ALBERT

Description: Peripheral T-cell lymphomas (PTCLs) are a heterogeneous group of non-Hodgkin lymphomas frequently associated with poor prognosis and for which genetic mechanisms of transformation remain incompletely understood. Using RNA sequencing and targeted sequencing, here we identify a recurrent in-frame deletion (VAV1 Δ778–786) generated by a focal deletion-driven alternative splicing mechanism as well as novel VAV1 gene fusions (VAV1-THAP4, VAV1-MYO1F, and VAV1-S100A7) in PTCL. Mechanistically these genetic lesions result in increased activation of VAV1 catalytic-dependent (MAPK, JNK) and non–catalytic-dependent (nuclear factor of activated T cells, NFAT) VAV1 effector pathways. These results support a driver oncogenic role for VAV1 signaling in the pathogenesis of PTCL.

Description: Abstract 2900 Poster Board II-876 Ph-negative myeloproliferative neoplasms: polycythemia vera (PV), essential thrombocythemia (ET) and primitive myelofibrosis (PMF) carry an acquired somatic mutation JAK2V617F in 95% (PV), and in 50 to 60% (ET or PMF) of the patients. Mutations of the TET2 gene have been observed with roughly similar frequencies in the three MPN, irrespective of the presence of JAK2V617F. Evolution to myelofibrosis or acute leukemia may occur with time in MPN patients. Although its molecular bases are poorly understood, the evolution is likely due to the acquisition of additional mutations. To investigate whether cytogenetic abnormalities are distributed differently according to type of transformation and to the JAK2 and TET2 statuses, the Groupe Francophone de Cytogénétique Hématologique has collected 82 patients with transformation of MPN. There were 66 (80%) acute myeloid leukemia or myelodysplastic syndromes (AML/MDS) and 16 (20%) myelofibroses (MF). Of note pipobroman (Pi) treatment seems to be associated with MF, and hydroxyuera (Hu) with AML/MDS evolution in our series. Statistical analyses of clinical, cytogenetic and molecular data are shown Table 1. On the cytogenetical point of view, several points are noteworthy. Some abnormalities were unevenly distributed: there were significantly more -7/del7q and -5/del5q in AML/MDS and tri1q and tri9 in MF. MF and PMF cytogenetic profile looked similar, suggesting a potential link between cytogenetic markers and the phenotype. Although the derivative chromosome der(1;7), observed in 9 patients, is responsible for a loss of 7q, it seemed different from patients with -7/del7q [excluding der(1;7)]. In the -7/del7q group, AML/MDS patients were more numerous than MF patients and the overall survival was shorter compared with the der(1;7) group (22/22 (100%) vs 6/9 (67%) AML/MDS, p=0.02; median: 4 vs 41 months, p=0.0007 respectively). Some specific associations could be observed, such as 17p deletions with 5q deletion (12/30, 40% vs 4/48, 8%, p=0.0007) and 20q deletion with der(1;7) (4/9 (44%) vs11/69 (16%), p=0.03). We detected 24/40 (60%) JAK2V617F and 8/25 (32%) TET2 mutations in transformed MPN, with all possible combinations between the wildtype and mutated forms of both genes. For one post-ET AML patient, JAK2V617F had been observed in a fraction of the granulocytes at the chronic phase. Analysis of blood cDNA obtained at chronic phase showed the same TET2 mutation as observed at acute phase. Because the blast cells were JAK2wt-TET2mut and carried a t(10;16)(q22;q23) affecting the CBFB gene, it is likely that the resulting non-MYH11 CBFB fusion gene transformed a JAK2wt-TET2 mutated progenitor that predominated in the chronic phase. In conclusion, no specific chromosomal abnormality was associated with TET2 or JAK2 mutations. Chromosomal abnormalities were associated with a type of transformation (AML/MDS or MF), suggesting a specific role in the process. In addition, association between some chromosomal abnormalities suggest a specific oncogenic cooperation.Table 1.n=82AML/MDS n=66 MF n=16 p univariate p multivariate Sex F39 (59%)5 (31%)nsnsPV/ET/PMF30/26/1013/3/0nsnsAge at diagnosis of MPN54 [20-82]55.5 [31-69]nsnsChronic Phase (duration, years)12 [2-34]14.5 [3-28]nsnsPrior treatments (n=73*)57*16..No treatment (n=6)60nsnsOne treatment (n=40)33 (58%)7 (44%)nsnsTreatments with Hu (n=57)48 (73%)9 (56%)0.03Treatments with Pi (n=41)26 (46%)15 (93%)0.00060.05Age at transformation66.5[37-92]68 [45-80]nsnsAbnormal karyotype62 (94%)16 (100%)nsnsComplex karyotype45 (68%)7 (44%)nsns-7/del7q28 (42%)3 (18%)0.07ns-7/del7q[without der(1;7)]22 (33%)00.0040.04-5/del5q28 (42%)2 (12%)0.03ns-13/del13q5 (8%)3 (19%)nsns-20/del20q11 (17%)4 (25%)nsns-17/del17p15 (23%)1(6%)nsns+1q14 (22%)9 (56%)0.01ns+95 (8%)4 (25%)0.04ns+811 (17%)3 (19%)nsnsdic17 (26%)3 (19%)nsnsder(1;7)6 (9%)3 (19%)nsnsAmplification MLL0 (0%)nsnsJAK2mut17/31 (55%)7/9 (78%)nsnsTET2mut6/19 (32%)2/6 (33%)nsnsMedian overall survival (months)448

Description: Introduction Extranodal NK/T-cell lymphoma (ENKTL) is a rare disease; in Western countries it represents less than 1% of all Non-Hodgkin lymphoma. When localized, ENKTL is associated with a good prognosis. In contrast, patients (pts) with a disseminated disease still have a dismal outcome despite the use of asparaginase (ASPA) containing regimens that have significantly improved the prognosis of this lymphoma. Production of neutralizing anti-ASPA antibodies leading to inactivation of the enzyme can reduce its activity. Inactivation of ASPA activity is correlated with a worse prognosis in acute lymphoblastic leukemia (ALL). Monitoring of ASPA activity is therefore recommended in ALL pts with 100 IU/L as threshold value of serum enzymatic activity considered to be sufficient for complete depletion of l-asparagine in serum. However, ASPA monitoring is not routinely performed in pts with ENKTL, despite the frequent use of ASPA-containing regimens. The main objective of this study was to determine the proportion of pts with an insufficient ASPA activity corresponding to production of neutralizing anti-ASPA antibodies, risk of allergic reaction and inefficacy of the drug. Methods Adult pts with histologically confirmed ENKTL who received an ASPA-containing regimen between 2014 and 2018 and had a monitoring of ASPA activity were included. ASPA activity measurement was usually performed with a quantitive enzyme assay 48 hours after the last ASPA injection of each cycle for native forms of ASPA and 14 days after injection of the pegylated form. Activity below 100 UI/L was considered as insufficient. ASPA activity was correlated with pts outcome. The choice of initial form of ASPA and reasons to switch between two forms of ASPA were also analyzed. Results From 2014 to 2018, a total of 21 pts received an ASPA-containing regimen and were monitored for ASPA activity. Median age was 53 years with 14 men and 7 women. More than half of these pts had a stage IV disease (n=11/21), 6 were in stage I and 4 in stage II. Fifteen pts were in first line and 6 pts were in relapse. Pts have received either native e-coli L-asparaginase (Kidrolase®: KID) (n= 13 in the treatment-naïve group, n=2 in the relapsing group) or a pegylated form of e-coli- L-asparaginase (Oncaspar®: ONC) (n=2 in the treatment-naïve group, n=4 in the relapsing group). Most of the pts received ASPA (8 injections at each cycle for native forms and 1 injection for the pegylated form) associated with gemcitabine, methotrexate and dexamethasone, plus oxaliplatine for disseminated diseases. Six pts had optimal ASPA activity, 3/6 had localized disease: 2 had persistent RC and 1 relapsed, 3/6 had a disseminated disease: 2 progressed during treatment and 1 relapsed. Fifteen pts displayed low ASPA activity, 12/15 pts with a KID containing regimen after 1 cycle (n=10) or 3 cycles (n=2) and 3/6 pts with an ONC containing regimen after the first cycle (n=2) or the second (n=1). Among these 3 pts, 2 have been previously treated with KID that could induce an immunization against ONC. Ten pts received a second form of asparaginase: Erwinia asparaginase (Erwiniase®: ERW) in 9 pts and ONC in 1 pt. In 9/10 cases, this switch was justified by detection