT

Description: Introduction: Myeloid malignant disorders are clonal diseases arising in hematopoietic stem or progenitor cells. Several somatic mutations involved in these diseases are currently known and routine molecular testing involves screening genes of therapeutic and prognostic significance. Mutational analysis of FLT3 in combination with NPM1 can be used to predict outcome and direct therapy in normal karyotype acute myeloid leukemia (AML). JAK2, MPL and CALR mutation detection complements the molecular diagnostic testing menu for myeloproliferative neoplasm’s (MPN): polycytemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). In addition, these molecular markers are utilized for minimal residual disease (MRD) detection, e.g. following stem cell transplants. Little is currently known about the lineage-specific distribution of some of these markers. In this study we aimed to assess the distribution of common genetic mutations in multiple lineages (lymphoid, myeloid, monocyte, multipotent progenitors, myeloblast and erythroid) of MPN and AML utilizing fluorescent activated cell sorting (FACS). Method: Different cell lineage fractions (lymphoid (CD3+), mature (CD16+) and immature (CD16dim) granulocytes, monocyte (CD14+), erythroid(CD36+), multipotent progenitors (34+) and/ or myeloblasts (CD117+) of unseparated bone marrow and peripheral blood specimens of myeloid disorders were sorted on a BD Aria 2. The patient specimens selected were positive for either JAK2V617F, MPLW515L or CALR Exon9 insertion/ deletion (MPN’s) or for NPM1 and/or FLT3 mutations (AML; diagnostic, relapse and minimal residual disease (MRD)). Fractions were subsequently analyzed for the presence of the respective mutation by PCR and/ or bi- directional sequencing. Results: All FACS purified CD34+ progenitors, myeloid and erythroid cell fractions of MPL W515L (3) or CALR exon9 (12) positive MPN specimens demonstrated the presence of mutations, respectively. Interestingly, JAK2V617F was present in the sorted erythroid cell fraction in 5/6 MPN cases tested. However, the granulocyte cell and blast cell fraction of one polycythemia vera specimen tested negative for the presence of Jak2V617F. All lymphoid CD3+ T-cell fractions were negative. The NPM1 exon 12 mutation was uniformly detected in progenitors and all myeloid cell fractions of 3/3 diagnostic, 2/2 relapse and 1/8 MRD AML specimens. For 5/8 MRD cases all lineages tested negative. Surprisingly, for two MRD cases the mutation was observed only in the unseparated and myeloid lineages but not in CD34+ blast fraction. Similar to the above findings, FLT3 mutations were detected in multipotent progenitors, and/ or myeloblasts collections of 4/4 diagnostic specimens. However, the mutation was absent in the granulocyte and monocyte fraction of one case. No detectable signals were observed in the cell fractions of 5 MRD specimens and in the CD3+ lymphoid cell fractions of all AML cases. Conclusion: We conclude that CALR and MPL mutations are uniformly detectable in the unseparated bone marrow specimens of MPN’s as well as separated progenitor, erythroid, granulocyte and monocyte fractions. Interestingly, JAK2 mutations can be exclusively found in the erythroid lineage in PV, whereas it can be absent in the granulocyte and blast compartment. This finding may have implications on specimen processing to ensure that erythroids are retained for clinical Jak2 testing. In addition, our results support the hypothesis that CALR Exon9 mutations are early event driver mutations in comparison to JAK2V167F. Both NPM1 and FLT3 mutations, in AML, were detected in unseparated specimens as well as in the multipotent progenitors or myeloblasts at diagnosis and relapse. However, the NPM1 mutation was observed in unseparated specimens and granulocyte cell fractions of 2 residual disease cases, whereas it was surprisingly absent in the CD34+ cell lineage fractions. Conversely, FLT3-ITD was exclusively found in the progenitor cells and absent in the granulocyte lineage of one case at diagnosis. Our findings reported here may be able to assist assay development efforts for diagnostic and residual disease mutation detection in myeloid disorders. In addition, flow cytometric assessment of monitoring specimens prior to molecular analysis may be beneficial to decide if cell enrichment steps can give additional evidence for the presence of residual disease. Disclosures Burnworth: HematoLogics Inc.: Employment. Bennington:HematoLogics Inc.: Employment. Fritschle:HematoLogics Inc.: Employment. Nguyen:HematoLogics Inc.: Employment. Verkamp:HematoLogics Inc.: Employment. Angela:Hematologics: Employment. Wentzel:HematoLogics Inc.: Employment. Broderson:HematoLogics Inc.: Employment. Loken:Hematologics: Employment, Equity Ownership. Wells:HematoLogics Inc.: Employment, Equity Ownership. Zehentner:HematoLogics Inc.: Employment, Equity Ownership.

Description: Children with neurofibromatosis type 1 (NF1) carry germline mutations in one allele of the NF1 gene and are predisposed to myeloid malignancies, particularly juvenile myelomonocytic leukemia (JMML). Disruption of the remaining NF1 allele can be found in malignant cells. Flow cytometric cell sorting techniques to isolate the malignant cell populations and molecular genetic methods to assay for somatic loss of the normal NF1 allele were used to study an unusual child with NF1 and JMML who subsequently had T-cell lymphoma. The data show that malignant JMML and lymphoma cells share a common loss of genetic material involving the normal NF1gene and approximately 50 Mb of flanking sequence, suggesting that the abnormal T-lymphoid and myeloid populations were derived from a common precursor cell. These data support the hypothesis that JMML can arise in a pluripotent hematopoietic cell.

