Kenderian, Saad S.

Abstract Background Predictors of outcomes after reduced intensity conditioning (RIC) stem cell transplantation (SCT) in chronic lymphocytic leukemia (CLL) are not well established. The Dana Farber (DF) investigators (Brown et al, leukemia 2013) developed a prognostic scoring model for overall survival (OS) and disease free survival (DFS) that assigned one point to each of comorbidity index, absolute lymphocyte count, LDH and disease status. The goals of the present study were to 1) validate the DF model 2) identify additional predictors of outcomes after SCT. Methods This study is a retrospective review of the Mayo Clinic CLL database and was approved by the Institutional Review Board. All CLL patients that underwent RIC-SCT were included. The prognostic significance of prognostic factors at time of RIC-SCT were analyzed, including the DF model. Survival was estimated and compared using the Kaplan Meier and Log Rank tests. Results From 2006 to 2012, 50 patients with CLL underwent RIC-SCT at the Mayo Clinic. Of these, 33 were male (66%) and the median age was 56 (29-69) years. The median time from diagnosis to RIC-SCT was 4.7 years (0.6-22.9). Indications for RIC-SCT were 17p deletion in 24 (48%) patients and purine nucleoside analogue (PNA) refractory disease in 26 (52%) patients. Transplant related mortality was 6% and non-relapse mortality at 5 years was 14%. Acute graft versus host disease (GVHD) developed in 30 (60%) patients and chronic (c) GVHD was noted in 32 patients (64%). The 5-year relapse rate was 38%. The DF prognostic score stratified three categories for OS (score of 0, 1-2, ≥ 3), but was not associated with DFS in this cohort. We next evaluated the impact of other patient, disease, and transplant characteristics on clinical outcome. Development of cGVHD post-transplant was the dominant predictor of both DFS (HR 0.26, 95% CI=0.10-0.69, P=0.006) and OS (HR 0.04, 95% CI=0.01-0.19, P<0.0001, figure 1). The presence of 17p deletion at time of RIC-SCT was associated with shorter DFS (HR 3.99, 95% CI=1.43-11.18, P=0.008), but did not impact OS. Developing cGVH but not DF score remained an independent predictor of OS on a multi-variate analysis including both factors. Given these findings, we evaluated what pre-treatment patient, disease, and transplant characteristics predicted for subsequent development of cGVHD. Patients with higher scores on DF prognostic model were less likely to develop cGVHD (score 0=66%, 1-2=76%, ≥3=31%; P=0.01). Three CLL characteristics (complete or partial remission at time of RIC-SCT, absence of 17p deletion, and absence of ZAP70 overexpression) were predictors for development of cGVHD while alemtuzumab exposure ≤3 months prior to RIC-SCT decreased likelihood of cGVHD. On multivariate modeling using these four predictors, only ZAP70 overexpression was an independent negative predictor of developing cGVHD (Table 1). Rates of cGVHD post RIC-SCT in ZAP 70 positive and ZAP70 negative patients were 50% and 92%, respectively (p=0.03). Conclusion This study found that while the DF prognostic score is an effective way to predict outcome prior to RIC-SCT, development of cGVHD post-transplant is ultimately the most significant predictor for both OS and DFS after transplant in patients with CLL. Pretransplant characteristics that predict subsequent cGVHD include DF prognostic score and ZAP70 status. This is the first report to identify biologic characteristics of CLL B-cells associated with development of cGVHD post-transplant. Disclosures: No relevant conflicts of interest to declare.

Abstract Background Allogeneic stem cell transplantation (allo-SCT) is a potentially curative option for patients with myelodysplastic syndromes (MDS). However, allo-SCT can be associated with significant morbidity and mortality along with a risk for post-transplant disease relapse. While many MDS prognostic models exist, a prognostic model specifically designed to predict post-transplant disease relapse is yet to be developed. Therefore, we carried out this single institution study. Methods After due IRB approval, the Mayo Clinic MDS database (1995-2012) was retrospectively reviewed. This database contains comprehensive information on MDS clinical and pathological characteristics, treatments and SCT. Primary outcomes analyzed included disease free survival (DFS), overall survival (OS) and relapse rates at five years post allo-SCT. In addition, we evaluated transplant related mortality (TRM), non-relapse mortality (NRM), and rates of acute and chronic graft versus host disease (GVHD). DFS and OS were calculated from the time of transplantation. The prognostic relevance of several disease and transplant specific characteristics were analyzed, including: age, gender, World Health Organization (WHO) categories, therapy related MDS, cytogenetics, International Prognostic Scoring System (IPSS) and IPSS-Revised (IPSS-R) at the time of MDS diagnosis, transfusion dependence, bone marrow and circulating blast count at transplant, serum ferritin levels, SCT Co-morbidity Index, donor source, HLA matching, CMV serostatus, and conditioning regimen. Multivariate analysis was performed using the Cox Proportional Hazard Model. Survival was estimated and compared using the Kaplan Meier and Log Rank tests, respectively. Results From 1995 through 2012, 96 consecutive patients with MDS underwent allo-SCT at the Mayo Clinic, Rochester. Of these, 62 were male (65%) with a median age of 54 (24-68 years). The median follow up was 31 (1-181) months. Twenty seven patients (28%) had therapy related MDS and 39 (40%) had MDS with a monosomal karyotype. IPSS-R risk stratification identified 55 (57%) patients with very high, 20 (21%) with high and 21 (22%) with intermediate/good risk disease. Fifty (52%) patients received a reduced intensity conditioning. The TRM was 8% and NRM at 5 years was 22%. Acute (grade 2 to 4) GVHD developed in 57 (59%) patients and chronic extensive GVHD was noted in 52 (54%) patients. Five-year relapse, DFS and OS rates were 24%, 42%, and 44%, respectively. In a univariate analysis, IPSS-R (high/very high, P=0.005), therapy related MDS (P=0.009), bone marrow blast count at transplant (≥10%, P=0.01), and the presence of a monosomal karyotype (P=0.05) were significantly associated with worse DFS. On a multivariable analysis, only high