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Background: The 2018 iwCLL guidelines recommend close observation of early stage CLL pts who do not meet indications for therapy ("watch and wait" strategy). Prior attempts at early therapeutic intervention in unselected early-stage CLL pts using alkylating agents such as chlorambucil and chemoimmunotherapy failed to show a significant benefit; and these therapies were associated with substantial toxicities. The introduction of Bruton tyrosine kinase (BTK) inhibitors has revolutionized the treatment landscape of CLL. The German CLL Study group recently presented results of the CLL12 study which demonstrated a significant improvement in event-free survival (EFS) among untreated early stage high risk CLL pts who received ibrutinib compared to placebo (median EFS not reached vs. 47.8 months, respectively; Langerbeins, EHA, 2019). Acalabrutinib is a more selective second-generation BTK inhibitor that has fewer adverse events in pts with CLL, and has shown equally impressive clinical activity for CLL pts. We are conducting an investigator initiated randomized phase 2 study to compare acalabrutinib with or without obinutuzumab (a glycoengineered anti-CD20 monoclonal antibody approved in the treatment of CLL) among high risk early stage CLL pts. Study Design: All pts with newly diagnosed (<2 years from registration) previously untreated early stage CLL who do not meet the 2018 iwCLL guidelines for initiation of therapy are eligible for enrollment in this study. Pts undergo risk stratification according to the CLL-International prognostic index (CLL-IPI) which consists of the following 5 variables: age >65 years (1 point), Rai stage I-IV (1 point), del17p and/or TP53 mutation (4 points), unmutated immunoglobulin heavy chain (IGHV) genes (2 points), and serum β2-microglobulin >3.5 g/dL (2 points). Pts with high (4-6) and very high (7-10) risk CLL-IPI are randomly (1:1) assigned to acalabrutinib 100 mg orally twice daily (Arm A) or acalabrutinib with obinutuzumab at a standard approved schedule (Arm B). Treatment with acalabrutinib is continued for a minimum of 2 years unless the patient has unacceptable side effects or withdraws consent. Pts with low (0-1) and intermediate (2-3) risk CLL-IPI score are assigned to an observation arm with follow-up once every 6 months for 2 years, and then according to routine clinical practice (Arm C). Endpoints: The primary endpoint of the intervention arms (Arms A and B) is the achievement of minimal residual disease (MRD)-negative complete remission in the bone marrow after 2 years of therapy. MRD is assessed using an 8-color flow cytometry with a detection limit of 0.01%. The primary endpoint of the observation arm (Arm C) is time to first therapy. Secondary endpoints for all arms are: progression-free survival, overall survival, and safety. Statistical design: A randomized trial comparing the experimental arm (acalabrutinib plus obinutuzumab) against the control arm (acalabrutinib alone) will be conducted as described by Rubinstein. A sample size of 36 pts per arm provides 80% power to detect an improvement in MRD-negative complete response rate from 10% to 30%, using a one-sided test at a significance level of 0.10 (EAST 6.4). We anticipate accruing an additional 8 high/very high risk pts (4 in each arm) to account for ineligibility, cancellation, or major treatment violation. The total enrollment for Arms A and B will be 80 pts. We will enroll 40 pts to Arm C; for a total enrollment of 120 pts. Key correlatives: Comprehensive profiling to assess the innate and adaptive immune system in paired peripheral blood and bone marrow will be conducted in all pts registered to Arms A and B at baseline, 12 and 24 months after enrollment. In addition, bone marrow hematopoietic function will be assessed in all pts at these time points. We will employ a CLL focused custom 61-gene panel to estimate tumor mutational burden as well as mutational profiles for each patient at baseline, 12, and 24 month time points, as well at the time of disease progression. Preliminary results: The trial is registered at clinicaltrials.gov NCT03516617. The trial opened to accrual at all three Mayo Clinic sites (Rochester, MN; Jacksonville, FL; and Scottsdale, AZ) in September 2018. Twenty-eight pts have been registered; the baseline characteristics are shown in Table 1. The trial is expected to complete enrollment in September 2020; and the primary analysis will be available in September 2022. Disclosures Parikh: Janssen: Research Funding; AstraZeneca: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; AbbVie: Honoraria, Research Funding; Acerta Pharma: Research Funding; Ascentage Pharma: Research Funding; Genentech: Honoraria. Ding:DTRM Biopharma: Research Funding; Merck: Research Funding. Ailawadhi:Pharmacyclics: Research Funding; Cellectar: Research Funding; Takeda: Consultancy; Amgen: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Celgene: Consultancy. Kenderian:Novartis: Patents & Royalties, Research Funding; Tolero: Research Funding; Humanigen: Other: Scientific advisory board , Patents & Royalties, Research Funding; Lentigen: Research Funding; Morphosys: Research Funding; Kite/Gilead: Research Funding. Chanan-Khan:Mayo Clinic: Employment; Ascentage: Research Funding; Millennium: Research Funding; Jansen: Research Funding; AbbVie: Research Funding; Xencor: Research Funding; Pharmacyclics: Research Funding; Merck: Research Funding. Kay:Infinity Pharmaceuticals: Other: DSMB; Celgene: Other: Data Safety Monitoring Board; Agios: Other: DSMB; MorphoSys: Other: Data Safety Monitoring Board. OffLabel Disclosure: Drug: Acalabrutinib Purpose: treatment of CLL

