Gliomas are aggressive neoplasms that diffusely infiltrate the brain and cause neurological symptoms, including cognitive deficits and seizures. Increased mTOR signaling has been implicated in glioma-induced neuronal hyperexcitability, but the molecular and functional consequences have not been identified. Here, we show three types of changes in tumor-associated neurons: (1) downregulation of transcripts encoding excitatory and inhibitory postsynaptic proteins and dendritic spine development and upregulation of cytoskeletal transcripts via neuron-specific profiling of ribosome-bound mRNA, (2) marked decreases in dendritic spine density via light and electron microscopy, and (3) progressive functional alterations leading to neuronal hyperexcitability via in vivo calcium imaging. A single acute dose of AZD8055, a combined mTORC1/2 inhibitor, reversed these tumor-induced changes. These findings reveal mTOR-driven pathological plasticity in neurons at the infiltrative margin of glioma and suggest new strategies for treating glioma-associated neurological symptoms.

While Chimeric Antigen Receptor (CAR) T cell therapy may result in durable remissions in recurrent large B cell lymphoma, persistence is limited and the mechanisms underlying long-term response are not fully elucidated. Using longitudinal single-cell immunoprofiling, here we compare the immune landscape in durable remission versus early relapse patients following CD19 CAR T cell infusion in the NCT02348216 (ZUMA-1) trial. Four weeks post-infusion, both cohorts demonstrate low circulating CAR T cells. We observe that long-term remission is associated with elevated native cytotoxic and proinflammatory effector cells, and post-infusion clonotypic expansion of effector memory T cells. Conversely, early relapse is associated with impaired NK cell cytotoxicity and elevated immunoregulatory cells, potentially dampening native T cell activation. Thus, we suggest that durable remission to CAR T is associated with a distinct T cell signature and pattern of clonotypic expansion within the native T cell compartment post-therapy, consistent with their contribution to the maintenance of response.

ABSTRACT:T-cell engager (TCE) therapy has demonstrated significant therapeutic efficacy in patients with hematologic malignancies. Durable responses have been linked with T-cell clonotypic expansion. We hypothesized that combining vaccine-educated T cells (veTcs) that induce the expansion of leukemia-specific T cells would enhance efficacy of TCE through greater induction of tumor-specific immunity. In this study, we explored a TCE targeting human CD123 on myeloid leukemia cells in conjunction with T cells stimulated by an autologous dendritic cell/acute myeloid leukemia fusion vaccine in a murine xenograft model. We demonstrated that the combination of CD123 TCE (SAR440234) and veTcs boosted tumor-specific T-cell immunity and enhanced antileukemia effect in vitro. Furthermore, in vivo SAR440234 and veTca combination treatment fully eradicated leukemia engraftment outperforming SAR440234 in conjunction with uneducated T cells. This effect was associated with an increase in cytotoxic T-cell subsets and clonotypic expansion. Thus, the combination of TCE with adoptive T-cell transfer of veTcs is a novel approach that merits further investigation in clinical trials.

Gliomas are highly aggressive brain tumors characterized by poor prognosis and composed of diffusely infiltrating tumor cells that intermingle with non-neoplastic cells in the tumor microenvironment, including neurons. Neurons are increasingly appreciated as important reactive components of the glioma microenvironment, due to their role in causing hallmark glioma symptoms, such as cognitive deficits and seizures, as well as their potential ability to drive glioma progression. Separately, mTOR signaling has been shown to have pleiotropic effects in the brain tumor microenvironment, including regulation of neuronal hyperexcitability. However, the local cellular-level effects of mTOR inhibition on glioma-induced neuronal alterations are not well understood. Here we employed neuron-specific profiling of ribosome-bound mRNA via 'RiboTag,' morphometric analysis of dendritic spines, and in vivo calcium imaging, along with pharmacological mTOR inhibition to investigate the impact of glioma burden and mTOR inhibition on these neuronal alterations. The RiboTag analysis of tumor-associated excitatory neurons showed a downregulation of transcripts encoding excitatory and inhibitory postsynaptic proteins and dendritic spine development, and an upregulation of transcripts encoding cytoskeletal proteins involved in dendritic spine turnover. Light and electron microscopy of tumor-associated excitatory neurons demonstrated marked decreases in dendritic spine density. In vivo two-photon calcium imaging in tumor-associated excitatory neurons revealed progressive alterations in neuronal activity, both at the population and single-neuron level, throughout tumor growth. This in vivo calcium imaging also revealed altered stimulus-evoked somatic calcium events, with changes in event rate, size, and temporal alignment to stimulus, which was most pronounced in neurons with high-tumor burden. A single acute dose of AZD8055, a combined mTORC1/2 inhibitor, reversed the glioma-induced alterations on the excitatory neurons, including the alterations in ribosome-bound transcripts, dendritic spine density, and stimulus evoked responses seen by calcium imaging. These results point to mTOR-driven pathological plasticity in neurons at the infiltrative margin of glioma - manifested by alterations in ribosome-bound mRNA, dendritic spine density, and stimulus-evoked neuronal activity. Collectively, our work identifies the pathological changes that tumor-associated excitatory neurons experience as both hyperlocal and reversible under the influence of mTOR inhibition, providing a foundation for developing therapies targeting neuronal signaling in glioma.

Background: Axicabtagene ciloleucel (Axi-cel), a CD19 directed CAR T cell therapy, results in durable response in a subset of patients with relapsed/refractory large B cell lymphoma (LBCL) in the absence of persistent circulating CAR T cells. Aim: We postulated that long-term efficacy of CAR T therapy depends on the downstream triggering of native T cell immunity. We performed single-cell transcriptomics of longitudinal peripheral blood (PB) samples and RNAseq of tumor samples from patients of the ZUMA 1 Axi-cel study. Methods: Single cell immunoprofiling (5’ expression + V(D)J, 10x Genomics) was performed on PB mononuclear cell samples from ZUMA-1 patients (N=32), collected at leukapheresis, 4 weeks, 6 and 12 months post Axi-cel infusion. RNAseq was performed on FFPE lymphoma samples (N=17). Patients were divided into 3 groups: non-responders, relapsed within 1 year from CAR T infusion, and long-term responders. A total of 405,775 cells passed quality check, capturing 73 cellular populations. Results: Long-term responders presented a distinct T cell landscape with increased CD8 T cells and CD8/CD4 ratios prior to CAR T therapy, compared to the other groups, with similar trends observed across time points. They also presented an increased abundance of 3 distinct CD8 T cell populations: (a) cells expressing cytotoxic and NK cell markers, (b) CD8 T effector memory cells characterized by CXCR4, TGFB1, and BCL3, and (c) proinflammatory CD8 T cells. In contrast, patients with early relapse showed increased levels of regulatory T cells pre-/post-CAR T infusion and lower abundance of CD4 cytotoxic T cells.Comparisons of the TCR repertoire pre-/post-CAR T demonstrated a greater clonal expansion of cytotoxic CD4 and CD8 T cell populations in the long-term responders, with high similarity of expanded clones post CAR T. Shared PB T cell clones and tumor antigen sequences derived from the RNAseq samples suggest an antigen-specific response driven by common epitopes. In contrast to the lack of expansion of T reg clones in responders, relapsed patients demonstrated high T reg-clonal expansion 6 months post treatment.Monocyte and NK cells were less prevalent in responders before treatment, driven by differences in phagocytic monocyte and inhibitory NK cell abundance. Modeling the interaction between monocyte and effector cell populations based on ligand receptor expression was suggestive of negative immunoregulatory impact on the T cell populations. Conclusion: The application of single-cell immunoprofiling on longitudinal samples from ZUMA-1 patients demonstrated distinct cellular and clonal profiles among long-term responders. These findings confirm our hypothesis of an important role for the native immune cell repertoire in response to CAR T therapeutics and can be utilized to further our understanding but also to potentially inform patient stratification, management, and treatment. Citation Format: Dimitra Karagkouni, Giulia Cheloni, Yered Pita-Juarez, Daniela Torres, Eleni Kanata, Zachary Avigan, Jessica Liegel, Dina Stroopinsky, Brodie Miles, Gayatri Tiwari, Jenny Kim, Mike Mattie, Jacalyn Rosenblatt, David Avigan, Ioannis Vlachos. Activation and clonotypic expansion of the native T cell repertoire identifies durable response to CD19 CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2257.

center between Jan 2017 to Feb 2023.The receipt of a bispecific antibody (BisAb) regimen was considered as a treatment event (TE), if a patient received two different BisAb's regimens over a 12-month period it would be considered as two TE.Clinical predictors of risk and infection data within the first 90 days was collected for each event.Results: Our cohort contains 90 patients with 123 TE where 40, 48 and 35 represent regimens with BCMA, GPRC5D and FcRH5 respectively.Within these 123 TE, 77 infection episodes were recorded between days 1 and 90.No infections were recorded in 68 TE, while 41 had one infection and 14 with >=2 infections (36 total).The most common infections recorded were -38% had Upper respiratory tract infection, 15% blood stream, 13% pneumonia, 14% GI, and 9% had CMV viremia/infection, 8% Urinary tract infections and 3% skin infections.Recurrent infections >1 was higher with BCMA directed therapies in the first 90 days (8.4 vs 17.5%).We divided the cohorts into no infection, 1 infection episode and greater than 1 infection episode.We observed no differences in baseline characteristics between the 3 cohorts including-HR, EMD, RISS, ECOG status, number of lines of prior therapy.On treatment parameters -ANC, ALC at D1, IgG levels, receipt of IVIG, CRS grade, tocilizumab use and treatment dose steroids were also not different between the 3 groups [0,1 and 2 infections].Multivariate analysis showed none of the covariates including receipt of BCMA vs non BCMA BisAb, HR MM, IgG at baseline, prior CART, or prior BCMA directed therapy to be significantly associated with an increased risk of infection.Conclusions: Our results demonstrate that early infection within 90 days is not associated with specific baseline risk factors.Importantly our analysis shows that patients who received prior immune engagers are not at an increased risk of early infections and that IgG levels, ALC and ANC were also not predictive.Other risk factors including duration of prior immune engagers should be explored to identify risk factors for recurrent infections.

Introduction: Multiple myeloma (MM), a clonal disorder of terminally differentiated plasma cells, is the second most common hematologic malignancy with ~57.9% 5-year survival rate. Current MM therapies are not curative and in most patients MM relapse. Aiming to restore antitumor immunity and counteract MM evolution, we have developed a personalized dendritic(DC)/MM cell fusion vaccine, whereby several tumor antigens are presented in the context of DC mediated co-stimulation. BMT CTN 1401 is a multicenter randomized phase II clinical trial (NCT02728102) evaluating the efficacy of the DC/MM vaccine combined with lenalidomide maintenance (Len) after autoHCT. 203 patients were enrolled from 18 centers. Aim: To evaluate the impact of the DC/MM vaccine on the establishment of anti-MM immune response we profiled the peripheral blood (PB) immune landscape at the single-cell level, with particular focus on the T cell compartment. Method: We performed single-cell immunoprofiling (gene expression + V(D)J sequencing) on 40 patients (3xDC/MM vaccine/Len/GM-CSF: N=20; Len/GM-CSF: N=10; Len: N=10). 160 PB mononuclear cells (PBMC) samples were collected at enrollment, prior to Len, after 1 and 3 vaccines and were processed using the 10x Genomics single cell 5' assay. Here we present the analysis relative to 52 PBMC samples from 13 vaccinated patients included in the initial study cohort. The remaining 108 PBMC samples have already been subjected to single-cell immunoprofiling and the analysis is ongoing. Results: 309,423 cells passed quality-check identifying 47 cell populations, corresponding to 20 major compartments. The T cell compartment (146,373 cells) was divided into 14 different cell populations including activated CD8, CD4, and NKT cells that exhibited a gradual increase during the course of the study. Relatively, TCR sequencing demonstrated a recovery of T cell clonal diversity and a progressive rise in the frequency of expanded clonotypes within the activated CD4 and cytotoxic T cell populations after vaccination. Consistently, we observed a progressively raised number of shared TCR clonotypes within the activated CD8 and CD4 T cell subsets. The identification of common epitope/paratope hotspots among the expanded clonotypes and the different patients revealed a higher proportion of shared TCR clonotype groups across patients after vaccination compared to the early post-transplant period, predominantly after 3 vaccinations. Conclusions: Assessment of PBMC samples from 13 vaccinated patients provided a detailed picture of the PBMC landscape. The constant T cell expansion in patients following vaccination coupled with the shared paratope/epitope hotspots and TCR signatures among patients indicated the TCR cross-reactivity and suggested for the establishment of an anti-MM immune response. Citation Format: Giulia Cheloni, Dimitra Karagkouni, Daniela Torres, David J. Chung, Nina Shah, Natalie S. Callander, Thinle Chodon, Yvonne Efebera, Nancy Geller, Peiman Hematti, Hillard Lazarus, Ehsan Malek, Philip L. McCarthy, Ajay K. Nooka, Jacalyn Rosenblatt, Aaron P. Rapoport, Robert J. Soiffer, Dina Stroopinsky, Edmund K. Waller, Marcelo C. Pasquini, Ioannis Vlachos, David Avigan. Dendritic cell/myeloma fusion vaccine with lenalidomide maintenance following autologous hematopoietic cell transplant induced T cell activation and expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6785.

Background: Axicabtagene ciloleucel (Axi-cel), a CD19 directed CAR T cell therapy, results in durable remission in a subset of patients with relapsed refractory large B cell lymphoma (LBCL) in the absence of persistent circulating CAR T cells. Aim: We postulated that long-term efficacy of CAR T therapy depends on the downstream triggering of native T cell immunity. To investigate this hypothesis, we performed single cell transcriptomic analysis of peripheral blood samples obtained at serial time points from patients participating in the ZUMA 1 Axi-cel study. We interrogated the T cell repertoire in patients who achieved durable remission compared to those experiencing disease relapse with respect to the expression of activated, cytotoxic, and inhibitory markers and clonotypic expansion of critical T cell subsets. Methods: Single cell immunoprofiling (expression + V(D)J sequencing) was performed using the 10x Genomics single cell 5' assay on PBMC samples from ZUMA-1 patients (N=32), collected at leukapheresis, 4 weeks, 6 months, and 12 months post Axi-cel. Based on clinical response, patients were divided into 3 groups: non-responders (N=8), relapsed within 1 year from CAR T infusion (N=9), and long-term responders (N=12). Three participants did not consent to the release of clinical outcomes. Results: A total of 405,775 cells passed quality check, capturing 73 cellular populations (Fig. 1a). T cells comprised the largest compartment with 28 different populations and 264,059 cells. Long-term responders demonstrated a distinct T cell landscape compared to relapsed patients, notable for a higher CD8/CD4 T cell ratio and increased expression of cytotoxic genes at all time points. Accordingly, activated CD8 cytotoxic effector memory T cell (Tem) populations were significantly increased in long-term responders compared to relapsed patients; especially two Tem populations, one characterized by high expression of CD44, GZMB and TGFB1 (Tem/TGFB1+), and a second highly expressing cytotoxic markers such as GZMA, GZMB, NKG7, CTS7, and CTSW (Tem/NKG7+). Following CAR T cell infusion, relapsed patients exhibited increased proportions of T regs and of T reg-like Th17 cells highly expressing FOXP3, IL2RA, and CTLA4. In contrast to all other CD4 populations, which were more abundant in the relapsed group, long-term responders presented higher abundance of CD4 cytotoxic T lymphocytes (CD4 CTL), characterized by high expression of both CD4-related and cytotoxic markers, including granzymes, and GNLY. Comparison of the TCR repertoire pre- and post-CAR T demonstrated a greater clonal expansion (TCRα/β-clonotype frequency > 1) of cytotoxic T cell populations in the long-term responders compared to relapsed and non-responder patients. In particular, higher clonotypic expansion was observed in the Tem/TGFB1+, Tem/NKG7+, and CD4 CTL populations (Fig. 1b). In contrast to our observations for the cytotoxic T cell populations, T regs were identified as more clonally expanded over time in the relapsed patients compared to the long-term responders. Conclusion: The application of single-cell immunoprofiling on longitudinal samples from CAR T cell treated LBCL patients from the ZUMA-1 trial demonstrated striking differences in cellular populations and clonal expansion patterns among patients who demonstrated long term remission compared to those who relapsed within 1 year following initial response. Reduced cytotoxic T cell expansion and increased proportions of immunomodulatory T cell populations were noted in relapsed patients compared to long term responders. These data provide insight into crucial factors that can be leveraged both to predict patient response and to further our understanding of long-term remission following CAR T cell treatment. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Introduction: Our group has pioneered a novel vaccine by fusion of patient-derived tumor with autologous dendritic cells (DCs) that presents an array of tumor antigens generating a polyclonal immune response. DC/AML vaccination led to expansion of leukemia-specific T cells with survival benefit in a phase II clinical trial. We postulated that ex vivo generation of vaccine-educated T cells would provide a powerful platform for adoptive immunotherapy with opportunity to augment T-cell functional potency prior to infusion. We report on an ex vivo system in which vaccine-educated T cells are further enriched for activated antigen-specific effector cells via an agonistic 4-1bb antibody. We report phenotypic and functional characteristics of 4-1bb-enriched vaccine-educated T cells. Methods: DC/AML fusion vaccines were generated from C57BL/6J mice DCs and syngeneic C1498 mCh/luc+ AML cells. Splenic T cells were co-cultured with autologous irradiated DC/AML fusions in presence of IL-2/7/15. Selection with biotinylated agonistic 4-1bb (3H3) was performed on vaccine-educated T cells followed by expansion with anti-CD3/CD28 activation beads. T cells were phenotyped for activation (CD25/CD69), immune checkpoints (PD1/LAG3/TIM3), memory (CD44+CD62L-) and enrichment (anti-rat H&L). Cytotoxicity was evaluated by luminescence. Mice were inoculated with C1498 and injected with T cells 7 days later. BLI imaging was performed and 100-day survival measured. Results: Vaccine-educated T cells demonstrated evidence of immune activation and memory phenotype compared to unstimulated naïve T-cell controls (TN) (7.24-fold, CD4+CD25+CD69+; 1.7-fold, CD3+CD44+CD62L-). Vaccine-educated T cells selected based on 4-1bb expression showed enhanced markers of activation (15.3-fold, CD4+CD25+CD69+) and memory phenotype (5-fold, CD3+CD44+CD62L-) compared to TN. Selection enriched for 4-1bb+ vaccine-educated T cells resulting in enhanced antigen-specific recognition as measured by tumor lysate induction of IFNg expression. Tumor specificity and activation was maintained following CD3/CD28-mediated expansion. The 4-1bb+ vaccine-educated T cells showed enhanced cytotoxicity (1.9-fold increase/TN at 10:1 E/T, P<0.0001). Phenotypic and functional analysis support 3-5 days as the optimal duration of time for T-cell vaccine education. In vivo, 60% of mice treated with 4-1bb+ vaccine-educated cells were alive at 60 days vs. 20% treated with unselected vaccine-educated cells. Conclusion: We demonstrate that vaccine-educated T cells subject to selection via an agonist 4-1bb antibody confer enhanced tumor selectivity and potency. Optimal duration for T-cell education was 3-5 days. T-cell stimulation and enrichment by agonistic 4-1bb selection enhanced cytotoxicity and memory phenotype. Thus, 4-1bb selection is a novel approach for antigen-specific T-cell enrichment for superior adoptive immunotherapy in AML. Citation Format: Kathrine S. Rallis*, Jessica Liegel*, Giulia Cheloni, Dina Stroopinsky, Poorva Bindal, Kenel Dufort, Daniela Torres, Isabella Saldarriaga, Samuel Herzlinger, Abigael Morin, Raphael Kesselman, Jeremy Rosenbaum, Georges Chedid, Sophia Adamia, Donald Kufe, Jacalyn Rosenblatt, David Avigan. 4-1bb selection augments DC/AML fusion vaccine-educated T cells for adoptive cell therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4076.

BACKGROUND:Pancreatic cancer is a highly lethal malignancy often presenting with advanced disease and characterized by resistance to standard chemotherapy. Immune-based therapies such checkpoint inhibition have been largely ineffective such that pancreatic cancer is categorized as an immunologically "cold tumor". In the present study, we examine the therapeutic efficacy of a personalized cancer vaccine in which tumor cells are fused with dendritic cells (DC) resulting in the broad induction of antitumor immunity. RESULTS:In the KPC spontaneous pancreatic cancer murine model, we demonstrated that vaccination with DC/KPC fusions led to expansion of pancreatic cancer specific lymphocytes with an activated phenotype. Remarkably, vaccination led to a reduction in tumor bulk and near doubling of median survival in this highly aggressive model. In a second murine pancreatic model (Panc02), vaccination with DC/tumor fusions similarly led to expansion of tumor antigen specific lymphocytes and their infiltration to the tumor site. Having shown efficacy in immunocompetent murine models, we subsequently demonstrated that DC/tumor fusions generated from primary human pancreatic cancer and autologous DCs potently stimulate tumor specific cytotoxic lymphocyte responses. CONCLUSIONS:DC/tumor fusions induce the activation and expansion of tumor reactive lymphocytes with the capacity to infiltrate into the pancreatic cancer tumor bed.

We have developed a personalized vaccine whereby patient derived leukemia cells are fused to autologous dendritic cells, evoking a polyclonal T cell response against shared and neo-antigens. We postulated that the dendritic cell (DC)/AML fusion vaccine would demonstrate synergy with checkpoint blockade by expanding tumor antigen specific lymphocytes that would provide a critical substrate for checkpoint blockade mediated activation. Using an immunocompetent murine leukemia model, we examined the immunologic response and therapeutic efficacy of vaccination in conjunction with checkpoint blockade with respect to leukemia engraftment, disease burden, survival and the induction of tumor specific immunity. Mice treated with checkpoint blockade alone had rapid leukemia progression and demonstrated only a modest extension of survival. Vaccination with DC/AML fusions resulted in the expansion of tumor specific lymphocytes and disease eradication in a subset of animals, while the combination of vaccination and checkpoint blockade induced a fully protective tumor specific immune response in all treated animals. Vaccination followed by checkpoint blockade resulted in upregulation of genes regulating activation and proliferation in memory and effector T cells. Long term survivors exhibited increased T cell clonal diversity and were resistant to subsequent tumor challenge. The combined DC/AML fusion vaccine and checkpoint blockade treatment offers unique synergy inducing the durable activation of leukemia specific immunity, protection from lethal tumor challenge and the selective expansion of tumor reactive clones.

Introduction: We are conducting a clinical trial in which patients with acute myeloid leukemia (AML) who are undergoing allogeneic transplant undergo post-transplant vaccination with DC/AML fusion cells. Allogeneic transplantation is uniquely curative for a subset of patients with AML, however, post-transplant relapse and graft versus host disease remain significant concerns. We have developed a promising leukemia vaccine in which patient derived AML cells are fused with donor-derived dendritic cells (DCs), presenting a broad array of antigens that capture the heterogeneity of the leukemia cell population. We hypothesize that DC/AML vaccination post-transplant would elicit the durable expansion of leukemia specific T cells within the donor T cell repertoire to effectively protect against disease relapse. Methods: Patients undergo collection and cryopreservation of leukemia cells at the time of diagnosis with AML. Patients who undergo an allogeneic transplant in complete remission from a matched related or unrelated donor (cohort A) or a haplo-identical donor (Cohort B) are assessed for eligibility to undergo leukapheresis for dendritic cell generation between day 25-45 post-transplant. In order to proceed with leukapheresis, patients must demonstrate donor hematopoietic recovery in the absence of ongoing grade 2 or higher GVHD. Patients initiate vaccination between day 70-100 post-transplant. 2 vaccines are given at 3 week intervals, in conjunction with GMCSF 100 mcg daily at the vaccine site for 4 days. A booster vaccine may be given 30-60 days following the taper of immune suppression, in the absence of GVHD. Results: To date, 12 participants have undergone vaccine generation. The median age is 62 years (range 23-74). 10 participants were enrolled to cohort A: 7 were transplanted with a matched unrelated donor and 3 were transplanted with a matched sibling donor. 2 participants were enrolled to cohort B following transplant from a haplo-identical donor. The mean yield of leukemia cells was 314 x106 (range 95-to 818-x106)and mean viability was 96%. For DC generation, patients underwent leukapharesis and adherent mononuclear cells were cultured with GM-CSF, IL-4 and TNFa. The mean yield of DCs was 131 x106 and viability 77%. Fusion vaccine was successfully generated in 11/12 patients, with mean fusion efficiency of 51% with viability of 76%. One patient had insufficient DC for vaccine generation. Mean Fusion Vaccine Dose was 4.7 x 106 fusion cells. 3 patients did not meet eligibility to initiate vaccination due to ongoing toxicity following transplant (2 patients) and GVHD (1 patient). 8 participants have initiated vaccine administration and are evaluable for toxicity and response. The most common side effects have been grade 1 vaccine site reactions (n=9 grade 1, n=1 grade 2). 4 patients developed GVHD that was determined to be possibly related to vaccination, at a median time of 16.5 days after vaccination (range 5-21 days). 2 of these patients developed grade 2 acute GVHD of the skin, one patient developed grade 2 gastrointestinal GVHD that subsequently evolved into moderate, chronic GVHD affecting the skin, GI tract, eyes and mouth, and one patient developed mild transaminitis attributed to liver GVHD. An additional 3 patients developed GVHD with a median time of 99 days post vaccination (range 91-123 days), assessed as being unlikely related to vaccine. 7 of the 8 patients remain in a CR at a median time of 15.5 months post-transplant (range 4.8-22.4 months). One patient relapsed 14.8 months post haplo-identical transplant. Immunologic response following vaccination is being assessed, with respect to the presence of leukemia-reactive T cells, T cells targeting previously identified leukemia- associated antigens, T cell clonality, T regulatory cells, and PD-1 expressing T cells. In the absence of treatment associated toxicity, a second cohort is planned, in which vaccine will be given in conjunction with decitabine. Conclusions: Vaccine generation using donor derived DC isolated following engraftment is feasible. Mild to moderate graft versus host disease has been observed in a subset of patients, and 7/8 vaccinated patients remain relapse free. Correlative science studies to assess immune response to vaccination, identify neoantigen targets, and characterize the immune milieu, will be reported. Disclosures Stone: Syros: Consultancy; Syntrix: Consultancy; Syndax: Consultancy; Stemline: Consultancy; Hoffman LaRoche: Consultancy; Macrogenics: Consultancy; Janssen: Consultancy; Gemoab: Consultancy; Elevate: Consultancy; Daiichi-Sankyo: Consultancy; Takeda: Consultancy; Trovagene: Consultancy; Pfizer: Consultancy; Otsuka: Consultancy; Novartis: Consultancy, Research Funding; Jazz: Consultancy; Celgene: Consultancy, Other: Data and safety monitoring board; Biolinerx: Consultancy; AstraZeneca: Consultancy; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Arog: Research Funding; Argenx: Consultancy, Other: Data and safety monitoring board; Agios: Consultancy, Research Funding; Actinium: Consultancy; AbbVie: Consultancy, Research Funding. Soiffer:Gilead: Consultancy; Rheos Therapeutics: Consultancy; Cugene: Consultancy; Precision Bioscience: Consultancy; Mana Therapeutics: Consultancy; VOR Biopharma: Consultancy; Novartis: Consultancy; Juno: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; alexion: Consultancy; Be the Match/ National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Kiadis: Membership on an entity's Board of Directors or advisory committees. Neuberg:Pharmacyclics: Research Funding; Celgene: Research Funding; Madrigak Pharmaceuticals: Current equity holder in publicly-traded company.

Introduction: CAR T cells have demonstrated unique potency for tumor cytoreduction and the potential for durable response in patients with advanced hematological malignancies. However, disease relapse remains a significant concern due to the emergence of antigen negative variants, tolerization of CAR T cell populations and lack of T cell persistence. We have developed a personalized cancer vaccine in which patient derived tumor cells are fused with autologous dendritic cells such that a broad array of tumor antigens is expressed in the context of DC mediated co-stimulation. Vaccination of patients with acute leukemia and multiple myeloma has been associated with the durable expansion of tumor specific lymphocytes in the bone marrow and peripheral blood, targeting of residual disease, and durable remission. We postulated that vaccination with DC/tumor fusions would enhance CAR T cell efficacy through the expansion of T cell clonal populations targeting tumor cells via the native TCR and the vaccine mediated enhancement of T cell activation and persistence. In addition, ex vivo engineered CAR T cells provide a substrate of functionally competent T cells with cytoreductive capacity in the setting of advanced disease. In the present study, we examined the potential synergy between CAR T cells targeting CD19 and syngeneic DC/tumor fusions. Methods/Results: CAR T cells and DC/tumor fusions were studied in the context of a murine A20 lymphoma model. CD19 CAR T cells were established through retroviral transduction of a CD19 CAR construct expressing CD28 and 41BBL syngeneic DC/A20 fusions were generated as previously described. Vaccine stimulated T cells were generated by coculturing splenocyte derived T cells with syngeneic DC/A20 fusion cells over a period of three days in a 10:1 ratio in the presence of low dose IL2. While CD19 CAR T cells effectively lysed a subset of A20 cells in a CTL, the addition of vaccine educated T cells increased the percentage of tumor cells undergoing CTL mediated lysis (20% vs 34%). We subsequently examined the interaction of vaccine and CAR T cells ex vivo using the IncuCyte S3 Live-Cell Analysis System which allows for live cell visualization of lysis of A20 cells over time. We studied the impact of combining vaccine educated and CAR T cells as well as an individual T cell population that underwent sequential vaccine mediated stimulation followed by transduction with the CD19 CAR. While vaccine educated and CAR T cells demonstrated potent lysis of A20 cells over time, coculture with either combined vaccine educated and CAR T cells or sequentially vaccine educated and transduced T cells demonstrated the highest levels of cytotoxicity that was maintained over time (1786 and 2338 signal overlap count per image at 23 hours compared to 123 of the control). Enhanced lysis by combined vaccine stimulation and CAR T cells was similarly demonstrated in another tumor cell line, 5TGM1, a multiple myeloma cell line transduced to express CD19. Cytotoxic killing of the 5TGM1-CD19 cells was most pronounced when combining vaccine educated and CAR T cells as compared to CAR T cells alone (33% vs 14%). Consistent with the broad targeting of vaccine educated as compared to the CAR T cell population, wild type 5TGM1 cells were recognized by the DC/tumor fusion stimulated cells in contrast to CAR T cells alone (40% vs. 8%). We subsequently examined the capacity of vaccine educated T cells in conjunction with CAR T cells to target A20 cells in an immunocompetent murine model. Mice were challenged with 1 x 10(6) A20 Mcherry-Luc and lymphoma engraftment was demonstrated at Day 7. Animals were then treated with 3 x 10(6) T cells consisting of CAR T cells, vaccine educated T cells or the combination. Serial bioluminescence imaging demonstrated greatest reduction in tumor burden using combined CAR T and vaccine educated T cells with 4/5 animals without BLI evidence of disease at day 13 after tumor challenge. Conclusions: In in vitro and immunocompetent murine models, we have demonstrated that combined therapy with T cells stimulated by DC/tumor fusions and CAR T cells exhibited potent lysis of murine lymphoma and myeloma cells as compared to the efficacy of CAR T cells or vaccine educated T cells alone. These findings suggest potent synergy between these modalities that may overcome recognized pathways of resistance including the broadening of the tumor specific response and vaccine mediated activation of CAR T cell populations. Disclosures Themeli: Covagen: Consultancy. Mutis:Janssen Research and Development: Research Funding; Celgene: Research Funding; Onkimmune: Research Funding; Genmab: Research Funding. Munshi:Adaptive: Consultancy; Amgen: Consultancy; Oncopep: Consultancy; Janssen: Consultancy; Celgene: Consultancy; Takeda: Consultancy; Abbvie: Consultancy. Kufe:Genus Oncology: Equity Ownership; Reata Pharmaceuticals: Consultancy, Equity Ownership, Honoraria; Nanogen Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Hillstream BioPharma: Equity Ownership; Victa BioTherapeutics: Consultancy, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees; Canbas: Consultancy, Honoraria. Rosenblatt:BMS: Research Funding; Amgen: Other: Advisory Board; Merck: Other: Advisory Board; BMS: Other: Advisory Board ; Parexel: Consultancy; Imaging Endpoint: Consultancy; Partner Tx: Other: Advisory Board; Dava Oncology: Other: Education; Celgene: Research Funding. Sadelain:Fate Therapeutics: Consultancy, Patents & Royalties; Memorial Sloan Kettering Cancer Center: Employment; Juno Therapeutics: Consultancy, Patents & Royalties, Research Funding. Avigan:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Partners Tx: Membership on an entity's Board of Directors or advisory committees; Partner Tx: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Parexel: Consultancy; Takeda: Consultancy.

Glioma cells diffusely infiltrate the surrounding brain tissue where they intermingle with nonneoplastic brain cells, including astrocytes, microglia, oligodendrocytes and neurons. The infiltrative margins of glioma represent the structural and functional interface between neoplastic and nonneoplastic brain tissue that underlies neurologic alterations associated with glioma, including epilepsy and neurologic deficits. Technological advancements in molecular analysis, including single cell sequencing, now allow us to assess alterations in specific cell types in the brain tumor microenvironment, which can enhance the development of novel therapies that target glioma growth and glioma-induced neurologic symptoms.

Abstract Diffusely infiltrating gliomas are the most common type of primary brain tumor seen in adults. Patients with low grade glioma (LGG) can survive for many years, but often suffer from seizures and cognitive impairment, and these symptoms are associated with an unfavorable prognosis. Glioma cells diffusely infiltrate cortical tissue, where tumor cells aggregate around neuronal cell bodies, a growth pattern referred to as perineuronal satellitosis, however the effects of tumor cells on neurons has not been well defined. To address this important issue we generated a mouse model that recapitulates the genetic and histological features of diffusely infiltrating LGG. In our model tumor growth is driven by PDGFA overexpression and p53 deletion in a RiboTag-Camk2a-Cre transgenic mouse. The RiboTag system allows for the isolation and sequencing of ribosome-bound transcripts from Camk2a neurons to obtain a measure of transcription and translation. Our analysis in non-tumor bearing brains identified neuron-specific genes that are highly regulated at the level of translation. mTOR signaling regulates cell growth, proliferation, and translation in response to diverse stimuli. To characterize mTOR signaling in our model we used immunohistochemical staining of pS6 as a marker of mTOR activity and found that neurons within the glioma infiltrated cortex have lower levels of pS6 staining compared to neurons in the surrounding cortex. To further assess these results we are using the RiboTag system to identify alterations in neuronal transcription and translation that occur in our model during glioma formation and in response to mTOR targeted treatments. These studies will provide new insights into the neuronal alterations contributing to seizures and cognitive impairment in glioma and enable the identification of potential molecular targets for novel therapies to treat the devastating consequences of cortical dysfunctions associated with glioma. Citation Format: Daniela Torres, Angeliki Mela, Sohani Das Sharma, Nicholas Hornstein, Peter Sims, Peter Canoll. Characterization of neuronal alterations in a new mouse model of low grade glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1841. doi:10.1158/1538-7445.AM2017-1841

Ribosome profiling has emerged as a powerful tool for genome-wide measurements of translation, but library construction requires multiple ligation steps and remains cumbersome relative to more conventional deep-sequencing experiments. We report a new, ligation-free approach to ribosome profiling that does not require ligation. Library construction for ligation-free ribosome profiling can be completed in one day with as little as 1 ng of purified RNA footprints. We apply ligation-free ribosome profiling to mouse brain tissue to identify new patterns of cell type-specific translation and test its ability to identify translational targets of mTOR signaling in the brain.