Secreto, Charla

Introduction: Chronic Lymphocytic Leukemia (CLL) is characterized by the accumulation of mature-appearing malignant lymphocytes (CLL B-cells) in the blood, marrow, lymph nodes, and spleen. Despite improved outcome with the introduction of novel BCR and BCL-2 inhibitors, disease progression is still a therapeutic challenge from either differential responses or acquired drug resistance. Recent studies in CLL reported alterations of the epigenetic landscape as well as mutations of genes encoding key chromatin machineries. These aberrant chromatin structures may provide novel therapeutic targets for CLL. Here, we identify aberrant chromatin features in CLL B-cells as novel therapeutic targets. Methods: Histones were extracted by acid from B cells derived from 10 random selected CLL patients and 10 normal donors and histone modifications were checked by western blot. For ChIP-seq study, published H3K27me3 ChIP-seq data (GSE113336) were downloaded from and analyzed (Control samples, n= 6; CLL samples, n=16). Gene ontology analysis used the Panther Classification System. Cell Survival was determined by CellTiter 96® AQueous Assay (Promega). Results: While most histone modifications do not vary between CLL and controls, H3K27me3 and H3.3S31ph are increased and decreased respectively, albeit variably, in CLL B-cells (Fig1. A and B). Notably, the low level of H3.3S31ph was observed in a subset of samples (7 of 10 CLL samples tested). To further investigate the biology and role of H3K27me3 in CLL, we analyzed its genome-wide distribution by chromatin immunoprecipitation followed by sequencing (ChIP-seq). Our analysis showed that the genes with increased H3K27me3 occupancy were mostly enriched in tumor suppression pathways (e.g., negative regulation of PI3K-Akt pathway) or down-regulated genes in CLL such as genes involved in the pro-apoptotic pathway (FAS) (Fig1. C and D). These results suggested that high enrichment of H3K27me3 may regulate the expression of these genes, contributing to CLL survival. H3K27 methylation, an important suppressive histone modification that is associated with transcription repression, is catalyzed by Polycomb Repressive Complex 2 (PRC2). Therefore, inhibition of Enhancer of Zeste Homolog 2 (EZH2), the catalytic subunit of PRC2, could be explored as a therapy approach in CLL. However, feedback activation of H3K27 acetylation (H3K27ac) can promote expression of pro-survival genes that confers EZH2 inhibitor (EZH2i) resistance, which limits its use in human malignancy. Thus, the epigenetic determinants that reliably overcome EZH2i resistance or sensitize cells to EZH2 inhibition have yet to be identified. As we observed that the CLL B-cells in a subset of CLL patients have low levels of H3.3S31ph, and a recent study showed the importance of H3.3S31ph for the enzymatic activity of p300 to acetylate H3 at lysine 27(Martire S et al., Nat Genet. 2019), we assessed the role of H3.3S31ph in the process of EZH2 inhibitor-mediated H3K27ac. Our results showed that inhibition of H3.3S31ph by CHK1 inhibitor MK-8776 abolished the activation of H3K27ac by EZH2i in MEC1 cells, which represents the patients who have CLL cells with relatively high level H3.3S31ph. However, we did not see a major increase of H3K27ac and H3.3S31ph in primary CLL B-cells with EZH2 inhibition (Fig. 1E), consistent with the relatively low expression of CHK1 protein in these cells (Fig. 1F). Because our data shows the requirement of H3.3S31ph in H3K27ac activation by EZH2 inhibition, we next tested if H3.3S31ph inhibition could overcome H3K27ac induced EZH2 inhibition resistance. We found that suppression of H3.3S31ph by CHK1 inhibitor MK-8776 sensitizes the CLL-like line MEC1 to EZH1/2 inhibition (Fig. 1 G). We then showed that an EZH2 inhibitor, Valemetostat, reduce the survival of the primary CLL B-cells (Fig. 1 H). These results suggest that the low level of H3.3S31ph may provide a therapeutic opportunity for CLL treatment with EZH inhibition. Conclusion: In summary, we have elucidated how epigenetic features in leukemic CLL B-cells (H3K27me3 and H3.3S31ph), can provide novel treatment targets for CLL (Fig. 1 I). Moreover, this study may provide a proof of concept to develop new treatment strategies based on epigenetic vulnerabilities in other hematological malignancies. Disclosures Parikh: GlaxoSmithKline: Honoraria; MorphoSys: Research Funding; Genentech: Honoraria; Ascentage Pharma: Research Funding; AbbVie: Honoraria, Research Funding; TG Therapeutics: Research Funding; Janssen: Honoraria, Research Funding; AstraZeneca: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; Verastem Oncology: Honoraria; Merck: Research Funding. Kenderian:Kite: Research Funding; MorphoSys: Research Funding; Tolero: Research Funding; Humanigen: Consultancy, Patents & Royalties, Research Funding; BMS: Research Funding; Gilead: Research Funding; Juno: Research Funding; Lentigen: Research Funding; Mettaforge: Patents & Royalties; Novartis: Patents & Royalties, Research Funding; Torque: Consultancy; Sunesis: Research Funding. Ding:Beigene: Membership on an entity's Board of Directors or advisory committees; Octapharma: Membership on an entity's Board of Directors or advisory committees; MEI Pharma: Membership on an entity's Board of Directors or advisory committees; alexion: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Research Funding; DTRM: Research Funding; Abbvie: Research Funding. Braggio:DASA: Consultancy; Bayer: Other: Stock Owner; Acerta Pharma: Research Funding. Kay:Oncotracker: Membership on an entity's Board of Directors or advisory committees; Juno Theraputics: Membership on an entity's Board of Directors or advisory committees; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Cytomx: Membership on an entity's Board of Directors or advisory committees; Agios Pharma: Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding; MEI Pharma: Research Funding; Abbvie: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Research Funding.