Background The phase 3 trial A041202 solidified the Bruton's Tyrosine Kinase (BTK) inhibitor ibrutinib as a standard of care for older patients with previously untreated CLL by showing superior progression-free survival (PFS) as compared with bendamustine plus rituximab. While ibrutinib is highly effective in previously untreated CLL, there do remain disadvantages to this therapy, specifically the low rate of complete response (CR) and therefore the need for continuous administration, which increases cost and toxicity. In older patients especially, toxicities with ibrutinib are common; 17% of patients had atrial fibrillation and 29% had grade 3 or higher hypertension on the A041202 study. Thus, strategies to decrease the exposure time to ibrutinib are of interest. Venetoclax is an inhibitor of BCL2 that has shown efficacy as a single agent and in combination with monoclonal antibodies, specifically the anti-CD20 monoclonal antibody obinutuzumab for patients with previously untreated CLL. One significant advantage to venetoclax is the ability to produce CRs and minimal residual disease negative (MRD-) responses. In this study, we compare ibrutinib plus obinutuzumab (IO) to ibrutinib plus venetoclax plus obinutuzumab (IVO) with a response-dependent discontinuation. While other studies have been designed with the goal of discontinuation of ibrutinib through combinations with venetoclax, no other study has been presented using a response-dependent discontinuation strategy. Study Design and Methods A041702 is a randomized phase 3 study led by the Alliance for Clinical Trials in Oncology that is currently enrolling through the NCI National Clinical Trials Network (NCTN). CLL patients age 70 years or older who are previously untreated and in need of therapy are eligible. Previous treatment of autoimmune complications with steroids or rituximab is allowed. Patients must have intermediate- or high-risk Rai stage, ECOG performance status 0-2, ANC ≥ 1000/mm3 unless due to marrow involvement, and platelets ≥ 30,000/mm3. CrCl must be ≥ 40 mL/min and AST/ALT ≤ 2.5x upper limit of normal. Patients with hepatitis B must have undetectable viral load, and patients must not have an intercurrent illness that is expected to limit survival to < 5 years. Warfarin and strong inhibitors or inducers of CYP3A4/5 are not permitted. Patients are initially preregistered to the study and submit a peripheral blood sample for central FISH analysis of del(17p). Patients who are registered are randomized 1:1 to Arm 1 (IO) or Arm 2 (IVO), and are stratified by Rai stage and presence of del(17p). IO consists of I daily starting cycle 1 day 1, and O dosed as standard starting cycle 1 day 1 and continuing to cycle 6 day 1. IVO consists of IO as in Arm 1, with V starting cycle 3 day 1 with standard 5-week ramp-up and continuing until cycle 14 day 28. At the end of 14 cycles, patients in both arms undergo response evaluation with central peripheral blood and bone marrow MRD testing. Patients on IO then continue I indefinitely. Patients on IVO who are in a bone marrow MRD- CR discontinue all therapy, and those who are not continue I indefinitely. The primary objective of the study is to compare PFS between IO and IVO using the strategy of response-dependent discontinuation. There is 90% power to detect a hazard ratio for PFS of 0.55 (corresponding to 5-year PFS rates of 70% and 82.187% for IO and IVO, respectively), at a one-sided significance level of 0.025 by a log-rank test. This design requires 128 events and 431 total evaluable patients assuming uniform accrual over the course of 3 years and minimum follow-up of 5 years. The study includes two interim analyses for superiority when 50% and 75% of the expected number of events have been observed and three interim analyses for futility when 25%, 50%, and 75% of the expected number of events have been observed. Conclusions A041702 is an ongoing phase 3 clinical trial using a novel response-dependent discontinuation method. Results of this study have the potential to change the standard of care for older patients with previously untreated CLL. The study is expected to accrue for 3 years beginning January 2019, and we welcome participation from sites throughout the NCTN. Support: U10CA180821, U10CA180882, UG1CA189823, U24CA196171; U10CA180820 (ECOG-ACRIN); https://acknowledgments.alliancefound.org; ClinicalTrials.gov Identifier: NCT03737981 Disclosures Woyach: Janssen: Consultancy, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; AbbVie: Research Funding; Karyopharm: Research Funding; Loxo: Research Funding; Morphosys: Research Funding; Verastem: Research Funding. Lozanski:Beckman Coulter: Research Funding; Boehringer Ingelheim: Research Funding; Stemline Therapeutics Inc.: Research Funding; Genentec: Research Funding. Ding:Merck: Research Funding; DTRM Biopharma: Research Funding. Hill:Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Consultancy, Honoraria; Celegene: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria; Takeda: Research Funding; Amgen: Research Funding; TG therapeutics: Research Funding; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Research Funding; Kite: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Stone:Argenx, Celgene, Takeda Oncology: Other: Data and Safety Monitoring Board/Committee: ; Novartis, Agios, Arog: Research Funding; AbbVie, Actinium, Agios, Argenx, Arog, Astellas, AstraZeneca, Biolinerx, Celgene, Cornerstone Biopharma, Fujifilm, Jazz Pharmaceuticals, Amgen, Ono, Orsenix, Otsuka, Merck, Novartis, Pfizer, Sumitomo, Trovagene: Consultancy. Byrd:Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Genentech: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S; Acerta: Research Funding; Novartis: Other: Travel Expenses, Speakers Bureau; BeiGene: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Genentech: Research Funding; BeiGene: Research Funding; Genentech: Research Funding; Acerta: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau.

