ALBERT

Description: Notch1-mutated T-ALL is an aggressive hematologic malignancy lacking targeted therapeutic options. Genomic alterations in Notch1-gene and its activated downstream pathways are associated with metabolic stress response and heightened glutamine (Gln) utilization to fuel oxidative phosphorylation (OxPhos) (Kishton at al., Cell Metabolism 2016, 23:649, Herranz at al., Nat Med, 2015, 21(10): 1182-1189). Hence, targeting NOTCH1-associated OxPhos and/or Gln dependency could constitute a plausible therapeutic strategy for T-ALL. In this study we examined metabolic vulnerabilities of NOTCH1-driven T-ALL and tested pre-clinical efficacy of novel mitochondrial complex I (OxPhosi) IACS-010759 and of glutaminase inhibitor CB-839 (GLSi) in T-ALL models including Notch1-mutated T-ALL cell lines, patient-derived xenograft (PDX) and primary T-ALL cells. We have previously reported and confirmed in this expanded study the anti-leukemia efficacy of IACS-010759 (EC50s 0.1-15 nM) (Molina at al., Nat Med, 2018, 24: 1036; Baran at al., Blood, 2018, 132:4020). Metabolic characterization demonstrated that OxPhosi caused striking dose-dependent decrease in basal and maximal oxygen consumption rate (OCR), ATP and NADH generation in T-ALL cell lines and primary T-ALL samples (p

Description: CD19-directed chimeric antigen receptor T cell (CAR-T) therapy has shown impressive results in children and adults with relapsed or refractory B-ALL or diffuse large B-cell lymphoma. However, 30 - 70% of initial responders will eventually relapse with CD19 antigen loss (CD19Neg) (Maude SL, et al. N Engl J Med. 2018). To avoid CD19Neg relapse, patients may undergo a hematopoietic stem cell transplant (HSCT). HSCT is an expensive and often morbid procedure that many physicians would prefer to avoid. The development of tools to accurately predict which patients are at risk for CD19Neg relapse would guide treatment decisions regarding HSCT or alternative therapies. Since CD19Neg relapses also occur in patients treated with other CD19-directed immunotherapies, like blinatumomab (Mejstríková E, et al. Blood Cancer J. 2017), a predictive model to detect patients at risk of CD19Neg relapse would have broader therapeutic impact. To address this problem, we performed CyTOF and RNA-seq analysis from paired patient samples collected before CD19-directed CAR-T administration and after CD19Neg relapse. High dimensional phenotyping by CyTOF clustered patient samples based on their mechanism of CD19 expression loss (frameshift mutation versus expression of intracellular isoforms), even before CAR-T administration. In addition, we identified identical immunoglobulin heavy and light chain RNA sequences before CAR-T administration and after CD19Neg relapse, suggesting that the clones destined to cause relapse are present at the time of CAR-T administration. Altogether, these results support our hypothesis that resistant tumor cells are present before CAR-T administration and could be discovered and interrogated for CD19Neg relapse prediction. To identify cell subpopulations responsible for driving CD19Neg relapse, we used the B cell developmental classifier previously developed in our lab (Good Z, et al. Nat Med. 2018). We observed a significant increase in the Early-non-BI population (CD38Pos CD24Pos CD19Neg CD20Neg CD3Neg CD16Neg CD61Neg cells) after CD19Neg relapse, suggesting that CD19 loss is associated with the loss of other B cell features. Since our classifier relies on CD19 to classify cells, we compared the resulting classification of cells when CD19 was included or excluded in the classifier. This change had minimal impact in cell classification from healthy bone marrow controls. However, when applied to the samples collected before CAR-T administration, we found a subpopulation of CD19Pos Pro-B cells that classified as Early-non-BI cells when CD19 was excluded from the classification. We hypothesize that these Pro-B "discordant" cells are those that lose CD19 expression to escape the immune pressure exerted by the CD19-directed CAR-T and mediate CD19Neg relapse. Further, we found Pro-B "discordant" cells in 77% of independent cohort of 22 B-ALL samples collected at the time of diagnosis, suggesting these cells exist in de novo B-ALL. We likewise identified a CD19Neg IgMPos Early-non-BI subpopulation in 4 healthy bone marrow and further studies are ongoing to characterize these cells. We continue to interrogate this candidate population as that responsible for CD19Neg relapse after CAR-T cell therapy. In addition, we performed differential expression analysis between paired samples collected before (CD19Pos) and after (CD19Neg) CAR-T therapy. Through the application of the developmental classifier, we identified that CD19 loss is associated with upregulation of key B cell transcription factors IKAROS, PAX5 and glucocorticoid receptor in the pre-pro-B to Pre-B stages. Moreover, after CD19 loss, there are also increases in levels of phosphorylated proteins pSYK, pSRC and pSTAT5, involved in IL7 receptor and pre-BCR signaling pathways, essential for B cell development. This suggests that CD19Neg cells activate unique tumorigenic pathways that may provide novel therapeutic opportunities. Exploration and validation of these therapeutic targets could significantly improve clinical outcome and care of patients with CD19Neg B-ALL. In conclusion, these results support the feasibility to predict patients at risk for CD19Neg relapse together with the mechanism behind it. Future studies will be conducted to confirm unique tumorigenic pathways in CD19Neg B cells and determine their therapeutic potential. Disclosures Mullighan: Illumina: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored travel; Amgen: Honoraria, Other: speaker, sponsored travel; AbbVie: Research Funding; Pfizer: Honoraria, Other: speaker, sponsored travel, Research Funding; Loxo Oncology: Research Funding. Grupp:Humanigen: Consultancy; CBMG: Consultancy; Novartis: Consultancy, Research Funding; Roche: Consultancy; GSK: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards; Cure Genetics: Consultancy.

Description: Background: Data on overall survival (OS) and adverse events (AEs) in patients with chronic lymphocytic leukemia (CLL) are mostly available from controlled trials, with limited data from routine clinical practice. We therefore conducted a population-based retrospective cohort study to assess OS, incidence of AEs, and economic burden in patients treated for CLL. Methods: Patients with CLL receiving ≥ 1 systemic therapy from 2013-2015 were selected from the Medicare claims database and followed through 2016. The date of the start of first observed therapy served as the index date. Patients were required to have at least 12 months of continuous Medicare enrollment with no evidence of systemic therapy for CLL and/or SCT before the index date. An observed therapy regimen was defined as the combination of all agents received within 35 days after (and including) the first claim for a systemic therapy drug. Therapy was considered ended upon switch to a different regimen or a gap ≥ 90 days after the last treatment. OS was assessed from the index date until the last follow-up or death using the Kaplan-Meier method. Incidence of hematologic and nonhematologic AEs during treatments were assessed for the most commonly observed regimens. The incidence of AEs was based on the presence of at least one claim containing an AE-specific diagnosis code during the treatment, regardless of any history of the AE before treatment initiation. All-cause direct medical costs were assessed from the Medicare's perspective. Results: We analyzed 7965 patients (median age=76 years) who met the inclusion criteria. In the overall study follow-up (across all observed therapy lines), ibrutinib monotherapy (Ibr; n=2708) was the most frequent regimen, followed by chlorambucil monotherapy (Clb; n=1620) and bendamustine/rituximab (BR; n=1485). Median length of follow-up from the index date was 19 months for Ibr, 21 months for Clb, and 24 months for BR. Median OS was reached only for Clb (40.8 months [95% CI = 38.6-not reached]). 24-month OS rates for Ibr, Clb, and BR recipients were 69% (95% CI = 68%-71%), 68% (95% CI = 65%-71%), and 79% (95% CI = 77%-81%), respectively. The incidence of the most frequent AEs (occurrence in 〉10% of patients) are presented in Table1 1; estimates in bold indicate that the incidence of the AE was higher by ≥ 5 percentage points than in the noted trials (Woyach, 2018, N Engl J Med; Burger, 2015, N Engl J Med). The mean per patient per month costs, among all patients, were $1,915 (SD = $2,453) during the baseline period and $8,974 (SD = $11,562) during the period after initiation of the first observed CLL-directed systemic therapy. Mean monthly all-cause costs increased by the number of AEs (from $5,144 [SD = $5,409] among those with 1-2 AEs to $10,077 [SD = $12,542] among those with ≥6 AEs). Conclusion: To our knowledge, this is the largest contemporary observational study reporting outcomes among CLL patients initiating treatments in a real-world setting. Over two-thirds of patients survived ≥2 years after start of the first observed therapy during the study period. Incidence for several hematologic and nonhematologic AEs during the common CLL therapies observed in this study appear to be higher than those reported in the noted clinical trials, highlighting potentially greater susceptibility to these AEs and an unmet medical need in Medicare patients with CLL treated in routine practice. This study also highlights a substantial economic burden that exists in the period after initiation of treatment for CLL. Disclosures Goyal: RTI Health Solutions: Employment. Nagar:RTI Health Solutions: Employment. Kabadi:AstraZeneca: Employment, Equity Ownership. Davis:RTI Health Solutions: Employment. Le:AstraZeneca: Employment, Other: Stocks. Kaye:RTI Health Solutions: Employment.

Description: Ras-related C3 botulinum toxin substrate 2 (RAC2), through interactions with reduced NAD phosphate oxidase component p67phox, activates neutrophil superoxide production, whereas interactions with p21-activated kinase are necessary for fMLF-induced actin remodeling. We identified 3 patients with de novo RAC2[E62K] mutations resulting in severe T- and B-cell lymphopenia, myeloid dysfunction, and recurrent respiratory infections. Neutrophils from RAC2[E62K] patients exhibited excessive superoxide production, impaired fMLF-directed chemotaxis, and abnormal macropinocytosis. Cell lines transfected with RAC2[E62K] displayed characteristics of active guanosine triphosphate (GTP)–bound RAC2 including enhanced superoxide production and increased membrane ruffling. Biochemical studies demonstrated that RAC2[E62K] retains intrinsic GTP hydrolysis; however, GTPase-activating protein failed to accelerate hydrolysis resulting in prolonged active GTP-bound RAC2. Rac2+/E62K mice phenocopy the T- and B-cell lymphopenia, increased neutrophil F-actin, and excessive superoxide production seen in patients. This gain-of-function mutation highlights a specific, nonredundant role for RAC2 in hematopoietic cells that discriminates RAC2 from the related, ubiquitous RAC1.

Description: Despite intense efforts, multiple myeloma remains incurable in most patients with the standard of care therapies. The plasma cell surface receptor B cell maturation antigen (BMCA) is highly expressed by myeloma cells and we recently demonstrated that 12 out of 25 heavily pretreated myeloma patients achieved a partial response or better after anti-BCMA CAR T cell treatment (VGPR, n=5; CR, n=1; sCR, n=1; Cohen et al., 2019, JCI 129(6):2210). To better understand the biological basis of this therapy, we identified key correlates of response using the pre-manufacturing apheresed T cells, the infusion product, and post-infusion T cells from the 25 patients in this cohort. As reported before, the disease characteristics, tumor burden, and CAR transduction efficiency did not correlate with therapy response. CAR T cell expansion, measured by the area under the curve of CAR qPCR in the first 21 days (AUC[0-21]), was highest in responding, lowest in non-responding patients (Jonckheere-Terpstra test, JT = 38, p=1.8x10^-6)(Fig.1A,B). Soluble BCMA, a biomarker of disease burden, shows a similar trend with response (Jonckheere-Terpstra test, JT = 54, p=1.2x10^-4). Furthermore, AUC[0-21] for CAR T cell expansion and soluble BCMA decline also strongly correlated (Spearman's rank correlation test, rho=0.82; p=2.41x10^-6), underscoring the quantitative relationship between CAR T cell expansion and tumor reduction. We have previously shown that response to CAR T cell therapy in CLL is largely determined by T cell memory function. To find if this extends to myeloma, we immunophenotyped apheresed T cells (or CAR-T precursor cells) and infusion product from the 25 patients. Phenotypically distinct T cell subpopulations were identified using shared-nearest-neighbor clustering method (PMID: 31178118) and their correlation with response to CAR T cell treatment was evaluated. This analysis revealed that among CD4+ and CD8+ CAR-T precursor cells, subpopulations representing naive and central memory T cells were enriched in T cells from responding patients, while non-responders displayed a distinctly activated effector phenotype at baseline. Additional analyses showed that apheresed CD8+ and CD4+ T cells from responder patients were non-cycling, granzyme B-negative, CTLA4[low] but otherwise largely immune checkpoint inhibitor-negative. CD8+ CAR-T precursor cells isolated from non-responders exhibited high expression levels of TIM3 or LAG3, and/or granzyme B, but not PD1, CTLA4, CD45RO or CD27. These data confirm the high activation, potential exhaustion and end-stage differentiation state of CAR-T precursor cells in this group. Similar analyses of infusion product CAR T cells did not reveal subpopulations associated with response. Clustering analysis of CD8+ CAR T cells within 20 days after infusion revealed a BCMA CAR-expressing cluster enriched in responding patients: a non-cycling, negatively regulated, Eomes-expressing central memory subset (cluster 0; Fig. 1E). Non-responding patients CAR-T cells displayed high levels of granzyme B and PD1 expression but were otherwise devoid of signs of activation (cluster 8; Fig. 1F). Furthermore, the abundance of CD8+ CAR-T cells with cluster 0 and 8 phenotype correlated significantly with in vivo expansion (AUC[0-21]; Fig. 1C). Four patients with a sufficiently high proportion of CAR expressing cells were phenotyped up to 125 days post-infusion. This analysis showed that the highly activated CAR T cell clusters 2 and 5 dominated at early phases post infusion but was rapidly replaced by non-cycling CAR T cells with downregulated CTLA4 and LAG3 but maintained expression of PD1 and TIM3 (cluster 0; Fig. 1D). Patient 27 with VGPR had a prominent effector population four months after infusion. BCMA-redirected CD4+ CAR T cells showed an enrichment of central memory phenotype CAR T cells in responding patients early after infusion, with high expression of Eomes, TIM3, and other immune checkpoint inhibitor molecules. This cluster also dominated the CD4 T cell repertoire in the first four months after infusion in the four responding patients. In conclusion, our data suggest that strategies to promote expression of Eomes and central memory function and reduce exhaustion in BCMA CAR T cells will enhance clinical activity. Further, these results underscore the "self-sustaining" feature of successful CAR T cell therapies in myeloma. Disclosures Pruteanu: Novartis: Employment. Cohen:Poseida Therapeutics, Inc.: Research Funding. Garfall:Tmunity: Honoraria, Research Funding; Amgen: Research Funding; Novartis: Patents & Royalties: inventor on patents related to tisagenlecleucel (CTL019) and CART-BCMA, Research Funding; Janssen: Research Funding; Surface Oncology: Consultancy. Lacey:Novartis: Patents & Royalties: Patents related to CAR T cell biomarkers; Tmunity: Research Funding; Novartis: Research Funding. Fraietta:Tmunity: Research Funding; Cabaletta: Research Funding; LEK Consulting: Consultancy. Brogdon:Novartis: Employment. Davis:Tmunity: Research Funding; Cabaletta: Research Funding. Levine:Tmunity Therapeutics: Equity Ownership; Avectas: Membership on an entity's Board of Directors or advisory committees; Vycellix: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Novartis: Consultancy, Patents & Royalties, Research Funding; Cure Genetics: Consultancy; Incysus: Membership on an entity's Board of Directors or advisory committees; Brammer Bio: Membership on an entity's Board of Directors or advisory committees; CRC Oncology: Consultancy. Milone:Novartis: Research Funding; Novartis: Patents & Royalties: patents related to tisagenlecleucel (CTL019) and CART-BCMA. Stadtmauer:Janssen: Consultancy; Tmunity: Research Funding; Amgen: Consultancy; Abbvie: Research Funding; Novartis: Consultancy, Research Funding; Takeda: Consultancy; Celgene: Consultancy. June:Novartis: Research Funding; Tmunity: Other: scientific founder, for which he has founders stock but no income, Patents & Royalties. Melenhorst:National Institutes of Health: Research Funding; Parker Institute for Cancer Immunotherapy: Research Funding; Novartis: Research Funding, Speakers Bureau; Colorado Clinical and Translational Sciences Institute: Membership on an entity's Board of Directors or advisory committees; Stand Up to Cancer: Research Funding; Incyte: Research Funding; IASO Biotherapeutics, Co: Consultancy; Simcere of America, Inc: Consultancy; Shanghai Unicar Therapy, Co: Consultancy; Genentech: Speakers Bureau.

Description: Background: Financial Toxicity (FT) is increasingly recognized as a major contributor to morbidity and mortality in a variety of cancers. Previous research has demonstrated patients with myeloproliferative neoplasms (MPNs) exhibit a substantial comorbidity burden and have an increased risk of mortality. The purpose of this study was to define rates of FT and the implications on morbidity and mortality in this population using patient reported data. Methods: All patients seen at the Levine Cancer Institute, a tertiary hospital-based specialty practice, were surveyed prior to their visit over a six-month period. All patients were aged ≥18 years and diagnosed with Philadelphia chromosome−negative classical MPNs including myelofibrosis (MF), polycythemia vera (PV), and essential thrombocythemia (ET). The survey consisted of the PROMIS Global-10 measure and two questions from the COST measure. FT was defined as scoring 4 or less (maximum: 10) in agreement with the COST questions: "I know that I have enough money in savings, retirement, or assets to cover the costs of my treatment" and "I am satisfied with my current financial situation." Patient disease and treatment characteristics were summarized with frequencies and proportions for categorical variables and medians and ranges for continuous variables. Correlation of numerical FT scores with PROMIS scores was assessed with Pearson correlation coefficients and ANOVA regression. Additionally, model selection was carried out using logistic regression to identify factors impacting the incidence of financial toxicity (where FT score 4 compared to patients with FT scores 4 (p =.287). There also appeared to be a separation of the survival curves when looking at both time from diagnosis and time from survey administration (Figures 2 and 3). Age, race, gender, insurance type, distance from the hospital, disease type, disease specific risk classification, medications utilized, and history of blood/marrow transplant were not found to be significantly different in the two groups. Conclusions: Patients with myeloproliferative neoplasms represent an extremely vulnerable population for financial toxicity with quantifiably increased distress related to this toxicity increasing morbidity and potentially mortality. These findings should be validated in a larger patient cohort and interventions devised to reduce financial distress. Disclosures Knight: Foundation for Financial Planning: Research Funding. Ai:InCyte: Speakers Bureau; Amgen: Speakers Bureau. Trivedi:Incyte: Speakers Bureau. Avalos:Best Practice-Br Med J: Patents & Royalties: receives royalties from a coauthored article on evaluation of neutropenia; Juno: Membership on an entity's Board of Directors or advisory committees. Symanowski:Boston Biomedical: Membership on an entity's Board of Directors or advisory committees; Carsgen Therapeutics: Membership on an entity's Board of Directors or advisory committees; Eli Lilly: Membership on an entity's Board of Directors or advisory committees; Immatics: Membership on an entity's Board of Directors or advisory committees. Grunwald:Amgen: Consultancy; Novartis: Research Funding; Genentech/Roche: Research Funding; Pfizer: Consultancy; Daiichi Sankyo: Consultancy; Trovagene: Consultancy; Agios: Consultancy; Incyte: Consultancy, Research Funding; Cardinal Health: Consultancy; Forma Therapeutics: Research Funding; Abbvie: Consultancy; Celgene: Consultancy; Merck: Consultancy; Medtronic: Equity Ownership; Janssen: Research Funding.

Description: Though hematopoietic stem cell transplantation (HSCT) is the preferred treatment for a variety of blood malignancies, its use is limited by the development of acute graft-versus-host disease (aGvHD). Type II innate lymphoid cells (ILC2s) are immune cells that play an important role in maintaining mucosal homeostasis, and our lab has previously shown that ILC2s in the gastrointestinal tract (GI) are sensitive to conditioning therapy prior to HSCT. Strikingly, we have demonstrated that the infusion of activated donor ILC2s markedly reduces aGvHD-associated mortality. We therefore wanted to investigate the mechanism of the loss of protective ILC2s from the GI tract. We hypothesized that ILC2s fail to repopulate the gut after HSCT due to inflammatory environmental cues that convert ILC2 precursors to an alternate, ILC1- or ILC3-like fate. Thus, we evaluated the impact of cytokines associated with commitment on murine ILC2s by exposing them to cytokines that may promote differentiation to an ILC1 or ILC3 fate (IL-1b/IL-12/IFN-γ and TGF-b/IL-6/IL-23, respectively). We found ILC2 cells acquired the ability to secrete TNF and IL-17 after in vitro skewing (with these lineage-defining cytokines. To test the ability of these "ex-ILC2" cells to home to other tissues in vivo, GFP-ILC2s were infused into recipients at the time of transplantation. We tracked GFP-ILC2s to the liver and spleen, where they made IFN-g and IL-17 and expressed transcription factors associated with the ILC1 and ILC3 lineages (Figure 1). Next we assessed the ability of cytokines alter ILC2 fate via epigenetic reprogramming by using ChIP-sequencing to evaluate the presence of histone marks that may underlie cellular plasticity. We show that these changes are associated with alterations in epigenetic marks around pioneer, lineage-determining factors. We therefore chose to test a screen of compounds known to modulate a variety of epigenetic targets to ask if they can maintain or convert ILC2s to alternate fates and identified a number of compounds that target bromodomains, methyltransferases, and histonedeacetylases, respectively, that alter the viability and differentiation of ILC2s into an "ex-ILC2"-like phenotype. Preliminary work suggests that maintenance ofG9a expression is able to rescue the loss of ILC2s, which is being tested in vivo. Taken together, these data provide new insights into mechanisms by which innate lymphoid cell precursors are epigenetically regulated, providing novel approaches to treating aGvHD following HSCT. Figure 1 Disclosures Davis: Triangle Biotechnology: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Pattenden:Triangle Biotechnology, Inc.: Equity Ownership, Other: Inventor on intellectual property. Serody:Merck: Research Funding; GlaxoSmithKline: Research Funding.

Description: Background Granulocyte colony-stimulating factor (G-CSF) is the standard of care for mobilization of hematopoietic stem cells (HSCs). G-CSF requires 4-7 days of injections and often multiple aphereses to acquire sufficient CD34+ cells for transplant. The number of CD34+ HSCs mobilized can be variable and patients who fail to mobilize enough CD34+ cells are treated with the combination of G-CSF plus plerixafor. G-CSF use is associated with bone pain, nausea, headaches, fatigue, rare episodes of splenic rupture, and is contraindicated for patients with autoimmune and sickle cell disease. MGTA-145 (GroβT) is a CXCR2 agonist. MGTA-145, in combination with plerixafor, a CXCR4 inhibitor, has the potential to rapidly and reliably mobilize robust numbers of HSCs with a single dose and same-day apheresis for transplant that is free from G-CSF. MGTA-145 plus plerixafor work synergistically to rapidly mobilize HSCs in both mice and non-human primates (Hoggatt, Cell 2018; Goncalves, Blood 2018). Based on these data, Magenta initiated a Phase 1 dose-escalating study to evaluate the safety, PK and PD of MGTA-145 as a single agent and in combination with plerixafor. Methods This study consists of four parts. In Part A, healthy volunteers were dosed with MGTA-145 (0.0075 - 0.3 mg/kg) or placebo. In Part B, MGTA-145 dose levels from Part A were selected for use in combination with a clinically approved dose of plerixafor. In Part C, a single dose MGTA-145 plus plerixafor will be administered on day 1 and day 2. In Part D, MGTA-145 plus plerixafor will be administered followed by apheresis. Results MGTA-145 monotherapy was well tolerated in all subjects dosed (Table 1) with no significant adverse events. Some subjects experienced mild (Grade 1) transient lower back pain that dissipated within minutes. In the ongoing study, the combination of MGTA-145 with plerixafor was well tolerated, with some donors experiencing Grade 1 and 2 gastrointestinal adverse events commonly observed with plerixafor alone. Pharmacokinetic (PK) exposure and maximum plasma concentrations increased dose proportionally and were not affected by plerixafor (Fig 1A). Monotherapy of MGTA-145 resulted in an immediate increase in neutrophils (Fig 1B) and release of plasma MMP-9 (Fig 1C). Neutrophil mobilization plateaued within 1-hour post MGTA-145 at doses greater than 0.03 mg/kg. This plateau was followed by a rebound of neutrophil mobilization which correlated with re-expression of CXCR2 and presence of MGTA-145 at pharmacologically active levels. Markers of neutrophil activation were relatively unchanged (20/µl CD34s in 92% (11/12) subjects compared to 50% (2/4) subjects receiving plerixafor alone. Preliminary data show that there was a significant increase in fold change relative to baseline in CD34+ cells (27x vs 13x) and phenotypic CD34+CD90+CD45RA- HSCs (38x vs 22x) mobilized by MGTA-145 with plerixafor. Mobilized CD34+ cells were detectable at 15 minutes with peak mobilization shifted 2 - 4 hours earlier for the combination vs plerixafor alone (4 - 6h vs 8 - 12h). Detailed results of single dose administration of MGTA-145 and plerixafor given on one day as well as also on two sequential days will be presented along with fully characterized graft analysis post apheresis from subjects given MGTA-145 and plerixafor. Conclusions MGTA-145 is safe and well tolerated, as a monotherapy and in combination with plerixafor and induced rapid and robust mobilization of significant numbers of HSCs with a single dose in all subjects to date. Kinetics of CD34+ cell mobilization for the combination was immediate (4x increase vs no change for plerixafor alone @ 15 min) suggesting the mechanism of action of MGTA-145 plus plerixafor is different from plerixafor alone. Preliminary data demonstrate that MGTA-145 when combined with plerixafor results in a significant increase in CD34+ fold change relative to plerixafor alone. Magenta Therapeutics intends to develop MGTA-145 as a first line mobilization product for blood cancers, autoimmune and genetic diseases and plans a Phase 2 study in multiple myeloma and non-Hodgkin lymphoma in 2020. Disclosures DiPersio: Magenta Therapeutics: Equity Ownership; NeoImmune Tech: Research Funding; Cellworks Group, Inc.: Membership on an entity's Board of Directors or advisory committees; Karyopharm Therapeutics: Consultancy; Incyte: Consultancy, Research Funding; RiverVest Venture Partners Arch Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; WUGEN: Equity Ownership, Patents & Royalties, Research Funding; Macrogenics: Research Funding, Speakers Bureau; Bioline Rx: Research Funding, Speakers Bureau; Celgene: Consultancy; Amphivena Therapeutics: Consultancy, Research Funding. Hoggatt:Magenta Therapeutics: Consultancy, Equity Ownership, Research Funding. Devine:Kiadis Pharma: Other: Protocol development (via institution); Bristol Myers: Other: Grant for monitoring support & travel support; Magenta Therapeutics: Other: Travel support for advisory board; My employer (National Marrow Donor Program) has equity interest in Magenta. Biernat:Medpace, Inc.: Employment. Howell:Magenta Therapeutics: Employment, Equity Ownership. Schmelmer:Magenta Therapeutics: Employment, Equity Ownership. Neale:Magenta Therapeutics: Employment, Equity Ownership. Boitano:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Cooke:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Goncalves:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Raffel:Magenta Therapeutics: Employment, Equity Ownership. Falahee:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Morrow:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Davis:Magenta Therapeutics: Employment, Equity Ownership.

Description: Introduction: Despite therapeutic advances, there remains a considerable need for novel therapies for B-cell lymphomas. Although a high proportion of patients (pts) show response to initial therapy, many fail to achieve durable remissions and experience recurrent disease. Agents that target molecular pathways associated with the development and progression of lymphoma are likely to be highly effective and are desirable. The p110δ isoform of the PI3K enzyme is mainly expressed in lymphocytes and has been an attractive therapeutic target, with several PI3Kδ inhibitors demonstrating meaningful efficacy in B-cell lymphomas. Targeting the p110β isoform may further overcome tumor growth and escape mechanisms by mitigating the upregulation of the PI3K/AKT pathway, particularly in PTEN-deficient lymphomas. KA2237 is an oral, potent and selective inhibitor of the PI3K β and δ isoforms. The aim of this first in human, phase I, open-label, single arm study (NCT02679196) was to investigate the safety, tolerability, pharmacokinetic properties and pharmacodynamic effects of KA2237, in order to determine the maximum tolerated dose based on dose limiting toxicity and assess preliminary anti-tumor activity in pts with R/R B-cell lymphoma. Methods: Pts ≥ 18 years (yrs) of age, ECOG ≤ 2, with B-cell lymphoma R/R or intolerant of established therapies (including rituximab) were enrolled using a 3+3 dose escalation (50-400mg) design. KA2237 was given orally on a once daily continuous schedule until progression or unacceptable toxicity. Anti-tumor activity was evaluated by computed tomography and, when available, integrating 18F-FDG positron emission tomography response assessment, at 8, 16 and 24 weeks. Response was assessed according to Lugano 2014 criteria. Pts received PJP prophylaxis. Results: 21 pts with B-cell lymphoma were enrolled (8 DLBCL [diffuse large B-cell], 5 FL [follicular], 3 MCL [mantle cell], 3 CLL/SLL [chronic lymphocytic leukemia/small lymphocytic lymphoma], 1 MZL [marginal zone], 1 WM [Waldenstrom]). Pts received KA2237 at 4 dose levels: 50mg (n=6), 100mg (n=3), 200mg (n=7) and 400mg (n=5) daily; 21 pts were evaluable for safety assessment. Pharmacokinetic profiles were favorable with mean plasma half-life of 17-33 hours, compatible with once daily oral dosing. Median age was 69 yrs (range 48-84) with 76% males; median number of prior therapies was 3 (range 1-6). Median follow up duration was 8.5 months (range 6.9-24.6). Median duration of drug exposure was 82 days (range 10-714 days). 86% of pts experienced treatment-related adverse events (TRAE). 43% of pts experienced a grade ≥ 3 TRAE, with rash (n=3), transaminitis (n=2) and pneumonitis (n=2) occurring in more than 1 pt. 29% discontinued treatment due to a TRAE with pneumonitis (n=2) occurring in more than 1 pt. One grade 5 TEAE (multifocal pneumonia) was observed. 19/21 pts were evaluable for response, ORR was 37% (4 CR, 3 PR). Responses were observed across lymphoma subtypes including DLBCL, FL, CLL and MCL. Responses were often durable (see Figure) and in 2 pts with DLBCL who achieved CR permitted consolidation by autologous stem cell transplantation. Conclusions: KA2237 is an oral, once a day, selective dual inhibitor of PI3K β/δ with a manageable toxicity profile and promising single-agent clinical activity in heavily pretreated R/R B-cell lymphoma. The recommended phase II dose is 200mg daily. The findings of this study support the further evaluation of KA2237. Figure. Disclosures Nastoupil: Novartis: Honoraria; Spectrum: Honoraria; Janssen: Honoraria, Research Funding; Gilead: Honoraria; Genentech, Inc.: Honoraria, Research Funding; Bayer: Honoraria; Celgene: Honoraria, Research Funding; TG Therapeutics: Honoraria, Research Funding. Neelapu:Acerta: Research Funding; Merck: Consultancy, Research Funding; Poseida: Research Funding; Unum Therapeutics: Consultancy, Research Funding; Karus: Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Incyte: Consultancy; Precision Biosciences: Consultancy; BMS: Research Funding; Allogene: Consultancy; Pfizer: Consultancy; Cellectis: Research Funding; Novartis: Consultancy; Celgene: Consultancy, Research Funding; Cell Medica: Consultancy. Fowler:Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; ABBVIE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Westin:Janssen: Other: Advisory Board, Research Funding; Genentech: Other: Advisory Board, Research Funding; Juno: Other: Advisory Board; Unum: Research Funding; Kite: Other: Advisory Board, Research Funding; Novartis: Other: Advisory Board, Research Funding; Curis: Other: Advisory Board, Research Funding; Celgene: Other: Advisory Board, Research Funding; 47 Inc: Research Funding; MorphoSys: Other: Advisory Board. Wang:Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Acerta Pharma: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding; MoreHealth: Consultancy, Equity Ownership; BioInvent: Consultancy, Research Funding; Aviara: Research Funding; BeiGene: Research Funding; Loxo Oncology: Research Funding; VelosBio: Research Funding; Pulse Biosciences: Consultancy; Juno Therapeutics: Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Dava Oncology: Honoraria; Kite Pharma: Consultancy, Research Funding. Beer:Karus therapeutics Ltd.: Employment. Cecil:Karus Therapeutics: Employment. Dow:Karus Therapeutics: Employment. McHale:Karus Therapeutics: Employment. Silva:Karus Therapeutics: Employment. Ward:Karus Therapeutics: Employment. Yavari:Karus Therapeutics: Employment. Shuttleworth:Karus Therapeutics: Employment.

Description: CD19-specific chimeric antigen receptor (CAR) T cell therapies have been highly effective against B cell malignancies. We previously demonstrated that differential responses to anti-CD19 CAR T cell therapy in chronic lymphocytic leukemia (CLL) are associated with early memory T cell signature in apheresed, pre-manufacturing T-cells (CAR T-cell precursors). We tested the hypothesis that the composition of CAR-T precursor cells determines clinical efficacy in adult and pediatric Acute Lymphoblastic Leukemia (ALL), Non-Hodgkin's Lymphoma (NHL), Multiple Myeloma (MM), and CLL. Apheresed T cells were engineered to express 4-1BB plus CD3-zeta-signaling CARs targeting CD19, or B cell maturation antigen (BCMA). The same 9-day manufacturing process was used for all trials. CAR T cell kinetics were monitored using a CAR gene-specific quantitative PCR assay and standard clinical response assessments were performed. Apheresed T cells from 36 CLL, 30 adult ALL, 58 pediatric ALL, 33 NHL, and 25 MM patients were immunophenotyped by flow cytometry. The CLL cohort was used to discover phenotypically distinct subpopulations associated with the two main response groups; these associations were validated in the remaining patient cohorts. Eight CD8+ T cell populations or clusters were identified using the shared-nearest-neighbor clustering method (PMID: 31178118) in the CLL cohort. T cell subsets exhibiting naive (cluster 6) or early memory (cluster 4) features were significantly enriched in responding patients, whereas an effector memory CD8 subpopulation (cluster 2) marked the non-responding patients. Mapping these clusters onto apheresed CD8+ T cells from the other four diseases showed that cluster 4 predicted response to CAR T cell therapy in NHL and myeloma but not in adult and pediatric ALL. We also examined the expression of activation-regulated molecules including HLA-DR, Ki67, and exhaustion-related molecules PD1, CTLA4, TIM3, and LAG3. A CD27+ CD8+ population expressing low level CTLA4 but none of the activation or negative regulatory molecules was significantly enriched in responding CLL patients; this cluster validated in NHL and myeloma. A similar analysis on apheresed CD4+ T cells identified an early memory population (cluster 6) enriched in CLL responders, which expresses CCR7 and CD27 but not CD45RO, CD127, CD28, or other late memory/effector molecules. However, this population did not validate in any of the other diseases. Though not statistically significant, the CD4+ clusters with the largest effect size for enrichment in responders from NHL and myeloma trials exhibited early memory T cell features and lack of HLA-DR expression, suggesting that quiescent early memory state in CD4 may also be associated with clinical responses. A separate analysis of checkpoint inhibitory receptors and activation markers in memory CD4 T cell subsets confirmed the early memory, non-activated state of this population in CLL and was validated in myeloma but none of the other diseases. In vivo activation was a shared theme in CD4+ T cells for non-responding patients as well, though these CLL-defined CD4+ apheresed T cells clusters did not significantly validate in other diseases. In summary, our data confirm and extend our predictive biomarker profile in CLL to mature B cell and plasma cell malignancies by showing that a non-cycling, non-activated early memory CD8+ T cell population in pre-manufacturing cells was validated as a biomarker in myeloma, and NHL. We also showed that responder-associated apheresed CD4+ T cells with early memory features identified in CLL after CD19 CAR T infusions are validated in myeloma after BCMA CAR T. Thus, differentiation state and in vivo activation, and potentially exhaustion, separate response groups. Our findings inform next-generation CAR T-cell manufacturing using the populations identified herein as a starting population. Disclosures Pruteanu: Novartis: Employment. Cohen:Poseida Therapeutics, Inc.: Research Funding. Garfall:Surface Oncology: Consultancy; Novartis: Research Funding; Janssen: Research Funding; Amgen: Research Funding; Tmunity: Research Funding. Milone:Novartis: Patents & Royalties: patents related to tisagenlecleucel (CTL019) and CART-BCMA; Novartis: Research Funding. Gill:Novartis: Research Funding; Tmunity: Research Funding; Carisma: Equity Ownership, Research Funding; Sensei: Consultancy; Aro: Consultancy; Fate: Consultancy. Frey:Novartis: Research Funding. Ruella:Nanostring: Consultancy, Speakers Bureau; Novartis: Patents & Royalties: CART for cancer; AbClon: Membership on an entity's Board of Directors or advisory committees. Lacey:Novartis: Patents & Royalties: Patents related to CAR T cell biomarkers; Tmunity: Research Funding; Novartis: Research Funding. Svoboda:Merck: Research Funding; BMS: Consultancy, Research Funding; Incyte: Research Funding; Pharmacyclics: Consultancy, Research Funding; Celgene: Research Funding; Kite: Consultancy; Seattle Genetics: Consultancy, Research Funding; Kyowa: Consultancy; AstraZeneca: Consultancy. Chong:Tessa: Consultancy; Novartis: Consultancy; Merck: Research Funding. Fraietta:LEK Consulting: Consultancy; Cabaletta: Research Funding; Tmunity: Research Funding. Davis:Cabaletta: Research Funding; Tmunity: Research Funding. Nasta:Rafael: Research Funding; Aileron: Research Funding; Takeda/Millennium: Research Funding; Incyte: Research Funding; Roche/Genentech: Research Funding; Merck: Consultancy; Atara: Research Funding; Debiopharm: Research Funding. Levine:CRC Oncology: Consultancy; Vycellix: Membership on an entity's Board of Directors or advisory committees; Tmunity Therapeutics: Equity Ownership; Novartis: Consultancy, Patents & Royalties, Research Funding; Cure Genetics: Consultancy; Avectas: Membership on an entity's Board of Directors or advisory committees; Brammer Bio: Membership on an entity's Board of Directors or advisory committees; Incysus: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy. Maude:Kite: Consultancy; Novartis: Consultancy. Schuster:Nordic Nanovector: Honoraria; Pfizer: Honoraria; AstraZeneca: Honoraria; Pharmacyclics: Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Loxo Oncology: Honoraria; Merck: Honoraria, Research Funding; Acerta: Honoraria, Research Funding; Novartis: Honoraria, Patents & Royalties: Combination Therapies of CAR and PD-1 Inhibitors with royalties paid to Novartis, Research Funding; AbbVie: Honoraria, Research Funding; Gilead: Honoraria, Research Funding. Stadtmauer:Celgene: Consultancy; Tmunity: Research Funding; Novartis: Consultancy, Research Funding; Takeda: Consultancy; Janssen: Consultancy; Amgen: Consultancy; Abbvie: Research Funding. Grupp:Novartis: Consultancy, Research Funding; Roche: Consultancy; GSK: Consultancy; Cure Genetics: Consultancy; Humanigen: Consultancy; CBMG: Consultancy; Novartis: Research Funding; Kite: Research Funding; Servier: Research Funding; Jazz: Other: study steering committees or scientific advisory boards; Adaptimmune: Other: study steering committees or scientific advisory boards. Porter:Incyte: Membership on an entity's Board of Directors or advisory committees; American Board of Internal Medicine: Membership on an entity's Board of Directors or advisory committees; Kite: Membership on an entity's Board of Directors or advisory committees; Glenmark Pharm: Membership on an entity's Board of Directors or advisory committees; Immunovative: Membership on an entity's Board of Directors or advisory committees; Genentech: Employment; Wiley and Sons: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. June:Novartis: Research Funding; Tmunity: Other: scientific founder, for which he has founders stock but no income, Patents & Royalties. Melenhorst:Novartis: Research Funding, Speakers Bureau; Parker Institute for Cancer Immunotherapy: Research Funding; Stand Up to Cancer: Research Funding; Incyte: Research Funding; IASO Biotherapeutics, Co: Consultancy; Simcere of America, Inc: Consultancy; Shanghai Unicar Therapy, Co: Consultancy; Colorado Clinical and Translational Sciences Institute: Membership on an entity's Board of Directors or advisory committees; Genentech: Speakers Bureau; National Institutes of Health: Research Funding.