Autologous Acute Myeloid Leukemia Research Articles

Phase 1/2 Study of Donor-Derived Anti-CD33 Chimeric Antigen Receptor Expressing T Cells (VCAR33) in Patients with Relapsed or Refractory Acute Myeloid Leukemia after Allogeneic Hematopoietic Cell Transplantation

Background and Significance: Although allogeneic hematopoietic cell transplantation (alloHCT) is a potentially curative therapy for patients with high-risk acute myeloid leukemia (AML), relapse occurs in 30% to 40% of alloHCT recipients and is associated with a 2-year post-relapse survival rate of less than 20%. Chimeric antigen receptor (CAR) T cells targeting tumor-associated antigens have demonstrated efficacy in relapsed/refractory (R/R) acute lymphoblastic leukemia and other hematologic malignancies, but there is limited clinical experience with CAR T cell therapies for AML. Current challenges for autologous AML CAR T cell therapy include the inability to harvest adequate numbers of functional, undifferentiated T cells as CAR T cell starting material. In addition, the potential presence of AML blasts in an autologous cell collection can interfere with T cell proliferation and function during the manufacturing process. To circumvent these impediments in patients with R/R AML after alloHCT, VCAR33 represents a CD33-directed CAR T cell product generated from lymphocytes from each patient's prior allogeneic stem cell donor. CAR T cell manufacture from HLA-matched donors will likely not only eliminate delays and failures in production due to lymphopenia but also improve T cell function by using healthy starting material. CD33 is a preferential target for AML CAR T cell therapy as it is expressed on the majority (>80%) of AML blasts and because prior clinical experience with gemtuzumab ozogamicin (GO; tradename: Mylotarg TM) has demonstrated the safety and efficacy of targeting CD33. Study Design and Methods: Study NCTxxxxxxxx* is a multi-center phase 1/2 study evaluating the safety and preliminary efficacy of VCAR33, donor-derived allogeneic CAR T cells targeting CD33 (Figure 1). The CAR construct used for the manufacture of VCAR33 contains a lintuzumab-derived binding domain and a CD28 co-stimulatory domain. Key inclusion criteria include adult patients with relapsed or measurable residual disease positive (MRD+) AML after undergoing alloHCT with an 8/8 HLA-matched related or unrelated donor. Patients who have undergone alloHCT with trem-cel, a CD33-deleted allogeneic stem cell product intended to facilitate the post-HCT treatment with CD33-directed therapies by reducing on-target off-tumor hematotoxicity, may also participate. Patients will be assigned to one of two study arms based on their AML disease burden: Arm A for morphologic disease with ≥ 5% blasts in the bone marrow, or Arm B for MRD+ defined as < 5% blasts in the bone marrow with ≥ 0.1% CD33+ leukemia cells by flow cytometry. The patient's prior stem cell donor undergoes apheresis for collection of mononuclear cells, which are used as starting material for VCAR33 manufacturing. Patients will receive lymphodepletion on days -5 to -2 with fludarabine (total 120 mg/m 2) and cyclophosphamide (total 1000 mg/m 2) followed by infusion of VCAR33 on Day 0. Each study arm will enroll and escalate independently according to a standard 3+3 trial design, starting at 1 x 10 6 CAR T cells/kg for Dose Level 1. The dose limiting toxicity monitoring period is 28 days, at which time patients will undergo evaluation of disease response. Secondary endpoints include incidence of cytokine release syndrome, graft-vs-host disease, and clinical response. Exploratory endpoints aim to correlate VCAR33 properties with clinical response by characterizing T cell phenotypes within the VCAR33 product and by examining VCAR33 expansion and persistence after infusion. Follow up on trial will continue for up to 2 years after infusion followed by long term monitoring for up to 15 years. Patients may undergo second alloHCT for consolidation of remission or for rescue of prolonged cytopenia due to on-target off-tumor effects of VCAR33. *NCT number pending. Clinical trial information submitted to CT.gov on July 19, 2023.

A personalized cancer vaccine that induces synergistic innate and adaptive immune responses.

To demonstrate potent efficacy, a cancer vaccine needs to activate both innate and adaptive immune cells. Personalized cancer vaccine strategies often require the identification of patient-specific neoantigens; however, the clonal and mutational heterogeneity of cancer cells presents inherent challenges. Here, we presentextracellular nanovesiclesderived fromalpha-galactosylceramide-conjugated autologous acute myeloid leukemia (AML) cells (ECNV-αGC)as a personalized therapeutic vaccine that activates both innate and adaptive immune responses, bypassing the need to identify patient-specific neoantigens. ECNV-αGC vaccination directly engaged with and activated both invariant natural killer T (iNKT) cells and leukemia-specific CD8+ T cells in mice with AML, thereby promoting long-term anti-leukemic immune memory. ECNV-αGC sufficiently served as an antigen-presenting platform that could directly activate antigen-specific CD8+ T cells even in the absence of dendritic cells, thereby demonstrating a multi-faceted cellular mechanism of immune activation. Moreover, ECNV-αGC vaccination resulted in a significantly lower AML burden and higher percentage of leukemia-free survivors among cytarabine-treated hosts with AML. Human AML-derived ECNV-αGCs activated iNKT cells in both healthy individuals and patients with AML regardless of responsiveness to conventional therapies. Together, autologous AML-derived ECNV-αGCs may be a promising personalized therapeutic vaccine that efficiently establishes AML-specific long-term immunity without requiring the identification of neoantigens. This article is protected by copyright. All rights reserved.

