ALBERT

Description: Background: Majority of MDS cases appear to be sporadic in nature, but 10-15% have clear familial basis due to predisposing mutations in genes such as RUNX1, GATA2, CEBPA and DDX41. Contribution of germline variants in sporadic MDS is not studied. This study attempts to address the contribution of germline variants in MDS pathogenesis. Methods: We performed amplicon-based massively parallel sequencing (AmpliSeq custom panel adapted for Illumina HiSeq2500 sequencing) on all coding regions of 29 myeloid genes for 144 MDS samples. After identifying the variants in five genes (TET2, MET, GATA2, ASXL1, NOTCH1), we tested an additional 96 MDS samples including therapy-related myeloid neoplasm (T-MN) using a Sequenom assay. We also analyzed WES data for these variants in 178 AML samples and 758 normal controls and AmpliSeq data for ASXL1 and TET2 variants in 655 CML samples. Results: Collation of all coding variants in the 29 myeloid genes sequenced identified germline variants occurring in primary MDS at frequencies significantly higher than expected when compared to the normal population (ExAC and matched cohort were similar) (Table 1). These variants occurred in 5 genes (TET2, MET, GATA2, ASXL1 and NOTCH1) at increased frequencies of 1.5-16.6 fold. Numerous MDS samples had multiple variants (4 with 4 variants, 4 with 3 variants, 18 with 2 variants) while 70 had 1 variant. The 3 germline MET variants have been previously investigated in solid tumorigenesis and likely generate MET variant proteins that contribute to numerous cancer types including MDS. Interestingly, 7/17 (41%) MDS cases with germline MET variants also had other cancers including pancreatic, gastric and laryngeal cancers. Of the TET2 variants, Y867H and P1723S were concurrent in 5 MDS, 5 AML and 6 CML samples indicative of them being on the same allele (i.e. a haplotype). They were seen at higher than normal frequency in MDS and AML, but were not significantly enriched in CML. We are currently confirming their coexistence on the same allele and assaying for decreased TET2 activity to determine whether one or both variants contribute to the phenotype. Other variants identified in MDS include the rare GATA2 (P161A) variant which is present in 1% of the population and the nearby common GATA2 (A164T) allele (~20%). These were mutually exclusive in our cohort and were seen at 3.9 and 1.5-fold, respectively, above the expected population frequency. We generated the P161A variant using site-directed mutagenesis and assayed for GATA2 transactivation activity in HEK293 cells with a GATA2-responsive LYL1 promoter-Luciferase construct (Figure 1). We also included empty vector (EV), wildtype (WT) GATA2 and T354M which is the most common highly penetrant autosomal dominant mutation leading to familial MDS/AML. As expected, T354M displayed a marked decrease in transactivation ability when compared to WT. The P161A variant similarly displayed loss-of-function in this assay, but not to the same magnitude as T354M. This is consistent with the hypothesis that reduced GATA2 function predisposes to myeloid malignancy where decreasing GATA2 activity correlates with increasing risk of developing malignancy. In our study 10/36 (28%) cases harboring these variants were T-MN cases. Apart from MET (E168D) (11.4-fold), the 2 rare variants with highest frequency in MDS versus controls were ASXL1 (N986S) (16.6-fold) and NOTCH1 (R912W) (6.5-fold). ASXL1 is an epigenetic regulator often mutated in hematopoietic malignancy and aberrant NOTCH1 function has been associated with myeloid and lymphoid malignancies. Conclusions: We have identified common and rare germline variants in genes involved in myeloid malignancy that may contribute to MDS pathogenesis. It remains to be seen whether they contribute to initiation, maintenance and/or progression of MDS and other hematopoietic malignancies. This is the first study reporting higher frequency of germline variants in sporadic MDS cases. Table 1. Frequency of germline variants in MDS, AML and CML in comparison to ExAC. Table 1. Frequency of germline variants in MDS, AML and CML in comparison to ExAC. Disclosures Hiwase: Celgene Corporation: Research Funding.