INTRODUCTION Mutations in BTK and PLCG2 have been reported to occur in ~80% of CLL patients (pts) who have progression of disease on ibrutinib therapy (Woyach, JCO 2017; Ahn, Blood 2017). These mutations are described as appearing months before actual relapse and thus considered as a potential predictive biomarker for future relapse (Quinquenel, Blood 2019). However, the outcomes of these pts after disease progression are not well described. In this study, we seek to investigate time to next therapy and overall survival (OS) following progression among CLL pts on ibrutinib therapy with and without these resistance mutations. METHODS Between 10/2012 and 6/2019, we identified 34 pts in the Mayo Clinic clinical CLL resource who progressed while receiving ibrutinib therapy and also had testing for BTK and PLCG2 mutation performed as part of routine clinical practice at either NeoGenomics Laboratories or The Ohio State University. OS was calculated from time of ibrutinib progression to last known alive or death date; OS was plotted using Kaplan Meier methods and was compared using the log-rank test between various groups (e.g., mutation positive vs negative; CLL progression vs Richter's). Cumulative incidence of time to next treatment in those who had a treatment after progression was adjusted for the competing risk of death. RESULTS Of 34 pts who progressed while receiving ibrutinib, 26 pts experienced CLL progression and 8 pts had Richter's transformation; baseline characteristics in Table 1A. The presence of a BTK or PLCG2 mutation was found in 20/34 (59%) pts (specific mutations in Table 1B). BTK mutation alone was present in 9 pts, 7 pts had PLCG2 mutation alone, and 4 pts had both mutations. Median time between a positive test and start of next therapy was 4 months (range 1-19 months) and did not vary between BTK vs PLCG2 mutations. Among the 26 pts with CLL progression, 18 (69%) pts had a mutation present: BTK alone (n=8), PLCG2 alone (n=6), both (n=4). Therapy following progression on ibrutinib in these pts was as follows: venetoclax (n=16; 11 pts who continued ibrutinib in combination), idelalisib (n=4), investigational treatments (n=2), continued ibrutinib alone (n=2), dose-adjusted EPOCH-R (etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab; n=1), and unknown (n=1). Twelve of the 26 pts with CLL progression on ibrutinib, including 8 pts with a prior resistance mutation detected, had subsequent progression of disease on the aforementioned next line therapy. Treatment of these patients consisted of the following: restarted ibrutinib in addition to current treatment of venetoclax (n=5), venetoclax (n=2), pembrolizumab (n=2; 1 pt with continued ibrutinib), obinutuzumab with continued ibrutinib (n=1), gemcitabine and vinorelbine with continued ibrutinib (n=1), and no further treatment (n=1). Among the 8 pts with Richter's transformation as the initial progression event on ibrutinib after mutation testing, 1 pt had a BTK mutation and 1 pt had a PLCG2 mutation. Treatments following progression on ibrutinib included multi-agent chemoimmunotherapy (n=3; 2 pts received rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone [R-CHOP] with continued ibrutinib and 1 pt received doxorubicin, bleomycin, vinblastine, dacarbazine [ABVD] alone), pembrolizumab (n=3; 1 pt in combination with continued ibrutinib), venetoclax in combination with continued ibrutinib (n=1), and venetoclax and obinutuzumab (n=1). The median time to next treatment (second line of treatment beyond ibrutinib) for the 31 pts who started another therapy following progression on ibrutinib was 16.7 months (95% CI 9.6-NE; Figure 1A) and was not significantly different for pts with or without a resistance mutation (p=0.57). Median OS for all 26 pts with CLL progression was 28.7 month and there was no difference according to presence or absence of a resistance mutation (median 28.7 months vs 18.2 months, p=0.53; Figure 1B). The 8 pts with Richter's transformation had a median OS of 7.1 months (95% CI 2.0-NE). CONCLUSION Approximately 60% of pts tested in this progression cohort had a BTK or PLCG2 mutation at time of or preceding progression on ibrutinib therapy. OS and time to next therapy did not differ statistically between pts with mutated vs non-mutated clones; however, caution should be applied with the conclusions given the limited sample size. Disclosures Ding: DTRM Biopharma: Research Funding; Merck: Research Funding. Kenderian:Novartis: Patents & Royalties, Research Funding; Tolero: Research Funding; Humanigen: Other: Scientific advisory board , Patents & Royalties, Research Funding; Lentigen: Research Funding; Morphosys: Research Funding; Kite/Gilead: Research Funding. Kay:MorphoSys: Other: Data Safety Monitoring Board; Infinity Pharmaceuticals: Other: DSMB; Celgene: Other: Data Safety Monitoring Board; Agios: Other: DSMB. Parikh:Ascentage Pharma: Research Funding; Genentech: Honoraria; Janssen: Research Funding; AstraZeneca: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; AbbVie: Honoraria, Research Funding; Acerta Pharma: Research Funding.