Clinical features of febrile neutropenia and bloodstream infection in autologous hematopoietic cell transplantation: Comparison to those in intensive chemotherapy for acute myeloid leukemia

BackgroundIn autologous hematopoietic cell transplantation (HCT), myelosuppression and mucosal damage are more severe than those in conventional chemotherapy because of high-dose chemotherapy, but the duration of neutropenia is shorter due to stem cell rescue. MethodsWe retrospectively evaluated febrile neutropenia (FN) and bloodstream infection (BSI) in 208 patients who underwent their first autologous HCT at our institution between 2007 and 2019. They were compared to those in patients who underwent intensive chemotherapy for acute myeloid leukemia (AML) (130 induction/salvage and 191 consolidation). ResultsThe median neutropenic period in autologous HCT, AML induction/salvage and consolidation was 9, 26.5, and 19 days, respectively. The incidence of FN was 93.8%, 92.3%, and 81.7%, and that of BSI in initial FN was 7.2%, 7.5% and 26.3%, respectively. The incidence of oral mucositis (≥ grade 2) was 63.1%, 9.2% and 12.2%, and that of diarrhea (≥ grade 2) was 53.3%, 9.2% and 6.4%, respectively. Although there were significant differences in the incidence of shaking chills, the degree of fever and the value of CRP between patients with and without BSI in initial FN of AML chemotherapy, no significant risk factors or predictive factors for BSI were identified in autologous HCT. ConclusionsThe profile of infectious complications in autologous HCT was characterized by a high incidence of FN maybe due to mucosal damage. On the other hand, the incidence of BSI was lower compared to that in AML consolidation chemotherapy.

Immune dysfunction signatures predict outcomes and define checkpoint blockade-unresponsive microenvironments in acute myeloid leukemia.

BackgroundImmune exhaustion and senescence are dominant dysfunctional states of effector T cells and major hurdles for the success of cancer immunotherapy. In the current study, we characterized how acute myeloid leukemia (AML) promotes the generation of senescent-like CD8+ T cells and whether they have prognostic relevance.METHODSWe analyzed NanoString, bulk RNA-Seq and single-cell RNA-Seq data from independent clinical cohorts comprising 1,896 patients treated with chemotherapy and/or immune checkpoint blockade (ICB).ResultsWe show that senescent-like bone marrow CD8+ T cells were impaired in killing autologous AML blasts and that their proportion negatively correlated with overall survival (OS). We defined what we believe to be new immune effector dysfunction (IED) signatures using 2 gene expression profiling platforms and reported that IED scores correlated with adverse-risk molecular lesions, stemness, and poor outcomes; these scores were a more powerful predictor of OS than 2017-ELN risk or leukemia stem cell (LSC17) scores. IED expression signatures also identified an ICB-unresponsive tumor microenvironment and predicted significantly shorter OS.ConclusionThe IED scores provided improved AML-risk stratification and could facilitate the delivery of personalized immunotherapies to patients who are most likely to benefit.TRIAL REGISTRATIONClinicalTrials.gov; NCT02845297.FUNDINGJohn and Lucille van Geest Foundation, Nottingham Trent University's Health & Wellbeing Strategic Research Theme, NIH/NCI P01CA225618, Genentech-imCORE ML40354, Qatar National Research Fund (NPRP8-2297-3-494).

P389: BISPECIFIC ANTIBODIES ACTIVATE AUTOLOGOUS LEUKEMIA-REACTIVE T CELLS IN ACUTE MYELOID LEUKEMIA

Background: Acute myeloid leukemia (AML) is a highly immunosuppressive disease with a high risk of relapse. This makes the finding of effective immunotherapy-based treatments important, but also difficult. T cell-engaging bispecific antibodies (TCEs) are designed to bind to both T cells and target cells, activate the T cells and thus induce an immune response against the leukemia cells without employing the MHC-T cell receptor (TCR) interaction. Several therapies of this kind are under development for treatment of AML. Surprisingly, both in vitro and in vivo, a subset of these TCE immunocoached T cells (ICTs) can subsequently target autologous AML cells and mediate efficient TCR-MHC-dependent AML cell killing in the absence of the TCE. This points to that a) a portion of the T cells present in an AML are leukemia-reactive but have been immunosuppressed - a suppression that can be reversed by the addition of a TCE, b) that this anti-AML T cell reactivation may play an important part of the mechanism of action of AML-targeted TCEs and c) that by understanding this reactivation mechanism, we will be able to design improved AML immunotherapies in the future. Aims: To understand the mechanisms by which a TCE induces reactivation of leukemia-reactive T cells (LRTs) in AML. Methods: T cells in biobanked AML patient bone marrow samples were activated with either an anti-CD3 x anti-CD123 TCE or a conventional anti-CD3 antibody for 5 days before isolating the ICTs. ICT assay: ICTs were washed to remove the TCE, and isolated ICTs were co-cultured with additional autologous bone marrow cells at different E:T ratios. Killing efficiency and T cell expansion were determined over several days using flow cytometry. Trogocytosis assay: ICTs were co-cultured with stained additional autologous AML cells for 1 h and T cell populations of interest were isolated using FACS. T cell repertoires were analyzed by targeted RNAseq of the TCR. Results: ICTs generated with a TCE kill autologous AML cells efficiently without further addition of the TCE. Adding additional TCE at this stage also does not increase the AML killing efficiency of the ICTs. ICTs generated with an activating anti-CD3 antibody show a similar AML killing efficiency and a similar trogocytotic behavior as TCE ICTs. Most of the TCR clones present in the AML bone marrow pre-stimulation were also represented among the ICTs and trogocytotic ICTs (ICTs that are directly targeting the AML cells after either TCE or anti-CD3 stimulation; Figure 1), suggesting that the bulk of T cells in an AML bone marrow represent heterogeneous immunosuppressed LRTs which can be equally well reactivated by a TCE or an anti-CD3 antibody. Trogocytotic ICTs generated from both types of T cell activation have a similar TCR distribution. ICTs derived from the bone marrow target autologous AML cells more efficiently than ICTs from peripheral blood. Image:Summary/Conclusion: Similarities between TCE ICTs and CD3 ICTs in regards to TCR distributions and killing efficiencies suggest that the TCE reactivates leukemia-reactive T cells via a CD3-dependent mechanism rather than a more complex proximity mechanism. Our data further suggests that T cells in the AML bone marrow are highly heterogeneous and leukemia targeted to a very high degree. In summary, AML bone marrow ICTs are targeting and killing leukemic cells efficiently in a polyclonal fashion and our results highlight that boosting this mechanism can leverage the clinical impact of AML TCEs and be utilized in other novel AML immunotherapy approaches.