or very high risk IPSS-R category (HR 7.8, P=0.005) and therapy related MDS (HR 3.9, P=0.04) retained their negative prognostic impact. Based on this finding, we developed a prognostic model that assigned one point to each of these two factors (low risk-0, intermediate-1 and high risk-2). This model successfully stratified patients based on DFS, with a 5-year DFS of 67%, 40% and 23% for low, intermediate and high risk categories respectively, P=0.0012. This model was also successful in risk stratifying patients with regards to OS (table 1, figure 1). The presence of chronic GVHD was associated with a significantly improved DFS (62% vs 24%, P<0.0001) and OS (78% vs 19%, P<0.0001), however, as this is a post-transplant outcome, it was not included in the analysis/model. Conclusions Although the IPSS-R has not been validated in therapy related MDS or in patients who have received MDS directed therapy, the high/very high risk categories along with therapy related MDS, serve as independent predictors of OS and disease relapse after allo-SCT. Using these two variables, our prognostic model efficiently stratified patients with regards to DFS, relapse rates, and OS. Given the smaller sample size validation in a larger patient cohort will be needed. Disclosures: No relevant conflicts of interest to declare.

Abstract Chimeric antigen receptor T cell (CART) therapy has developed as a powerful and potentially curative therapy in hematological malignancies over the last few years. CD19 directed CART cells have resulted in impressive complete response rates of ~90% in acute lymphoblastic leukemia that are durable for the majority of patients. However, the overall response rates in other malignancies such as chronic lymphocytic leukemia are around 50%. This could be partially related to CART exhaustion and dysfunction induced by leukemia cells. In this study, we aim to evaluate the role of inhibitory receptors/pathways in inducing CART cell dysfunction and exhaustion in hematological malignancies. As a tumor model, we used an acute myeloid leukemia (AML) cell line (MOLM14) and primary AML samples and treated them with CD33 or CD123 directed CART cells (second generation CARs using 4-1BB and CD3z signaling domains and a lentiviral vector). Incubation of primary AML samples or MOLM14 cell line with CD33 or CD123 directed CARTs resulted in a significant up-regulation of PD-L1 on tumor cells after 24 hours of incubation (0% on day 0 vs 80% on day 1, P <0.001), and up-regulation of PD-1 and TIM-3 on T cells 3-7 days post co-culture (8% of T cells expressed PD-1 on day 0 vs 43% on day 3, P=0.03 and 13% of T cells expressed TIM-3 on day 0 vs 71% on day 3, p=0.001, Figure 1). For in vivo experiments, we used NSG (NOD-SCID-g-/-) mice and engrafted them with the MOLM14 cell line. Treatment of these AML xenografts with suboptimal doses of CD33 or CD123 CARTs resulted in initial anti-tumor responses, followed by disease relapses in 40-60% of the mice (Figure 2A). T cells were isolated from the bone marrow of these mice and analyzed for differential expression of inhibitory receptors. There was a significantly increased up-regulation of TIM-3 receptors on T cells isolated from mice with relapsed disease compared with T cells isolated from mice in remission after CART cell therapy (Figure 2B). Next, we investigated the role of adding checkpoint blockade to improve T cell function ex vivo after CART cell therapy. Marrows of mice that relapsed after CART cell therapy contained both residual CART cells and leukemia and were used to model the administration of checkpoint blockade in the setting of CART cell exhaustion. Cells were cultured with PD-1 or TIM-3 blocking antibodies or the combination of both (10 ug/ml for 72 hours). CART cell effector functions such as cytokine production and Ki-67 proliferation marker improved in the presence of checkpoint antagonists especially when both PD-1 and TIM-3 blocking antibodies were combined (figure 2C). Finally, we tested the combination of checkpoint blockade with CARTs in AML xenografts. In this approach, we treated MOLM14 xenografts with suboptimal doses of CD33 or CD123 directed CARTs or with control untransduced T cells (UTD), with or without checkpoint blocking antibodies. NSG mice bearing MOLM14 AML xenografts were established. Engraftment was confirmed by bioluminescent imaging. The tumor bearing mice were then treated with suboptimal doses (0.25-0.5 x106 total T cells I.V) of CD33 or CD123 directed CARTs or with control untransduced T cells (UTD). Mice also received PD-1 blockade, TIM-3 blockade or the combination of both on days 3, 6, 9 and 12 post T cell therapy, with the rationale for early checkpoint blockade being based on our in vitro observations of early upregulation of inhibitory ligands on AML after exposure to CART cells. Mice were then followed with serial imaging to assess disease burden. The addition of checkpoint antagonists to untransduced T cells, in particular anti-TIM3, did not lead to an anti-leukemic effect. However, the addition of PD-1 or TIM-3 blockade to CART cell therapy resulted in a synergistic anti-tumor activity as shown in Figure 3. The durable complete response rate was: 45% for treatment with CART123 alone, 80% for treatment with CART123+PD-1 blockade, 100% for treatment with CART123+TIM-3 blockade, and 80% for treatment with CART123+ both PD-1 and TIM-3 blockade). Our preclinical results indicate that PD-1 and TIM-3 pathways are involved in CART exhaustion and dysfunction in AML. Combination of checkpoint inhibitors with CART cells may lead to enhanced efficacy in AML and other hematological malignancies. Current studies are investigating mechanisms of synergy and the role of these combinations in other hematological malignancies. Figure 1. Figure 1. Figure 2. Figure 2. Figure 3. Figure 3. Disclosures Kenderian: Novartis: Patents & Royalties, Research Funding. Ruella:Novartis: Patents & Royalties, Research Funding. Porter:Novartis: Patents & Royalties, Research Funding. June:University of Pennsylvania: Patents & Royalties: financial interests due to intellectual property and patents in the field of cell and gene therapy. Conflicts of interest are managed in accordance with University of Pennsylvania policy and oversight; Novartis: Research Funding. Gill:Novartis: Patents & Royalties, Research Funding.