Background: The 2008 International Working Group for CLL (IWCLL) criteria define MBL as a clonal B-cell disorder with a peripheral blood B-cell count of <5 x 109/L, in the absence of cytopenias(s), lymphadenopathy and/or organomegaly on physical examination, and no other concomitant lymphoproliferative disorder. In the presence of palpable lymphadenopathy and/or organomegaly, and a B-cell count of < 5 x 109/L, a diagnosis of small lymphocytic lymphoma (SLL) is established. A study by Gentile et al (Am J Hematol. 2013) reported that 29 out of 62 individuals with clinically identified MBL (42%) had lymphadenopathy identified on CT imaging. Notably, however, after a median follow-up of 35 months, the rate of progression among cases of MBL with lymphadenopathy identified on CT imaging was only 6.9% (2/29 patients), which was no different than in cases of MBL without lymphadenopathy on CT imaging (rate of progression, 9%; 3/33 patients). Our study sought to 1) determine if lymphadenopathy and/or organomegaly detected by imaging studies performed for unrelated reasons in individuals with MBL can identify a subset with shorter time to first CLL therapy (TFT) and overall survival (OS); and 2) compare outcomes of individuals with MBL who have incidentally detected lymphadenopathy/splenomegaly and SLL patients. Methods: We used the Mayo Clinic CLL Database to identify individuals with high-count MBL (absolute B-cell count: 0.5 - 4.9 x 109/L) and divided them into the following three cohorts: a) Cohort A: no imaging studies available at MBL diagnosis; b) Cohort B: imaging studies done within one year of MBL with no evidence of lymphadenopathy and/or organomegaly; and c) Cohort C: imaging studies done within one year of MBL with lymphadenopathy and/or organomegaly, attributable to MBL. All individuals with MBL were first seen at Mayo Clinic after 1/1/2002; those with a concomitant lymphoproliferative disorder within 3 months of diagnosis were excluded. Patients with SLL seen during the same time interval were identified as a comparison cohort. We compared the baseline characteristics (Kruskal Wallis for continuous and Chi-square for categorical variables) and TFT and OS across the three MBL cohorts, and patients with SLL. Cumulative incidence of TFT was adjusted for the competing risk of death. Age- and sex-adjusted OS was analyzed using inverse weights methods. Results: 657 individuals with high-count MBL with a median follow-up of 6.7 years were identified: 415 (63%) individuals were in Cohort A, 142 (22%) in Cohort B, and 100 in (15%) Cohort C. Compared to Cohort B, individuals in Cohort C were more likely to have unmutated IGHV, high expression of CD38, and higher beta-2 microglobulin level (Table 1). SLL patients were younger, had higher rate of unmutated IGHV, and had high expression of CD49d compared to MBL individuals in Cohort C (Table 1). There was suggestive evidence of a difference in TFT between Cohorts B and C (estimated 10-year treatment rate 28.3% vs. 41.6%; p=0.16; HR 1.62 95% CI 0.84-3.15). TFT was significantly shorter in SLL patients compared to those with Cohort C (estimated 10-year treatment rate 71% vs. 41.6%, respectively, P<0.001; Figure 1A). There was a trend toward shorter OS in Cohort C compared to Cohort B (estimated 10-year OS rate 53.7% vs. 64.2%, respectively, P=0.09; Figure 1B). In contrast, there was no difference in OS among MBL individuals in Cohort C compared to those with SLL (estimated 10-year OS rate 56.9% vs. 62.6%, P=0.72). Summary/Conclusion: Our findings demonstrate that individuals with MBL who have incidentally identified lymphadenopathy/splenomegaly at diagnosis are more likely to have an unfavorable risk profile, shorter TFT and OS compared to patients who did not have lymphadenopathy/splenomegaly at MBL diagnosis. Additionally, these individuals have a longer TFT but similar OS compared to SLL patients seen during the same time interval. If externally validated, these findings have significant implications for individuals with newly diagnosed MBL. Disclosures Ding: Merck: Research Funding; DTRM Biopharma: Research Funding. Kenderian:Novartis: Patents & Royalties, Research Funding; Tolero: Research Funding; Humanigen: Other: Scientific advisory board , Patents & Royalties, Research Funding; Lentigen: Research Funding; Morphosys: Research Funding; Kite/Gilead: Research Funding. Kay:MorphoSys: Other: Data Safety Monitoring Board; Infinity Pharmaceuticals: Other: DSMB; Celgene: Other: Data Safety Monitoring Board; Agios: Other: DSMB. Parikh:AstraZeneca: Honoraria, Research Funding; Janssen: Research Funding; AbbVie: Honoraria, Research Funding; Acerta Pharma: Research Funding; Ascentage Pharma: Research Funding; Genentech: Honoraria; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding.

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 Despite the remarkable outcomes and recent FDA approval of CD19 directed chimeric antigen receptor T (CART19) cell therapy in B cell malignancies, the durable responses in diffuse large B cell lymphoma are less than 40% and CART activity in chronic lymphocytic leukemia (CLL) is further limited. This is thought to be related to loss of CART persistence, poor trafficking to lymph nodes and inhibition by the leukemic microenvironment. Therefore, strategies to enhance CART cell function to overcome these limitations are needed. Recent studies have shown that abnormal expression of the receptor tyrosine kinase (RTK) AXL is associated with poor prognosis in human cancers. AXL signaling is associated with tumor proliferation, survival, metastasis, and drug resistance. Inhibition of AXL RTK with TP-0903, a high affinity AXL inhibitor has been found to induce robust apoptosis of CLL B cells. Based on the significant modulation of T cell functions observed with BTK inhibitor, we examined the role of AXL RTK inhibition with TP-0903 on T cell function in CLL and other B cell malignancies. First, we investigated the effect of AXL inhibition on T cell phenotype in normal donors. When naïve T cells were stimulated with PMA/Ionomycin and cultured with low dose TP0903, cytokine production was favorably altered through the promotion of Th1 and reduction of Th2 cytokines. This was associated with a significant reduction of inhibitory receptors (Fig 1a). Western blot of T cell lysates suggests low dose TP-0903 results in inhibition of LCK. When effector T cells and regulatory T cells (Treg) were treated with TP-0903 for 3 days, there was a preferential reduction of Treg (Fig 1b). Next, we investigated the influence of TP-0903 on CART19 cell phenotype and functions. Here, we used 41BB costimulated, lentiviral-transduced CART cells. Similar to our findings on naïve T cells, TP-0903 treatment led to polarization of CART cells into a Th1 phenotype when T cells were stimulated with the CD19+ mantle cell lymphoma (MCL) cell line JeKo or with leukemic B cells isolated from CLL patients (Fig 1c). TP-0903 treatment also significantly downregulated inhibitory receptors on activated CART cells, including a reduction of canonical cytokines known to be associated with the development of cytokine release syndrome (CRS) (Fig 1c). The combination of CART19 cells and TP-0903 yielded a synergistic antitumor activity against JeKo in vitro, at low E:T ratios (Fig 1d). Western blot of T cell lysates revealed phosphorylation of LCK was remarkably reduced in the presence of TP-0903, suggesting a mechanism for the observed Th1 polarization. We compared the transcriptome of activated CART cells treated with TP-0903 and more than 100 genes were differentially expressed compared to non-treated cells. Among these genes, immune synapse related genes such as cell junction and cell migration related genes were significantly increased in activated CART cells treated with TP-0903. To investigate the effect of AXL RTK inhibition of CART cells with TP-0903 in vivo, we established MCL xenografts through the injection of 1.0x106 of JeKo into NSG mice. A week after the injection of JeKo, mice were treated with either vehicle alone, TP-0903 (20mg/kg/day) alone, 0.5x106 of CART19 alone, or TP-0903 (20mg/kg/day)+0.5x106 of CART19. Three weeks after the treatment, mice were rechallenged with 1.0x106 of JeKo. Mice treated with CART19 and TP-0903 rejected the JeKo tumor challenge while mice previously treated with CART19 alone redeveloped JeKo, suggesting that AXL inhibition enhanced CART cell persistence (Fig 1e). Finally, we validated our preclinical findings in a correlative analyses of Phase I clinical trial of TP-0903 for patients with solid tumors (NCT02729298). Blood T cells from 3 patients were isolated and analyzed before and a week after treatment with TP-0903. Similar to our findings, there was a significant reduction in Tregs, reduction of inhibitory receptors and polarization to a Th1 phenotype. These findings will be further investigated in a planned Phase I clinical trial of TP-0903 in relapsed/refractory CLL (NCT03572634). In summary, we demonstrated for the first time that AXL inhibitior is capable of polarizing T cells into a Th1 phenotype, downregulates inhibitory receptors, reduces CRS associated cytokines and synergizes with CART cells in B cell malignancies. These findings encourage further study of TP-0903 as an enhancer of T cell immunotherapies. Disclosures Mouritsen: Tolero Pharmaceuticals: Employment. Foulks:Tolero Pharmaceuticals: Employment. Warner:Tolero Pharmaceuticals: Employment. Parikh:Janssen: Research Funding; Abbvie: Honoraria, Research Funding; AstraZeneca: Honoraria, Research Funding; MorphoSys: Research Funding; Pharmacyclics: Honoraria, Research Funding; Gilead: Honoraria. Ding:Merck: Research Funding. Kay:Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene: 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; Infinity Pharm: 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; 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; Morpho-sys: Membership on an entity's Board of Directors or advisory committees. Kenderian:Tolero Pharmaceuticals: Research Funding; Humanigen: Research Funding; Novartis: Patents & Royalties.

Abstract Introduction: The most effective initial therapy for older adults with CLL has not yet been established due to the lack of comparison of chemoimmunotherapy (CIT) and targeted therapy with the Bruton's Tyrosine Kinase (BTK) inhibitor ibrutinib. CIT has been the gold standard since studies showing that addition of CD20 antibody to chemotherapy prolongs survival. Bendamustine plus rituximab (BR) is one standard, more aggressive CIT regimen for patients (pts) age 65 or older. While ibrutinib has been FDA approved for untreated CLL since 2016, it has only been compared to chlorambucil, which is relatively ineffective, and never before to aggressive CIT. Additionally, the benefit of the addition of rituximab to ibrutinib in this setting has not been prospectively studied in a phase 3 trial. As part of a randomized phase 3 trial, the Alliance sought to answer these important clinical questions. Pts and Methods: Alliance A041202 is a multicenter NCI National Clinical Trials Network phase 3 study comparing BR (Arm 1) with ibrutinib (Arm 2) and the combination of ibrutinib plus rituximab (Arm 3) to determine whether ibrutinib-containing regimens are superior to CIT in terms of PFS. Additionally, this study sought to determine if adding rituximab to ibrutinib would prolong PFS over ibrutinib alone. At time of progression, pts on Arm 1 could cross over to Arm 2. Eligible pts were those age ≥ 65 years with previously untreated, symptomatic CLL. Pts had a CrCl ≥ 40 mL/min, bilirubin ≤ 1.5 x ULN, and no significant life-limiting intercurrent illness or need for warfarin treatment. Pts were stratified based upon Rai stage, Zap-70 methylation performed centrally, and del(17)(p13.1) or del(11)(q22.3) by local interphase cytogenetics and were randomized 1:1:1 to each arm. With 166 pts per arm, the trial was powered to detect an improvement in 2-year PFS from 61% in Arm 1 to 75% in Arms 2 or 3 (HR=0.586) using two one-sided log-rank tests with type I error rate of 2.5% and 90% power. The Alliance Data and Safety Monitoring Board approved the data release after meeting the protocol-defined efficacy threshold at a planned interim analysis with a one-sided critical value of 0.001538. These data were locked July 2, 2018; updated results will be presented at the meeting. Results: Between 12/9/2013 and 5/16/2016, 547 pts were registered and randomized (Arms 1: 183, 2: 182, and 3: 182). Median age was 71 years and 67% of pts were men. High-risk Rai stage (stage III/IV) was seen in 54%, unmethylated Zap-70 in 53%, and del(17p) or del(11q) by local FISH in 28%. Local vs centralized FISH was performed for del(11q) and del(17p) with agreement between local and central results in 94% (Kappa=0.80) and 97% (Kappa=0.76) of pts, respectively. 