Abstract BACKGROUND: Green tea has long been touted as a health promoting substance. The active chemical compounds in green tea are called polyphenols or catechins. Epigallocatechin gallate(EGCG) is the major catechin in green tea. We previously reported the in vitro ability of EGCG to induce apoptotic cell death in chronic lymphocytic leukemia(CLL) B-cells in vitro (Blood 104:788). After publication of our findings, clinical activity in individuals using over the counter green tea extracts were reported (Leuk Res 30:707). Based on this information, we opened a phase I/II trial of green tea extracts for patients with asymptomatic, early stage CLL in fall of 2005. METHODS: The purpose of the phase I portion of this trial was to determine the optimal dose of EGCG in the Polyphenon E preparation for chronic daily administration and define tolerability in CLL patients. Previously untreated patients with asymptomatic, Rai stage 0–II CLL not currently meeting National Cancer Institute(NCI) Working Group(WG) Criteria for treatment were eligible for participation. Polyphenon E with a standardized dose of EGCG was obtained from NCI. The phase I portion of the trial was designed with 8 dose levels(range 400–2000 mg orally BID) using the standard 3 patient per dose level design. Patients remained on study up to 6 months. Grade 2 adverse events attributed to study treatment that did not respond to supportive care were considered dose limiting toxicity. The trial was designed to administer Polyphenon E in the fasting state. After accrual to dose levels 1 and 2, the U.S. FDA mandated all U.S. trials of Polyphenon E administer drug in the fed state. Accordingly, drug was administered in the fed state for dose levels 3–8. Trough plasma EGCG levels were measured 1 month after initiation of therapy. Response was classified using the NCI WG Criteria. RESULTS: As of August 2007, 33 patients have been accrued to dose levels 1–8. The maximum tolerated dose(MTD) has not been reached. Side effects have generally been mild. The most common toxicities were nausea(grade 1: 42%; grade 2: 3%), elevation in SGOT (42%; all grade 1), and abdominal pain (36%; all grade 1). To date, no patient has had a sustained 50% reduction in both absolute lymphocyte count (ALC) and lymphadenopathy that would meet the NCI WG criteria for partial response. A majority of patients have had a reduction in ALC(Table). Among the 10 patients who had palpable adenopathy at study enrollment, 7 patients experienced at least a 50% reduction in the sum of the products of all nodal areas at some point during treatment. Trough plasma EGCG levels after 1 month of treatment ranged from 2.93974 ng/mL(median 40.5 ng/mL). Plasma levels did not clearly relate to the degree of reduction in ALC suggesting sensitivity to Polyphenon E may relate more to characteristics of the leukemic clone than plasma EGCG levels. CONCLUSION: Daily oral EGCG in the Polyphenon E preparation was well tolerated by CLL patients in this phase I trial. The MTD has not been reached. As classified by the NCI WG criteria, no partial or complete remissions have been observed to date, however declines in ALC and lymphadenopathy have been observed in the majority of patients. The phase II portion of this trial will open at Mayo Clinic Fall 2007. Best reduction in ALC n % of patients At least 10% decline 25 76% At least 20% decline 14 42% At least 30% decline 8 24% At least 40% decline 4 12% At least 50% decline 2 6%

Abstract Background: CLL is still an incurable lymphoid malignancy. The current standard of care is to treat only patients with obvious clinical progression as defined by the National Cancer Institute Working Group in 1996 (NCI–WG 1996). High risk CLL can be identified at diagnosis by a variety of tests including fluorescence in situ hybridization (FISH), immunoglobulin heavy-chain variable region (IgVH) analysis, and expression of ZAP-70 or CD38. With this information we can identify patients with high risk, early stage disease who are candidates for novel low toxicity therapies that could alter the natural course of their disease. Our hypothesis was that combination monoclonal antibody (MoAb) therapy using alemtuzumab and rituximab would significantly reduce the high risk clone in early stage CLL. Methods: This phase II trial was conducted with IRB approval and accrued the planned 30 patients between January 2005 and July 2007 at Mayo Clinic Rochester. The study enrolled consenting patients with Rai stage 0–II CLL without NCI–WG 1996 criteria for treatment who had high risk CLL as defined as one or more of the following 17p13–, 11q22–, unmutated (UM) IgVH (< 2%) and expression of ZAP–70 (≥ 30%) and/or CD38 (≥20%). Treatment was one 30 day cycle (alemtuzumab 3 mg, 10 mg, 30 mg days 1–3 then 30 mg 3 × week × 4 weeks with all doses subcutaneously and rituximab at 375 mg/m2/week IV × 4 doses from day 8). Patients received 7 days of allopurinol and antimicrobial