Abstract Background: The 2016 revision to the World Health Organization (WHO) classification of myeloid neoplasms has specifically categorized germline mutations that are associated with myeloid clonal evolution (Arber et al. Blood 2016). This group consists of myeloid neoplasms with an isolated germline predisposition (CEBPA, DDX41), myeloid neoplasms associated with congenital thrombocytopenia (ETV6, RUNX1, ANKRD26) and germline myeloid neoplasms with multi-organ dysfunction (GATA2, chromosomal breakage disorders, telomere biology disorders etc). We carried out this study to describe the clinical spectrum of germline disorders with predisposition to myeloid neoplasms as categorized by the 2016 WHO classification revision. Methods: After Institutional Review Board (IRB) approval, the adult and pediatric bone marrow failure syndrome database (1990-2016) and the electronic medical record were queried for germline disorders involving GATA2, CEBPA, DDX41, ETV6, RUNX1, ANKRD26, Down syndrome and Noonan syndrome. Chromosomal breakage assays (Diepoxybutane/Mitomycin-C), flow-fluorescent in-situ hybridization (FISH) for telomere length assessment, Fanconi anemia complementation assays and Sanger/Next Generation sequencing (NGS) for the aforementioned germline disorders with myeloid predisposition were carried out in Clinical Laboratory Improvement Amendments (CLIA)-certified laboratories. These disorders were then classified based on the 2016 WHO classification revision. Results : 54 individuals (37 families) were included in the study. Eleven (20%) patients belonging to 5 families were identified as having germline mutations with a preexisting platelet disorder: ETV6 (n=1), ANKRD26 (n=5), RUNX1 (n=5). Forty-three (79%) patients (32 families) had inherited syndromes with multi-organ dysfunction: GATA2 (n=11, 26%), bone marrow failure syndromes (n=14, 33%) and telomere biology disorder (n=14, 33%). There was one patient with neurofibromatosis with a germline PTPN11 mutation who developed juvenile myelomonocytic leukemia, while there were three patients with Down syndrome; 2 with transient abnormal myelopoiesis and one who developed acute megakaryocytic leukemia. The clinical phenotype, prevalence and characteristics of myeloid clonal evolution and outcomes are presented in Table 1. No patients with germline CEBPA or DDX41 mutations were identified. Patients with germline platelet disorders did not have any prominent non-hematological manifestations. Erythrocytosis (20%) with long-standing thrombocytopenia (100%) was a unique feature associated with ANKRD26 mutations. Non-hematologic clues such as human papillomavirus (HPV)-driven warts, primary lymphedema (Emberger syndrome) and frequent atypical infections with monocytopenia were seen in patients with germline GATA2 mutations, and preceded myeloid clonal evolution (morphologic, cytogenetic and molecular). Notably, the age at presentation and penetrance of myeloid transformation was variable, with individuals from the same family developing symptoms during the first decade of life and others remaining asymptomatic to date (fifth decade). Somatic ASXL1 mutations were detected in all 3 (100%) patients with GATA2 mutations and in one patient with ANKRD26 mutation that developed myeloid clonal evolution. In our study myeloid clonal evolution was seen in 40% with RUNX1 mutations, 27% with GATA2 mutations, and 20% with ANKRD26 mutations. We could not calculate the same for bone marrow failure syndromes as the total number of cases seen are still being assessed. Outcomes with allogeneic stem cell transplantation were favorable in appropriately selected patients (Table 1). Conclusion : The 2016 WHO revision to the classification of myeloid neoplasms highlights the importance of recognition and molecular characterization of germline mutations (syndromic and non-syndromic) with risk for myeloid clonal evolution. While some of these disorders (GATA2, Fanconi anemia, telomere biology disorders) may have important non-hematological clues, many present with isolated thrombocytopenia (RUNX1, ETV6). The age and frequency of myeloid evolution is highly variable. Acquisition of somatic ASXL1 mutations at the time of clonal myeloid transformation highlights the role of epigenetic dysregulation in disease evolution. Disclosures Kenderian: Novartis: Patents & Royalties, Research Funding.