Description: Chromosomal translocations involving 11q23, resulting in rearrangements of the mixed lineage leukemia gene (MLL, re-named KMT2A) are frequent events in childhood leukemia. MLL is highly promiscuous, with approximately 80 fusions now characterized. Although fluorescence in situ hybridization (FISH) has high specificity for detecting MLL-rearrangements (MLL-r), sensitivity is limited and the translocation partner gene (TPG) cannot always be identified. In contrast, long-distance inverse-PCR (LDI-PCR) permits sequence-specific characterization of MLL breakpoints and the resultant fusion gene, which can then be used for monitoring minimal residual disease (MRD). A limitation of LDI-PCR is the relatively large input of DNA (≈ 1μg) required, with a blast cell percentage of 〉 20-30% to achieve sufficient sensitivity. Next-generation sequencing (NGS) approaches such as RNAseq and whole-genome sequencing (WGS) have the potential to identify multiple gene fusions, however their ability to detect the full spectrum of MLL fusions is limited by coverage, read depth and thereby cost. Such limitations can potentially be overcome with targeted sequencing panels, although their performance against "gold standard" assays, such as LDI-PCR, is unknown. We therefore aimed to assess the ability of a novel, targeted NGS approach for characterizing patient-specific MLLgene rearrangements from low inputs of RNA. The Archer™ FusionPlex™ Heme and Myeloid panels utilize anchored multiplex PCR-based enrichment (AMP-E) to rapidly enrich a number of targets, including MLL, creating libraries for NGS. The NGS libraries are generated using rapid workflows and are compatible with nucleic acid inputs of ≈ 20-200ng. Briefly, double stranded cDNA is generated from patient RNA and subjected to end repair, adenylation and ligation with unique, half-functional adaptors. Following two rounds of nested PCR with primers attached to common sequencing adaptors, the resulting target amplicons become functional and ready for clonal amplification and sequencing. Using AMP-E, we tested 23 paediatric MLL-r samples (15 ALL, 8 AML) that had previously been analyzed by LDI-PCR and were known to harbor 8 different MLL fusions, including MLL-AFF1 (n = 8), -MLLT3 (5), -MLLT10 (3), -ELL (2), -DCP1A (1), -MLLT1 (1), - AFF3 (1), and -TNRC18 (1). A patient sample known to express BCR-ABL1 was used as a positive control and a cytogenetically normal AML sample in remission was used as a negative control in each panel. The median blast count for samples analyzed was 86.1% (range 25%-97%). On average, 100ng of RNA was used per sample, with RIN values ranging from 2.7 to 9.1. Libraries generated using either the Archer™ FusionPlex™ Heme or Myeloid kit were sequenced to sufficient read depths by Illumina MiSeq® and NextSeq®, respectively. Bioinformatic analyses were performed with the Archer™ Analysis 4.1 software. Results were then compared with fusions identified by LDI-PCR. There was high concordance between AMP-E and LDI-PCR, with all MLL fusion genes identified by LDI-PCR also detected by AMP-E. Of note, an ALL sample with t(11;19), unable to be characterized by LDI-PCR, was identified by AMP-E to express MLL-MLLT1. The control BCR-ABL1 fusion was identified in every run and there were no false-negative results. Furthermore, AMP-E identified multiple MLL-fusion transcripts in 56.5% of patients. Analysis of paired diagnosis-relapse samples from an AML patient with MLL-MLLT3demonstrated that the two discrete transcripts present at diagnosis persisted at relapse, with emergence of a third transcript. In summary, detection of MLL gene fusions in acute leukemia using AMP-E is both sensitive and specific. The low RNA requirement, rapid workflow, compatibility with Illumina MiSeq® and cloud-based proprietary analysis software, together with the array of additional fusions and mutations detected by the Archer™ panels, show promise for translation into clinical diagnostic settings. The persistence of discrete transcript isoforms at relapse also highlights the potential for AMP-E to identify multiple, patient-specific MLL fusion transcripts which may have utility in refining prognostication, MRD monitoring and informing future functional studies of MLL-driven leukemogenesis. Disclosures No relevant conflicts of interest to declare.