prophylaxis against PCP and herpes virus infections for 7 months. CMV testing by PCR was done weekly during treatment, then monthly × 6. Results: All 30 patients have completed therapy and 27 have been evaluated for response. The median age of these 27 patients was 62 yr (range 29–77) with 8 patients > 70 years. There was a male predominance (67%) with median time from diagnosis to treatment of 0.7 yr (range 0.1 – 6.1). Stage (Rai) at the start of therapy was 0 in 7 (26%), I in 19 (70%), and II in 1. High risk markers were 17p13– in 9 (33%), 11q22– in 7 (26%), UM IgV and expression of either ZAP–70 or CD38 in 11 (41%). All 27 patients completed therapy without interruption. Non hematological grade 3–4 toxicity occurred in 3 patients (2 drug reactions caused by SMX/TMP, 1 CMV reactivation responsive to IV therapy). Response evaluation at 2 months after completion of therapy using NCI–WG 1996 criteria showed an ORR of 93% with 12 (44%) CR, 8 (30%) nPR, and 5 (19%) PR. Two (7%) patients had disease progression. Median duration of follow up was 14.1 months (range 1.9 – 27.2). Median time to disease progression in the 25 responding patients was 14.4 months (95% CI 5.9 – 22.4). Seven (26%) patients have received subsequent treatment for CLL (median 5.2 months, range 2.4 – 20.1). A minimal residual disease assay using 3-color flow cytometry on peripheral blood was negative in 6 of the 7 patients with CR who had no evidence of residual CLL on immunohistochemical examination of the bone marrow. These 6 patients all remain in sustained CR (median follow up 15 months, range 2 – 27.2). Conclusion: Alemtuzumab and rituximab is an effective and tolerable therapy in patients with high risk early stage CLL. A randomized controlled trial is now required to test if this intervention is better than the standard observation approach. In addition, this combination MoAb regimen could be used as a platform to develop even more effective combination treatments for patients with CLL.

Abstract Myeloid cell factor-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 protein family that associates with tumor cell survival and drug resistance in chronic lymphocytic leukemia (CLL). Increased Mcl-1 expression is associated with failure to achieve remission after chemotherapy with fludarabine and chlorambucil in CLL patients. However, the influence of Mcl-1 expression has not been examined in CLL trials using treatment regimens that contain rituximab, which has shown substantially improved outcomes for a large subset of patients and have become a mainstay in the therapy of newly diagnosed CLL. We previously reported that combination chemoimmunotherapy with pentostatin, cyclophosphamide, and rituximab (PCR) has significant clinical activity with low accompanying toxicity in previously untreated CLL patients, and is especially well tolerated in older patients in whom the use of fludarabine may be associated with prohibitive toxicities. As part of this study, we prospectively investigated association of Mcl-1 protein expression with response and progression-free survival. Eligible patients received a regimen consisting of pentostatin (2 mg/m2), cyclophosphamide (600 mg/ m2), and rituximab (375 mg/m2) given intravenously on day 1 of a 21-day cycle for a maximum of 6 cycles. Responses were assessed according to NCI 1996 criteria and included bone marrow evaluation and two-color flow cytometry two months after completion of therapy. Flow cytometry-negative status was defined as less than or equal to 1% CD5+/CD19+ cells. Of the 64 patients evaluated in this trial, clinical responses were seen in 58 (91%), with 26 (41%) complete responses (CR), 14 (22%) nodular partial responses (nPR), and 18 (28%) partial responses (PR). Lysates from peripheral blood cells obtained pre-treatment were analyzed for Mcl-1 expression by immunoblot. Mcl-1 as a continuous variable was not found to be associated with other commonly described risk factors. However, Recursive Partitioning Analysis (RPA) was devised employing Mcl-1 expression as a continuous variable, which revealed an optimal cut point of 0.85. At this cutoff, flow cytometry-negative status was significantly different between the two groups (p=0.01) and median PFS was significantly higher (p=0.02) in patients with Mcl-1 levels of <0.85 (50.8 vs. 18.7 months). No difference by Mcl-1 expression was noted in other pre-treatment or response parameters. Our data describes the first prospective validation of Mcl-1 over-expression adversely influencing both the likelihood of attaining a flow cytometry-negative complete remission and extended progression free survival. Mcl-1 expression was also independent of other risk factors, indicating additional benefit for this measure in assessing patients. Mcl-1 expression may therefore predict poor response to chemoimmunotherapy, and these findings advocate pursuing therapeutic agents targeting this important anti-apoptotic protein.