525 (96%) pts were eligible and included in the primary PFS analysis (Arms 1: 176, 2: 178, and 3: 171). With median follow-up of 32 months (mo), median PFS was 41 mo in Arm 1 and has not been reached in Arms 2 or 3 (HR comparing Arm 2 to 1 is 0.40 with one-sided p&lt;0.0001; HR comparing Arm 3 to 1 is 0.41 with one-sided p&lt;0.0001; HR comparing Arm 3 to 2 is 1.01 with one-sided p=0.48). 2-year PFS estimates were 74%, 87% in 2, and 88% in Arms 1, 2, and 3 respectively. At this time, there are no significant differences in overall survival (OS) among arms (p=0.87), median OS has not been reached for any arm, and 2-year OS estimates were 95%, 90%, and 94% in Arms 1, 2, and 3, respectively. Adverse events (AEs) were compared among arms using Fisher's exact tests. Grade 3+ treatment-emergent AEs were seen in 428 of 537 evaluable pts with 61%, 41%, and 38% of pts experiencing Grade 3+ heme AEs (p&lt;0.0001) and 60%, 72%, and 71% of pts experiencing Grade 3+ non-heme AEs (p=0.03) in Arms 1, 2, and 3 respectively. Grade 5 AEs were seen in 5 (2.8%), 14 (7.8%), and 14 (7.7%) pts (p=0.07). Unexplained or unwitnessed death over the entire observation period was seen in 2 (1.1%), 7 (3.9%), and 4 (2.2%) pts (p=0.24) in Arms 1, 2, and 3 respectively. Conclusions: This international phase 3 trial demonstrates that ibrutinib produces superior PFS to standard CIT in older pts with CLL and justifies it as a standard of care treatment for pts age 65 and older. The addition of rituximab does not prolong PFS with ibrutinib. While ibrutinib represents a major therapeutic advance, toxicities and also cost justify future efforts to reduce the need for long-term continuous treatment. Support: K23CA178183, R01CA183444, U10CA180821, U10CA180882, U24CA196171, Clinicaltrials.gov identifier: NCT01886872 Figure. Figure. Disclosures Ding: Merck: Research Funding. Bartlett:Astra Zeneca: Research Funding; ImaginAB: Research Funding; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Bristol-Meyers Squibb: Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Affimed: Research Funding; Janssen: Research Funding; Novartis: Research Funding; Merck & Co: Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Immune Design: Research Funding; Forty Seven: Research Funding; Novartis: Research Funding; Millennium: Research Funding. Brander:BeiGene: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; TG Therapeutics: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Genentech: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Novartis: Consultancy, Other: DSMB; AbbVie: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Pharmacyclics, an AbbVie Company: Consultancy, Honoraria, Research Funding; Teva: Consultancy, Honoraria; Acerta: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; DTRM: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding. Barr:AbbVie, Gilead: Consultancy. Parikh:Gilead: Honoraria; Pharmacyclics: Honoraria, Research Funding; MorphoSys: Research Funding; Janssen: Research Funding; AstraZeneca: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding. Coutre:Celgene: Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Pharmacyclics LLC, an AbbVie Company: Honoraria, Research Funding; Gilead: Research Funding; Beigene: Consultancy; AbbVie: Consultancy, Research Funding. Lozanski:Novartis: Research Funding; BI: Research Funding; Genentech: Research Funding; Stem Line: Research Funding; Coulter: Research Funding; Beckman: Research Funding. Larson:Ariad/Takeda: Consultancy, Research Funding; BristolMyers Squibb: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Research Funding. Erba:Amgen: Research Funding; Juno: Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; MacroGenics: Consultancy; Juno: Research Funding; Janssen: Research Funding; Seattle Genetics: Consultancy, Research Funding; Janssen: Research Funding; Juno: Research Funding; Agios: Consultancy, Speakers Bureau; MacroGenics: Consultancy; Incyte: Consultancy, Speakers Bureau; Seattle Genetics: Consultancy, Research Funding; Takeda/Millenium: Research Funding; Novartis: Consultancy, Speakers Bureau; Takeda/Millenium: Research Funding; Incyte: Consultancy, Speakers Bureau; MacroGenics: Consultancy; Celgene: Consultancy, Speakers Bureau; Janssen: Research Funding; Novartis: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Astellas: Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; MacroGenics: Consultancy; Daiichi Sankyo: Consultancy, Research Funding; Pfizer: Consultancy, Other: grant; Astellas: Research Funding; Juno: Research Funding; Janssen: Research Funding; Novartis: Consultancy, Speakers Bureau; Amgen: Research Funding; Agios: Consultancy, Speakers Bureau; Astellas: Research Funding; Agios: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Amgen: Research Funding; Pfizer: Consultancy, Other: grant; Pfizer: Consultancy, Other: grant; Astellas: Research Funding; Amgen: Research Funding; Agios: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Jazz: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Pfizer: Consultancy, Other: grant; Jazz: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Jazz: Consultancy, Speakers Bureau; Seattle Genetics: Consultancy, Research Funding; Celgene: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Takeda/Millenium: Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Celgene: Consultancy, Speakers Bureau; Takeda/Millenium: Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee. Owen:Janssen: Honoraria, Research Funding; Celgene: Research Funding; AstraZeneca: Honoraria, Research Funding; Pharmacyclics: Research Funding; F. Hoffmann-La Roche Ltd: Honoraria, Research Funding; AbbVie: Research Funding; Merck: Honoraria; Teva: Honoraria. Abramson:Bayer: Consultancy; Novartis: Consultancy; Merck: Consultancy; Karyopharm: Consultancy; Seattle Genetics: Consultancy; Verastem: Consultancy; Humanigen: Consultancy; Juno Therapeutics: Consultancy; Gilead: Consultancy; Celgene: Consultancy; Amgen: Consultancy.