Abstract Patients with Hodgkin lymphoma (HL) who relapse or are refractory to first-line therapy have a poor prognosis and some of these patients require innovative therapeutic approaches. Our group and others have demonstrated the clinical efficacy of anti-CD19 chimeric antigen receptor T cells (CART19) for B cell malignancies. However, B cell antigens such as CD19 are typically absent from Hodgkin Reed-Sternberg (HRS) cells. Targeting the CD30 antigen using CART cells has met with limited clinical success to date. In HL the neoplastic HRS cells often represent ~1% of the tumor mass and the remainder is comprised of a highly immunosuppressive tumor microenvironment (TME). Within the TME, tumor-associated macrophages (TAM) have a key role in promoting tumor growth and inhibiting the anti-tumor immune response, and the presence of TAM in HL is associated with a poor prognosis. HL therefore represents an excellent model of tumor-induced immunosuppression that can potentially represent a barrier to successful CART therapy. The objective of this study was therefore to develop an anti-HL CAR T cell immunotherapy that would also overcome the immunosuppression of the HL microenvironment. We sought to define a tumor antigen that was co-expressed on HRS and on TAM. Using immunohistochemistry and flow cytometry we confirmed previous reports that CD123 (the IL-3Rα chain) is expressed on HRS in 50-60% of HL patients and in 100% HL cell lines (HDLM-2, KMH2, SUPHD1, and L428). Importantly, CD123 was also seen on several HL-associated immune cells of the TME, including TAM. Exposure of macrophages to HDLM-2 cells polarized them to an M2-like phenotype (Figure 1 A) with expression of CD123. Luminex analysis of HDLM-2/TAM co-culture supernatants revealed high levels of IL-13, and blockade of IL-13 partially reversed the immunosuppressive phenotype. We then developed a model of TAM-mediated CAR T cell inhibition, using immunosuppressive M2-like macrophages derived by exposure to IL-4 or to HDLM-2 cells. These macrophages could suppress “third party” CART19 proliferation in response to B-acute lymphoblastic leukemia. We then used anti-CD123 CART cells (CART123) to target TAM. Importantly, CART123 actively recognized and killed TAM, thereby resisting TAM-mediated inhibition (as opposed to control CART19 cells) (Figure 1 B). We therefore sought to investigate the utility of anti-CD123 CART for the treatment of HL (initial results for this part presented at ASH 2014). In vitro, CART123 specifically degranulate, proliferate, produce cytokines and kill HL cells. A clinically-relevant xenograft model of HL was generated using luciferase+ HDLM-2 cells in NSG mice. In this model mice showed progressive increase in tumor burden over approximately 6 weeks, reproducing the indolent nature of the human disease. At day ~43 mice were randomized to receive 1.5 million CART123 cells or control T cells. CART123 induced complete and durable eradication of disseminated tumor within 14 days, leading to 100% relapse-free and 100% overall survival at 8 months while mice treated with control T cells had a median survival of 128 days (Figure 2 A). Tumor elimination was associated with extensive CAR T cell expansion as detected by flow cytometry in serial peripheral blood bleedings. In order to prove the formation of an immunological memory, at day 250 CART123 treated mice were re-challenged with the HDLM-2 cell line. The tumor was promptly rejected, associated with a re-expansion of CART123 cells in the peripheral blood (~10 months after T cell injection) leading to an overall survival advantage as compared to controls (Figure 2 B). In summary, we showed that human CD123-redirected T cells display potent therapeutic activity against disseminated HL. In Hodgkin Lymphoma (HL) CD123 is expressed on malignant Reed-Sternberg cells as well as in M2-polarized tumor associated macrophages (TAMs): importantly CART123 can target simultaneously both the HRS and the TAM without being resistant to immunosuppression. We have previously demonstrated that CART123 can lead to myelosuppression in preclinical models, suggesting that our findings could be translated to treat patients with refractory HL in the context of stem cell transplantation using “short-acting” RNA-CAR123 T cells or depletable lentivirally-transduced CART123. Disclosures Ruella: Novartis: Patents & Royalties. Kenderian:Novartis: Patents & Royalties, Research Funding. Wasik:Gilead Sciences: Equity Ownership; Seattle Genetics: Honoraria; Novartis: Research Funding; University of Pennsylvania: Patents & Royalties: NPM-ALK as an omncogene; University of Pennsylvania: Patents & Royalties: CAR T-cells; Gilead Sciences: Research Funding; Pharmacyclics: Research Funding. June:Novartis: Honoraria, Patents & Royalties, Research Funding; Johnson & Johnson: Honoraria; Pfizer: Honoraria; Celldex: Consultancy, Equity Ownership; Immune Design: Consultancy, Equity Ownership; Tmunity Therapeutics: Equity Ownership; Novartis: Honoraria, Patents & Royalties, Research Funding. Gill:Novartis: Patents & Royalties, Research Funding.