Abstract Background: This is an initial report of a correlative laboratory study of an ECOG clinical trial, E2903, to investigate an array of prognostic factors that are potentially associated with the clinical outcome in previously treated, high risk Chronic Lymphocytic Leukemia (CLL) patients. The ultimate goal of this study is to develop a prognostic model for this group of patients. Method: We have previously reported (ASH, 2007) on initial clinical and toxicity results using a combination of PCR followed by Campath. To date we have clinical response data on 37 patients and have conducted correlative prognostic factor analysis on these patients at entry to the study. The prognostic parameters assessed were fluorescence interphase hybridization (FISH) panel, CD38, ZAP-70 and IGVH (mutated vs. unmutated) status and plasma levels of pro- and anti-angiogenic cytokines. In addition, features such as clinical stage, age, sex and laboratory parameters including total white blood count, absolute lymphocyte count (ALC) and beta 2 microglobulin (b2m) were studied as predictors of response to PCR. Results: As of July 2008, the response data for the first 41 (the accrual goal is 110) patients who started the induction treatment are available. Of these 41, 3 patients are ineligible and one patient had no response data. The median age was 63 (range 51–76) with 29 males and 8 females, median b2m was 4 (range 2–28), 11 (31%) were Rai stage 0–2, and 26 (69%) were Rai 3–4. The median number of prior treatments was 2 (range 1–5); 15 of 23 (65%) patients tested for IGVH were unmutated, while on FISH analysis 4 had del 6q, 8 had del 11q, 4 had del 17p and 30 patients had complex FISH defects (>1 defect). Despite the prevalence of high risk features in this cohort of patients, 17 out of 37 responded (best response=partial response), 18 were stable and 2 had progressive disease with an overall response rate of 46%. Prognostic parameters most strongly associated with a clinical response included CD38 negative (p=0.008), ZAP-70 negative status (p=0.01) and mutated status (p=0.03). Responses were independent of age, sex, b2m, ALC, number of prior therapy or FISH defects. Responders showed a prolonged progression-free survival (PFS) compared to the PFS of non-responders (i.e., 2-yr PFS 29% vs. 0%, respectively, p<0.0001). Prognostic parameters most strongly associated with PFS included being both ZAP-70 negative (p=0.0009) and CD38 negative (p=0.004). Also, ZAP-70 negative and CD38 negative status was a strong predictor of favorable PFS (p=0.002). Mutated status was borderline significant (p=0.07) in univariate analysis and there was no obvious correlation of baseline angiogenic cytokine plasma levels with PFS. These results also hold in a multivariable Cox model. In the Cox model, mutated status was significantly associated with PFS (HR=0.2, p=0.01). Conclusion: We believe that the PCR regimen is highly effective at inducing responses in previously treated relapsed or refractory CLL patients who carry high risk prognostic markers. Thus, while no CRs were seen all but 2 patients had a PR or were stable after 6 cycles of PCR. The prognostic parameters most strongly associated with predictors of clinical outcome appear to be ZAP-70, CD38 and mutation status. The ability to attain a response also appears to be important for achieving a prolonged PFS. In summary, we believe that the strong clinical activity of PCR in a high risk group of CLL patients provides more evidence for pursuing the regimen as a platform for other combinations. In addition, we have generated a first level prognostic model that will continue to be refined as we proceed to complete this trial.