Transgenic Expression of IL15 Retains CD123-Redirected T Cells in a Less Differentiated State Resulting in Improved Anti-AML Activity in Autologous AML PDX Models.

Immunotherapy with T-cells expressing bispecific T-cell engagers (ENG T-cells) is a promising approach to improve the outcomes for patients with recurrent/refractory acute myeloid leukemia (AML). However, similar to T-cells expressing chimeric antigen receptors (CARs), their antitumor activity is limited in the setting of chronic antigen stimulation. We therefore set out to explore whether transgenic expression of IL15 improves the effector function of ENG T-cells targeting CD123-positive AML. T-cells expressing CD123-specific ENG (CD123-ENG) ± IL15 were generated by retroviral transduction from peripheral blood T cells from healthy donors or patients with AML. In this study, we characterized in detail the phenotype and effector functions of ENG T-cell populations in vitro and in vivo. IL15-expressing CD123-ENG (CD123-ENG.IL15) T-cells retained their antigen-specificity and effector function in the setting of chronic antigen exposure for more 30 days of coculture with AML blasts in contrast to CD123-ENG T-cells, whose effector function rapidly eroded. Furthermore, CD123-ENG.IL15 T-cells remained in a less differentiated state as judged by a high frequency of naïve/memory stem T-cell-like cells (CD45RA+CCR7+/CD45RO−CD62L+ cells) without evidence of T-cell exhaustion. Single cell cytokine profiling using IsoPlexis revealed enhanced T-cell polyfunctionality of CD123-ENG.IL15 T-cells as judged by effector cytokine production, including, granzyme B, IFN-γ, MIP-1α, perforin, TNF-α, and TNF-β. In vivo, CD123-ENG.IL15 T-cells exhibited superior antigen-specific anti-AML activity and T-cell persistence in both peripheral blood and tissues (BM, spleens, and livers), resulting in a significant survival advantage in one AML xenograft model and two autologous AML PDX models. In conclusion, we demonstrate here that the expansion, persistence, and anti-AML activity of CD123-ENG T-cells can be significantly improved by transgenic expression of IL15, which promotes a naïve/TSCM-like phenotype. However, we also highlight that targeting a single tumor antigen (CD123) can lead to immune escape, reinforcing the need to develop approaches to target multiple antigens. Likewise, our study demonstrates that it is feasible to evaluate autologous T cells in AML PDX models, which will be critical for future preclinical evaluations of next generation AML-redirected T-cell therapies.

Immunosuppression and outcomes in adult patients with de novo acute myeloid leukemia with normal karyotypes

Acute myeloid leukemia (AML) patients rarely have long first remissions (LFRs; >5 y) after standard-of-care chemotherapy, unless classified as favorable risk at presentation. Identification of the mechanisms responsible for long vs. more typical, standard remissions may help to define prognostic determinants for chemotherapy responses. Using exome sequencing, RNA-sequencing, and functional immunologic studies, we characterized 28 normal karyotype (NK)-AML patients with >5 y first remissions after chemotherapy (LFRs) and compared them to a well-matched group of 31 NK-AML patients who relapsed within 2 y (standard first remissions [SFRs]). Our combined analyses indicated that genetic-risk profiling at presentation (as defined by European LeukemiaNet [ELN] 2017 criteria) was not sufficient to explain the outcomes of many SFR cases. Single-cell RNA-sequencing studies of 15 AML samples showed that SFR AML cells differentially expressed many genes associated with immune suppression. The bone marrow of SFR cases had significantly fewer CD4+ Th1 cells; these T cells expressed an exhaustion signature and were resistant to activation by T cell receptor stimulation in the presence of autologous AML cells. T cell activation could be restored by removing the AML cells or blocking the inhibitory major histocompatibility complex class II receptor, LAG3. Most LFR cases did not display these features, suggesting that their AML cells were not as immunosuppressive. These findings were confirmed and extended in an independent set of 50 AML cases representing all ELN 2017 risk groups. AML cell-mediated suppression of CD4+ T cell activation at presentation is strongly associated with unfavorable outcomes in AML patients treated with standard chemotherapy.

Ex vivo isolation, expansion and bioengineering of CCR7+CD95-/or CD62L+CD45RA+ tumor infiltrating lymphocytes from acute myeloid leukemia patients' bone marrow.

T cell based immunotherapies can be applicable to acute myeloid leukemia (AML). Therefore, the selection of optimal T cells, cell manufacturing, and therapeutic T cell engineering are essential for the development of effective adoptive T cell therapies for AML. Autologous tumor-infiltrating lymphocytes (TILs) have been in clinical trials to treat solid malignancies. Herein, we assessed whether TILs can be isolated from the bone marrow (BM) of AML patients, expanded ex vivo and utilized as a novel therapeutic strategy for AML. To this end, firstly we analyzed the immunophenotypes of a series of primary BM samples from AML patients (N = 10) by flow cytometry. We observed a variable amount of CD3+ TILs (range ∼2.3–∼32.6% of mononuclear cells) among BM samples. We then developed a novel protocol that produced a three-log ex vivo expansion of TILs isolated from AML patient BM (N = 10) and peripheral blood (PB) (N = 10), including from patients with a low number of CD3+ T cells, within 3, 4 weeks. Further, we identified previously described naïve T cells (CCR7+CD95-/or CD62L+CD45RA+) in AML BM and PB samples, which seemed to be required for a successful TILs ex vivo expansion. Finally, we showed that the expanded TILs could: (1) cause cytotoxicity to autologous AML blasts ex vivo (90.6% in control without T cell treatment vs. 1.89% in experimental groups with PB derived T cells and 1.77% in experimental groups with BM derived TILs, p < 0.01), (2) be genetically engineered to express CYP27B1 gene, and (3) infiltrate the BM and reside in close proximity to pre-injected autologous AML blasts of engrafted immunodeficiency mice. Altogether, these results provide a rationale for further studies of the therapeutic use of TILs in AML.