of low ASPA activity. Measurement of enzymatic activity in these 9 pts showed satisfactory levels in 2/5 pts treated with ERW and monitored for ASPA activity and in the pt receiving ONC, 4/6 pts with a localized form and 1/3 with a disseminated form are in persistent RC. Six pts with low ASPA activity including one case with a localized form and 5 cases with a disseminated disease, did not receive another form of ASPA, they all progressed or relapsed. Conclusion More than 2/3 of pts had sub-optimal ASPA activity after 1 to 3 cycles of ASPA containing regimens. This finding is probably due to the development of anti-ASPA inhibitory antibodies and may explain the poor outcome of pts with a disseminated disease despite the remarkable efficacy of ASPA in this disease. Although the series reported here is small and heterogeneous, our results still suggest a better outcome in pts with good ASPA activity or in case of switch between ASPA molecules in the context of low activity. ASPA activity monitoring should be recommended in pts with ENKTL, to avoid allergic reaction and ineffective treatment by switching ASPA molecules. Pegylated forms of ASPA, or encapsulated in red cells may, be less immunogenic, should be used in the first line setting instead of native forms. Table. Table. Disclosures Bachy: Celgene: Consultancy; Janssen: Honoraria; Gilead Sciences: Honoraria; Takeda: Research Funding; Sandoz: Consultancy; Amgen: Honoraria; Roche: Research Funding.

Description: Peripheral T-cell lymphomas (PTCLs) are a heterogeneous group of aggressive non Hodgkin lymphomas with poor prognosis. Molecular and cytogenetic studies have shown a prominent role for kinase fusion oncogenes, mostly NPM-ALK, in ALK+ anaplastic large cell lymphomas (ALCLs) and ITK-SYK kinase in unspecified PTCLs. To gain further insight on the genetics and pathogenic mechanisms of aggressive PTCLs we performed an integrated mutation analysis using whole exome sequencing (n=12) and RNAseq (n=35) data. This analysis identified 288 candidate coding somatic mutations in 268 genes including known recurrent mutations in the TET2, DNMT3A and IDH2 epigenetic factor genes and pointed to the FYN kinase gene as a new recurrently mutated oncogene in T-cell transformation. The FYN tyrosine kinase is, with LCK, the predominant SRC family kinase found in T lymphocytes and plays an important role in T-cell activation upon T-cell receptor (TCR) stimulation. FYN mutations in PTCL included a FYN L174R mutation detected in one AITL patient sample, a FYN R176C allele recurrently found in two PTCL NOS cases and a FYN Y531H mutation present in a PTCL NOS sample. Notably, each of these alleles are predicted to specifically disrupt the inhibition of FYN kinase activity by the C terminal SRC kinase (CSK). Thus, structure analysis of FYN and FYN mutant proteins predicted that FYN L174R and, most prominently, FYN R176C and FYN Y531H can disrupt the inhibitory interaction of the FYN SH2 domain with the CSK-phosphorylated Y531. Consistently, pull down assays using GST-FYN-SH2 recombinant proteins and biotinylated C-terminal FYN peptides encompassing Y531 showed abrogation of the interaction between FYN-SH2 and P-Y531 in each of these mutants. In agreement with these results, expression of FYN L174R, FYN R176C and FYN Y531H resulted in increased levels of FYN activation. Moreover, CSK expression effectively inhibited wild type FYN, but failed to abrogate FYN L174R, FYN R176C or FYN Y531H activation. In contrast, pharmacologic kinase inhibition with dasatinib, a multikinase inhibitor which blocks ABL1 and SRC kinases, effectively abrogated the activity of FYN L174R, FYN R176C and FYN Y531H mutant proteins and suppressed the growth of cells transformed via expression of activated FYN mutant alleles. Overall these results support an oncogenic role for FYN activating mutations in the pathogenesis of PTCL and support a role for SRC kinase inhibitors for the treatment of this disease. Disclosures: No relevant conflicts of interest to declare.