Abstract Introduction: Anti-CD19 chimeric antigen receptor T cells (CART19) and bi-specific anti-CD19/CD3 antibodies (blinatumomab) generate unprecedented complete response rates of 45-90% in relapsing/refractory acute lymphoblastic leukemia (r/r B-ALL). However, a subset of patients treated with these targeted approaches will relapse and a significant portion of these relapses are characterized by the loss of detectable CD19 (about 30% of relapses after blinatumomab and up to 50% after CART19), a clear manifestation of immunoediting. Hence, novel effective strategies are needed in order to be able to treat those patients and ideally prevent antigen-loss. CD123, the interleukin-3 receptor alpha, is involved in hematopoiesis and has been shown to be expressed in several hematologic neoplasms, including acute myeloid leukemia (AML) and more recently also B-ALL. Targeting CD123 with chimeric antigen receptor T cells (CART123) was shown to lead to deep and long-term responses in human primary AML xenografts. The goal of this study was to pre-clinically evaluate the impact of targeting CD123 and CD19 with chimeric antigen receptor T cells for the treatment and prevention of CD19-negative leukemia relapses occurring after CD19-directed therapies. Results: We analyzed the expression of CD123 in 42 r/r B-ALL samples and found that CD123 is highly and homogeneously expressed on the surface of most B-ALL blasts (81.75%, range: 5.1-99.6), making it a promising candidate for targeted therapy in B-ALL. Moreover, CD123 was also found to be expressed in the putative leukemia stem cells (LSC), identified as CD34-pos CD38-neg. Notably, in some Ph+ B-ALL samples we found CD19-ve CD123+ve cells with a BCR-ABL translocation by FISH, suggesting that these cells too are malignant. The expression of CD123 was detected in all (n=6) CD19-negative B-ALL blasts analyzed after relapse from CART19 treatment (Figure 1). These findings indicate that CD123 represents an ideal marker to target CD19-neg ALL blasts occurring after CART19 or blinatumomab. Therefore, we generated anti-CD123 chimeric antigen receptor T cells costimulated with 4-1-BB using a lentiviral vector (CART123). We then evaluated the CART123 anti-B-ALL efficacy both in vitro and in vivo against primary B-ALL and cell line (NALM-6). CART123 showed intense anti-B-ALL ex vivo activity, as defined by specific CD107a degranulation, cytokine production, cytotoxicity and proliferation, not statistically different from that of CART19. In order to test the role of CART123 to target CD19-negative relapses we developed a novel in vivo model, engrafting immunodeficient NSG mice with blasts obtained from a patient relapsing with CD19-ve disease after CART19 treatment. At day 14 mice were randomized to receive CART19, CART123 or control T cells (untransduced, UTD). CART19 and control T cell treated mice had no anti-tumor activity, while CART123 led to complete eradication of the disease and long-term survival. We next developed a murine model to test the hypothesis that a combined approach simultaneously targeting CD123 and CD19 could treat and prevent CD19-negative relapses. NSG mice were injected with a mixture of primary CD19-neg and CD19-pos blasts from the same patient that were labeled with different click beetle luciferases (red or green) in order to be able to track the respective clones in vivo. Mice were then randomized to receive UTD, CART19 or the combination of CART19 and CART123 (same total dose of T cells). As shown in Figure 2, mice treated with UTD had progression of both leukemic clones (CD19-pos and CD19-neg) while CART19 showed rapid progression mostly of the CD19-neg disease (red luciferase); on the contrary only mice treated with the combination of CART123 and CART19 showed rapid clearance of the disease, with improved overall survival (64 days for CART19, not reached for CART19+CART123). As a final strategy, we expressed both CAR19 and CAR123 in the same T cells and showed potent anti-leukemia activity (CD107a degranulation 81.7%). Conclusions: Here we demonstrate that CD123 is expressed in CD19-negative B-ALL relapses occurring after CD19-directed therapies, and that combining CART123 cells with CART19 cells is an effective therapy for the treatment and prevention of antigen-loss relapses in B-ALL murine xenografts. Disclosures Ruella: Novartis: Patents & Royalties, Research Funding. Kenderian:Novartis: Patents & Royalties, Research Funding. Scholler:Novartis: Patents & Royalties. Lacey:Novartis: Patents & Royalties, Research Funding. Melenhorst:Novartis: Patents & Royalties, Research Funding. Hunter:Surface Oncology - SAB: Membership on an entity's Board of Directors or advisory committees, Research Funding. Porter:Novartis: Patents & Royalties, Research Funding. June:University of Pennsylvania: Patents & Royalties: financial interests due to intellectual property and patents in the field of cell and gene therapy. Conflicts of interest are managed in accordance with University of Pennsylvania policy and oversight; Novartis: Research Funding. Grupp:Novartis: Consultancy, Research Funding. Gill:Novartis: Patents & Royalties, Research Funding.

Abstract Background. Many children and adults with acute myeloid leukemia (AML) relapse or are incurable with current treatment modalities, highlighting a need for alternative therapies. Chimeric antigen receptor (CAR) T cells targeting CD123 have demonstrated potent anti-leukemia activity in murine xenograft models of human AML. However, CD123-redirected T cell treatment of mice engrafted with normal human hematopoietic cells resulted in profound myeloablation, raising concerns for hematologic toxicity in patients with AML who may be treated with such therapies. We hypothesized that T cell deletion after CD123-redirected T cell-induced eradication of AML could minimize this bystander toxicity without impairing leukemia control, thereby increasing the therapeutic window of anti-AML CAR T cell immunotherapy. Methods. To test this hypothesis, we compared three termination strategies in human AML xenograft models: (1) T cell ablation with the anti-CD52 antibody alemtuzumab after treatment with T cells lentivirally-transduced with anti-CD123-41BB-CD3ζ (CART123), (2) T cell ablation with the anti-CD20 antibody rituximab after treatment with CART123 engineered to co-express CD20 (CART123/CD20), and (3) treatment with "biodegradable" anti-CD123 mRNA-electroporated CAR T cells (RNA-CART123). Mice engrafted with luciferase-expressing human AML cell lines (MOLM14, MOLM13, U937) or primary AML specimens (n=3) were treated with CD123-redirected CAR T cells as above. For T cell depletion studies, alemtuzumab 1 or 5 mg/kg was injected intraperitoneally (IP) at 1-4 weeks after 1x105-106 CART123 to determine optimal dosing and timing of T cell ablation. In subsequent studies, rituximab 10 mg/kg was injected IP 4 weeks after 1x105 -106 CART123/CD20, or 1x107 RNA-CART123 were injected intravenously at 5, 9, and 16 days after AML engraftment. Mice were followed by weekly bioluminescent imaging and/or quantitative flow cytometry analyses of blood, spleen, and/or bone marrow. Results. CART123 treatment of CD123+ AML xenografts induced marked T cell expansion and leukemia eradication in vivo, resulting in long-term animal survival (p<0.0001 vs untransduced T cell-treated controls). Minimal xenogeneic graft-versus-host effects were observed. One dose of alemtuzumab rapidly eliminated T cells in all tested models with best efficacy of 5 mg/kg dosing at 4 weeks post-CART123. CART123/CD20 inhibited AML proliferation with similar kinetics to those of CART123, and 1 dose of rituximab at 4 weeks post-CART123/CD20 infusion rapidly eliminated T cells while preserving leukemia remission. Alemtuzumab or rituximab alone did not inhibit AML proliferation in non-CART123-treated xenograft models vs AML-only controls (p=1.00). Mice with CART123- or CART123/CD20-induced AML remission at time of T cell ablation remained leukemia-free for ≥12 weeks, and animal survival did not differ from that of CD123-redirected CAR T cell-treated mice that did not undergo T cell depletion (p=1.00). In contrast, early depletion of T cells with alemtuzumab at 1, 2, or 3 weeks post-CART123 resulted in failure to eliminate AML with subsequent leukemia progression and animal death. Furthermore, AML rechallenge of animals with alemtuzumab- or rituximab-ablated T cells resulted in rapid leukemia proliferation without T cell re-expansion, confirming completeness of T cell depletion. Non-ablated mice demonstrated CAR T cell re-expansion with rejection of CD123+ leukemia rechallenge (p<0.0001). RNA-CART123 rapidly eliminated AML and facilitated long-term animal survival, although RNA-CART123 had expectedly shorter persistence in vivo than did CART123 or CART123/CD20. Conclusions. Alemtuzumab and rituximab completely eliminated CD123-redirected CAR T cells in human AML xenograft models. Sustained leukemia remission required CART123 or CART123/CD20 persistence for 4 weeks prior to T cell termination via alemtuzumab or rituximab post-CART123 or CART123/CD20, respectively. Ongoing studies are investigating efficacy of T cell elimination in additional xenograft models and against other anti-AML CAR T cell immunotherapies. Results from these studies may help to identify promising T cell termination strategies that will augment efficacy of CAR T cell therapy in patients with AML, particularly prior to stem cell transplantation. RNA-CART123 trials in patients with relapsed/refractory AML will open soon. Disclosures Off Label Use: depletion of CAR T cells with alemtuzumab or rituximab. Kenderian:Novartis: Patents & Royalties, Research Funding. Ruella:Novartis: Patents & Royalties, Research Funding. Aplenc:Sigma Tau: Consultancy. June:Novartis: Patents & Royalties, Research Funding. Grupp:Novartis: Consultancy, Research Funding. Gill:Novartis: Patents & Royalties, Research Funding.

Abstract Hodgkin lymphoma (HL) generally carries a good prognosis. However, 10-15% of patients relapse or are refractory to first-line therapy. These patients have a poor prognosis and would benefit from innovative approaches. Our group and others have demonstrated the clinical efficacy of anti-CD19 chimeric antigen receptor redirected T cells (CART19, CTL019) for refractory B cell malignancies. Despite the B-cell origin of the malignant Hodgkin Reed-Sternberg (HRS) cells, B-cell antigens, in particular CD19, are typically not expressed in HL. We sought to define a HL-associated cell membrane antigen that could be targeted by CAR T cells. Given the relative paucity of the malignant cells and the importance of the immunosuppressive tumor microenvironment in HL, the ideal target would be expressed on neoplastic cells as well as on infiltrating immune cells in order to provide robust stimulation of the CAR T cells. Immunohistochemistry for novel HL targets on 10 patient samples revealed that 5/10 patients expressed CD123 on the HRS cells. CD123 was also seen on immune cells of the microenvironment in most samples. CD123 is the α chain of the receptor for interleukin-3 (IL-3), an important cytokine in hematopoietic growth and differentiation that has been previously shown to promote HL cell line growth (Aldinucci et al, Leuk & Lymph, 2005). As primary HL is non-engraftable in mice we turned to immortalized HL cell lines and confirmed that CD123 is expressed by flow cytometry and Q-PCR in four different HL cell lines (HDLM-2, KMH2, SUPHD1, and L428). To determine the role of IL-3 signaling in HL we engrafted NOD-SCID-γ-chain KO mice that overexpress human cytokines including IL-3 (NSG-S mice) with the luciferase-expressing HDLM-2 cell line. After i.v. injection, the neoplastic cells progressively formed disseminated soft tissue masses. Serial injections of a neutralizing anti-IL3 antibody slowed the growth of tumor, suggesting that CD123 may be a particularly relevant target in HL. We therefore sought to investigate the utility of anti-CD123 CAR T cells (CART123) for the treatment of HL. We have recently described the activity of CART123 in human acute myeloid leukemia (Gill et al, Blood, 2014). Our construct is a 2nd generation CAR, comprising 4-1BB co-stimulatory and CD3-ζ chain signaling domains with an anti-CD123 scFv. In vitro, CART123 specifically degranulate, proliferate, produce cytokines and kill HL cells (Table 1). Moreover, long-term co-culture (20 days) of CART123 with HDLM-2 cells at a 1:1 ratio led to T cell proliferation and complete elimination of HL cells by day 4. To confirm these in vitro data, we developed a rigorous in vivo model injecting 1 million luciferase+ HDLM-2 cells i.v. on day 0. Serial bioluminescent imaging (BLI) demonstrated low level of tumor on day 7, which was followed by gradual increase in tumor burden over approximately 6 weeks, reproducing the indolent nature of the human disease. At day 43 when the tumor burden was 20-fold higher than baseline, mice were treated with 1.5 million CART123 cells or control T cells. CART123 induced complete and durable eradication of disseminated tumor within 14 days, leading to 100% relapse-free and 100% overall survival at 6 months (Figure 1 and 2). Tumor elimination was associated with extensive CAR T cell expansion as detected by flow cytometry in serial peripheral blood bleedings. In summary, we show for the first time that human CD123-redirected T cells display potent therapeutic activity against disseminated HL. We have previously demonstrated that CART123 lead to myelosuppression, suggesting that our findings could be translated to treat patients with refractory HL with a combined CART123 and rescue autologous bone marrow transplantation. Table 1 In vitro activity of CART123 compared to untransduced control T cells (UTD) against a HL cell line (HDLM-2). IN VITRO EXPERIMENT CART123* UTD CD107a Degranulation (4 hrs, E:T = 1:5) 59.3% 2.69% Specific Killing (24 hrs) E:T = 2:1 57% 5% E:T = 0.25:1 27% 1% Proliferating cells (CFSE based) (5 days, E:T = 1:1) 96.4% 20% Cytokine production (24 hrs, E:T = 1:1) (Luminex, MFI) INF-γ 38,265 42 IL-2 85,604 0 TNF-α 10,684 55 MIP-1β 40,038 111 IL-6 16,425 110 GM-CSF 99,915 285 *All P values are <0.05 when compared to UTD Figure 2 Figure 2. Disclosures Ruella: Novartis: Research Funding. Kenderian:Novartis: Research Funding. Shestova:Novartis: Research Funding. Chen:Novartis: Research Funding. Scholler:Novartis: Research Funding. June:Novartis: Patents & Royalties, Research Funding. Gill:Novartis: Research Funding.

Abstract Relapsing/refractory (r/r) B-cell Acute Lymphoblastic Leukemia (ALL) is associated with a poor prognosis in both pediatric and adult patients. Novel therapies targeting CD19 on leukemic blasts, such as anti-CD19 Chimeric Antigen Receptor T cells (CART19, CTL019) or bi-specific anti-CD19/CD3 antibodies (blinatumomab) induce significant responses in this population. However, CD19-negative relapses have been reported in 5-10% of patients following CART19 or blinatumomab therapies. This is likely due to selective pressure on leukemia sub-clones by these potent anti-CD19 agents. Hence, novel effective immunotherapies are needed in order to treat these patients. In order to identify potential additional B-ALL antigens, samples from 20 r/r patients (including two that relapsed with CD19-negative disease after treatment with CART19 therapy) were screened using a custom Quantigene RNA panel (Affymetrix) and expression on cell surface was confirmed by multiparametric flow cytometry. The IL-3 receptor α (CD123) was one of the most highly and homogeneously expressed antigens in the blasts of 16/20 r/r ALL patients, and 2/2 CD19-negative relapses. Therefore, we sought to investigate the role of CART targeting CD123 (CART123) against r/r B-ALL, focusing on treating patients with CD19-negative relapses after prior anti-CD19 directed therapy. CART123 was shown to be effective in eradicating acute myeloid leukemia in xenograft mouse models but its role in ALL has not been investigated (Gill et al, Blood, 2014). We used a 2nd generation CAR123 construct that comprised a 4-1BB (CD137) co-stimulatory domain. T cells were lentivirally transduced and expanded using anti-CD3/CD28 beads. Head-to-head in vitro comparisons between CART123 and CART19 revealed similar rates of proliferation, CD107a degranulation, cytokine production and cytotoxicity when CART were co-cultured with the CD19+CD123+ B-ALL cell line NALM-6 and with primary B-ALL blasts. For in vivo evaluation, we utilized the primary ALL model that was developed by our group (Barrett et al, Blood, 2011). In this model, primary blasts obtained from ALL patients were passaged in NOD-SCID-γ chain KO (NSG) mice, and transduced with GFP/luciferase. We injected NSG mice with 2 million primary ALL blasts i.v. (CD19+, CD123+) and after engraftment, mice were treated with CART19, CART123 or control untransduced T cells (1 million i.v.). Mice treated with control T cells succumbed quickly to disease, while mice treated with either CART19 or CART123 showed tumor eradication and long term survival (Figure 1). We then evaluated the role of CART123 in the treatment of leukemia obtained from an ALL patient that relapsed with CD19-negative disease after CART19 treatment. Both CART123 and CART19 were incubated with CD19-negative ALL blasts; CART123, but not CART19 resulted in significant degranulation, robust cytokine production, and potent cytotoxicity. To confirm these results in vivo, we established a unique model of CD19-negative B-ALL xenograft. We used primary CD19-negative blasts obtained from a pediatric patient that relapsed after CART19 therapy; CD19-negative blasts were passaged in vivo in NSG mice and stably transduced with GFP/luciferase. Importantly, the blasts retained their CD19-negative phenotype. After engraftment, mice were treated with CART19, CART123 or control T cells. CART19 and control T cells had no anti-tumor activity, while CART123 resulted in a complete eradication of the disease and long term survival in these mice (Figure 2). In conclusion, CART123 represents an important additional approach to treating B-ALL, in particular due to its activity against CD19-negative relapses. Since we have previously shown that treatment with CART123 can lead to myelosuppression, CART123 should be employed to eradicate disease prior to allogeneic transplantation. Future direction may include combining CART123 with CART19 preemptively in order to avoid CD19 antigen escapes. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Ruella: Novartis: Research Funding. Kenderian:Novartis: Research Funding. Shestova:Novartis: Research Funding. Scholler:Novartis: Research Funding. Lacey:Novartis: Research Funding. Melenhorst:Novartis: Research Funding. Nazimuddin:Novartis: Research Funding. Kalos:Novartis: CTL019 Patents & Royalties, Research Funding. Porter:Novartis: Research Funding. June:Novartis: Patents & Royalties, Research Funding. Grupp:Novartis: Consultancy, Research Funding. Gill:Novartis: Research Funding.