Single and Dual Targeting Chimeric Antigen Receptor T-Cell Therapy in Acute Myeloid Leukemia

BACKGROUND: Discovery of chimeric antigen receptors (CARs) specific for tumour-associated antigens are emerging to be an effective form of immunotherapy for cancer treatment in recent years. However, the lack of a compelling acute myeloid leukemia (AML)-specific cell surface antigen and the safety concerns for myeloid-directed CAR T therapies causing prolonged myeloablation/aplasia which necessitate bone marrow transplantation make it challenging to develop CARTs for AML. In spite of these challenges, the high relapse rate of the disease i.e. 43% and 18% patients never attaining clinical remission (CR) with front-line induction treatments highlight an unmet need for developing improved CAR T vectors with enhanced specificity towards leukemic blasts in refractory/resistant cases with poor cytogenetics. Therefore, we aim to develop improved CAR T vectors for AML that produce safe and consistent responses in patients with high-risk disease. Herein, we demonstrate the in-vitro data for (a) efficacy of a second-generation CAR expressing six single-chain variable fragments (scFv) with different affinities for CD123 [interleukin three receptor alpha (IL3RA; CD123), a molecule over expressed on AML blasts and leukemic stem cells (LSC)] and (b) evaluate the cytotoxic effects of a dual targeting CARCD123/CD33 (against CD123 and CD33; an important myeloid marker specifically expressed on bulk AML disease) to enhance specificity towards leukemic cells therefore reducing "on-target off-organ effects". METHOD: Six lentiviral vectors with CAR against CD123 were constructed i.e. two high affinity (4nM kD &amp; 4nM kD with a point mutation resulting in amino acid change K136Q), two moderate (56nM kD &amp; 56nM kD with mutation at A105G) and two low affinity vectors (101nM kD &amp; 101nM kD with mutation at V24G). To improve the specificity of the single targeting CARCD123, the high affinity (4nM kD, K136Q) vector was utilized to generate two dual targeting (CARCD123/CD33) constructs containing the activation domain (CD3ζ) directed against CD33 and the costimulatory domain (either CD28 or 41BB) directed against CD123. All constructs were transduced (MOI 1:5) into peripheral blood mononuclear cells (PBMCs) from healthy donors or AML patients and their cytotoxicity was examined by flowcytometry on leukemic cell lines; Kg1, U937, K562 [Fig:1a], Ramos wild type (CD19+, CD123-), artificially engineered Ramos cells (transduced by lentiviral vectors with CD123 and/or CD33 cDNA) i.e. Ramos 123 (CD123+), Ramos 33 (CD33+), Ramos 123/33 (CD123+ and CD33+) and AML mononucelar cells (MNCs). RESULTS: Flowcytometric analysis confirmed the expansion of T cells from PBMCs and cytotoxicity of the eight CAR constructs against target cells in in-vitro co-culture assay. High affinity CARCD123 (4nM kD &amp; 4nM kD K136Q) T cells demonstrated enhanced cytotoxicity [Fig 1a] compared to moderate (56nM kD, 56nM kD A105G) CARCD123 in all leukemic cell lines while the low affinity (101nM kD, 101nM kD V24G) vectors had no effect. Efficacy of the high affinity CARCD123 constructs was validated on Kg1 [Fig 1b] and Ramos 123+ target cells by the increasing effector: target ratios (1:2, 1:4 &amp; 1:10). Similar cytotoxic effects were also consistently observed against autologous AML MNCs (target cells) [n=4] and allogenic (effector cells are PBMCs from healthy donors) AML MNCs [Fig 1c] [n=3]. T cell activation was confirmed by ELISA and showed increased IFN-γ (500-2000 fold) and TNF-α (150-200 fold) levels after 24hr co-culture. Furthermore, we also elucidated the exclusive cytotoxicity of the two dual targeting CARCD123/CD33 in Ramos 123+/33+ cells [Fig 1d] with no effect being observed on Ramos 123+, Ramos 33+ and Ramos wild type (123-/33-) cell lines. This confirmed the absence of non-specific targeting, validated the improved specificity of the CARs towards leukemic cells and demonstrated a potential to reduce deleterious "on-target but off organ effects". CONCLUSION: In summary, we illustrate in-vitro data establishing the importance of scFv on CAR T cell cytotoxicity and exemplify for the first time an improved specificity of CARTs by targeting two antigens simultaneously in AML. Future work will involve examining the in-vivo dynamics of CAR CD123 and CAR CD123 CD33 on the hematopoietic system and on disease pathogenesis with an aim to proceed to phase I clinical trial. Figure 1 Disclosures Mufti: BMS, Novartis: Research Funding; Abbvie, Novartis: Consultancy.