Abstract Introduction: Richter transformation (RT) refers to transformation of chronic lymphocytic leukemia (CLL) to an aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL). Most studies on the management of RT were either small retrospective series or early phase non-randomized trials before the era of novel agents. The natural history, prognostication and optimal treatment of patients with RT remain undefined. Here we report the clinical characteristics and outcomes of a large series of RT from a single center. Methods: Biopsy-confirmed RT (limited to non-Hodgkin lymphoma) diagnosed from 4/1993 to 4/2018 were identified from the Mayo Clinic CLL database. Clinical characteristics, treatment information and follow-up data were abstracted by chart review. Overall survival (OS) was defined as time from RT diagnosis to death from any cause and analyzed using the Kaplan-Meier method. Statistical analysis was done in SAS 9.4. Results: A total of 204 patients with CLL who developed RT were identified. The median age at CLL diagnosis was 62 years (range 22-85), and 148 (73%) were male. The median time to transformation was 4.7 years (range 0-34.5). Prior to RT, 68 (33.3%) patients received no treatment for CLL, 109 (53.4%) received chemoimmunotherapy (CIT) only, and 27 (13.2%) received at least one novel agent (idelalisib, ibrutinib, or venetoclax) for CLL. The median lines of CLL therapy prior to RT was 2 (range 0-13). The median age at RT diagnosis was 69 years (range 30-88). Pathology of RT was DLBCL and high grade B-cell lymphoma in 193 (94.6%) and 11 (5.4%) patients, respectively. The median LDH was 306 IU/L (range 99-9000). 62/125 (49.6%) patients had bulky disease (≥ 5 cm), and the median PET SUVmax was 13.9 (range 2.9-30.0). 45/131 (34.4%) patients had del(17p) or TP53 mutation, 12 (9.2%) had del(11q), 21 (16.0%) had trisomy 12, 27 (20.6%) had del(13q), and 25 (19.1%) had normal FISH. The CLL and RT were clonally related in 12/21 (57.1%) patients. For the transformed lymphoma, cell of origin by Han's algorithm was germinal center B cell-like (GCB) and non-GCB in 31/100 (31.0%) and 69/100 (69.0%) patients, respectively. EBV was positive in 14/52 (26.9%) patients. The median Ki-67 was 80% (range 10-100). Myc and Bcl-2 were positive by IHC in 31/43 (72.1%) and 83/103 (80.6%) patients, respectively; 27/56 (48.2%) were double-expressors. MYC, BCL2, and BCL6 rearrangement was positive by FISH in 18/68 (26.5%), 10/34 (29.4%), and 4/31 (12.9%) patients, respectively; 8/66 (12.1%) were double/triple-hit. The most common first-line treatment (Table 1 notes) of RT was R-CHOP-like regimen (n=114, 65.5%). Other treatments included R-EPOCH-like (n=6, 3.4%), high-intensity chemotherapy (n=15, 8.6%), novel agents (eg, ibrutinib, venetoclax, pembrolizumab; n=19, 10.9%), other chemotherapy (n=12, 6.9%), and palliative therapy (n=8, 4.6%). Response to first-line treatment was CR in 57 (38.0%), PR in 33 (22.0%), SD in 18 (12.0%), and PD in 42 (28.0%) patients. The median OS of the entire cohort after RT diagnosis was 12.0 months. The median OS for patients who received no prior CLL treatment, CIT only or at least one novel agent for CLL were 65.5, 7.3, and 12.0 months, respectively (P<0.0001; Figure 1). Of note, in patients who received CIT only for CLL, ~10% and 60% received high-intensity and R-CHOP/R-EPOCH-like chemotherapy, respectively, as first-line RT therapy. In contrast, in patients who had prior novel agents for CLL, 56% and 26% were treated with novel agents and R-CHOP/R-EPOCH-like chemotherapy, respectively, as first-line RT therapy. Patients with or without del(17p)/TP53 mutation had a median OS of 8.3 and 12.8 months, respectively (P=0.046). Patients who were treated with high intensity chemotherapy, R-CHOP/R-EPOCH-like regimens, novel agents, and other therapies for RT had a median OS of 35.1, 14.4, 10.9 and 6.1 months, respectively (P=0.02; Figure 2). OS comparisons by CLL/RT clonal relationship, double expressor or double/triple-hit status are shown in Table 1, with no significant differences noted. Conclusions: Over two thirds of RT were the non-GCB subtype, and about half were Myc/Bcl-2 double expressors. Patients who developed RT without prior CLL therapies had a significantly better OS. In contrast, patients who had received prior CLL therapies had poor outcomes. Myc/Bcl-2 double expressor and MYC/BCL2/BCL6 double/triple hit status had no impact on OS. Disclosures Kenderian: Humanigen: Research Funding; Novartis: Patents & Royalties; Tolero Pharmaceuticals: 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; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: 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; Janssen: Membership on an entity's Board of Directors or advisory committees; Acerta: Research Funding; Cytomx Therapeutics: 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; Gilead: Membership on an entity's Board of Directors or advisory committees. Parikh:Janssen: Research Funding; Abbvie: Honoraria, Research Funding; AstraZeneca: Honoraria, Research Funding; MorphoSys: Research Funding; Gilead: Honoraria; Pharmacyclics: Honoraria, Research Funding. Ding:Merck: Research Funding.