Description: CD33 is expressed on leukemic blasts of most patients with acute myeloid leukemia (AML) and is the target for gemtuzumab ozogamicin (GO), a toxin-conjugated anti-CD33 monoclonal antibody. CD33 expression of leukemic blasts was prospectively quantified within the context of COG AAML0531, a phase III randomized study for de novo AML in which patients were randomized to receive conventional chemotherapy (Arm A) vs. GO + conventional chemotherapy (Arm B) to determine the impact of CD33 expression on outcome within the context of this GO randomization. CD33 mean fluorescent intensity (MFI) of leukemic blasts was prospectively quantified in 825 diagnostic specimens. Patients were divided into quartiles (Q1-Q4) based on CD33 expression values and these levels were correlated with disease characteristics and outcome by treatment arm for the total study cohort and by cytogenetic/molecular disease risk-group. Analysis of 3 year outcome by treatment arm (N= 412 for Arm A vs. N=414 for Arm B) demonstrated that patients with high CD33 expression (Q4) in Arm A (no GO) had an overall survival (OS) from diagnosis of 55% vs. 70% for those with lower CD33 expression (Q1-3, P=.014) with a corresponding disease-free survival (DFS) from complete remission (CR) of 41% and 57%, respectively (P=.010). In contrast, for the patients in Arm B (receiving GO therapy) those with and without high CD33 expression had a similar OS from diagnosis (67% vs. 72%, P=.290) with a corresponding DFS from CR of 57% vs. 64%, respectively (P=.255). Comparison of the patients with the highest CD33 expression (Q4) who were treated with (N=105) and without (N=101) GO demonstrated that those who received GO had an OS from diagnosis of 67% versus 55% (P=.196) with a corresponding DFS from CR of 57% vs. 41% (P=.052). Analysis by cytogenetic/molecular disease risk group also showed that the effect of CD33 expression levels on outcome differed by treatment arm. Among intermediate risk (IR) patients on Arm A (N=200), those with high CD33 expression (Q4) had an OS from diagnosis of 52% vs. 62% for those with lower CD33 expression (P=0.194) with a corresponding DFS from CR of 28% vs. 53% respectively (P=.012). Conversely, for IR patients treated with GO (N=197), outcomes were similar for patients with high (Q4) and low (Q1-3) CD33 expression (OS from diagnosis of 65% vs. 64%, P=.923, DFS from CR of 50% vs. 53%, P=.687). The loss of prognostic impact of high CD33 expression for patients in Arm B may be due to improved response to GO in those with high CD33 expression (OS of IR patients in Q4 from study entry: Arm A (N=65) 52% vs. Arm B (N=70) 65%, P= .234, DFS from CR of IR patients in Q4: Arm A 28% vs. Arm B 50%, P=.033). Accurate sub analysis of the high-risk (HR) group was not feasible due to the very small number of HR patients with high CD33 expression (Q4) in Arm A (N=9) and Arm B (N=16). Similar trends were, however, observed in the low-risk (LR) group. LR patients with high (Q4) CD33 expression treated on Arm A (no GO) had an OS from diagnosis of 69% vs. 84% for those with lower CD33 expression (P=.092) with a corresponding DFS from CR of 68% vs. 64% respectively (P=0.803). For patients in Arm B (GO) those with and without high CD33 expression had an OS from diagnosis of 94% vs. 86%, respectively (P=.316) with a corresponding DFS from CR of 85% vs. 76% (P=.344). Like IR patients, those LR patients with high CD33 expression (Q4) who received GO trended towards improved outcome compared to Q4 patients treated without GO (LR OS from diagnosis: Arm A 69% vs. Arm B 94%, P= .069, LR DFS from CR: Arm A 68% vs. Arm B 85%, P=.195). However, given the small number of LR patients in Q4 (N= 27 Arm A, N=17 Arm B) we cannot state the significance of this finding with certainty. Taken together our results suggest that, for patients enrolled on AAML0531, high CD33 expression was associated with adverse outcome for those who received standard therapy and GO treatment negated the negative effect of high CD33 expression on clinical outcome for the entire study cohort and in IR and LR patients. This finding may reflect GO’s CD33 dependent mechanism of targeting and the potential for more efficient targeting in the setting of high antigen expression.It is also plausible that repeated exposure to GO, as seen within the context of treatment for all LR and some IR patients (e.g. those that did not undergo hematopoietic stem cell transplant), may also contribute therapeutic benefit within the context of high CD33 expression. Disclosures: No relevant conflicts of interest to declare.

Description: Key Points Coexpression of NUP98/NSD1 and FLT3/ITD in AML is associated with very low complete remission rates and poor survival. It is the interaction between NUP98/NSD1 and FLT3/ITD that determines poor outcome in NUP98/NSD1-associated AML.