LAG3 Inhibition Decreases AML-Induced Immunosuppression and Improves T Cell-Mediated Killing

Background: Acute Myeloid Leukemia (AML) is an aggressive hematologic malignancy with known immune dyregulation. In addition to their capacity to rapidly divide, AML cells directly inhibit the activation and proliferation of immune cells in culture. Immunosuppressive features observed in the bone marrow of AML patients include upregulation of Tregs and production of immunosuppressive cytokines (e.g., TGFβ). Irradiating AML cells diminishes their immunosuppressive capacity while maintaining antigen presentation, leading to increased activation of T cells in co-culture. We subsequently identified the immune checkpoint LAG3 as an important mediator of AML-induced immunosuppression and LAG3 modulation as potential treatment strategy. Methods: Normal PBMC were isolated from healthy donors. PBMC were co-cultured with non-irradiated and irradiated (40 Gy) human AML cell lines (Kasumi1 (K1), THP1) separately at a 1:2 ratio. On day 3 of co-culture, immunophenotypic characterization of T cells was performed on a flow cytometer using the following surface markers: CD3, CD4, CD8, CD25, CD137, CD154, PD-1, TIM3, TIGIT, and LAG3 and intracellular IFNg and FOXP3. Supernatant from co-culture media were analyzed for cytokine (IL-2, IL-6, IL-10 &amp; TGFβ) secretion by ELISA. CFSE-labeled AML cells were incubated with healthy donor PBMCs in the presence or absence of LAG3, then viability was measured by 7-ADD on flow cytometry. PBMCs were also isolated from AML patients' peripheral blood and mononuclear cells were isolated from their respective bone marrow samples. Primary AML cultures were established in RPMI complete media with 20% FBS. CFSE-7-ADD killing assay was conducted after incubation of AML cells with autologous PBMCs. Results: Healthy donor PBMC co-cultured with irradiated K1 AML cells showed higher intracellular IFNg expression (11.8% ± 3.1 v. 7% ± 3.3; n=7, P=0.012) and higher CD137 expression (9.3% ± 1.21 v. 5.7% ± 3.4; n=7, P&amp;lt;0.001) on CD8+ T cells, and higher CD154 expression on CD4+ cells (44.7% ± 20.3 v. 26.3% ± 14.2; n=5, P=0.002) when compared to the non-irradiated K1-PBMC co-cultures. There were fewer Tregs (CD4+ CD25+ FOXP3+) in the PBMC co-cultured with irradiated K1 cells (1.96% ± 0.37 v. 3.39% ± 0.58; n=4, P=0.03) compared to the non-irradiated K1-PBMC co-cultures. LAG3 expression on CD8+ T cells co-cultured with irradiated K1 was decreased (11.8% ± 2.4 v. 17.5% ± 2.5; n=4, P=0.002) compared to the PBMC co-cultured with non-irradiated K1 cells. No other changes in checkpoint expression on CD8+ T cells were observed. No changes were observed in MHCI or PDL1 expression on non-irradiated K1 AML cells before or after co-culture with PBMC. We observed similar findings with healthy donor PBMC co-cultured with a different AML cell line, THP1; CD137 expression was higher on CD8+ T cells (17.6% v. 6.5%; P=0.02, n=3). ELISA of the supernatant of culture media showed higher mean OD for secreted TGFβ in the non-irradiated AML co-cultures compared to the irradiated AML co-cultures at 6 hours (2.5 v. 2.0, P=0.03, n=3) and 72 hours (7.9 v. 5.3, P=0.04, n=3). Adding anti-LAG3 antibody (3DS223H; 100 µg/ml) to PBMC co-cultured with non-irradiated AML cells resulted in higher IFNg (16.3% v. 6.6%, P=0.01, n=4) and CD137 expression (6.5% v. 4.1%, p=.007, n=4) on CD8+ cells and fewer Tregs (1.7% v. 3.8%, P=.04, n=4) compared to no antibody added. Healthy donor PBMC (n=3) were incubated with CFSE labeled AML cells (K1 and THP1) separately at an effector:target ratio of 5:1. The addition of anti-LAG3 antibody lead to increased killing of both K1 and THP1 AML cells at 4 and 24 hours (Figure 1A). To eliminate the HLA mismatch effect, we incubated PBMC from AML patients with autologous AML cells in the presence or absence of anti-LAG3 (Figure 1B). MHC-I blocking (W6/32, 30 µg/ml) lead to inhibition of cell mediated killing in the presence of anti-LAG3 (Figure 1B). Conclusion: In this in vitro model, AML cells showed immunosuppressive features with decreased activation of CD8+ T cells, upregulation of Tregs, increased secretion of TGFβ and higher expression of LAG3 on CD8+ T cells. Antibody blocking of LAG3 mitigated this effect, resulting in increased activation of T cells, fewer T regs and improved MHC-I-mediated killing against AML cells. These results demonstrate that the immunosuppressive effects of AML cells can be modulated through inhibition of LAG-3, suggesting a potential strategy for future combination therapy in AML. Disclosures Lin: Jazz Pharmaceuticals: Honoraria; Pfizer: Membership on an entity's Board of Directors or advisory committees.

Tumor infiltrating lymphocytes from acute myeloid leukemia marrow can be reverted to CD45RA+ central memory state by reactivation in SIP (Simulated Infective Protocol)

Simulated Infective Protocol (SIP) is an ex-vivo culture system modeled after the temporal changes of essential cytokines in an acute infection, and previously proven successful in converting T lymphocytes harvested and activated from peripheral blood of normal donors, to revertant CD45RA + Central Memory T lymphocytes (Tcmra) demonstrating properties akin to T Memory Stem Cells (Tscm). In this study, we applied similar SIP on tumor infiltrating lymphocytes (TIL) from bone marrow of patients diagnosed with acute myeloid leukemia (AML), and replicated the feasibility to convert activated TILs into Tcmra phenotype. These revertant Tcmra lymphocytes re-expressed CD45RA+, CCR7+, CD62L + and CD127+, shown improved survivability with longer telomere length, expressed memory properties including higher Eomes to Tbet ratio, and exhibited cytotoxicity against autologous AML blast cells.

Assessment of the presence and anti-tumor potential of tumor-infiltrating lymphocytes in patients with acute myeloid leukemia.