Abstract Background: Synthetic lethality (SL) is characterized by the chemical inhibition of multiple aberrant genes to differentially kill malignant cells. We investigated small-molecule combinations for SL through in vitro and in vivo screening and optimization studies (as in the granted patents in USA and China) and demonstrated the synergistic potential of best-in-class combinations of targeted agents, drug repositioning, immune modulation and low-dose combinations. We hypothesize that BTK and mTOR inhibition coupled with an IMID will target multiple key signaling pathways, improve differential apoptosis and target acquired drug resistance. DTRM-555, an optimized mechanism-based combination, consists of the clinically differentiated BTK inhibitor DTRMWXHS-12 (or DTRM-12), everolimus (EV) and pomalidomide (POM). In xenograft tumor models, DTRM-555 administered orally has demonstrated superior efficacy over monotherapy at very low dose combinations of the three agents (1/18 of DTRM-12, 1/6 of EV, and 1/6 of POM). DTRM-12 monotherapy has been safe and well tolerated in simultaneous phase Ia trials (US and China) with preliminary efficacy across 50 mg through 400 mg once daily (QD). Here we report the US clinical results of the oral combination therapies DTRM-505 (DTRM-12 plus EV) and DTRM-555 (DTRM-12 plus EV plus POM) for the first time (NCT02900716). Methods: The safety and anti-tumor activity of the oral doublet therapy DTRM-505 and the oral triplet therapy DTRM-555 are evaluated using a "3+3" study design. Enrollment was conducted concurrently with a phase Ia study of DTRM-12 monotherapy; with DTRM-505 opened for accrual when monotherapy DTRM-12 cleared the 200-mg dose level. Eligible patients are at least 18 years old, having ECOG performance status less than 2 with relapsed/refractory chronic lymphocytic leukemia (CLL), diffuse large B cell lymphoma (DLBCL), mantle cell lymphoma (MCL), follicular lymphoma (FL) or classical Hodgkin lymphoma (cHL). Study treatment is administered daily for 21 consecutive days over a 28-day cycle. The dose-limiting toxicity (DLT) period was defined during the first cycle of therapy, and treatment was continued until disease progression or unacceptable toxicity. Patients underwent tumor evaluations every 2 months and response was recorded using revised response criteria (IWCLL and Cheson 2014). Results: Between 9/2016 and 7/2018, 19 patients have been treated with DTRM-12 monotherapy in the USA (6 pts, 50-300 mg) and China (13 pts, 50-400 mg). Patients have tolerated up to 23+ cycles of DTRM-12 monotherapy. Seven patients, including DLBCL, CLL, MCL, FL and cHL, have been treated with oral doublet therapy DTRM-505 for 2 to 12 cycles. Three patients (2 DLBCL, 1 FL) have been treated with oral triplet therapy DTRM-555, including one patient transitioned from the doublet DTRM-505 under an exploratory arm. No patient has discontinued due to an adverse event (AE) and no DLT has occurred. Recurring AEs are mostly grade 1 or 2 and responses have been seen with DTRM-505 and DTRM-555 across diverse lymphoma histologies (See Tables). All patients evaluable for response demonstrated partial response to DTRM-505 and DTRM-555, with 2/7 (doublet) and 3/3 (triplet) patients remaining on therapy. Conclusion: The maximum tolerated dose has not been reached for DTRM-12 monotherapy and for the current fixed dose doublet and triplet combinations. Toxicities have been mild and repeated cycles of study treatment have been well tolerated without delays of subsequent treatment cycles. Enrollment continues for refractory lymphoma patients to demonstrate the safety and efficacy for the first-in-class oral triplet therapy DTRM-555. Disclosures Huntington: Janssen: Consultancy; Bayer: Consultancy; Celgene: Consultancy. Schuster:Merck: Consultancy, Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; OncLive: Honoraria; Dava Oncology: Consultancy, Honoraria; Physician's Education Source, LLC: Honoraria; Nordic Nanovector: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals Corporation: Honoraria, 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. He:Zhejiang DTRM Biopharma Co. Ltd.: Other: Founder and CEO; Zhejiang DTRM Biopharma LLC: Other: Founder and CEO. Shen:Zhejiang DTRM Biopharma LLC: Other: Clinical Operations Director. Kennard:AbbVie, Gilead, Verastem: Consultancy. Dwivedy Nasta:Incyte: Research Funding; Takeda/Millenium: Research Funding; Debiopharm: Research Funding; Pharmacyclics: Research Funding; Rafael/WF: Research Funding; Aileron: Research Funding; Roche: Research Funding; Merck: Other: DSMC; Celgene: Membership on an entity's Board of Directors or advisory committees. Landsburg:Takeda: Consultancy; Curis: Consultancy, Research Funding. Porter:Novartis: Other: Advisory board, Patents & Royalties, Research Funding; Genentech: Other: Spouse employment; Kite Pharma: Other: Advisory board. Svoboda:Bristol-Myers Squibb: Consultancy, Research Funding; TG Therapeutics: Research Funding; Kyowa: Consultancy; Regeneron: Research Funding; Merck: Research Funding; Seattle Genetics: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding; KITE: Consultancy. Song:Peking University Cancer Hospital (Beijing Cancer Hospital): Employment. Zhu:Beijing Cancer Hospital: Employment. Brander:Pharmacyclics, an AbbVie Company: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; TG Therapeutics: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Novartis: Consultancy, Other: DSMB; Genentech: Consultancy, Honoraria, Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; Teva: Consultancy, Honoraria; Acerta: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; DTRM: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding; BeiGene: Other: Institutional research funding for non investigator initiated clinical trial, Research Funding. Ding:Merck: Research Funding. Mato:Pharmacyclics, an AbbVie Company: Consultancy, Research Funding; AstraZeneca: Consultancy; Regeneron: Research Funding; Celgene: Consultancy; Acerta: Research Funding; TG Therapeutics: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Portola: Research Funding; Johnson & Johnson: Consultancy; Prime Oncology: Honoraria; Medscape: Honoraria.

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.