Abstract Introduction: Monoclonal B cell lymphocytosis (MBL) is an asymptomatic expansion of clonal CD19+/CD5+ B cells with less than 5x109/L cells in the peripheral blood and without other manifestations of chronic lymphocytic leukemia (CLL). Approximately 1% of MBL evolves to CLL requiring therapy per year; thus it is critical to develop more precise tools to identify which MBL will progress to CLL and require treatment. Patients and Methods: In this study, we performed targeted deep sequencing (TDS) on 49 high-count MBL individuals (median B-cell count 3.7x109/L; range 0.8-4.9x109/L) and explored the mutation status of 20 driver genes recurrently mutated in CLL. We analyzed the clonal evolution in 45 of these 49 MBLs by screening 2-4 sequential samples (average time between samples 56 months, range 10-119 months). At last follow-up, 19 cases (39%) had progressed to Rai>0, and 10 cases (20%) required treatment. Tumor and germ line DNAs were isolated from sorted CD5+/CD19+ and CD5-/CD19- cell populations, respectively. Overall, 154 samples from 49 MBL cases (105 tumor and 49 germ line) were screened using semiconductor sequencing technology. The latter genetic information was integrated with relevant clinical and biological parameters, and we evaluated the effect of driver mutations and clonal expansion on time to CLL progression and time to treatment (TTT). Results and Discussion: Our cohort consisted in 17 women and 32 men, with a median age of 66 years (range: 44-80). Five cases presented secondary diseases, including melanoma, lung and bladder cancer. Clinical and biological parameters were collected, including IGHV mutation status (mutated 66%, unmutated 34%), ZAP70 and CD49 expression (25% each). At presentation, 46% of cases had del(13q), 27% trisomy 12, 6% del(11q), and 4% del(17p). Overall, we found somatic non-synonymous mutations in 23 of 49 MBLs (47%) at the initial time point including 22% of cases with more than one mutated driver gene. The average depth of coverage was 730x, thus allowing the identification of small subclonal mutations. Recurrent mutations were found in most of the drivers: CHD2, DDX3X (8% of cases), FBXW7, NOTCH1, SF3B1 (6% each), ATM, BCOR, BIRC3, BRAF, KRAS, MED12, MYD88 and ZMYM3 (4% each). Furthermore, ITPKB, POT1, SAMHD1 and XPO1 were mutated in only one case, whereas no mutations were found in HIST1H1E, RIPK1 and TP53. In 4 individuals, we found two mutations in the same gene (BRAF, DDX3X, KRAS and SAMHD1). Genes that are known to be associated with disease progression in CLL were either mutated with significantly lower incidence (NOTCH1, SF3B1) or not mutated (TP53). Mutations were detected on average 45 months (range 9-73) prior to progression to CLL Rai>0 indicating the early origin of most driver gene mutations in the MBL/CLL continuum. The presence of driver mutations in MBL was associated with shorter TTT (median TTT: present: 96 months vs. not present: not reached, HR: 5.52, 95% CI: 1.2-26.2, P =0.015). Next, we looked at clonal expansion of driver mutations over time (defined as >2-fold change in the allelic frequency of driver mutations between time points). Of 20 MBLs with mutations at baseline who had sequential samples available, 10 cases showed clonal expansion. Seven out of 10 MBLs who required therapy showed clonal expansion, which was detected on average 15 months (range 6-30 month) prior to treatment. Finally, the detection of clonal expansion was significantly associated with reduced TTT (median TTT: clonal expansion: 21 months vs. no clonal expansion: 84 months, HR: 7.79, 95% CI: 1.94-31.3, P <0.001). Conclusion: We have confirmed the existence of recurrent mutations in most CLL putative driver genes at the premalignant MBL stage many years before progression to CLL. Furthermore, the early identification of driver mutations and its clonal expansion predicts a shorter TTT. Of note, clonal evolution under selective pressure has recently been linked to the onset of CLL progression after therapy. In this study, we characterized the clonal dynamics in the pre-malignant stages of the disease and underlined its impact on clinical outcome. Despite the relatively small size of the cohort, these findings suggest that the sequential monitoring of MBL individuals with a simple and reliable technique, such as TDS, will be at least of prognostic use and thus its incorporation in the disease stratification and clinical management should be further tested. Disclosures Fonseca: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Applied Biosciences: Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Binding Site: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Onyx/Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Kay:Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Tolero Pharma: Research Funding; Genentech: Research Funding; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Hospira: Research Funding.