Purpose: Assessing the possibility of finding tumor-infiltrating lymphocytes (TIL) in bone marrow of acute myeloid leukemia (AML) patients and evaluating the anti-tumor activity of these TIL against autologous AML cells.Patients and methods: TIL were immunomagnetically isolated by using anti-CD3 from bone marrow samples of 20 patients at the presentation of AML or four weeks upon completion of chemotherapy. TIL were ex vivo expanded for two weeks and immunophenotyped. Functionality in terms of cytokine secretion and cytotoxicity was assessed by γ-interferon quantitation and Elispot assay, respectively.Results: TIL were detected in bone marrow samples of 50% (10/20) of the patient cohort. They were noted to highly express CD137 and PD-1 and display a significantly higher anti-tumor reactivity compared to that of autologous peripheral blood lymphocytes. TIL could be expanded in co-cultures with irradiated feeder cells supplemented with interleukin (IL)-7 and IL-15.Conclusion: Data suggested the presence of reactive γ-interferon-secreting TIL in AML patients. They are expandable and possess anti-tumor activity, which might have a great potential in the development of adoptive cellular therapy for AML.

IL-15/IL-15Rα/CD80-expressing AML cell vaccines eradicate minimal residual disease in leukemic mice

AbstractEngineered autologous acute myeloid leukemia (AML) cells present multiple leukemia-associated and patient-specific antigens and as such hold promise as immunotherapeutic vaccines. However, prior vaccines have not reliably induced effective antileukemic immunity, in part because AML blasts have immune inhibitory effects and lack expression of the critical costimulatory molecule CD80. To enhance induction of leukemia-specific cytolytic activity, 32Dp210 murine AML cells were engineered to express either CD80 alone, or the immunostimulatory cytokine interleukin-15 (IL-15) with its receptor α (IL-15Rα), or heterodimeric IL-15/IL-15Rα together with CD80 and tested as irradiated cell vaccines. IL-15 is a γc-chain cytokine, with unique properties suited to stimulating antitumor immunity, including stimulation of both natural killer and CD8+ memory T cells. Coexpression of IL-15 and IL-15Rα markedly increases IL-15 stability and secretion. Non-tumor-bearing mice vaccinated with irradiated 32Dp210-IL-15/IL-15Rα/CD80 and challenged with 32Dp210 leukemia had greater survival than did mice treated with 32Dp210-CD80 or 32Dp210-IL-15/IL-15Rα vaccines, whereas no unvaccinated mice inoculated with leukemia survived. In mice with established leukemia, treatment with 32Dp210-IL-15/IL-15Rα/CD80 vaccination stimulated unprecedented antileukemic immunity enabling 80% survival, an effect that was abrogated by anti-CD8 antibody-mediated depletion in vivo. Because, clinically, AML vaccines are administered as postremission therapy, we established a novel model in which mice with high leukemic burdens were treated with cytotoxic therapy to induce remission (<5% marrow blasts). Postremission vaccination with 32Dp210-IL-15/IL-15Rα/CD80 achieved 50% overall survival in these mice, whereas all unvaccinated mice achieving remission subsequently relapsed. These studies demonstrate that combined expression of IL-15/IL-15Rα and CD80 by syngeneic AML vaccines stimulates effective and long-lasting antileukemic immunity.

An antibody derived from a cured AML patient to identify a unique epitope on CD43 (CD43s) as a novel target for acute myeloid leukemia and myelodysplastic syndrome.

7009 Background: Immunotherapy for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) is hampered by the lack of tumor-specific targets. Methods: We took advantage of the tumor-immunotherapeutic effect of allogeneic hematopoietic stem cell transplantation (HSCT) and searched the B cell repertoire of a patient with a lasting and potent graft versus AML response for AML-specific antibodies. Results: We identified a donor-derived B cell clone that produced an IgG1 antibody, AT1413, that specifically interacted with AML cell lines, with the patient’s autologous AML blasts, but not with lymphocytes or with cells from liver, colon, skin and other tissues. AT1413 recognized a unique, not previously described, sialylated epitope on CD43 (CD43s). CD43s is overexpressed on all types of AML and MDS, as illustrated by its reactivity with freshly isolated blasts of each of more than 60 randomly selected AML and MDS patients in our clinic, representing all WHO 2008 AML and MDS classes. AT1413 induced antibody-dependent cell-mediated cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC) of target cells in vitro. To investigate the effect of AT1413 in vivowe first generated mice populated with human effector cells (NK cells, CTL and myeloid cells) by injecting human hematopoietic stem cells into new born immunodeficient mice. After establishment of a human immune system in these mice we inoculated luciferase labeled AML cells via tail vein injection. Following engraftment of the tumor we dosed the mice biweekly with AT1413 or a control antibody. We observed strongly reduced numbers of AML cells in AT1413- but not in control antibody treated mice. Importantly, AT1413 treatment was tolerated well and did not affect numbers of non-malignant human myeloid cell in these mice. Conclusions: We have obtained an antibody from a cured AML patient which recognizes a unique sialylated epitope on CD43 (CD43s) that is selectively over-expressed on all WHO 2008 types of AML and MDS. This antibody was able to eliminate AML cells in vivo and therefore has high therapeutic potential.

Identification of Naturally Presented HLA Ligands of Enriched Leukemic Progenitor Cells for Peptide-Based Immunotherapy in Acute Myeloid Leukemia (AML)