Description: Peripheral T-cell lymphomas (PTCLs) are a heterogeneous and poorly understood group of aggressive non Hodgkin lymphomas with poor prognosis. To gain further insight on the genetics and pathogenic mechanisms of aggressive PTCLs we performed whole exome sequencing of matched tumor and normal DNA samples from 12 PTCL patients including 6 PTCL not otherwise specified (PTCL-NOS) tumors, 3 angioimunoablastic (AITL) T-cell lymphomas, 2 nasal type NK-/T-cell lymphomas and one enteropathy-associated T-cell lymphoma (EATL). This analysis identified 288 candidate coding somatic mutations in 268 genes and a mean mutation load of 24 non synonymous mutations per sample (range 4 – 57). Among these we noted the presence of a recurrent heterozygous mutation in the RHOA small GTPase gene (RHOA G17V) present in two independent AITL samples and one PTCL NOS biopsy. Analysis of a broad and diverse panel of 126 PTCL samples identified the presence of the RHOA G17V allele in 32 samples with a high prevalence in AITL (24/36, 67%, P 〈 0.001) and PTCL NOS cases (8/44, 18%, P 〈 0.002). The RHOA protein belongs to the Rho family of small GTPases, a group of Ras-like proteins responsible for linking a variety of cell-surface receptors to different intracellular signaling proteins. As is the case for RAS and most other small GTPases, RHOA activation is mediated by guanine exchange factors (GEFs), which catalyze the switch of RHOA from an inactive GDP-bound to an active GTP-bound state. Thus, and to test the functional significance of the RHOA G17V mutation we analyzed the capacity of this mutant to load GTP. This analysis revealed that RHOA G17V fails to incorporate GTP in response to an activated GEF in vitro. Moreover, and consistent with its inability to bind GTP, RHOA G17V failed to interact with rhotekin, a RHOA effector protein that selectively interacts with the GTP-bound active form of RHOA. However and most notably, the lack of RHOA G17V activation is not the result of a defect in RHOA-GEF interaction as RHOA G17V pull down assays demonstrated effective binding of this mutant protein to activated GEF proteins in T-cells. Based on these results we proposed an inhibitory role for RHOA G17V via sequestration of active GEF proteins. Consistently, while forced activation of RHOA signaling by GFP-RHOA overexpression induced loss of adhesion and round cell morphology in HEK293T cells, transfection of GFP-RHOA-G17V induced increased elongation and cellular protrusions as result of RHOA inactivation. In addition, immunoflourescence analysis of actin stress fiber formation by RHOA demonstrated effective abrogation of RHOA mediated cytoskeleton remodeling in cells expressing RHOA G17V. Overall these results show novel insight on the genetic basis of PTCLs and demonstrate a prominent role for RHOA G17V in the pathogenesis of AITL via disruption of RHOA signaling. Disclosures: No relevant conflicts of interest to declare.

Description: Peripheral T-cell lymphomas (PTCL) are malignant and highly aggressive hematologic tumors arising from mature post thymic T-cells. The diagnosis of PTCL includes diverse lymphoma subgroups, altogether accounting for about 15% of all non-Hodgkin lymphomas. Despite much effort in developing reliable diagnostic markers, the diagnosis of PTCLs is challenging and 20-30% of cases are diagnosed as PTCL-NOS (not otherwise specified). This heterogeneous and poorly defined group of lymphomas is frequently characterized by chemotherapy resistance and a very poor prognosis. Here we report the presence of recurrent driver activating genetic alterations in the VAV1 gene in PTCL, NOS. RNA-seq analysis of a comprehensive series of 154 PTCLs and targeted sequencing identified VAV1 gene fusions with different partners including VAV1-THAP4, VAV1-MYO1F and VAV1-S100A7. In all cases the resulting oncoproteins lack the C-terminal SH3 domain of VAV1, a motif implicated in the negative regulation of VAV1 signaling, leading to increased activation of VAV1 catalytic-dependent (MAPK, JNK) and non-catalytic-dependent (NFAT) VAV1 effector pathways. In addition, and most notably, we also identified focal microdeletions at the VAV1 intron 25-exon 26 boundary, which result in the activation of an alternative intraexonic splice acceptor site and the consequent expression of mis-splicing-driven mutant transcripts harboring a recurrent VAV1 Δ778-786 in-frame deletion. Mechanistically, the VAV1 Δ778-786 mutation removes 9 amino acids proximal to the C-terminal VAV1 SH3 domain and induces in increased VAV1 activation and signaling in biochemical assays. In all, these results support a driver role for oncogenic VAV1 signaling in T-cell transformation of major importance for the design of targeted therapies for the treatment of PTCL, NOS. Disclosures No relevant conflicts of interest to declare.

Description: We recently reported a truncating deletion in the NFKBIE gene, which encodes IκBε, a negative feedback regulator of NF-κB, in clinically aggressive chronic lymphocytic leukemia (CLL). Because preliminary data indicate enrichment of NFKBIE aberrations in other lymphoid malignancies, we screened a large patient cohort (n = 1460) diagnosed with different lymphoid neoplasms. While NFKBIE deletions were infrequent in follicular lymphoma, splenic marginal zone lymphoma, and T-cell acute lymphoblastic leukemia (

Description: Deregulated NF-κB signaling is a hallmark of most, if not all, lymphoid malignancies, and recurrent gene mutations in both the canonical and non-canonical NF-κB pathway are known to lead to NF-κB activation. However, the full compendium of NF-κB gene mutations in lymphoid malignancies remains to be elucidated. Recently, we reported a 4-bp truncating mutation in the NFKBIE gene, which encodes IκBε, a negative regulator of NF-κB, in patients with chronic lymphocytic leukemia (CLL). The NFKBIE deletion was enriched in clinically aggressive CLL patients (7-8%) and associated with a worse clinical outcome. At the functional level, NFKBIE-deleted CLL showed reduced IκBε levels and decreased p65 inhibition, along with increased phosphorylation and nuclear translocation of p65, compared to wildtype patients. Preliminary data has indicated an increased frequency of NFKBIE aberrations in other lymphoid malignancies as well. To explore this further, we screened for NFKBIE deletions in a large cohort of patients diagnosed with a range of different lymphoid neoplasms. Overall, NFKBIE deletions were identified in 76 of 1414 patients (5.4%). While NFKBIE deletions were relatively infrequent in patients diagnosed with follicular lymphoma (3/225, 1.3%), splenic marginal zone lymphoma (3/175, 1.7%), and T-cell acute lymphoblastic leukemia (1/94, 1.1%), moderate frequencies were observed among diffuse large B-cell lymphoma (18/521, 3.5%), mantle cell lymphoma (8/189, 4.2%), and primary CNS lymphoma (1/34, 2.9%) patients. In contrast, a remarkably high frequency of NFKBIE deletions (41/176 cases, 23%) was observed among primary mediastinal B-cell lymphoma (PMBL) patients. Noteworthy, the prevalence of NFKBIE-deleted PMBL cases was similar in the different contributing centers. All PMBL patients in the present series received a CHOP based treatment regime; in ~75% of cases rituximab was added and ~25% were treated with dose intensified schemes. For the latter, the vast majority of patients received CHOEP, while individual cases were treated with MegaCHOEP, DA-EPOCH or ACVBP. Regarding clinicobiological associations, there were no significant differences between NFKBIE-deleted and wildtype PMBL patients with respect to age, sex, Ann Arbor stage, IPI risk-groups, extranodal or bone marrow involvement, bulky disease, and LDH elevation. However, NFKBIE-deleted patients were more likely to be refractory to primary chemotherapy (31% vs. 3%, P=.001) and had a shorter overall survival compared to wildtype patients (5-year overall survival: 63% vs 84%, P=.013). In multivariate analysis (including age, gender, Ann Arbor stage, IPI, and NFKBIE mutation status), NFKBIE mutation status (95% CI: 1.23-10.61; HR: 3.61; P=0.020) remained an independent factor for poor prognosis. In summary, we document NFKBIE deletions as a common genetic event across B-cell malignancies, albeit at varying frequencies. The high frequency of NFKBIE deletions in PMBL alludes to the critical role of this aberration in the pathophysiology of the disease. NFKBIE deletions were associated witha worse clinical outcome, hence potentially representing a novel poor-prognostic marker in PMBL. *Contributed equally as first authors. **Contributed equally as senior authors. Disclosures Stamatopoulos: Gilead: Consultancy, Honoraria, Research Funding; Abbvie: Honoraria, Other: Travel expenses; Novartis: Honoraria, Research Funding; Janssen: Honoraria, Other: Travel expenses, Research Funding.

Description: Abstract 318 Aberrant junctions involving the switch regions of the IGH locus are frequent in the non-GCB subtype of diffuse large B cell lymphomas (DLBCL), suggesting that some deregulation of the class switch recombination process (CSR) participates in the acquisition of genomic abnormalities in this pathology. To address the impact of this defect on the B cell receptor (BCR) itself we characterized the variable and constant regions of the immunoglobulin heavy chain by RT-PCR in 51 cases. Our results show that, in contrast with most GCB cases, almost all non-GCB DLBCL express an IgM (25/28 vs. 9/23; in non-GCB and GCB cases, respectively, P=0.0002; Fisher's exact test). We addressed the molecular bases of this IgM restriction by studying the configuration of the IGH loci. We found frequent legitimate and illegitimate switch junctions in IgM+ DLBCLs by genomic PCR (in 25/34 cases), showing that CSR is activated during lymphomagenesis but does not modify the isotype of the BCR. Interestingly, fluorescence in situ experiments using a probe directed against the Cμ gene showed that class switch recombination (CSR) occurs symmetrically on the two IGH alleles in IgG+ cases (5/5 tested cases) and only asymmetrically in a majority of IgM+ cases (8/11 tested cases). This finding indicates that the expression of an IgM does not result from a global failure of the CSR machinery but instead from a specific lack of recombination on the productive IGH allele. In line with this hypothesis we observed that the large internal deletions in the switch μ region (Sμ) which are known to be frequent in this pathology are specific to IgM+ cases (15/34 IgM+ vs. 0/15 IgG+ cases, P=0.0018; Fisher's exact test) and cluster on the productive IGH alleles (7/7 cases characterized by allele specific PCR), suggesting that the loss of the Sμ repeats plays a direct role in IgM stabilization by reducing the probability that the Sμ region could be involved in CSR. Finally, we observed that the non-GCB signature is associated with a higher level of somatic mutations in the 5'Sμ region (median mutation rates 4.51% vs. 2.07% in non-GCB and GCB cases, P=0.034, Mann-Whitney Test) with a strong bias toward C〉T and G〉A transitions suggesting repeated AID activations. We found the same bias it the BCL6 and PAX5 genes but not in VDJ exons, suggesting that the aberrant mutations in multiple oncogenes in this pathology result specifically from repeated CSR attempts rather than from VDJ hypermutation. Together, our data show that, in non-GCB DLBCL, lymphomagenesis occurs in IgM+ B cells which are repeatedly induced to switch but which fail to modify the isotype of their BCR. We hypothesize that the stabilization of this specific isotype is an important contributor to pathogenesis which allows repeated CSR activations in germinal centers and the accumulation of genomic abnormalities. Disclosures: No relevant conflicts of interest to declare.