Introduction: Bone marrow stromal cells (BMSCs), a major component of CLL microenvironment influences CLL B-cell survival. We have utilized an in vitro BMSC model system and found unique alterations in CLL B-cells with short term BMSC co-culture that point to previously unidentified biologic changes in the CLL B-cells that may influence CLL B-cell signaling and their drug resistance. Methods: Purified primary CLL B-cells (n=41) from previously untreated CLL patients were cultured alone or co-cultured with primary BMSCs from either normal individuals (n=24) or CLL patients (n=18) at a 50:1 ratio in AIMV medium. After 48 hours, separated CLL B-cells or BMSCs were examined by immunoprecipitation/Western blot analyses to assess the presence of intracellular signal proteins and real time PCR to determine the RNA level expression. In separate experiments to assess CLL B-cell response in co-culture with BMSC, purified CLL B-cells were treated with the following agents at sub lethal doses; fludarabine, chlorambucil, ibrutinib and venetoclax as single agents. Results: Consistent and significant increase in expression of Axl receptor tyrosine kinase for both mRNA and protein levels was observed in CLL B-cells co-cultured with BMSCs compared to CLL B-cells cultured alone. We also detected significantly increased expression of β-catenin at the protein level in CLL B-cells co-cultured with BMSCs. In contrast there was no significant change in β-catenin or Axl protein expression in the co-cultured BMSCs. Co-culturing of CLL B-cells with BMSCs using transwells confirmed that the upregulation of both Axl and β-catenin is dependent on the direct contact of CLL B-cells with BMSCs. Experiments showed that the increased Axl level in co-cultured CLL B-cells was independent of Axl kinase activity. Furthermore, the CLL B-cells from co-culture also had clear upregulation of downstream P-ERK-1/2 but no change in P-AKT(Ser473). Next we reasoned that if increases in Axl and β-catenin are related to drug resistance then CLL B-cells should have increases in those proteins when cultured with drugs and in presence of BMSCs. Treatment with chemotherapeutic or targeted therapy drugs, (i.e. fludarabine, chlorambucil, ibrutinib, venetoclax) with sublethal doses was found to lead to increase in expression levels of both β-catenin and Axl in co-cultured CLL B-cells. However these increases were significantly over that seen with simple co-culture of CLL B-cells with BMSCs. Since CLL B-cells were less sensitive to these latter chemotherapy drugs in presence of BMSCs, this suggests to us a role for both Axl and β-catenin in stromal mediated CLL B-cell drug resistance to these agents. Moreover, high nuclear β-catenin and P-ERK-1/2 levels were also detected in co-cultured CLL B-cells. It is also known that ERK associates with and inactivates GSK-3β resulting in the up-regulation of β-catenin. We found upregulation in P-GSK-3β (Ser9) an inactive molecule which can result in increasing accumulation of β-catenin. Inhibition of P-ERK-1/2 using the ERK inhibitor PD98059 in co-cultured CLL B-cells inhibited β-catenin as well as Axl expression levels. Furthermore, it has been shown that Axl expression can be regulated by c-Jun activity. In that regard we have observed upregulation of P-c-Jun(Ser73) which can enhance Axl level in co-cultured CLL B-cells and inhibition of c-Jun activity using SP600125 (c-jun upstream JNK inhibitor), as well inhibited the Axl expression. Finally, we studied 5 CLL patients before and while being treated with ibrutinib/chemo-immuno therapy for the expression of CLL B-cell Axl, β-catenin, P-ERK-1/2, P-c-Jun(Ser73) levels. We found that 2 patients had increase in Axl expression, 4 patients had increased β-catenin and P-ERK-1/2 levels and 3 patients showed increase in P-c-Jun(S73) level after the therapy. Conclusion: Here we show that marrow stromal cell contact with CLL B-cells consistently mediate increased expression in both β-catenin and Axl in CLL B-cells (Figure1). The mechanism for this may, in part, via activated ERK and c-Jun levels (Figure1). We believe that these changes in both molecules are associated with leukemic B-cell survival and drug resistance (Figure1). These studies suggest that a further understanding of the roles of Axl and β-catenin in the CLL B-cells mediated by contact with BMSC will help to develop potential strategies for the management of CLL disease resistant to various drugs. Disclosures Warner: Tolero Pharmaceuticals: Employment. Bearss:Tolero Pharmaceuticals: Employment. Kay:Agios: Other: DSMB; Infinity Pharmaceuticals: Other: DSMB; Celgene: Other: Data Safety Monitoring Board; MorphoSys: Other: Data Safety Monitoring Board.