Several studies demonstrated that peptide-based cancer immunotherapy can induce specific immune responses and affect clinical outcome in a variety of different cancer entities. We recently conducted a study, which directly characterized the antigenic landscape of acute myeloid leukemia (AML) by mass spectrometric analysis of naturally presented HLA ligands and identified a panel of AML-specific CD4+ as well as CD8+ T-cell epitopes as suitable targets for T-cell based immunotherapy (Berlin et al. Leukemia 2015). One main reason for the high relapse rates in AML patients after standard polychemotherapy and allogeneic stem cell transplantation is the presence of minimal residual disease (MRD), which is associated with the persistence of leukemic stem cells (LSCs) in the bone marrow of patients. For clinically effective immunotherapy it is therefore indispensable to target the highly chemotherapy resistant LSCs.Here we present a mass spectrometry-based study, which for the first time analyzes the naturally presented HLA ligandome of stem cell enriched (LSCenr) fractions of primary AML samples to identify novel LSC-associated antigens using the approach of direct peptide isolation and identification. The enrichment of LSCs was performed using fluorescence-activated cell sorting of the originally described phenotype of lineage-negative CD34+CD38- cells of PBMCs from eight AML patients. The original stem cell containing population of 1-3% within the PBMCs of most patients was enriched to >90% purity with cell counts of 20-200x106 for the LSCenr fraction per sample. Consistent with our own previous results, all samples showed comparable expression levels of HLA class I molecules on primary leukemia blasts as well as for the LSCenr fractions, with HLA class I molecule counts ranging from 145,000 to 175,000 molecules/cell for the LSCenr fractions.To specifically identify leukemia-associated antigens on LSCenr cells, the HLA ligandome results obtained from the sorted LSCenrfractions were combined with data acquired from AML blasts of 20 AML patients (HLA class I n=19, HLA class II n=20) in previous studies as well as our normal tissue database that comprises 153 HLA class I and 82 HLA class II ligandomes of various healthy tissues (e.g. blood, bone marrow, spleen, kidney, liver, brain, skin, ovary, bowl).We identified more than 14,600 different naturally presented HLA class I ligands representing ~6,500 source proteins on LSCenr fractions of primary AML samples (n=8) and their autologous blast cells by mass spectrometry. Overlap analysis of the HLA class I ligandomes of LSCenr fractions and autologous AML blasts with the benign peptidome revealed 45.4% (3,132/6,896) and 40.2% (4,922/12,244) of the LSCenr fraction and the autologous AML blast ligandomes to be represented in the benign-associated HLA ligandome, respectively. 79.1% (5,458/6,896) of the mapped LSCenr fraction ligandome was also presented on autologous AML blasts. 1,029 (14.9%) of these identified HLA class I ligands were presented exclusively on LSCenr fractions and not found on autologous AML blasts, previously analyzed AML blasts or any benign tissue.Furthermore, we were able to identify more than 8,000 different naturally presented HLA class II ligands representing ~1,700 source proteins. Overlap of the HLA class II ligandomes revealed 45.0% (2,800/4,624) and 39.9% (2,706/6,790) of the LSCenr fraction and autologous AML blast ligandomes to be represented in the benign-associated HLA ligands, respectively. The HLA ligandomes of the LSCenr fraction and the autologous AML blasts showed an overlap of 69.7% (3,224/4,624). 941 (11.5%) HLA class II ligands showed exclusive representation in the LSCenr fraction ligandomes and were never identified on AML blast or benign tissue.These LSC-associated peptides represent highly interesting targets for immunotherapeutic approaches in AML patients and will be further evaluated for their potential to elicit a specific T-cell response.Taken together these preliminary results prove the feasibility of our approach to enrich leukemic progenitor cells of primary AML samples for the successful isolation and identification of HLA presented peptides associated with enriched leukemic progenitor cells. DisclosuresSchuster:Immatics Biotechnologies GmbH: Employment. Kowalewski:Immatics Biotechnologies GmbH: Employment.

Generating Peripheral Blood Derived Lymphocytes Reacting Against Autologous Primary AML Blasts.

Expanding on our prior studies with cord blood T cells, we hypothesized that primary acute myeloid leukemia (AML)-reactive autologous T cells could be generated ex vivo under immunomodulatory conditions. We purified AML and T cells from 8 newly diagnosed high-risk patients. After 2 weeks expansion, T cells were stimulated with interferon-γ-treated autologous AML weekly × 3, interleukin-15, and agonistic anti-CD28 antibody. Cytotoxic T cells and ELISpot assays tested functionality; reverse transcriptase quantitative polymerase chain reaction tested AML and T-cell gene expression profiles. On the basis of combined positive ELIspot and cytotoxic T cells assays, T cells reactive against AML were generated in 5 of 8 patients. Treg proportion declined after cocultures in reactive T-cell samples. AML-reactive T cells displayed an activated gene expression profile. "Resistant" AML blasts displayed genes associated with immunosuppressive myeloid-derived suppressor cells. We discuss our approach to creating primary AML-reactive autologous T cell and limitations that require further work. Our study provides a platform for future research targeting on generating autologous leukemia-reactive T cells.

Microrna 29b Mediates Immune Evasion of Natural Killer Cells in Acute Myeloid Leukemia