Abstract Chimeric antigen receptor T cells (CART) hold great promise for the treatment of B cell neoplasms as multiple clinical studies show high complete response rates with anti-CD19 CART. However, widespread clinical use of this novel immunotherapy is limited by cytokine-release syndrome (CRS). CRS is characterized by high fevers and a systemic inflammatory response that is at times fatal. CRS is associated with elevation of multiple inflammatory cytokines (IFNγ, TNFα, IL-6 and others) and may be treated with the anti-IL6 receptor antibody tocilizumab and/or steroids. Importantly, approaches to prevent CRS are currently lacking. The Bruton's tyrosine kinase inhibitor ibrutinib has been approved for relapsing chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) and is now extensively used in B cell neoplasms. Our group has recently demonstrated that the rational combination of ibrutinib with CART19 leads to enhanced anti-tumor responses in preclinical model of MCL, CLL and B-cell acute lymphoblastic leukemia (ALL). In addition ibrutinib has been shown to modulate T cell cytokine production. We therefore hypothesized that ibrutinib would reduce CART19-mediated CRS without impairing the anti-tumor efficacy of these cells. We developed a novel xenogeneic model of CRS by intravenously injecting NOD/SCID/gamma-chain deficient (NSG) mice with primary human MCL cells. Since CRS has been associated with high tumor burden we allowed the tumor to grow for up to 50-60 days, at which time the mice developed palpable splenomegaly. We then injected i.v. 1x106 human CART19 cells or medium (PBS). By day 2 after the infusion, mice that received CART19, but not mice receiving PBS alone, began to display clinical signs of distress (reduced mobility, hyperventilation, generalized weakness, emaciation, hunched bodies, withdrawal and poor motor response) and experienced early death, as compared to controls (p<0.05), clinically resembling CRS. At day 4 after CART19 infusion, we collected blood and measured serum concentration of 30 cytokines by Luminex assay. Importantly, CART19-treated mice, but not control mice, showed significantly elevated serum concentrations of several human cytokines, including IL-6, IFNγ, TNFα, IL-2 and GM-CSF (p<0.05). Having established a clinically relevant model of CRS in the context of B cell neoplasms treated with CART19, we sought to understand if the addition of ibrutinib to CART19 would reduce this early toxicity. We treated high-tumor burden mice with either CART19 plus ibrutinib or CART19 plus vehicle. Of note, mice treated with the CART19/ibrutinib combination experienced prolonged overall survival (OS) as compared to mice receiving CART19 alone (median OS 17.5 days vs. 5 days, p<0.05) (Figure 1 A) Importantly, serum cytokines evaluated on day 4 were significantly reduced in ibrutinib-treated mice, including IL-6, IFNγ, TNFα, IL-2 and GM-CSF (Figure 1 B). In vitro studies revealed that ibrutinib reduced cytokine production by CART cells as well as by MCL cells, leading us to postulate that both CRS and its successful prevention involve cross-talk between immune cells and cancer cells. Studies to dissect the pathogenic pathway are in progress. In summary, CRS is a major obstacle to the widespread applicability of CART therapy. We here report a novel, clinically relevant xenograft model of CRS developing in B cell neoplasms as a result of CART19 therapy. Furthermore, we show that ibrutinib reduces CART19-mediated CRS and prolongs survival by inhibiting the production of inflammatory cytokines from both CART and tumor cells. Having previously shown that ibrutinib does not impair T cell expansion in vivo and indeed enhances the anti-tumor effect, we suggest that the CART19-ibrutinib combination could be a novel strategy to prevent CRS in B-cell lymphomas as well as in B-cell acute lymphoblastic leukemia. Our institution recently opened clinical trial (NCT02640209) where CART19 (CTL019) is added to ibrutinib in CLL patients who have not achieved a complete response after 6 months. Disclosures Ruella: Novartis: Patents & Royalties. Kenderian:Novartis: Patents & Royalties, Research Funding. Melenhorst:Novartis: Patents & Royalties, Research Funding. Wasik:Gilead Sciences: Equity Ownership; Seattle Genetics: Honoraria; Novartis: Research Funding; University of Pennsylvania: Patents & Royalties: NPM-ALK as an omncogene; University of Pennsylvania: Patents & Royalties: CAR T-cells; Gilead Sciences: Research Funding; Pharmacyclics: Research Funding. Lacey:Novartis: Research Funding. June:Novartis: Honoraria, Patents & Royalties, Research Funding; Celldex: Consultancy, Equity Ownership; Tmunity Therapeutics: Equity Ownership; Immune Design: Consultancy, Equity Ownership; Pfizer: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Johnson & Johnson: Honoraria. Gill:Novartis: Patents & Royalties, Research Funding.