The current paradigms of known peripheral immune abnormalities in B-Chronic Lymphocytic Leukemia (CLL) are not able to consistently explain patient complications and it is difficult to correct a given CLL patient's immune status. Here, we expand on our initial report demonstrating bone marrow (BM) hematopoietic dysfunction in untreated CLL patients (Manso et al., Leukemia volume 33, pages 638-652, 2019). CLL patient BM had significantly reduced frequencies and short-term functional capacity of hematopoietic stem and progenitor cells (HSPCs). Additionally, the remaining progenitors exhibited increased protein levels of the key hematopoietic transcriptional regulators GATA-2 and PU.1. We further evaluated the frequency and function of myeloid stem cells from controls and untreated CLL patients by limiting dilution analysis in long-term culture-initiating cell (LTC-IC) assays. Over the 5 week duration of the assay, we observed delayed and partial recovery of myelopoiesis from CLL-derived HSPCs (Figure 1A). These data suggest that removal of HSPCs from the CLL leukemic microenvironment partially recovers their ability to sustain myelopoiesis. A known inflammatory mediator and hematopoiesis-modulating cytokine that is constitutively produced by CLL cells, TNF-α, induced increased expression of GATA-2 and PU.1 in specific HSPC subsets and reduced formation of short-term colony forming units in vitro. Addition of TNF-α to LTC-IC assays resulted in a striking ablation of myelopoiesis in a dose-dependent manner, partially reproducing the ex vivo results (Figure 1B). To further assess the direct impact of CLL cells on HSPC biology, isolated HSPCs from controls were exposed in vitro to leukemic CLL cells. The co-culture induced overexpression of GATA-2 and PU.1 in distinct HSPC populations, recapitulating our ex vivo findings (Figure 1C-D). When cell-cell contact was inhibited by use of Transwell inserts, an intermediate increase in GATA-2 and PU.1 was observed, highlighting the contributions of both soluble mediators and cell-cell contact to HSPC alterations. In both direct and Transwell co-culture conditions, overexpression of GATA-2 and PU.1 was reversed when TNF-α was neutralized (Figure 1E-F). Taken together, these findings indicate a significant role for CLL-derived TNF-α in HSPC modulation and expand our previous observations of BM dysfunction in untreated CLL patients. This data offers new molecular insight into the contribution of the leukemic microenvironment to altered hematopoiesis, contributing to immunodeficiency in CLL, and identifies TNF-α as a potential therapeutic target for correction of hematopoiesis in CLL disease. Disclosures Ding: Merck: Research Funding; DTRM Biopharma: Research Funding. Parikh:AstraZeneca: Honoraria, Research Funding; MorphoSys: Research Funding; AbbVie: Honoraria, Research Funding; Acerta Pharma: Research Funding; Pharmacyclics: Honoraria, Research Funding; Janssen: Research Funding; Ascentage Pharma: Research Funding; Genentech: Honoraria. Novak:Celgene Coorperation: Research Funding. Kay:Agios: Other: DSMB; Celgene: Other: Data Safety Monitoring Board; Infinity Pharmaceuticals: Other: DSMB; MorphoSys: Other: Data Safety Monitoring Board.

Abstract Introduction: Given the established role of PD-1 in mediating immune suppression in chronic lymphocytic leukemia (CLL), we tested and reported the efficacy of PD-1 blocking antibody pembrolizumab in relapsed and transformed CLL patients. A selective response of pembrolizumab (~40%) in patients with RT, particularly after prior ibrutinib, was observed (Ding, Blood, 129:3419). Correlative analysis showed PD-1 expression in tumor B-cells of patients with RT and aggressive CLL after progression on ibrutinib. PD-1, an inhibitory receptor expressed on CLL T-cells, inhibits the immune synapse and cytotoxic T cell functions via the interactions with its ligands. However, the expression pattern and role of PD-1 in tumor B-cells is not well defined. In this study we investigated the functional implication of the PD-1 signaling axis in B-cell pathobiology in CLL and RT patients. Methods: 26 CLL-involved lymph node (LN) and 20 RT-involved LN were tested for PD-1 expression by immunohistochemistry (mouse clone NAT105, Abcam). For in vitro study, we checked PD-1 expression in 11 lymphoma cell lines and 1 CLL cell line by both flow cytometry and Western blot (WB) analysis. Effect of PD-1 knockdown using CRISPR/Cas9 system (Addgene) and over-expression of PD-1 using pLEX-lentiviral (Thermoscientific) or pRetro-retroviral (Clonetech) system were evaluated on pro-survival and apoptotic signaling pathways by Western blot analysis. Gene expression signatures in CLL and RT patients were also evaluated by Illumina-based RNA sequencing using FFPE-nodal tissue obtained by clinical biopsy (Tempus Labs; Chicago, IL). Results: The expression of PD-1 was significantly increased in RT-LN compared to CLL-LN. (mean ± SEM in RT vs. CLL, 30.6 ± 4.7 vs. 11.5 ± 2.8, p < 0.001). PD-1 expression was highest in patients with RT where the immediate prior CLL therapy was ibrutinib (Figure 1A). Among all cell lines tested for PD-1 expression, the expression of PD-1 by WB and flow was highest in Mino (mantle cell lymphoma line), followed by moderate expression in Jvm2 (B-PLL line) and Mec1 (CLL line), and very low-level expression in both Jeko-1 (B-NHL line) and lymphoma line 'Karpas299'. CRISPR/Cas9 mediated depletion of PD-1 in Mino cells inhibited constitutively active