Natural killer (NK) cells are innate effector cells that can spontaneously recognize and kill cancer cells. While important in inducing long-term disease free survival (DFS) in the setting of killer immunoglobulin-like receptor (KIR) mismatch for acute myeloid leukemia (AML), harnessing NK cells to kill autologous or self AML blasts to extend DFS has had no success. In this study, we uncover one potential mechanism by which AML blasts can evade NK cell cytotoxicity. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that has now been shown to be expressed in immature human NK cells. Furthermore, activation of AHR in these immature cells suppresses human NK cell maturation and function. We and others have shown that human AML blasts secrete ligands that can activate AHR, leading us to hypothesize that AML may evade autologous NK cell cytotoxicity in part by inhibiting NK cell maturation. Expression of microRNA (miR)-29b has previously been shown to suppress the expression of transcription factors Tbx21 (TBET) and Eomesodermin (EOMES), both of which are critical for terminal NK cell differentiation and function. Here we show that AHR is able to directly regulate the expression of miR-29b and thus may serve as the link between AML and immune evasion of NK cells. We first identified putative AHR binding sites within the proximalpromoter of miR-29b, suggesting that AHR may directly regulate miR-29b expression. To test this, we transfected the AHR responsive HepG2 human cell line with a miR-29b promoter driven luciferase reporter and measured luciferase activity after treatment with the known AHR agonist, FICZ, compared to vehicle control. We discovered that cells treated with 6-formylindolol[3,2-b]carbazole (FICZ) had increased luciferase activity compared to cells treated with vehicle control (P<0.05). This effect was subsequently shown to be directly mediated by AHR, as mutation of the putative AHR binding site as well as siRNA targeting of AHR mRNA both significantly diminished the induced luciferase activity (P<0.01). We then established the importance of miR-29b in human NK cell development by transducing immature NK cells, characterized as Lin(-)CD117(+)CD94(-), with a miR-29b knockdown virus and testing for the ability of these cells to become mature [i.e., Lin(-)CD117(-)CD94(+)] NK cells, after two weeks in IL-15 and FICZ. Indeed, in early experiments, knockdown of miR-29b resulted in increased percentages of mature NK cells compared to cells transduced with control virus (16.8% compared to 3.6%, respectively), despite being cultured with an AHR agonist. Finally, utilizing a translational in vivo murine AML model developed by our laboratory that recapitulates human AML, we have found that AML blasts harvested from these leukemic mice release an AHR agonist (P < 0.01), similar to previous reports that have described AHR ligands being produced by human AML blasts. In addition,NK cells isolated from these mice have increased levels of miR-29b when leukemic, compared to NK cells from wild type control littermates, consistent with our hypothesis that AHR regulates miR-29b expression. Thus, we propose that AHR, when activated by AML-derived ligands, upregulates miR-29b in NK cells to ultimately suppress the primary regulators of NK cell maturation and function, resulting in immune evasion (See Figure). [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Cellular Reprogramming Allows Generation of Autologous Hematopoietic Progenitors From AML Patients That Are Devoid of Patient-Specific Genomic Aberrations.

Current treatments that use hematopoietic progenitor cell (HPC) transplantation in acute myeloid leukemia (AML) patients substantially reduce the risk of relapse, but are limited by the availability of immune compatible healthy HPCs. Although cellular reprogramming has the potential to provide a novel autologous source of HPCs for transplantation, the applicability of this technology toward the derivation of healthy autologous hematopoietic cells devoid of patient-specific leukemic aberrations from AML patients must first be evaluated. Here, we report the generation of human AML patient-specific hematopoietic progenitors that are capable of normal in vitro differentiation to myeloid lineages and are devoid of leukemia-associated aberration found in matched patient bone marrow. Skin fibroblasts were obtained from AML patients whose leukemic cells possessed a distinct, leukemia-associated aberration, and used to create AML patient-specific induced pluripotent stem cells (iPSCs). Through hematopoietic differentiation of AML patient iPSCs, coupled with cytogenetic interrogation, we reveal that AML patient-specific HPCs possess normal progenitor capacity and are devoid of leukemia-associated mutations. Importantly, in rare patient skin samples that give rise to mosaic fibroblast cultures that continue to carry leukemia-associated mutations; healthy hematopoietic progenitors can also be generated via reprogramming selection. Our findings provide the proof of principle that cellular reprogramming can be applied on a personalized basis to generate healthy HPCs from AML patients, and should further motivate advances toward creating transplantable hematopoietic stem cells for autologous AML therapy. Stem Cells 2013;33:1839–1849

Augmentation of autologous T cell reactivity with acute myeloid leukemia (AML) blasts by Toll-like receptor (TLR) agonists.

This study investigated whether TNF-α, Toll-like receptors (TLRs) 7/8 agonist resiquimod (R848), the TLR4 agonist lipopolysaccharide (LPS) and their combinations can enhance autologous AML-reactive T cell generation in an in vitro culture. AML peripheral blood or bone marrow mononuclear cells were cultured in medium supplemented with GM-CSF/IL-4 to induce dendritic cell (DC) differentiation of AML blasts (AML-DC). The impact of TNF-α, LPS, R848 and their combinations on AML-DC cultures was analyzed. Significantly enhanced CD80, CD40, CD83, CD54, HLA-DR and CD86 expression of AML cells was observed by addition of TNF-α, LPS, R848 alone or combinations. Induced CD80 expression of AML cells was significantly higher through the combination of TNF-α, LPS and R848 (T+L+R) than that by T alone. CTL induced from T+L+R, T+R, T+L, L+R and R, but not T, L alone stimulated cultures showed significantly higher IFN-γ release than the medium control in response to autologous AML cells. IFN-γ release by T+L+R was significantly higher than T or L alone, and T+R was significantly higher than T alone. CTL generated from T+L+R, T+L, T+R, L+R and L alone exerted significantly higher AML cell killing than medium control. AML cell killing by T+L+R and T+R was significantly higher than T or R alone. These results indicate that the combination of T+L+R induces a significantly enhanced antigen presentation effect of AML-DC. We speculate that the complementary effects of reagent combinations may better address the heterogeneity of responses to any single agent in AML cells from different patients.

In Vitro Generation of Cytotoxic CD4 Lymphocyte Response against Autologous Acute Myeloid Leukemia

Relapsed and refractory disease shortens the survival of acute myeloid leukemia (AML) patients. Therefore, additional therapy apart from conventional chemotherapy and stem cell transplantation is urgently needed, especially in eradicating residual leukemic stem cells. The identification of leukemia associated antigens, and the observation that administration of allogeneic T cells may mediate graft versus leukemia effect paved the way to develop various immunotherapy strategies. Effective provision of both tumor antigen and co-stimulation are essential for strategies aimed at enrolling cytotoxic T- lymphocytes to eradicate leukemic cells. In this study, we attempted to up-regulate co- stimulators on leukemic cells (termed “dendritisation” to mimic dendritic cells in providing strong co-stimulation) and couple with inherent leukemic antigens to generate specific antileukemic T-lymphocytes against autologous blast cells. Our study shows evidence of distinct cytotoxicity of CD4 positive T lymphocytes against autologous blast cells. Dendritised AML blasts were able to function with antigen presenting capability, while still phenotypically existing as blast cells. This was also achievable for a wide range of subtypes of AML, making it a potential immunotherapy against AML.