Description: Background: Mixed phenotype acute leukemia (MPAL) is a high risk leukemia with features of acute myeloid (AML) and acute lymphoblastic leukemia (ALL), either due to co-expression of antigens of multiple lineages, or the presence of multiple immunophenotypically distinct populations. WHO 2008 classifies MPAL as T/myeloid (T/M), B/myeloid (B/M), MLL rearranged (MLL) MPAL, BCR-ABL1 (Ph+) MPAL, and MPAL not otherwise specified (NOS). Patients are managed with divergent chemotherapeutic approaches with survival estimates of 50-70%. Apart from Ph+ and MLL rearrangement, the genetic basis of MPAL is poorly defined. Our goal was to define the molecular basis of MPAL, and to compare with potentially related forms of leukemia (AML, T-ALL and early T-cell precursor (ETP) ALL) as a rational foundation for future trials. Furthermore, we examined whether multi-lineal cases harbor genetically distinct subclones, or arise from the acquisition of founding alterations in a multi-lineage hematopoietic progenitor. Methods: 155 cases of pediatric leukemia initially diagnosed as MPAL were studied by central pathology review and/or central flow cytometry (134 cases), confirming the diagnosis according to WHO criteria in 115 cases (fig. 1). Median age was 7 years (0-18) with 52 T/M, 37 B/M, 15 MLL, 8 NOS, and 2 Ph+ (fig. 2). Samples were studied by whole genome and/or exome, RNA sequencing, and SNP array analysis. 44 multi-lineal samples were flow sorted into 2-4 lymphoid, myeloid, and ambiguous subpopulations (15 T/M, 19 B/M, 7 MLL, 1 Ph+, 2 NOS) and subjected to exome sequencing and SNP array. Mutational data were compared to data from 196 AML, 39 ETP-ALL, and 245 T-ALL cases. Results: We identified 35 recurrently mutated genes, the most common of which were WT1 (21%), FLT3 (18%), NRAS (16%), JAK3 (11%), RUNX1 (11%), KMT2D (9%), PTPN11 (9%), ASXL1 (7%), and CREBBP (7%). T/M and B/M subtypes are characterized by distinct patterns of genomic alteration. 48% of T/M cases harbored in-frame chimeric fusion, several of which are described in T-ALL, including ETV6-NCOA2 and ZEB2-BCL11B, NUP214-ABL1 and PICALM-MLLT10, and novel fusions involving hematopoietic regulators (e.g. ETV6-MAML and MNX1-IKZF1). 42% of B/M cases had in-frame fusions of ZNF384 with CREBBP, EP300, and TCF3, while we also identified isolated fusions involving ERG and NF1. Mutations of Ras signaling genes were present in 50% of B/M cases, in contrast to 10% of T/M cases. Epigenetic modifying genes, including CREBBP, SETD2, KMT2D, EZH2 and SUZ12 were mutated in 45% of the combined T/M and B/M cohorts. Cases with MLL gene rearrangements had few sequence alterations. In comparison to other subtypes of leukemia, the mutational spectrum of T/M MPAL, with alterations in transcription factors (60% cases), epigenetic genes (50%) and JAK-STAT signaling (35%) was more similar to ETP-ALL (64%, 72%, 44%) and T-ALL (49%, 60%, 21%) than to AML (19%, 21%, 11%). Similarly, B/M cases have increased alterations in these pathways (42%, 42%, 25%) compared to AML. Sequencing of MPAL subpopulations revealed that 27% of cases had the same SNVs/indels in each subpopulation, and 47% of cases had at least two-thirds of mutations present in each subpopulation. All multi-lineal cases with alterations of regulators WT1 and RUNX1 showed similar allele frequencies of these mutations in all populations. Alternatively, cases with mutations in signaling (FLT3, NRAS, KRAS, PTPN11) or epigenetic regulatory genes (CREBBP, KMT2D, SETD2) only showed consistent presence of alterations across each subpopulation in 60% of the cases. Conclusions: Our analysis has shown that T/M and B/M MPAL are distinct subtypes of leukemia. B/M MPAL is characterized by frequent RAS pathway mutations and ZNF384 fusions with multiple different fusion partners, suggesting that this gene plays a critical role in hematopoietic development for progenitor cells with B lymphoid and myeloid potential. The findings of mutational similarity to ETP ALL, and sharing of genomic lesions between subclones in the majority of cases strongly suggests that MPAL represents part of a spectrum of immature leukemias that arise in a hematopoietic progenitors that may propagate multiple immunophenotypic populations. These results will guide the design of therapeutic strategies for each subtype of MPAL and ETP ALL, and xenografts representative of each subtype are being used to examine sensitivity to therapeutic agents. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Loh: Abbvie: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Zwaan:Pfizer: Research Funding; Pfizer: Consultancy. Reinhardt:Pfizer: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Other: Travel Accomodation. Inaba:Arog: Research Funding. Mullighan:Loxo Oncology: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees; Amgen: Speakers Bureau.

Description: Introduction Most children with acute myeloid leukaemia (AML) harbour fusion genes which are ideal targets for molecular minimal residual disease (MRD) monitoring. However, evidence of prognostic significance is currently lacking and consequently most current paediatric AML treatment protocols rely on flow cytometric (FCM) evaluation to allocate treatment. Molecular MRD techniques provide significantly greater sensitivity and specificity and could allow more accurate outcome prediction, and consequently more personalised therapy, which is highly relevant in a disease where treatment related mortality, morbidity and relapse remain significant. Methods Between June 2016 and February 2019, MyeChild01 enrolled 170 children aged 0-18y with newly diagnosed AML who were randomly assigned to induction therapy with liposomal daunorubicin or mitoxantrone with cytarabine with or without gemtuzumab ozogamicin. Consolidation treatment was determined by karyotype, mutational profile and MRD status. Comprehensive centralised diagnostic assessment consisted of: Karyotype and fluorescence in-situ hybridisation (FISH) using a custom panel of probes to detect paediatric AML-associated gene fusions.PCR based screening for mutations in FLT3, NPM1 and CEPBA.Targeted capture of known fusion loci and paired end sequencing.RNA-seq using the Illumina TruSight fusion panel. Where a fusion gene was identified, RT-qPCR assays were designed and optimised for each patient. NPM1 mutation was also used as an MRD target if present. Paired PB and BM samples were requested after each cycle of treatment. Patients could have sequential monitoring after completion of therapy although this was not mandated. For this analysis, patients with core-binding factor (CBF) leukaemias i.e. inv(16)(p13q22) or t(8;21)(q22q22) with transcript levels above previously defined thresholds (Yin et al, 2012) were considered MRD positive. For all other targets, amplification in at least 2/3 replicates at

Description: Cytogenetically normal acute myeloid leukaemia (CN-AML) accounts for approximately 25%-30% of paediatric AML cases and carries a high risk of relapse. Minimal residual disease (MRD) is an essential factor in predicting relapse in acute leukaemia but is difficult to track for many CN-AML patients, due to the lack of a distinct and stable molecular marker. Consequently, new biomarkers are urgently required for MRD monitoring of the disease. Splicing variants, products of another hallmark of human cancers, aberrant splicing, have been shown informative in predicting responses to cancer treatment. Therefore, we characterized splicing events according to different cytogenetic features by targeted RNA-seq and interrogated the use of splicing variants in MRD monitoring of CN-AML. A total of 29 AML samples, collected from 18 de novo paediatric AML patients (median age 5.66 years, range 0.67 - 16.38 years) were analysed for this study. Among the 29 samples, 52% harboured a chromosome translocation, 21% were cytogenetically normal, and 28% showed a complex karyotype (defined as having 3 or more cytogenetic features). 100ng of total RNA, extracted from peripheral blood or bone marrow were subjected to library preparation using the Archer™ FusionPlex™ Heme and Myeloid panels, then sequenced using Illumina MiSeq® or NextSeq®. Novel splicing events and genetic mutations were identified by the Archer Dx analysis software in conjunction with normalisations against the library size and probe numbers. Splicing variants were validated using splicing junction-specific probe assays. Our results revealed 3249 novel splicing events in 29 AML samples. These events were classified into 4 major types (65% intron retention, 10% exon skipping, 8% exon out of order and 8% intra-exon gap), and 9 minor events that were combinations of the major types (9%). The number of splicing events per sample was not associated with the disease status or the presence of the mutations in the spliceosome encoding gene, SF3B1 or U2AF1. Instead, splicing variants were associated with cytogenetic features. Of note, an intron 13 retention of the KMT2A (MLL) gene was identified in all CN-AML samples, and was consistently expressed approximately 100 times higher in the CN-AML compared to other AML cases or remission samples. To assess whether KMT2A intron 13 retention could be a potential molecular MRD marker to monitor CN-AML, we measured its expression in samples from 5 independent CN-AML patients who had available samples for 3 time-points of disease progression. Our results demonstrated, with 95% detection power, that KMT2A intron 13 retention was differentially expressed at different time points (Figure 1). Moreover, the expression level of this splicing variant correlated with disease progression in every patient examined. In conclusion, these data suggest that intron 13 retention of KMT2A may be a novel molecular marker for MRD monitoring in CN-AML. Disclosures No relevant conflicts of interest to declare.

Description: Rearrangements of the mixed lineage leukemia gene (MLL, re-named KMT2A) result in aggressive leukemia. Current risk stratification of MLL-rearranged (MLL-r) leukemia is directed by the fusion partner gene and, increasingly, by minimal residual disease (MRD) assessment after induction therapy. The clinical significance of quantifying fusion transcript levels in leukemia patients is firmly established in chronic myeloid leukemia and acute promyelocytic leukemia but is less well studied in MLL-r patients. Real-time quantitative PCR (RQ-PCR) is the standardized assay for molecular MRD monitoring in patients with MLL-rearranged leukemia. However, this method is less precise when few leukemic cells are present, thus limiting its application for highly sensitive MRD monitoring. Droplet digital PCR (ddPCR) allows for absolute quantification of fusion transcripts when multiple copies of fusion transcripts are present per cell. Therefore, we aimed to evaluate whether determining MLL fusion transcript levels by ddPCR could improve the sensitivity of MRD monitoring in MLL-r leukemia. A total of 44 diagnostic and follow-up samples obtained from paediatric MLL-r leukemia patients (26 ALL, 18 AML) were subjected to targeted next-generation sequencing to obtain patient-specific fusion sequences. MLL fusion transcripts were quantified by ddPCR in a total of 17 samples obtained from 4 paediatric AML patients with MLL fusions involving MLLT3 (n = 3) and MLLT10 (n = 1). Fusion-specific probe assays were designed from each of the patient specific fusion sequences for MRD assessment by ddPCR. To determine the detection limit of this method in quantifying MLL fusion transcripts, two MLL-r AML cell lines (MV4-11 and THP-1), and one MLL-wt cell line (Kasumi-1) were used. MLL fusion transcript level of detection of ddPCR was determined by serially diluting MLL-r cDNA into MLL-wt cDNA (Kasumi-1). Using 20ng of MLL-r cDNA in 200ng diluent as the highest concentration, a 10-fold dilution series was performed to make concentrations ranging from 10−2 to 10−7. Each ddPCR reaction mixture contained 11ul of cDNA mix as template with 1X Supermix no dUTP (Bio-Rad), 500 nM of both F/R primers and 250 nM of 5'-FAM labelled probe (IDT). Droplets were generated using a QX200 Droplet Generator (Bio-Rad). A general thermal cycler protocol with annealing at 61°C for 1 minute was performed and positive fluorescence droplets were read using QX200 Droplet Reader (Bio-Rad). MRD of patient samples, derived from ddPCR, was then compared to MRD derived from DNA-based RQ-PCR, following the guidelines established by the EuroMRD group. Our ddPCR method showed high reliability and sensitivity, with the detection limit determined to be 10-5 for a cell line with low MLL fusion transcript expression (THP-1), and 10-6 for a cell line with high MLL fusion transcript expression (MV4-11). Comparison of results obtained by RQ- PCR and ddPCR in a total of 17 diagnostic and follow-up samples from 4 AML patients showed excellent/good concordance between methods for 13 samples with moderate MRD levels. The 4 samples with low levels of MRD (10-4 to 10-5) below the quantitative range as defined by EuroMRD for RQ-PCR were all detectable by ddPCR, highlighting that ddPCR could provide robust and highly sensitive MRD assays compared to the standardized RQ-PCR assays. In conclusion, ddPCR is a promising technique that can reproducibly and reliably quantify MLL-r transcripts for MRD monitoring of MLL-r leukemia. Highly sensitive and robust molecular MRD monitoring by ddPCR holds promise for improving response-based therapeutic stratification and prediction of molecular relapse before overt hematological relapse. Disclosures No relevant conflicts of interest to declare.

Description: Replicative immortality depends on telomerase activation in the majority of cancers including acute myeloid leukemia (AML). Imetelstat is a covalently lipidated 13-mer oligonucleotide that competitively inhibits telomerase activity. Clinical efficacy of imetelstat has recently been reported in essential thrombocythemia and myelofibrosis. We investigated the efficacy of imetelstat in AML using a randomized trial in patient-derived xenografts (PDX). To establish an AML PDX cohort, primary bone marrow (BM) or peripheral blood (PB) samples from 31 AML patients were transplanted into NOD.Cg Prkdcscid Il2rgtm1Wjl Tg (CMV-IL3,CSF2,KITLG)1Eav/Mlo (NSGS). Engraftment was defined by reconstitution of BM and spleen with CD33+ donor cells, PB circulating blasts, anemia or thrombocytopenia. The success rate for engraftment was 70.4% and was independent of cytogenetics. Fifteen independent AML patient samples (n=12 recipients/sample) were tested for efficacy of imetelstat. After engraftment, mice were randomized and treated with imetelstat (15 mg/kg body weight) or control phosphate-buffered saline (PBS) intraperitoneally every 48-72h. Across the entire cohort, survival was improved for imetelstat- vs. PBS-treated PDX (Hazard ratio PBS: 5.299; 3.379 ± 8.312; p 〈 0.0001; Cox proportional hazards model). Imetelstat delayed the expansion of human AML cells in 14 PDX (93.3%). AML patient samples were divided into 2 groups based on survival outcomes, "Sustained responders" (imetelstat extended survival 〉 2-fold or 〉 4 weeks; 9 AML patient samples; 60%) or "Poor responders" (6 AML patient samples, 40%). European LeukemiaNet (ELN)-karyotypic subtypes differed trend-wise between groups: favourable (100% sustained, 0% poor response to imetelstat); intermediate-1, intermediate-2 and poor (45.5% sustained, 54.5% poor response to imetelstat; p = 0.1, Fisher's exact test). Next generation sequencing revealed baseline AML PDX genetic profiles. FLT3, NRAS, TET2, RAD21 as well as 15 genes annotated in DNA damage, cell cycle regulation and apoptosis were mutated exclusively in the sustained responders group. Poor responders revealed mutations in ETV6, FANCM, MKI67, WT1 and 16 additional genes regulating growth factor independence and evasion of apoptosis. Imetelstat response was associated with reduced quiescence and induction of γ-H2AX levels in AML populations (n=4-6 / group / 3 individual AML patient samples): γ-H2AX (MFI normalized to PBS; PBS: 1.0 ± 0.02; imetelstat: 1.24 ± 0.02; p 〈 0.0001, Student's t test), quiescence (%Ki67-diploid AML cells; PBS: 11.62% ± 0.87; imetelstat: 6.9% ± 0.68; p 〈 0.001, Student's t test). The presence of spliceosome mutations (SRSF2, U2AF1) was not correlated with response (p = 0.5; Fisher's exact test). To investigate the effects on normal human hematopoiesis, CD34-enriched cord blood was transplanted into NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG, n=5-6/group/donor in 2 replicate experiments). Engraftment was confirmed at 4 weeks post-transplant by PB chimerism (〉=1%). Mice were treated with imetelstat or vehicle control from 4 weeks. After 10 weeks treatment, BM cellularity and donor engraftment were significantly reduced whereas the frequency of the CD34+CD38low HSC-enriched population was unchanged (donor 1 PBS: 0.35% ± 0.03%, imetelstat: 0.23% ± 0.06%, p = 0.1; donor 2 PBS: 0.45% ± 0.05%, imetelstat: 0.92% ± 0.35%, p = 0.2, Student's t test). HSC cell cycle and γ-H2AX levels were unchanged. PB and spleen B-cell engraftment were reduced (donor 1 spleen PBS: 77.74% ± 4.66%, imetelstat: 45.48% ± 9.03%, p 〈 0.05; donor 2 spleen PBS: 93.95% ± 0.40%, imetelstat: 89.1% ± 2.52%, p = 0.09, Student's t test), whereas the myeloid lineage was elevated or relatively preserved (donor 1 spleen PBS: 3.29% ± 0.71%, imetelstat: 7.53% ± 1.6%, p 〈 0.05; donor 2 spleen PBS: 1.20% ± 0.12%, imetelstat: 4.49% ± 1.60%, p = 0.07, Student's t test). In summary, imetelstat demonstrates efficacy in a significant proportion of AML PDX (60%, 9 out of 15 individual AML patient samples). Robust responses to imetelstat were associated with favourable cytogenetic risk groups and mutations in pathways controlling DNA damage. The effects on normal human hematopoiesis were modest and predominantly seen in the B-lymphocyte lineage with relative preservation of myeloid and stem cell populations. Further study is warranted to understand the preclinical and clinical efficacy of imetelstat in AML. Disclosures Lane: Janssen: Other: i have done consulting (once) for janssen..

Description: Key Points Activation of innate immune receptors induces an antiapoptotic signal and proliferation in ZAP-70–positive CLL dependent on Syk activation. TLR9 activation autonomously induces BCR signaling in ZAP-70–positive CLL based on an auto/paracrine feedback loop involving immunoglobulin M.