Akt, p70S6K and mTOR pathway, accompanied by significant downregulation of the anti-apoptotic proteins, Bcl-2, Mcl-1 and XIAP, but P-ERK1/2 was not affected. Constitutive lentiviral (pLEX-PD-1)-mediated overexpression of PD-1 in Jeko-1 and doxycycline regulated inducible retroviral (pRetro-PD-1) mediated overexpression of PD-1 in Karpas299 activated Akt, mTOR and p70S6K pathway. Overexpression of PD-1 in Jeko-1 significantly increased Bcl-2 and Mcl-1 and in Karpas299 increased Bcl-2, Mcl-1 and XIAP expression (Figure 1B). A parallel genetic analysis using RNA sequencing was performed on 5 nodal tissues involved by either RT or progressive CLL after these patients developed clinical progression after prior ibrutinib therapy. In all 5 patients, overexpression of PD-1 was associated with increased expression of Bcl-2 and mTOR regardless of the genetic mutations detected (including TP53, ATM, BTK, NOTCH1, XPO1, SF3B1, TET2 etc). However, in 2 patients who received prior chemoimmunotherapy, similar overexpression of gene signature was not observed by RNA sequencing analysis, alternative pathways including Met or NFkB overexpression was detected. Given these clinical and laboratory findings, we have treated 2 RT patients with a combination of BTK and Bcl-2 inhibitors (ibrutinib and venetoclax, respectively) whose CLL transformed after prior ibrutinib. Significant reduction of tumor burden was observed in both cases with one complete response and one mixed response. Conclusion: An increased expression of PD-1, Akt/mTOR and Bcl-2 gene signature was first observed in RT patients after prior ibrutinib therapy. PD-1 overexpression in the tumor B-cells of RT and progressive CLL patients likely regulate AKT/mtOR to upregulate Bcl-2. Targeting both BTK and Bcl-2 pathways in addition to PD-1 blockade appear to be a promising strategy to treat these aggressive diseases. Disclosures Parikh: Gilead: Honoraria; Janssen: Research Funding; Abbvie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; AstraZeneca: Honoraria, Research Funding. Kenderian:Novartis: Patents & Royalties; Tolero Pharmaceuticals: Research Funding; Humanigen: Research Funding. Ansell:Takeda: Research Funding; Trillium: Research Funding; Affimed: Research Funding; Celldex: Research Funding; Merck & Co: Research Funding; Regeneron: Research Funding; LAM Therapeutics: Research Funding; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Pfizer: Research Funding. Kay:Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees. Ding:Merck: Research Funding.

Abstract Peripheral immune dysfunction in B-Chronic Lymphocytic Leukemia (CLL) is well-studied and likely relates to the incidence of serious recurrent infections and second malignancies that plague CLL patients. However, the current paradigms of known immune abnormalities are not able to consistently explain these complications and it is not easy to correct CLL patient immune status. Here, we expand on our preliminary reports that demonstrate bone marrow (BM) hematopoietic dysfunction in early and late stage untreated CLL patients. We found reduced short-term functional capacity of hematopoietic progenitors in BM using colony forming unit assays (Figure 1A-C) and flow cytometry revealed significant reductions in frequencies of hematopoietic stem and progenitor cell (HSPC) populations (exemplified by Lin-CD34+ HSPCs, Figure 1D). We further report that protein levels of the transcriptional regulators HIF-1α, GATA-1, PU.1, and GATA-2 are overexpressed in distinct HSPC subsets from CLL patient BM, providing molecular insight into the basis of HSPC dysfunction. Interestingly, sustained myelopoiesis, evaluated by limiting dilution analysis in long-term culture-initiating cell (LTC-IC) assays maintained for five weeks, revealed no difference between healthy controls and CLL patients. These new data indicate that when HSPCs are removed from the leukemic microenvironment for ample in vitro culture time, they recover the ability to sustain myelopoiesis. To further assess the impact of the CLL microenvironment on HSPC biology, isolated HSPCs (CD34+ BM cells) from healthy controls were exposed in vitro to known leukemic microenvironment constituents. Exposure to TNFα, a cytokine constitutively produced by CLL B cells, resulted in rapid increases in PU.1 and GATA-2 proteins (Figure 2A-D). Similarly, addition of TNFα to the LTC-IC assay resulted in a striking ablation of myelopoiesis, even at the highest input cell concentration. Further, overexpression of PU.1 and GATA-2 were observed in HSPCs following co-culture with CLL B cells, a result that was not recapitulated when cells were exposed to IL-10, another cytokine constitutively produced by CLL B cells. These findings indicate specific components of the leukemic microenvironment are involved in HSPC modulation. Together, these findings expand on our previous observations of BM hematopoietic dysfunction in untreated CLL patients and offer new molecular insights into the contribution of the leukemic microenvironment on immunodeficiency in CLL. Disclosures Ding: Merck: Research Funding. Parikh:Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; Janssen: Research Funding; Abbvie: Honoraria, Research Funding; Gilead: Honoraria; AstraZeneca: Honoraria, Research Funding. Kay:Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Infinity Pharm: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cytomx Therapeutics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding.